CA1324425C - Tank inventory and leak detection system - Google Patents

Abstract

TANK INVENTORY AND LEAK DETENTION SYSTEM
ABSTRACT OF THE DISCLOSURE
A controller including a digital processor is connected to flow meters and overfill gauges suitable for placement in the fill ports of underground storage tanks at, for example, a gasoline service station.
The station dispenser pumps are also connected to the controller. In addition, probes, including tank liquid level probes, line pressure probes, and leak probes capable of detecting small quantities of liquid leaking from the system, are also connected to the controller.
Processor software programs use stored decision criteria relating liquid conditions external of the storage tank system and liquid conditions internal of the storage tank system and its contents to provide audio and visual indications of the status of the liquid storage system and its contents.

Description

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1~2~42~ ``

. . . '.`. .:-. ~.; -The foregoing re~erences re~1ect just a small portton of the ~ --avallable 1~quld level measur~ng de~ces. Desp~te the extensive research and deve~opment that has gone tnto ltquld level gauging, the preferred method of taktng in~entory in underground storage tanks . . . .. .
rematns the dlpsttck. The present tnventton has for the f~rst time ~ `
co~bined external leak detect~on sensors wlth internal level gauging ~` :
sensors ln ~ untque system which results in important advantages, parttcularly for underground gasoline storage tanks, whtch system makes electronlc ~nventory control practtcal.
SUMMARY OF THE INVENTION
It is ~n ob~ect of the lnventlon to provlde a llqutd status `- `
detector ha~tng both external leak detectton sensors and lnternat ltqutd ;~
teve1 gauglng sensors.
It ls ~ further ob~ect of the tn~entlon to proYide th- above ob~ect ~ ; ;
tn a ltqutd status detector ln which the ablltty to detect small quantlties of llqutd external of a liquld storàge tank enhances the ablllt~ of tbe system to accurately determtne the amount of ltqutd ln , ~-~ ` the system.
. .
It ls ~ further ob~ect of the tnvention to provlde a tlquid status detector in ~blch sensors lnternal of a tlquld storage system enhance :
t h ab~ttty of sensors external of the storage system to detect and locate lea~s in the storage system. ~ -The ln~entton provldes a tank lnventory and teak detect~on system compr)slng: external detect10n means for detecttng one or more condltlons of ltquid external of the storage s~stem and for proYtding an external liqutd stgnal; lnternal detectton means for detect~ng one or 132~25 more conditions of liquid internal of the storage system and for producin~ an internal liquid signal; means for storing decision criterta relating one or ~ore of the external liquid conditions and one or more of the tnternal liquid conditions; and ind kating means communlcat~ng with the means for storing and respons~ve to the external l~quid slgnal and the internal liquid s~gnal for providing an indtcation of the status of the liquid storage system and its contents. ~he external detection means preferably comprises a means for detectlng the presence of a small quantity of hydrocarbon ltquid. ~he external detectlon means preferably further comprises collecting means ~or collecttng llquld, float means configured to ftt withln the collectlng means and occupy~ng the ma~or portlon of its volume at the l~qu~d-float tnterface, and a sensing means attached to the float for provid~ng the external ltqutd slgnal.
Alternatively, the external detection means comprises a vapor sensor and a means for locattng the vapor sensor between the walls of and near the botton of a double-~alled tank. Preferably the tnternal detection means comprlses measure~ent means for measurlng the quantity of l~qutd tn the storage system. Preferably the measurement means comprtses llquld level means for measurlng the l~qu~d level ln the storage system and at least one temperature sansor means for senslng the temperature of the llqu~d ln the storage system. Preferably the means for storlng comprlses means for stor~ng dectston cr~terta for tetermlnlng the locatlon of a leak ln the llqutd storage system and the lndlcating means tncludes means for ~ndtcatlng the locatton of a leak ln the llquid storage system.
Heretofore, lnternal tank level gauglng systems have not been ~
trust~orthy. Relatlvely large level changes correspondlng to `
:: `:

132~42~
signif~cant volume changes Can be caused by relatively common rhanges ln liquid te~perature, for example. As another example, standing waves between layers of liquid at different te~peratures can ex~st for relatively long periods and disrupt sensing systems. Further, the most common form of leakage, l.e., leakage from coupl~ngs and connecting p~ping may occur during volume transfers which can mask the~. However, lt has been d~sco~ered that properly placed external leak detectors can detect ~nute quantities of leaking liquid. For example, ~t has been ~
found that leaked fluids tend to collect in sumps and small amounts, `~ `
e.g, ~ cupful, can qu~ckly be detected. In the present lnvent~on senslt~e external leakage sensors are used to check the lnternal gauglng system el~m~nating many false alarms whlch plagued pre~ous systems. Numerous other features, ob~ects and advantages of the lnventlon ~111 become apparent from the follow~ng deta~led description ~hen read ln conlunct~on with the accompanying drawlngs.
BRIEF DESCRIPTION OF ~HE DRA~INGS ~`
In the dra~ngs:
FI6. lA ls ~ dlagramatlc vlew of a preferred embodlment of a tank Inventory and leak detector system accordlng to the lnventlon ln a typlcal operatlng envlronment;
FI6. lB ls a block dlagr~m of the preferred embodlment of the lnventlon; ;`
FI6. 2 ts a block dlagram sho~ng details of the lnterconnection of the controller and probes shown ln the embodlments of FI6S. lA and lB~
F16. 3 sho~s ~ preferred form~t for a dlgltal command output by the tontroller : ,`
'' `"" `

132~25 ~ 16. 4 iS a ~lock circutt diaQram of the probe communications network of the embodiment of FI6. 2;
FI6. S is a detailed electrical circult diagram of the commun~cation module of ~IGS. 1, 2 and 4;
~ I6. 6 is a block circuit diagram of the controller of FI6S. lA and lB
FI6. 7 is a detailed c~rcu~t diagram of the controller command stgnal interface sho~n;
~ I6. 8 is a detalled circuit dtagram of the controller status slgnal interface;
FI6. 9 ts a block d~agram of a llquid level sensor module according to the ~nvent~on;
tI6. 10 ls a block d~agra~ of a leak sensor module accord~ng to the lnvention; `~`
FI6. 11 is a deta~led electr~cal clrcult diagram of an exemplary :
preferred sensor module c~rcult board;
FI6. 12 sho~s the sensor elements which are connected to the . `.
clrcuit board of Ft6. 11 to form the sensor module of Fl6. 9;
Ft6. 13 sho~s the sensor elements ~h~ch are connected to the `
clrcùlt board of Fl6. 11 to fonm the sensor module of tIG. 10;
Fl6. 14 shows an exemplary well and float for detectlng m~nute quantltles of leaklng llqutd;
Ft6. 15 shows an exemplar~ vapor detectlon sensor and the means for tocatlng It bet~een the walls of a double-walled tank;
:
Fl6. 16 sho~s an exemplary placement of the sensor of FIG. 15 bet~een the ~alls of a double-~alled tank;

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FIG. 17 is a flow chart showing the preferred main mlcroprocessor program accord~ng to the inventisn;
F16. 18 is a block diagra~ of the preferred fl11 flow unit;
FI6. 19 is a flow chart sho~ing the preferred Monitor Mode sub-program;
FI6. 20 is a flo~ chart showln~ the preferred line pressure probe check sub-program;
FlG. 21 is a flow chart showing the preferred external probe check sub-program;
FI6, 22 is a flo~ chart showing the preferred annular space probe check sub-program;
FI6. 23 ls a f1O~ chart showlng the preferred tank lnventory portlon of the ~aln program; and FI6. 24 ls a flow chart showlng the preferred alarm program.
DESCRIP~ION Ot ~HE PREFERRED EMBODIMEN~
Ft6. lA lllustrates the preferred embodtmænt of the lnventlon as it ;, ~y be tnstalled at a gasollne statton. FI6. lB ls a block clrcutt dtagram of the preferred embodlment of the lnvention. A controller 40, ~hlch preferably lncludes a computlng unlt 43, a prlnter 41~ a dlsplay ~2. an aud~ble alan~ 45, relays 44 and keyboards 92, ts located ln an ;`
offlce ln servtce statlon 33. ~he controller 40 receives inventory `~
lnput data over transmlsslon line 32, lnventory output data over transmlsslon llne 31, and llquld status lnformatlon over transmlsslon ~-llne 30. A flow unlt 22 lncludes a flow meter 22A located ln tank ftll port 28 and an overflow gauge 22C, wh1ch provlde inven~ory lnput data to controller 40 vla llne 32. Flow meters such as 21A, ln pumps 21 provlde -lnventory output data to controller 40 via line 31. Senslng probes, ' ~"'.

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such as 23 throu~h 27, ~etect the status of thelr env~ronment and provide sj~nals over transmiss~on line 30 to the controller 40. Some probes, such as 24 and 27 extend down wells, such as 36 and 37 respectively, external to gasoline tanks 39A, 39B and 39C. Others such as 26, are placed between the walls 38A and 38B of a double-walled tank such as 39C. Other probes, such as 25 extend lnside the tanks to measure the llquid level in the tanks. St~ll other probes, such as 23 measure the pressure in llquid transfer plpes such as 34. ~he lnvention contemplates that other types of probes may atso be used. h r slmplicity, only exemplary probes are shown in ~I6~ lB.
Each probe includes a probe communicat~on module, such as 24B and 25B, a typ~cal one of which is shown ln FI6S. 2 and 4 at 29B. Each probe also lncludes a sensor module, such as 24C and 25C, a typical one of ~hich ls shown in FI6S. 2 and 4 at 29C. As ~ill be seen in deta~l belo~, each communicatlon module ls essentlally ldentlcal while the sensor module may vary widely dependlng on the particular phys~cal condltlon lt ls lntended to detect.
In the preferred embodiment lnventory data ls provlded to controller 40 by flo~ meters ln pumps 21 and ln dellYery ports such as 28 ~hene~er llquid ls added to or remo~ed from the tanks 39A, 39B and 39C. Probe data is reqùested by the controller 40 vla a com~and slgnal at frequent lntervals. The command s~gnal preferably comprlses a probe ldentlfler slgnal and a data slgnal formated as shown ln FIG. 3. The ~`
co~mand slgnal ls passed along transmlss~on llne 30 from the controller ~ `-40 to the probe communlcator modules, such as 29B. The slgnal is decoded ~lthln the communlcation module (see FIG. 4) and the data s~gnal ls passed to the sensor module such as 29C. Typ~cal sensor modules are ~324~25 shown in FIGS. 9 and 10~ In these ~cdu1es the data s~gnal is passed via data input lines suc~ ~s 48 and 148 to a multiplexer 134. Sensors such as 130, 131, 132, 140 and 141 in the sensor modules provide status slgnals to the multiplexer 134 over channels 136 and 146. ~he information ~n the data s~gnal tells the multiplexer which data channel to se1ect, and the multiplexer appl~es the signal on the selected channel to a voltage to frequency converter such as 135 and 147, which con~erter outputs an osc~llating signal which ts applied to the probe -output -SO (FI6S. 2, 4 and 5) through the commun~cation module 29B
s~ttch 63 when the identifier s~gnal whlch agrees wlth a local probe address is appl~ed to decoder 60.
Upon receiv~ng the osc~llatlng slgnal from the probes, the controller status stgnal lnter~ace 96 (FI6. 6) counts the number of osctllat~ons occurrlng over ~ predetermlned tlme perlod and presents the count to a processor 90 wh~ch utill~es decls~on criterla stored in `~
~emor~ 91 to provtde an lndlcatlon of the system status wh~ch may take the forn of messages on prlnter 41 or llquid crystal display 42, an alann on audlo ~lar~ 45, an externa1 alarm vla relays 44 wh~ch may actlvate ~ recorded message on phone 46 or speaker 47, or a report on an external d~ta ten~n~l 49~ Or the status slgnals in comb~natlon wlth the declslon crlterla could cause the processor to tr~gger a pump 48 to re~ove lea~lng pollutants. Keyboards 50 and 51 on controller 40 may be used to lnput d~ta, commands and otherwlse communlcate wlth the system.
~ urnlng no~ to a more detalled descrlptlon of the preferred embodlment of the tnventlon, FI6. 2 shows the 1nterconnectlon between the probes and the controller. ~he controller 40 ls connected to the probes v~a a transm~sston line 30 ~hlch ln the preferred embod~ment ls a six-wire cable. Each probe, such as 29, preferably includes a ~unct10n box, such as 29A, a com~unication module, such as 29B, and a sensor ~odule, such as 2gC. Preferably the junction box (29A) and the communication module (29B) are identlcal for each probe. ~he sensor `~
module may be a liquid sensor in a well such as 35 (F~gure lA), a liqutd level sensor such as 25C, a between-the-wall vapor sensor such as 26B, a line pressure sensor such as 23C~ or any one of a num~er of different liquid status sensors. Examples of such sensors àre descrtbed below ln reference to FI6S. 9-16. Com~unications modules are shown at 24B, 25B
ant 26B in FI6 lA. The junction boxes are not shown tn FI6. lA as the sc~le ls not sufficient to show them clearly. ~he ~ùnctton box and the communicatton module ~111 be d~scussed tn terms of the junctton box 29A
and communicatton module 29B, although lt ts understood that these portlons are preferably the same for all probes~ The preferred `
com~untcatlon ~odule ts dtscusset below wtth reference to FIGS. 2, 4 and 5. rhe controller ~ncludes a poslttve powèr output termtnal (~PO), a negative power output ter~tnal t-Po). a postttve tdenttfter signal output ter~tnal (~IO), a negattve tdenttfter slgnal output termtnal (-~0), a postttve status s~gnal lnput termtnal (+SI), and a negatlve `-status slgnal lnput ter~lnal (-SI). ~he Junctton box 29A tncludes, at the left, poslttve and negattve lnput power termtnals (+PI, -PI), posttlYe and negatlve ldenttftèr stgnal tnput termtnals (+II, -Il), posltlve and negattve status slgnal output termtnals t+SO, -SO) each of whtch are connected to the correspondtng termtnal on the controller (~PI
to +PO, -PI to -PO, +II to +IO, etc.). On the rtght the ~unctton box lncludes postttve and negattve power output termtnals (+PO, -PO), posttlve and negattve ldenttfter stgnal output termtnals (+IO, -10) and . ~ ' . . ': ..
."''.''.`'' ' 132~4~
positive and negat~Ye status signal input terminals (~SI, -SI) which are connected to the corresponding terminals on the next ~unct~on box (~PO
to ~PI, -PO to -PI, ~IO to +II, -ID to ~ SI to +SO and -SI to -SO).
The junct~on box terminals are connected to the communlcation module as will be clear from the discussion of Figures 4 and 5.
In the preferred embodiment, the identif~er s~gnal ~s part of a --16-bit digital Manchester encoded command sent by the controller 40 to ~ -the probes. The format for this command is shown ~n Flgure 3. The first four btts and the eleventh and twelfth bits are ftxed. AO through ``
A4 represent the identifier slgnal. Up to 32 probes may be addressed by these 4 blts. DO through D3 represent a data word which may be used to control the sensor module. Thts ~ord mdy be used to address one of stxteen data channels.
FI6. 4 shows ~ block c~rcu~t diagram of the system commun~cation net~ork. The co~unlcation network porttons of the controller include optocoupler 54, transistor 55 and reststors 56, 57, S8 and 59. Reslstor 59 ts connected between the Vcc ~nternal power source (an approx~mately 5 volt power suppl~) of the controller and ~IO output termtnal. The collector of transistor 55 ~s connected to the -IO output term~nal. The e~ttter of trans~stor 55 is connected to ground and the base ~s connected to ground through restster 57 and to the ldenttf~er s~gn~l (dlglt~l word) output through reslster 58. The posltlve status slgnal lnput tern~nal (~SI) ls connected to the anode of the optocoupler d~ode, and the negatlve status s~gnal ~nput termlnal (-SI) ~s connected to the cathode. The e~teer of the optocoupler ~s connected to ground whlle the collector ls connected to the Vcc power supply through resistor 56 and to the status slgnat lnput.
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~ he communication module includes decode circu~try 60, decrement circuitry 61. encade c~rcu~rr 62, optocoup~ers 64 and 65, ~nverters 66, 67, 68 and 69 and nesistors 73~ 74, 75 and 76. ~he ldentlfler slgnal input terminals ~II and -II are connected across the optocoupler 64 diode with the positive connected to the anode and the negat~ve connected to the cathode. ~he emitter of optocoupler 64 ls connected to the probe ground and the collector ls connected to the probe power supply Ybb (an approxlmately 5 volt power source) through reslstor 74 and to the lnput of in~erter 6g. The output o~ ln~erter 69 ~s connected to the input of the decode logic 60. The decode loglc compares the 5-bit probe identlfler address A0 through M to the local address, and ~`
~f lt matches, places a s~gnal on the select (sel) output whlch is applted to swltch 63 to cause It to sNltch to the local probe status tn llne. If the ldentlfler address does not match the local address lt ls sent to decrement loglc 61 ~here lt ls decremented by one and passed to the encode logtc 62. A slgnal ls also placed on the select output to cause s~ltch 63 to swltch to the status`slgnal probe lnput. The data ~ord W through D3 ls passed to the encode loglc and to the sensor module data lnput. The decode loglc also checks the dlg~tal data word for ~alldlty, and lf lt ls v~lld, lt places a slgnal on the data valld output ~hlch ls applled to the encode loglc 62 to cause it to apply the encoded slgnal to the lnput of lnverter 66. The output of lnverter 66 ls connected to the -10 tenmlnal. ~he ~I0 termlnal ls connected to the ~`
Ybb po~er source through reslstor 76. The ~SI termlnal ts connected to -`
the anode of the optocoupler 65 dlode and the -SI termlnal to lts cathode. The emltter of the optocoupler 65 ls connected to ground and the collector ls connected to the Ybb source through res~stor 75 and to ,`."'~."." ', ~ . .

132~25 the input of ~nverter 67. The output of inverter 67 ls connected to the status signat probe input of switch 63. The output of switch 63 ~s connected to the ~nput of in~erter 68. The output of inverter 68 ls connected to the -S0 terminal, and the ~S0 terminal ls connected to the Ybb po~er source through resistor 73.
FIG. 5 is a detalled electrical circu~t diagram of the co~municatlons Fodule. In addit~on to the parts discussed ~n reference to ~I6. 4, the clrcuit includes a DC to DC converter 82, and lnverters 83 and 8~. The decode logic 60 and decrement log~c 61 are implemented together uslng decoder 77, shlft reglsters 78 and 79 and adders 80 and 81. The encode logic compr~ses encoder 62. The ~PI and -PI inputs are connected to a OC to DC converter ~hich provtdes tsolation of the probe po~er supply, ~nd ground ~solatlon between probes. The DC to DC
conv-rter ~lso pen~lts an lnput voltage of 24VDC. Thls h~gher dtstrlbutlon voltage reduces the current dr~ln of each probe on the dlstr~butlon s~stem, thereby reductng the IR losses ln the transmlsslon llne 30, ~llo~lng the use of more probes. The outputs of the converter 81 provlde the probe po~er source Ybb ~nd the probe ground. The numbers ~lthln the rect~ngles representing the IC chlps 77, 78, 79, 80, 81 and 62 ~ndlc~te the lnputs/~utputs of those ch~ps wh~ch are explalned ln the llter~ture provtded ~lth the partlcular chlps (see below). The output of lnverter 69 ls connected to the SI lnput of decoder 77. The DV
output of deeoder 77 ls connected to the SDI lnput of encoder 62. The SO ~nd DC outputs of decoder 77 ~re connected to the D and CLK inputs ``
respect~ely of shlft reglster 78. The DC output ls also connected`to ~`
the CLK lnput of shlft reglster 79. The DRS output of decoder 77 is -~
connected to the MR ~nputs of shtft reglsters 78 and 79 through lnverter , 132~2~

83. The Dl through D15 inputs of decoder 77 are connected to ground. The Q7 output of shi~t register 78 is connected to the D
input of shift register 79 while the Q6 output is connected to the A0 input of adder 81. The Q0 through Q3 outputs of shift register 78 are connected to the D12 through D15 inputs of encoder 62 and also to the sensor module terminal block 87 with the D3 (Q0~ line being inverted by inverter 84. The Q0 through Q3 outputs of shift register 79 are connected to the A3 through A0 inputs respectively of adder 80. The B0 through B3 inputs of adders ~0 and 81 are connec~ed to the Vbb voltage source. The Sl through S4 outputs of adder 80 are connected to the D4 through D7 inputs respectively of encoder 62. The CI input of adder 81 is grounded. ~he cO output o~ adder 81 is connected to the CI input ôf adder 80 while the Sl output is connected to the D9 input of ~ ,.. ': . .
encoder 62. The D0 output of encoder 62 is applied to the input of inverter 66. The sensor module ground and voltage source inputs are connected to the communications module ground and voltage ~ource~ Vbb, respectiv~ly through terminal block 87. The :, .~ .,.. ,:
other connections are as discussed in reference to Figure 4. ; `~

In th preferred embodiment, encoder 62 is a ~`~

Manchester coder~decoder Suptertex type ED9~ adders 80 and 81 are 4-bit addor~ National Semiconductor type 74HC283, shift registers "
;..` : . .
78 and 79 are RCA type CD74HC164, decoder 77 is a Supertex type "~ ` `

ED5 ~anchoster coder/decoder, optocoupler-Q 54, 64 and 65 are ~`
,.-:: ' .
~oxa~ Instruments* typo TIL153's, transistor 55 i9 a type PN2222, tho inverters 66 through 69 and 83 and 84 are a National Semiconductor Schmitt hex inverter-type 74HC14, DC to DC ~ -converter 81 is a 24 volt to 5 volt converter, resistors 57, 59, : `~
73 and 76 are 1~ ohm, 58 is a 2K ohm resistor, *Regi~tored Trade Mark - -. -- , ", . . ..
-. .-.: " '.~:.' . :
B `~

132~2S :--14- '" ~ '' ' ::
.
res~stors 56, J3~ ~4 and 75 are IOK o~, and swltch 63 ts a quad multiplexer type CD74HC157 from RCA
FI6. 6 shows a block c~rcu~t d~agram of the preferred ~ -embod~ment of the controller 40~ It comprlses a processor 90, a memory 9~, keyboards 92, outputs 93, co~mand slgnal interface 95, status signal ~nterfate 96, flow unlt interface 97, and pump meter ~nterface 98. The '~
processor recelves lnstructton from keyboards 92, data from interfaces ~`
96, 97 and 98, and ut~lizes declston crlterla stored ln memory 91 to ``
actlYate appropr~ate outputs 93. ~he processor 90, memory 91, keyboards ~
92 ~nd o~tputs 93 ~y be any one of a number of such components that are - ' ~ell-kno~n ln the art; as for ex~ple the processor, memory, keyboards, "
d1sp ~ , etc. descrlbed ln Unlted States Patent No. 4,736,193 i~
and No- 4-74~0~77 on lnventlons of Laurence S. Slocum and Sara M
`~ SS nn for P ~ ble Flu1d~ ~tectors Thus, th-se components will not be dlscussed further hereln~ rhè co mand s~gnàl lnterface 9S and ~ ' ` ;
st t~ ~s1gnal lnterf~ce 96 ar , hQ e~ver, un~qùe ~n the fleld of flu~d dè`tectors`and tberefore ~lll h descr~b:ed ln detall The flow unlt ~ ' lnterface 97 an~d thè and the pump`meter lnterface 98 are conventlonal RS~232 lnterfices and ~111 not be dtscussed further here~n ~'' FI6. 7 show* the d ta11ed c~rcult dlagram for the command s~gnal`
rf~ce 95. It comprlses p~ral~lel lnterface adapter 100, transm~tter reslstors 103,~5~,~58~a ~ 59, and capacltors 104 and 105. The !r~ on the ~ntegrat d cl~-cults, sùch~ as parallel lnterface adaptor ~'; '~' 0 ~near`t ~ connectlng llnè~refer to~the pln numbers of the c~rcuits, r' '~" ' .
hll- the letters ln~`the lnterlor refer to the lnternal slgnals ~he nurb rs 5, 8, 9 a~d 27 through 36 plns of the parallel lnterface adapter àre~connected to the~data and`tlm1ng outputs of the processor as ~`'' `' .~: .

~ , f, ', '.,. ~: .
. _ ~ . .. . .

- 132~2~

BACK6ROUND OF ~HE ~N~ENT10 1. F~eld of the In~ention The lnvention in general relates to 1iquid status detectors, such ~ ` -as those that detect hydrocarbon liqutd leaklng from underground storage tanks, and ~n particular a detector that combines both internal tank ~`
lnventory sensors and extern~l leak sensors in a s1ngle system.
~ 2. Descr~Ptlon of the Pr~or Art U~S. Pat. No~ 4,221,125, on an lnventlon of John N. Ol~ver and ` ``
Lou~s M. Sandler, No~ 4,646,069 issued to Raymond J. Andre~aslch et al, No. 4,C60,026 tssued to Brl~n L.~Chandler and No. 4,116,045 on an tnvent10n of Bronson M. Potter, are exempl~ry of systems for detecting ~ ;
the presence of leaklng tlquid. ~yptcal?y such systems lnclude leakage ~probes that ~re bur~ed in the Ylclntty of hydrocarbon storage tanks, `~
pl~ced bet~een the ~ ls of double-wal1ed hydrocarbon storage tanks, or "-"` ~
`other~tse placed ext-rnally of storage tanks to detect llqu~d leaking ~ -`
fro~ the tanks. ~he probes are generàlly connected vla wlres to a c-ntr-l eontroller, ~hlch may be 10cated, for example, ln a service - ` st~t10n o fftce, and ~htch mon1tors the probè status. In additlon, a tde n rte~Y of systems have k en known for many years for measur~ng the ltqu1d level ~tthin t nks for~the purposes of gaug~ng the amount of .; ;`
11qutd ~n the tank ~nd or for~detecttng the leakage of 11quid from the ~ ;
~u~ t~nk. See for example Unlted States Patents No. 2,775,748 issued to R.
` L. Rod, et ~?, No. 3,017,771 lssued to F.R. Bonho~me, No. 4,571,987 ~ -issued to J.A. Horner, No. ;,604,893 lssued to F.J. Senese, et al; No. Hl -4~637,254 ~ssued to J.F. Dyben, et al~; No. 4,646,560 lssued to ~. W. ; -Màresca, ~r., et al, and No. 4,646,569 lssued to H. F. Cosser. ~

~p :.: .. : . .

132~42~ -appropriate to trans~it the probe address and senson modute data. The number 6 pln ls connected to the device enable c~rcu~try assoc~ated wlth the processor. The number 7 through 4 pins of adapter lO0 are connected to the ~ through lO pins rèspectively of transmitter lOl. The number 40 pin of adapter lO0 ~s connected to the number 6 pin of transmltter lOl.
~he number 18 through 21 p~ns of adapter 100 are connected to the 14 through ll pins respectively of transmitter lOl. The number 14 pin of adapter lO0 ~s connected to the number 4 p~n of transmltter lOl. The number ~ pin of transmitter lOl ~s connected to the system voltage source, Vcc, through capacltor 105, and the number 15 pln ls also connected to the Vcc voltaqe. The number 18 pln of transmitter lOl is connected to the number 2 pin through capacitor 104 and to the number 1 ptn through reslstor 103. The number 16 pin of transmitter lOl and the number 26 pin of adapter lO0 are connected to the Ycc voltage and the number 17 p~n of transm1tter lOl and the number 7 pin of adapter lO0 are connected to ground. ~he nunber 5 pln of transm~tter lOl provides the output conmand slgnal to the probes whlch ls also the Identlfler Slgnal Output sho~n tn FI6. 4.
The com~Rnd s~gnal interface clrcult 95 works as follows. The parallel Interf~ce ~dapter lO0 ls connected to the processor and other ele~ents of the clrcult so as to provlde the probe address (ldentlfler stgnal) on lts PA0 through PM outputs and the sensor data slgnal on tts PB0 through PB3 outputs. Pln 14 of the adapter lO0 strobes the tr~ns~ltter lOl ~hen the ldent~fler s~gnal and sensor stgnal ts at the adapter outputs and transmltter lOl then transmlts the slgnal as a Mbnchester encoded serlal dlgltal slgnal on output pln 5. The clrcuit comprlslng trans~stor 55 and reslstors 57 and 58 is a buffer clrcu~t, `~

132~42~

~hile the circuit comprising resistor 103 and capacitors 104 and 105 ls an RC c~ock ~h~ch provides the ti~ing ~or transm~tter 101. In the preferred embodiment parallel interface adapter 100 is a type 82C55A and transmitter 100 is a type ED-9 Manchester ~ransmitter whlle resistor 103 is 40 K ohms and capacitors 104 and 105 are 1,000 ptcofarads and 100 p~cofarads respectively wh~ch provide a lOK hertz timtng signal.
Turning now to ~6. 8, the detailed circu~try for the status signal interface 96 ts sho~n. It includes parallel ~nterface adapter 110, counters 111 and 112, one-shot latches, 115 and 116, counter 117, Schm~tt-tr~gger tnverters 119 and 120, resiStors 56, 122 and 125 and cap~citors 123 and 124~ The nwmbers 5,8,9, 17, and 27-36, pins of ~-adapter 110 are connected to the processor 90 and the number 6 p~n ~s connected to the ch~p select clrcuitry assoctated wlth processor 90.
The number 26 p~n of adapter 110 ~s connected to the Ycc voltage. while the number 7 pln ts connected to ground. The 1 through 7 p~ns of counter 112 are connected to the 3, 2, 1, 40, 39, 38 and 37 pins respectlYely of ~dapter 110. The number 15 pin of counter 112 is connected to the number 4 ptn of adapter 110, whtle the number 15 pin of counter 111 ts connected to the number 18 ptn of adapter 110. The `
number 1 through 7 ptns of counter 111 are connected to the 19 through 25 p~ns respecttYely of adapter 110. The number 13 and 16 plns of adapter 110 ~re connected to the Q output of latch 116. The number 10 ptn of adapter 110 ls connected to the reset lnputs of latches 115 and 116 and to the tnput of ~nverter 120. The number 16 plns of counters 111 and 112 are connected to the Vcc voltage whtle the~r number 8 and 14 ptns are connected to ground. Thetr number 10 plns are each connected `;
to the Q output of latch 116, thelr number 11 plns to the output of .

132~25 1nverter llg, and their nu~ber 13 pins to the Q output of latch 115.
The number 12 pin of counter 112 is also connected to the Q output of latch 11~ while the number 12 pin of counter 111 ls connected to the number 9 pin of counter 112. ~he CX output of latch 115 1s connected to its RJC input through capacitor 124, wh~le the CX output of latch 116 ls connected to its R/C ~nput through capacltor 123. The R/C lnput of latch 1~5 is also connected to the ~cc voltage through reslstor 125 while the RIC input of latch 116 is also connected to ~cc through reslstor 122. ~he B inputs of latches 115 and 116 are connected to the Vcc voltage. The A ~nput of latch 115 ls connected to the Q7 output (nu~ber 3 pln) of counter 117 white the A lnput of latch 116 ls connected to the Q output of latch 115. The number 14 pin of counter 117 ~s connected to Vcc ~hlle lts number 7 pin ls grounded. The clock lnput tnumber 1 p~n) of counter 117 is connected to the processor tlmer funct~on, nMROUT0. ~he reset lnput of counter 117 ls connected to the `
output of lnverter 120. ~he lnput of lnverter 119 ls connected to the nu~ber 5 pln of optolsolator 54, whlch provldes the Status Slgnal In slgn~l sho~n ln FI6. 4.
~ he st~tus s~gnal lnterf~ce operates ~s follows: After processor 90, ~s descrlbed abo~e ln reference to FI6. 7, sends a command to a probe ~sklng for lts status, lt w~lts ~ tlme long enough for the command to go out ~long the probe commùnlc~tlon net~ork ~nd the probe that was ~ddressed to report the status requested. It then addresses the -p~r~llel lnterf~ce adapter 110 causlng lt to strobe the reset 1nputs of the counter 117 ~nd latches 115 ~nd 116. ~h1s causes the l~tches to turn on the counters 111 ~nd 112 to beg1n read~ng the frequency com~ng ln on the ~SI ~nput term1n~1 and counter tl7 to beg~n clock1ng a t1me 132~2~
period over which the frequency will be read. The t~me ~s controlled by the processor via the ~MROUTO funct~on. If the processor 1s ask~ng for a status that requires a high reso1ution reading of the SI signal com~ng ln, it will put a low frequency slgnal as TIMROUTO, and lf it ls asklng for a status that requires a low resolutlon reading, it will put a h~gher frequency signal as ~MROUTO. The counter 117 will then count for a predetermined number of counts which deflne length of time period over which the SI slsnal will be read. ~hen counter 117 times out, lt actlYates the one-shots 115 and 116 which shut down the counters 111 and 112. The processor then tells the parallel interface adapter 110 to read the count of counters 111 and 112, whlch are connected to operate ~ -~
as a slngle 16 bit connector, ~h~ch the adapter does and reports the count read back to the Processor 9G. It then slgnals the processor lt ls flnlshed vla the INT2 s~gnal output on p~n 17.
The count of counters 111 and 112 wh~ch is reported to the processor 90 ~s a dlgltal slgnal related to the frequency of the voltage controlled osclllator 135, 147 in the probe ~n whlch the fluld status was sensed. The m~croprocessor uses the ~MROUTO frequency to determlne ~n ~bsotute value of the osclllator frequency. h r example the ~nverse of the TMROUTO frequency ls proportlonal to the perlod over which the voltage controlled osclllator frequency ~as read. If the count of coun k rs 111 and 112 ts multlplted by the tnverse of TMROUTO, a number ls obt~ned whtch is proportlonal to the aver~ge osclll~t10n frequency `~` ;
of the VCO, or ~verage of the status slgnal, over the perlod. If the lo~er TMROUTO frequency ls output by the processor, then the perlod will be longer and the number of osclllatlons averaged over wtll be greater ~nd the resolutlon of the status slgnal wlll be h~gher. The processor .,:.' `.: . `

1~2~425 90 uti)izes the dig~ta~ status signal to pro~lde an indicat~on of the sensed condit~on as ~ill be discussed below.
In the preferred enbodiment, paralle1 lnterface adapter 110 ls a type 82655A, counters 111 and 112 are each type 74HC590 eight- blt counters, latches 115 and 116 are type 74HC221, counter 117 ~s a 74HC4020, inverters 119 and 120 are 74HC14's, reslstors 122 and 125 are each 2 K oh~s and capacitor 123 and 124 are each 1000 plcofarads.
~ he flow meters 21A ln pumps 21 are conventlonal digital meters as are comnonly used ln serv~ce stations. Such meters are designed to co~municate vla a conventlonal RS-232 interface 98 whlch ls well-known ln the art.
~ urntng no~ to the description of an exemplary sensor module, FI6. 9 sho~s ~ block circult dlagram of a ltquld level sensor module~
such as 25C. ~h~s module ~ncludes a liquid level sensor 130, a water sensor 131, te~perature sensors 132, ~ultlplexer 134, and voltage to frequency converter 135. hch of the sensors 130, 131, ~nd 132 apply -voltage stgn~ls to multlplexer 134. The data lnput llnes 148 from terrln~l block 87 are also connected to ~ultlplexer 134. Respondlng to the d~ta stgnals on llnes 148 ~htch orlglnated ln the controller 40, the ~ulttplexer plaees on converter 135 the voltage correspondlng to the statùs requested by the controller~ Converter 135 converts the voltage ~ :
to a frequency slgnal whlch ~s the status slgnal, and outputs the status --stgnal to the local probe status ter~lnal of termlna1 block 87. Thls slgnat co~prlses an lnternal llquld slgnal.
Flgurc 10 sho~s a block electrlcal clrcult dlagram of another exe~plary sensor ~odule, a sensor lntended to be placed ln a we11, such as 36 (FI6. 1), and whlch dlfferentlates between water, hydrocarbon and , 1~2~23 air. ~his module includes a water/hydrocarbon sensor 140, a llquld/gas sensor 1~1, togtc circuit 142, analog switch 143, voltage dlvider 144, multiplexer 134, and voltage to frequency converter 147. The sensors 140 and 141 each apply voltage signals to logic clrcu~t 142 which determines if hYdrocarbon. water or a~r ~s present and appl1es a slgnal indicat~ve of ~hich is present to analog switch 143. Voltage divlder 144 e~ploylng a reference voltage level from con~erter 147, generates three analog voltage levels which are appl~ed to switch 143. Swltch 143 appltes one Of the voltage le~els, whlch ls determined by the lnput from logic c~rcu~t 142~ to multiplexer 134. ~hè data signal from controller 40 ls applled to multiplexer 134 vla data input tlnes 148. Converter 147 also applles a temperature signal lndicatlve of the temperature of the IC chlp to multlplexer 134. In response to the data command from controller 40 and uslng a reference voltage from ~oltage to frequency ` `
converter 147, ~ultlplexer 134 places one of the voltages provided by the dlvtder 144 or the temperature signal voltage to converter 147 whlch converts lt to a frequency slgnal and applles thts slgnal to the local `~`
probe status termlnal of ter~lnal block 87. Thls slgnal comprises an external llquld slgnal. :-In the preferred embodlment of the lnventlon, the llqutd level sensor module of FI6. 9 and the llquld sensor module of FIG. 10 are lmptemen kd on a slngle clrcult board whlch ls shown ln FIG. 11.
Dlfferent clrcults are connected on the board and dlfferent components are connected to the board ~la termlnal block connector l50A to pro~lde ~; ;
the two dlfferent sensor modules. The components that are connected to -ten~tnal block 150A to for~ the llquld level sensor of FIG. 9 are shown ln FI6. 12, ~hlle the components that are connected to the terminal ~.

132~2~

block 150A to ~ono tbe llquid sen50r mDdule of tIG. 10 are shown 1n Fl6.
13.
Referring to FI6. 12, in the preferred embodiment the sensor for the liquid level module comprises temperature sênsors 210, 211, 212, ltquid level sensor 215, conductlng electrode tips 21t and 218 and connector 150B. ~he temperature sensors 210, 211 and 213 are preferably located at dlfferent depths of tank 390, the level sensor is mounted vert~cally in the tank, and the conduct~ng tlps 217 and 218 are located at or near the bottom of the tank. the wlres 219 connect the sensor and the connector 150B ~hlch plugs lnto converter 150A ln the probe sensor ~odule clrcuit board located at the top of probe sensor module 25C.
Referrlng to ~I6S. 13 and 14 the llquid sensor ~odu1e sensors lnclude condustlng electrode t~ps 221 and 222 mounted on a float 225 ~hlch ls losated ln a wetl, such as 36, external to the tanks 39A, 39B
and 3gC. th wells, such as 36, are located and the flll ls placed around the~ so that any llquld leak~ng from a tank wlll seep lnto the ~ell. ~he float 225 ls free to ~ove up and down the well as the llqu~d level tn the ~ell rlses and falts, and the conductlng tlps 221 and 222 are ~ounted on the float so that they extend lnto the upper portion of the llquld 226. A float swltch 224 ls moùnted in the float and the swltch and conductlng tlps 221 ~nd 222 are connected by wlres 228 to connector lSOC ~hlch plugs lnto connector l50A mounted ln the clrcult bo~rd located near the top of the well. The float 225 ls deslgned so that most of the volu~e of the ~ell at the level of the llquld surface 22~ ls`occupled by the bo`qy of the float. thus, especlally lf ground w~ter ls present, a ver~ small amount of hydrocarbon (or other llquld ~`
; ' ''' ' ` ~''" ". ' . . . -: ;

1324~à

that f10ats on water), for exa~ple a cup or so, wtll be suffictent to activate the lea~ probe~
A vapor sens~r type leak probe 26 is shown tn FI6. 16 being -;
tnstalled in a double-walled tank. In this probe the sensor module 26C
~nc~udes a sensor unit 232 which is placed between the walls 233, 234 of the double-walled tank and electronlcs in a probe cap 245. Sensor unit 232 ts shown ln FI6. 15 together with neans 231 for tnserttng the sensor unit between the walls of a doublè-walled t~nk. The sensor unit 232 contains the vapor sensor element, the untt havlng openings 233 for vapor to reach the sensor e1ement. A cable 235 and a fish 226 provtde a ~eans 231 to tnstall the sensor untt 232 between the walls 243, 244 of a `~
double-w~lled t~n~. An electrtcal cable 237 connects the sensor unlt 232 to the rest of the sensor ~odule 230 and the probe communtcatton ~ `~odule 239 ~htch ~re cont~tned tn the c~p 245 whtch closes the port 240 through ~htch the sensor ts tnserted. V~por probes 26 lnstalled as sho~n h~ve been found to be ~ble to sense small le~ks, tnvolvtng less th n ~ cupful of h~drocarbon, bet~een the walls of ~ double-walled tank.
Tht slgn~l provlded by v~por probe 26 ls ~n external ltqutd stgnal.
A det~tted electric~l clrcult dtagram of the preferred sensor ~Qdule clrcult bo~rd ls sho~n tn BI6. 11. The ctrcutt tncludes multtplexer 134, logtc/~n~log swttch I.C. 151 whtch functtons both as logtc ctrcutt 1~2 ~nd an~log s~ttch 143, voltage to frequency converter 135, volt~ge to frequency converter 147, tnverters 152 through 157, const~nt current dtode 160, dtodes 161 and 162, potenttometers 165 ` ``
.: . , .
through 170, c~p~cltors 171 through 176, reststors 180 through 198, Jumpers 201, 202, 203, ~nd connectors 87B and 150A. The 6D or ground pin of connector 87B connects to the board system ground whtle the Vbb ~

'~.:,.~. ``

. .

132~42~
pin connects ~c the system vo?tage line. The status p~n connects to the number ~ pin of coR~erter 14~, the number 14 p~n of converter 135 and the Vbb voltage through resistor 185. The DO dat~ input of connector 878 connects to the number 11 pin of multlplexer 134 and the number 11 pin of logic/s~itch lSl through Jumper 201. Note that the solld line on jumpers 201, 202 and 203 indicates the connect~on for the level sensor module of FI6.` 9, while the dotted line tndicates the connection for the liquid sensor module of FIG. 10. Loglc/switch lSl and converter 147 are not required for the level sensor module of FI6. 9 and may be omitted in the boards for the module, while converter 135 is not required for the fluid sensor module of FI6. 10 3nd may be omitted in boards intended for that module~ Oata lnput Dl ls connected to pln 10 of multiplexer 134 and to pln 10 of loglc/switch 151 through`jumper 203. Data input D2 is connected to p~ns 9 of multiplexer 134 and logtc/switch lSl. D~ta tnput D3 is connected to the number 6 pin of logic/sw~tch lSl through jumper 202, whll~ data input D3 -is connected to pln 6 of multlplexer 134. ~he conducff ng ttp lnput p-in C of connector 150A ls connected to the input of ln~erter 154 and the anode of diode 161 through capacitor 175; the lnput of inver k r lS4 ls ~lso connected to the Vbb voltage through resistor 186. Inverters 152r etc. ~re ~ hex lnverter chlp. the voltage lnput of whlch ls connected to the Vbb voltage and the ground of which ls grounded. ~he output of lnverter 153 ls connected to the input of lnverter 152 through capacitor 173, whlle the output of lnverter 152 is connected to the lnput of lnverter 153 and also ls connected to lts own lnput through reslstor 181. ~he output of lnverter 153 is connected to the cathode of dlode 161 ~nd the anode of the diode ls connected to the lnput of inverter 154. ~he output of inverter 154 ls connected to the ` - ' . ~
~ ;

i32~2~

input of inverter 7~, dnd the output of inverter 155 ls connected to the anode ~f d~ode 162. ~he cathode of diode 162 ls connected to the input of inverter 156, to ground through capacitor 176, and also to ground through resistor 194. ~he output of inverter 156 is connected to the ~nput of ~n~er~er 157. The output of ~ merter 157 is connected to the number 5 pln of multiplexer 134 through res~stor 196, and the same pin ls also connected to ground through resistor 195. The output of `
lnverter 157 is also connected to pin 10 of logic/switch 151 through jumper 2Q3 in the llquld sensor ~odule embodiment. One side and the ad~ustable contact of each of potentiometer 168, 169 and 170 is connected to ground ~hile the other slde is connected to p~ns 14, 15 and 12 respectlvely of multlplexer 134 through resistors 187, 188 and 189 respecttvel~; plns 14, 15 and 12 are also connected to the numbers 1, 2, and 3 te~perature lnputs (Tl, t2 and ~3) of connector 15oA. ~he 1evel 1 lnput, Ll, of connector 150A is connected to the number 1 pln of multlple~er 134 and to the Vbb voltage through constant current dlode 160, w~th the cathode of the d~ode toward the level 1 Input. ~he level 2, L2, lnput of connector 150A ~s connected to the number 13 ptn of -~ulttplexer 134 and also to ground through reslstor 19~. ~he float s~tteh tnput, F, of connector 150A ls connected to the number 11 pln of loglc/s~ttch 151 through Jumper 201 ln the llquid sensor module e~bodt~ent, and also to the Vbb voltage source through reslstor 198~
~he Y and 6 ptns of connector 150A are conn`ected to the Vbb voltage and ground respectlvely. rhe number 13 and 15 plns of loglc/swltch 151 are connected to ground through reslstor 191 and also connected to its nu~ber 12 pln through reslstor 193. The number 12 p~n ls also connected to the number 14 ptn through reslstor 192; the number 14 p~n ~s also .

132~2~

connected to the number 4 p~n of m~ltiplexer 134, to the adjustable input of p~te~ti~eete~ , and t~ the number 4 pin of converter 147 through resistor 190. The number 7 and 8 plns of logic/switch 151 and multlplexer 134 are all grounded, ~hile the number 16 pln of each are connected to the Ybb voltage. The number 3 p~ns of each are connected to the number 2 pln of converter 147 and the number 5 pin of conYerter 135. The number 2 pin of multiplexer 134 is connected to the number 6 pin of converter 135 and to the number 3 pin of converter 147. ~he number 1 pln of con~erter 147 is connected to ground through res~stor 180, the nu~ber 5 and 10 pins are grounded and the number 6 p~n ls connected to t~e nu~ber seven pin through capacltor 171. ~he number 8 pin of converter 147 ls connected to the adjustable lnput of potentlometer 165 and to p~n 13 of con~erter 135. The two s~des of potentlometer 165 are connected to pins 9 and 10 respectlvely of converter 135~ Pln 13 of converter 135 ~s tlso connected to the Vbb voltage through res~stor 184 and to ground through capacltor 174. Pln 11 of converter 135 ls connected to pln 12 through capacltor 172. P~ns 3 and ~ of con~erter 135 are connected to one slde of potentiometer 167 thr~ugh reslstor 183. ~he other slde of potentiometer 167 ts connected to ground. ~he ad~ustable lnput of potentlometer 167 ls connected to ground. Ptns 1 ~nd 8 of converter 135 are also connected to ground.
Pln 7 of converter 135 ls connècted to one slde of potentiometer 166, ~hlle the other sl k of the potentlometer is connected to ground through resls k r 182.
In the preferred embod~ent of the lnventlon multlplexer 134 and loglc/analog sw~tch 151 are type CD4051BCN mult~plexers, voltage to frequency converter 147 and 135 are type AD537JH V/F converters ~ ;
' ` ~:, "' ', 132~i425 ava~lable from Ana~o~ De~ices, inverters 152 through 157 are lmplemented in a single hex inverter type CD4069CN, diodes 161 and 162 are of type IN914~s, constant current diode 160 ~s a type IN5297, potentiometer 165 is a 20K ohm, lS turn potentiometer, 166 ~s a lOK ohm, 15 turn ;
potentiometer, 167 is a 200 K ohm, 15 turn potentiometer, 168, 169 and 170 are 100 oh~, 15 turn potentiometers, capacitors 172, 173, 174, 175 and 176 are .01 ~icrofarad, 4700 plcofarad, 10 mlcrofarad, .1 microfarad and 1 mlcrofarad respecttvely. Reslstors 180 through 198 are lK ohm, 220K ohm, 60.4 ~ ohm, 909 ohm, 100 ohm, 5K ohm, 270K ohm, 953 ohm, 953 ohm, 953 ohm, 24K ohm, 24K ohm, 2~K ohm, 24K ohm, lOOK ohm, lOK ohm, 90K
oh~, 10 ohm, and lOOK ohm respectively~ In the preferred embodiment of the sensors of FI6. 12 and 13 the temperature sensors 210, 211, and 212 ~re type AD590 te~4erature sensors ~ nllable from Analog Devices, level sensor 215 ls preferably a Metr~tape nM level sensor ava~lable from, Hetrltape, Inc., P. 0. Box 2366, Littleton, MA 014C0, the float 225, flo~t s~ltch 22~, ~nd conductlng electrode tlps 221 of the fluid sensor of FI6. 13 ~re ~ float assembly of the type used wlth the tD probe serles ~FD241R, FD 241S, FD241P) av~llable from Pollulert Systems, Inc., P. O. Box 706, Indlanapolls, IN 46206-0706 and as descrlbed ~n Unlted St~tes P~tent No. 4,442,405 Issued to Raymond J. Andre~aslch. The conducttng electrode tips 217 and 218 are electrodes as descr~bed ln the foregolng patent, preferably made of stalnless steel or plattnum, and connectors lS0~, 150B ~nd 150C ~re prefer~bly stake ~nd header connectors ~hlle connectors 87A and 87B ~ire preferably 1510D male and fe~ale connectors, or both connectors m~y be hard w~red.
~ urn~n~ now to a summary of the functlon of the l~quld level sensor module of FI6S. 9, 11 ~nd 12 ln con~unctton w~th the controller 40 and 1324~25 probe com~unicatlon s~stem, the llquid level sensor has the princ~pal functio~ of ~easuring the l~quld level in a storage tank such as 39C.
It also measures the temperature at three depths along the sensor.
Water in the storage tank is detected via conductance electrodes 217 and 218 installed at the bottom of the level sensor modute 25C. The l~quld level is transduced into an analog s~gnal by the Metrttape TM level sensor 215 which mdy be described as a long varlable res~stor the submerged part of whlch is short-circuited by hydrostat~c pressure of the l~quid in whlch lt is ~mmersed. ~he temperature sensing is accomplished by two-terminal electron~c devlces 210, 211 and 212 whtch conduct current in direct proport~on to thelr absotute or Kelv~n temperature. T~o reference voltages, V Ref Htgh and V Ref Lo~, are also measured and reported by the sensor, one near the top and one near the bottom of the analog s~gnal range, these data belng necessary to enable the controller 40 to decode the telemetered data. Finally, a slgnal, V
temp, representlng the temperature of the electron~cs package ~s a nll~ble for transmlsslon to the controller 40 upon comnand.
~ Referrlng to FI6. 9, an elght-channel analog multtplexer 134 under com~Rnd of a three-blt dlgltal word from the controller selects one from u~ong an ensemble of eight analog lnput channels 136 and connects lt to the lnput of voltage to fre~uency converter 135. The output of converter 135 ls ~ symmetrlc square wave`whose frequency is directly proportlonul to the an~log lnput voltage. Thls slgnal ls well suited for transmlss~on through the probe chaln to the contro11er 40, where lt ls decoded by countlng technlques and ~nterpreted w~th respect to reference slgnals transm~tted through the same chaln. Two of the analog 132~2~

~nput signals to the mw~tiplexer are auxiliary outputs of the converter 135. lhe sisnal flow is other~ise straight forward.
Referring to Flgures 11 and 12, the liqu~d level sens1ng clrcu1t consists of a Metritape ~M variable resistor 215 excited by a constant current diode 160. ~he res~stance of the level sensor 215, and hence the voltage across lt, ~s proportlonal to the length of the sensor whlch ls ln alr. The difference between the air helght and the sensor overall height ls taken to be the depth of llquld ~n the storage tank. A 10 ohm reference resister 19~ ls inserted between the level sensor 215 and ground. The voltage across this resistor when exclted by the 1 ma constant current source ls a 10 mY level called low. Thls is done ln preference to uslng zero volts as a reference level to avoid requ~rlng converter 135 to operate at the extreme of its range. `
The te~perature sensors 210, 211 and 212 are semlconductor devlces ~hlch are t~o-ten~inal current sources that conduct a current which ls proportlonal to the absotute or Kelvln temperature wlth a nomlnal scale factor of 1 ~lcrounp per degree Kelvln. hr temperature 1, the sensor 210 ~s read out b~ convert~ng lts current lnto the voltage across grounded reslstor 187. Varlable reslstor 168 is a scale factor trlm ~hlch ls o~ployed as a slngle polnt callbratlon ad~ustment. The result ls ~ scale factor of 1 mllllvolt/degree Kelvin. remperatures 2 and 3 are read st~llarly.
~ he water/bydrocarbon sensor ctrcult consists of a multivibrator, an alternatlng-c~rrent conductance-senslng clrcult, and a hatf-wave rectlfler and fllter clrcult. A convent~onal CMOS free-runnlng ~41tlvlbrator ls formed by lnverters 152 and 153, res~stor 181, and cap~cltor 1~3. A square ~ave at about SOOHz ls present at the output of 1324~2~

inYerter ~53. ~hen the conducting tips 21? and 218 are ~n a~r or o~l, capacitor 175 ls effectively not in the clrcu~t and the square wave appears at the input of inverter ~4 ~nd the output of ~nverter 155.
D~ode 162 and capacitor 176 form a peak detector which ~s d~scharged by res~ster 1~4. ~hen the square wave is present at the output of ~nverter 155, a high ~evel is present at the input of inverter 156 and hence at the output of lnverter 157. ~hen water is present between the conducting t~ps 21~ and 218 capacitor 175 ls effectively connected to ground and the voltage at the input of ~nverter 154 does not have tlme to rlse slgnlf~cantly from the lo~ level to whlch it ~s set by the eonductlon of dlode 161; that is, there ls lnsufficlent current flow through res~ster 186 to charge capacltor 175 during the poslttve half perlod of the ~ultlvlbrator. In effect, the square wave ls shorted to ground by capacltor 175 and the ~ater conductance across the conducttng tlps 21~ and 218. Accordlngly, dlode 162 does not conduct and a low level obtalns at the lnput of lnverter 156 and at the output of inverter 157,~the latter of ~hlch const1tutes the loglc slgnal whlch lndicates that ~ater ls present. ~he ctrcuit output swttches sharply at a conductlng tlp reslstance of about 150K ohm. ~he threshold resistance can be lncreased by lncreasing the value of reslster 186.
An e~ght channel analog ~ult~plexer lntegrated clrcu~t 1-~4 suff~ces for the level sensor, though the other ~ultlplexer 151 ls avallable lf expanslon to ~ore channels ls deslred. ~he outputs (pln 3) of the ~ultlplexers 134 and 151 are hard~lred together because a hlgh level on the lnhlblt llne (pln 6) of the deselected chlp places all of lts analog ``~s~ttches ln the hlgh lmpedance state.

~`` ~,, 3~
- 132~2~

Tke ~oltage to ~re~uency con~erter jntegrated circuit 135 produces a square ~ave logic signa~ output having a fre~uency that ~s proportlona1 to the analog tnput s~gnal voltage wtth a nominal scale factor of 10 K Hertz/volt. As used ln this circu~t, the lnput impedance seen by tAe anatog input source ~s about 250 me~ohms, wlth an ~nput blas current of 100 na. Therefore, errors due to loading and tnput current are less than 0.1 X and are thus negltgible. In order to secure the maximum dynamic range of which the converter 135 is capable, it is necessary to null the ~nput a~plifier. This ls accomplished with potentiometer 165.
~ he scaltng equat~on relatlng output frequency to input signal voltage tn thls circuit ~s: F out ~ V~n/10 (reslstance 183 + res~stance 167) x capacltance 172. Potentiometer 167 ls used to adjust the scale factor. ~he V~F converter 135 prov~tes the voltage reference output on pin 7 whtch ts speclf~et as 1 volt ~ 5X. Potent~ometer 166 ls used to create a prectse 900 ~V ~ lmV reference called Vref hlgh, whlch ts connected to the ~ultlplexer 134 at pln 4.
Another output s~gn~l from the converter 135 ts a thenmometer output representtng the chtp absolute temperature w~th a scale factor of 1 mV/~ ~ 2X. lhe tnltlal caltbratlon ~s speclfled dS raiseline accurate ~thln ~ 5 Kelvtn degrees at room temperature~ Thls reference output ls connected to the multtplexer 134 at ptn 2 and ls used to tndtcate the temperature of the sensor module electronlcs package. Thls terperature ~ay be used by processor 90 ln a conventlonal fashlon to correct the recetved converter frequency as ~nd~cated 1n the manufacturer's spectflcaff ons provlded w~th the VC0 ch~p. Such correctlon ts not necessary tf the voltage levels prov~ded to the ,... .

132~2~

voltage ~ontro77ed oscil7ator are spaced more w~dely than the changes ~n frequercy due to temperature and/or if the probe ctrcutt temperature ts relatively stabte.
turntng now to a sumnary of the function of the l~qutd sensor modu~e of FI6S. 10, 11, 13 and 14, ~n conjunction with the controller 40 and the probe communlcaticn system; the purpose of the ltqutd sensor module 149 ls to detect the presence of ltquid and detenmine Nhether the liquid is hydrocarbon or water. A float swttch 224 detects that ltquid is present; an electrical conductance c~rcult 140 discrlmlnates between hydrocarbon and ~ater. ~hese two lnputs to a logtc ctrcutt 142 ;~
determlne which of three analog levels is presented to voltage-to-frequency-con~erter 147. The resultlng one of three frequencles ls transmltted through the probe chaln to the controller 40 to be decoded by a countlng technlque. Referrlng to the block dtagram In Ftgure 10, a water/hydrocarbon sensor 140 gtves a togtc signal whtch ts hlgh when electrlcal reslsttvit~ between conductlng tlps 221 and 222 ls above a threshold value (~bout 150K ohm) and low when the res~stlvlty ls below thc threshold. Thus ~ low output slgnlfles that water ts present betwcen thc tlps~ The float swttch 224 generates a logtc stgnal slgnlfytng that flotatton has occurred. A loglc clrcult processes these two tnputs and controls an analog swttch 143 to connect one of `
three analog levels generated by voltage dlvlder 144 to multtplexer 134.
Input slgnals from the controller 40 control the analog channel selected by the ~ultlplexer 134. In the llqutd sensor 149, four multlplexer channels 146 are utllt2ed; they ~re: alr-o~l-water stgnal, refere~ce volt~ge (nomln~l 1 volt); 2ero vott reference; and thermometer output slgnal. Converter 147 generates a symmetrtc square wave of ~ frequency : : . - :

132~25 which is directly proportiona~ to the analog voltage output of multiplexer 134, rh~s square wa~e signal is suitable for transmlss~on thru the Communication module chain to the processor ~n the controller 40. The proportional~ty constant is nom~nally lOK Hertz/volt. Two analog output s~gnals are also generated by the converter 147: a one-volt reference level which is used to drive voltage d~vider 144; a thermometer signal which is directly proportional to the absolute (Kelvtn) te~perature of the converter integrated circutt chip 147, and which has a proporttonality constant of 1 millivolt/degree Kelvin. ~he latter slgnal is used to monttor the temperature of the fluid sensor electronlcs package. Referrtng to Figure 11, because of commonal~ty of functlon, both the liquid sensor 149 and the level sensor 139 are constructed on the same prlnted ctrcuit board by suttable lnclusion or om~sston of components and suitable placement of three ~umper connectlons 201, 202 and 203. ~he curved dashed ltnes on the schematlc dtagr~m tndtcate the requ~red ~umper connecttons for the liquid sensor 149; the soltd curved ltnes are the ~umpers for the le~el sensor 139.
~he ~ater/hydrocarbon sensor clrcult 140 operates as described above tn the discusston of the level sensor 139 to produce a logtc stgnal at the output of ~nverter 157 whtch ts applted to ptn 10 of logtc/switch 151 tn the llqutd sensor e~bodt~ent.
rhe float s~ttch 224 ts a magnettcally actuated s~ngle-pole stngle-thro~ sw~tch ~h~ch ~s connected to the grounded electrode tlp 221 1n the float asseEbly 225 when no llqu~d ts present. Flotation causes the n oat s~ttch 224 to open. ~he swltch ls connected to Vbb through restster 198 and, vla the dashed ~umper 201, to ptn 11 of logtc/sw~tch 151, a channel select tnput. Hence flotatton causes a htgh level at 132~25 p~n 11. The output of the water/hydrocarbon sensor circuit connects vla dashed ~umper 202 to p~n 10, another channel select lnput of logic/switch 151. Pln 9 of logic/switch 151 ~s held low by software co~mands from the controller 40. Integrated clrcu~t logic/swltch 151 is a ~ultlplexer chip which is used in the fluid sensor both as log~c circuit 142 and as multipole analog switch 143. Its channel select inputs are exploited for the~r ability to do simple loglc on two binary lnput signals and express the result by selecting one from the ensemble of analog lnput slgnals connected to the channel tnputs. ~he voltage dlv~der clrcult 144 provldes voltage le~els of 0.75, 0.5 and 0.25 volts ~`
to plns 12. 13, 14 and 15 respectively of log~c/swttch 151. The log~c ts such as to produce the relationship codifled ln table 1 between condltlons and analog voltages at the output, ptn 3, of loglc/
swttch 1.
~ABLE I
Condttlon Loglc Log~c Analog Swltch Frequency of VF
Input InputOutput pin 3 Converter Output - -ptn 11 pln 10 pln 9 Air Lo~ Hlgh.25 vo~t Z048H2 011 Htgh Hlgh .5 4096 Hz ~ter Hlgh Lo~ .75 6144 Hz ' .' The output of p~n 3 ts applled as the analog tnput signal to volt ge to frequency converter 147, pln 2. Output frequencles as shown ln Table 1 are produced tn response to the detected conditlons.
Hote that the output plns 3 of the two multlplexer chlps 151 and 134 are h~rd~lred together; thls ls feaslble because the Inhlbit lnput, ptn 6, ts under soft~are control. ~hen the lnhiblt lnput ls hlgh all .. . .

`` `` 132~25 analog switches go to the high impedance state. Converter 147 also provides a reference voltage of l.o volt on its pin 4 which is used to drive the voltage divider 1~4 and is connected to multiplexer 134, pin 4, so that it may be monitored by the controller 40. Converter 147 also produces a thermometer output signal on its pin 3 which is an analog signal proportional to the absolute or Kelvin temperature of the V/F chip with a scale factor of lmV/R. This signal also connects to multiplexer 134 at pin 2. The scale factor of the converter 147 is set by capacitor 171 and resistor 180 according to the relation: F = V/10 x resistance 180 x capacitance 171, with the values shown, the s scale factor is 10 XHz/volt. Note that capacitor 171 should be mounted close to the pins to which it connects to avoid errors due to pickup and stray capacitance.
The above description of the sensor module for the liquid level probe and the liquid probe is exemplary. From the description it should be clear that any sensing element that has an output signal in the form of a voltage can be incorporated into such a probe by adjusting it to an ~. .. .
appropriate voltage level, gating the voltage with a ~;
multiplexer or s~llar gate, applying the voltage to a ~`
voltage to freguency converter, and applying the resulting output of the converter to a communication module as described above. In the preferred embodiment such a circuit is~ provided for the vapor probe 26 and the line pressure ~ -probe 23. The vapor probe electronics to produce the above-.
mentioned voltage level is known and the mechanical packaging `
and method for installing it between the walls of a double-., , ~ . ~
walled tank is as described in United States Patent -~ '. . ..

' ' ` 132~2~
-35- ~:

No.` 4,779,45Q. ` The llne pressure sensor 23C ~s pre~era~ly a sensor incorporating an electron~c clrcuit as descrlbed tn United States Patent No. 4,835,71~ to produce t~o voltages, one lndicating a tr~p po~nt at about 3 ps~ and another indtcating a tr~p p~tnt of about 7 ps~. These volta~es are ~- -presented to a log~c ctrcuit and analogue switch similar to those "
sho~n ln ~I6~ 10 to provide the stgnals to the multiplexer (such as m 134) whtch are passed on to the controller. These s~gnals from the line pressure probe 23 also compr~se an tnternal llqutd signal. -`
Turn~ng no~ to FI6. 17, ~ block dtagram of the flow unit 22 ls sho~n. The unit comprlses flow meter 22A, ovèrflow gauge 22C, flow ` "
meter lnterface 250, overflow ~nterface 252, mlcroprocessor 255 and ~"
RS232 port 257~ The flow ~eter ls preferably a htgh accuracy turh~ne flo~ ~eter such as a Cox model No.F-3/4 manufactured by the Schutte and Koerttng Dtvtston of Ametek, Inc., 3255 ~ Stetson Avenue, Hemet, Cal~fornla 92343 although other conventlonal flow meters may be used.
Overflo~ gauge 22C ls preferably a ~odel No. 73 made by Magnetrol ~ -Internattonal, 4300 Belmont Road, Downers Grove, Illtnots 60515. - : ``
`~ ~although other conventional overflow gauges may be used. The outputof the preferred flo~ meter 22A ls a sertes of pulses of a frequency ~` -wh~ch ls proportlonal ~to the flow rate through the flow meter. Thus, the slgnal recetved by flo~ meter lnterface 250 ~s stmilar to that ~ -recelved by status stgnal l~nterface 96 and can be handled simllarly. i `` ~
In thls case ho~ever, the reset strobe ls preferably ~n~tiated either ~` :
by a keyboard co~mand com~un~cated v~a cable 32, port 257, and ~ - :
~; m~croprocessor 255 prior to dellvery. The output of overflow gauge `22C ls a voltage s~gnal of a predeterm~ned voltage level, and, 3~, '"' .' .~ "
'~., "': ~.`., .

-- 132~25 therefore, interface 252 is a simple voltage bridge which adjusts the input voltage to a suitable level for input to microprocessor 255. Microprocessor 255 is preferably a type HD63701VOP or HD6301Vl, both of which are made by Hitachi, although many other microprocessors could be used. Its primary function is to store the output of the flow meter 22A
between interruptions from the controller 40; preferably it also performs averaging and corrections that would otherwise have to be done by controller processor 90, thus saving controller time for monitoring functions. RS232 port 257 communicates between microprocessor 255 and the controller RS~32 interface 97~ The signal from flow unit 22 also comprises an internal liquid signal.
Turning now to FIGS. 17 and 19 through 23, the flow charts of the preferred controller processor programs are shown~ The main program is s D arized in FIG. 17. The progra~ initializes the system and performs maintenance routines after it is turned on. These initializations and maintenance routines are conventional and will not be .
discussed herein. These routines preferably contain a timing interrupt as described, for example, in Uhited States Patent ~o. 4,736r193. Nhenever a specified key on keyboard 51 is hit, such as the exit key, the software enters the program mode in which the system may be programmed. The main program is interrogated approximately once each minute and enters the monitor mode which is shown in FIG. 19. In the monitor mode, the flow unit 22 is interrupted to see if the flow meter is running. If it is, the program enters a fill mode subroutine which '' '' . '' ;- ```' " ~ .

132~425 checks the leYel gauge e~er~ fiYe seconds. ~hen the h~gh alanm of the level gauge indicates that the tank ~s approach~ng full, the system enters a tank full mode and checks the overflow gauge then goes ~nto alarm mode tn which appropriate ~isual and aud~o signals of the approach~ng fu~l condition are prov~ded. The system w~ll cont~nue checking the overflow gauge at f~ve second lntervals unt~l the flow ~eter shuts off. Thereafter the system will recommence checking the `
overflow gauge 22C each time the flow meter turns on, untll the tank l~qu~d leve~ falls below the high level alarm of the level gauge and deacttvates the high level alarm. ~hen the flow meter turns off. the system checks the level gauge and overflow gauge one more ttme then progresses to monttor the line pressure probes, the external probes, ~nd the annular space probes. The preferred programs for these monitor~ng functlons are shown tn FI6S. 20, 21 and 22 respectively. ``
As d~scussed above, the preferred t~ne pressure probe 23 returns a stgnal that dlfferentt~tes between three pressure levels, t.e. less then about 3 psl, between 3 pst and 7 ps~, and above 7 ps~. The progr~m sets a low ltne pressure flag whenever the l~ne pressure drops belo~ 7 psl and a llne leak flag whenever the llne pressure drops below 3 pst. These flags are ut~lt2ed tn the alarm program to provide alan~s and also pro~lde addtttonal declslon crlter~a whlch are lncorporated tnto the extern~l probe and tank ~nventory mode subroutlnes. The ltne pressure subroutlne ts called each tlme the llne pressure clock times out. The clock ~s a programmable software clock whtch ls preferably set to about 2 m1nutes. ;~ -The external probe subrout~ne ls shown ln FIG. 21. Th~s subroutlne ls called each tlme the external probe clock tlmes out;
`' :;, :

1~2~2~ ~ -this sofb~are eloe~ is also preferab~y set to about tlme out at about 2 m~nute ~ntervals, This subroutlne util k es the stored declston criterla provided by data input by various probes and sensors and by other subroutlnes t~n the fonm of flags) to provide a more reliable and more detailed response to storage system leaks than could be provided b~ any prior art leak detection system If there are no probes alarmlng the system si~ply records this fact and returns to the monitor ~ode subrout~ne If one or more probes report a hYdrocarbon condltlon, the subrouttne checks to see if a loss flag has been set, l e ~hether the tank lnventory subrouttne (see below) has determlned a tank volume loss or the ltne pressure subroutlne has detenmined llne loss If so. than a ~aJor leak flag is immedlately set The ~a~or leak flag ls also set if ~ore than one probe ls reporttng a `` `
hydrocarbon condltlon Other~lse the leak flag ls set Next the progra~ checks to see lf an overflow flag has been set, and lf so lt sets the splll flag lndtc~tlng that a splll (as opposed to a leak) has llkel~ occurred ~lnally the progran checks lf a low llne pressure flag has been set, and lf so the low llne pressure locatlon (assumlng aore than one ltne pressure probe ln the system) are compared wtth the probes reporttng hydrocarbon condlttons and lf any correlate, ltne leak locatlon fl~gs are set ~hlch are used to provlde indlcatlons on prlnter 41 and dlspl~y 42 (or vta perlpherals 49) showtng the location of the leaks.
rhe annular space pro h checks subroutlne ls shown ln ~IG 22 rhts subroutlne ls called up by a programmable software clock that ls preferabl~ set to about 4 ~lnutes If the annular space probes, such as 26, do not report any hydrocarbon presence, the system returns to 132~425 monitor mode. If a probe is reporting the hydrocarbon condit~on, the hydrocarbon in annular space flag is set. If there is also a tank volume loss flag set for the same tank then the major leak flag ~s set. If an external leak flag is set, and the leak correlates w~th the tank in ~hich the annu~ar probe is reporting hydrocarbon, then tank failure flag is set indicating that both the inner and outer tanks have been penetrated.
~ he tank inventory program which forms part of-the main program is shown in fI6. 23. This program ls returned to wherever the processor 40 is not performing other tasks, and continually recycles ` -ltself so long as the microprocessor is not called on to do other tasks. 6enerally, the full calculation to complete this program wil1 `
take several minutes of processor time. If either the dispensing pumps or the fill flow meter are operating, the program will read and record the necessary data then deviate to a short-form calculation ~hich estimates the tank volume. If a tank volume loss is found in "`
the estlmate mode an estimated volume loss flag is set. This flag is su~f~cient to set off alarm lndications when lt shows up in ~`
conblnatlon ~th other leak or loss flags, such as in the external leak probe and annuiar leak probe monitorlng programs, but will not of itself cause the system to go into alarm. If both the d~spense and lnput flo~ meters are not operating, the system does a full accuracy c~lculatlon of the tank ~olume. ~his calculatlon is such that it is ~ ;
~ased on prevtous catculations and thus durlng long periods of pùmps and meter shutdo~ns, such as overnight, very accurate inventory calculations can be made. Even ln the accurate mode, the system will not sound an alan~ the first tlme a tank volume 10ss or gain ~s ~`
, ... .

132~2~ .
calculated, unless there is a leak flag set, ln whlch case the votume loss fla~ is f~ediately set and the syste~ goes to the alarm program.
If no leak flag ls set, then the system will set the volume loss flag and go ~nto alarm whenever two gains or two losses ln a row are calculated with no intervening calculations showlng no galn or loss.
~ he alar~ program is sho~n in FI6. 24. ~he program provldes appropriate audio and v~sual lndications of the various alarm conditlons that have been flagged~ These lndicatlons may vary from ~nstallat~on to installation and ~ay be program0ed lnto the memory 91 vla keyboards 92 (50,51). Such lndtcatlons are known in the art and wlll not be dlscussed ln detall hereln. ~he alarm program also places a record of the alarm event ln ~emor~ 91. Thls record may be assessed vla ke~boards 92 or remote ter~tnal 49. ~hen the approprlate lndicatlons have been given and the record stored, the system returns to the progra~ lt exlted.
As h~s been descrlbed above, the comblnatlon of the external and tnternal sensors ln one syste~ per~lt more detalled analysis of the `~`
tank sltuatton. Mbreover, ~s has been dlsclosed, the comblned system ~akes lt posslble to d~sc~rd ~larms that may be suspect. Further, the eo~blned syste~ per~ts probes to be set at more sensltlve detect~on levels ~ithout tncreasing, and even decreaslng false alarms. In partlcular, the lnventory ca~culatlon can ln practke be made much ~ore accuratel~; thls ls belleved to be due to the lncreased tnfonnatlon servlng to smooth out the errors ln the calculatlon ln ~uch the s~ne ff~y that lnfonn~tlon on addltlonal varlables lmprove the ``
ccuracy of calculatlon of the solutlon of slmultaneous equattons.
Thus the accuracy ~nd rellablllty of the combined system ls increased ;',':'.
'' ~',' `

1324~25 nuch more dramatically than would be expected from s~mply addlng together the capabilities of the two ~ndependent systems.
A novel tank lnventory and leak detect~on system wh~ch makes electron~c tank gauging practical has been described whtch has mdny other adYan~ages. It is evident that those sk~lled ln the art may now make many uses and modlfications of the spectflc embodiment descr~bed without departing from the ~n~ent~e concepts. For exdmple, different level, leak and other probes ~qy be used~ rhe software may be :
reconflgured, for example, ~lth the decls~on crlteria belng employed ln the alarm program in some ~nstances rather than in the Monttoring Mok . Equlvalent electronlc components and clrcuits may be ^-substituted~ Consequently, the ln~entlon ls to be construed as erbrac~ng each and every novel feature and no~el comblnat~on of `h`;
~e~tures present ln the fluld status detectlon syst-~ descrl~ d.

','-,,~

.. . .

., .
,... ... .
.
~'~

Claims (7)

1. Tank inventory and leak detection apparatus for detecting the status of a liquid storage system and its contents, said apparatus comprising:
external detection means for detecting one or more conditions of liquid external of said storage system and for providing an external liquid signal;
internal detection means for detecting one or more conditions of liquid internal of said storage system and for producing an internal liquid signal;
means for storing decision criteria relating one or more of said external liquid conditions and one or more of said internal liquid conditions; and indicating means communicating with said means for storing and responsive to said external liquid signal and said internal liquid signal for providing an indication of the status of said liquid storage system and its contents.

2. The apparatus of claim 1 wherein said external detection means comprises a collecting means for detecting the presence of small quantities of hydrocarbon liquid.

3. The apparatus of claim 2 wherein said external detection means further comprises a float means configured to fit within said collecting means and occupy the major portion of its volume at the liquid-float interface, and a sensing means attached to said float for providing said external liquid signal.

4. The apparatus of claim 2 wherein said external detection means comprises a vapor sensor and a means for locating said vapor sensor between the walls of an near the bottom of said double-walled tank.

5. The apparatus of claim 2 wherein said internal detection means comprises measurement means for measuring the quantity of liquid in said storage system.

6. The apparatus of claim 5 wherein said measurement means comprises liquid level means for measuring the liquid level in the storage system and at least one temperature sensor means for sensing the temperature of the liquid in the storage system.

7. The apparatus of claim 1 wherein said means for storing comprises means for storing decision criteria for determining the location of a leak in said liquid storage system and said indicating means includes means for indicating the location of said leak in said liquid storage system.