CN103542954B - A kind of high-precision thermocouple input module and measuring method - Google Patents
A kind of high-precision thermocouple input module and measuring method Download PDFInfo
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- CN103542954B CN103542954B CN201310470168.4A CN201310470168A CN103542954B CN 103542954 B CN103542954 B CN 103542954B CN 201310470168 A CN201310470168 A CN 201310470168A CN 103542954 B CN103542954 B CN 103542954B
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Abstract
The present invention relates to a kind of high-precision thermocouple input module, comprise isolator, amplifier, AD conversion unit, controller, D/A conversion unit and electronic switch, isolator is connected with thermopair, the output terminal AD conversion unit of amplifier, the output terminal connection control device of AD conversion unit, it is characterized in that: the earth terminal of isolator outwards draws ground interface while ground connection, the voltage output end of isolator outwards draws two interfaces simultaneously, controller according to the signal obtained by AD conversion unit to D/A conversion unit output feedback signal, the output terminal of D/A conversion unit outwards draws output interface.Another technical scheme of the present invention there is provided a kind of high-precision thermopair input measurement method, adopts above-mentioned thermocouple input module.Advantage of the present invention is: ensure that the overall absolute precision of thermocouple signal is at 0.1 ~ 0.2 DEG C, relative accuracy can reach 0.005 ~ 0.01%, can meet the real needs of industrial control process.
Description
Technical field
The present invention relates to a kind of high-precision thermocouple input module and measuring method, for improving the measuring accuracy of the thermoelectricity occasionally small-signal such as millivolt, belonging to instrument for automatic control technical field.
Background technology
Thermopair is connected to form closed-loop path in its end by the metal wire of two kinds of different components, the one end being directly used as measuring media temperature is called working end (also referred to as measuring junction), the other end is called cold junction (also referred to as compensation end), when there is temperature difference between working end and cold junction, just have electric current in loop to pass through, now just there is thermopower (Seebeck effect) between two ends, according to circumstances select the voltage that different metal materials just can draw approximately and temperature difference is proportional to export.But this voltage is all very very little, the thermoelectrical potential that such as more modal nickel chromium triangle-nisiloy K type thermocouple-270 DEG C ~ 1372 DEG C is corresponding is-6.458mV ~ 54.886mV, and the thermoelectrical potential that nickel chromium triangle-cupronickel E type thermocouple-270 DEG C ~ 1000 DEG C is corresponding is-9.835mV ~ 76.373mV.
The signal processing method of the thermocouple input module of scattered control system (DCS) or programmable control system (PLC) dispatch control system obtains the thermopower (millivolt voltage signal) produced by thermopair, analog electrical signal is it can be used as to be amplified to volt voltage signal through amplifier, be input in the numerical data of control chip via analog to digital converter (ADC) again, by control chip or transfer to host computer to table look-up according to Graduation Number or adopt the process of temperature estimation model formation to convert actual temperature to.
Early stage due to semiconductor technology backwardness relatively, in order to overcome the slow and problem that memory span is little of control chip processing speed, adopt various temperature estimation model formation to process.Along with the technical indicator of control chip processing speed and memory capacity significantly promotes, adopt the most original small error tabling look-up to overcome temperature estimation model formation and actual temperature.
From surface, thermocouple signal measuring accuracy can focus on analog to digital converter (ADC), general analog to digital converter adopts 12, although analog to digital converter theoretical resolution is 1/4096 (namely 2/10000ths), the reason but the temperature due to the components and parts such as reference voltage and resistance of the components and parts such as amplifier and analog to digital converter is waftd etc., the measuring accuracy of in fact whole thermocouple signal is generally between 0.1 ~ 0.2%, even if analog to digital converter is brought up to 13 or 14, even 15 by some producer, but overall measurement accuracy can not improve how many.
In industrial stokehold, this relative accuracy is also little for valve seat opening, pressure, flow, liquid level, electric current and voltage etc. the process variable problem of topworks, but for temperature signal, because it does not have concrete range ability, generally thermocouple input module is the thermocouple signal of compatible various Graduation Number, the thermoelectrical potential signal adopted has enough upper limit nargin, be converted to the temperature range upper limit and can reach 2000 DEG C, at this moment relative accuracy be converted to absolute value can to 2 DEG C ~ 4 DEG C.And in fact, low temperature generally can occur in device start process, when industrial process normally runs, main temperature course parameter can carry out change by a small margin at a higher temperature.Such as, when 600MW ultra supercritical thermal power generation unit boiler superheater outlet temperature is more than 50% declared working condition, temperature is run substantially between 560 ± 10 DEG C; range of temperature is at 20 DEG C; if and use as boiler safety guard signal; jump stove value and be also only 597 DEG C, temperature variation is that the absolute error of+37 DEG C at this moment 2 DEG C ~ 4 DEG C just seems very serious.
Summary of the invention
The technical problem to be solved in the present invention is the precision ensureing thermocouple signal.
In order to solve the problems of the technologies described above, a technical scheme of the present invention there is provided a kind of high-precision thermocouple input module, comprise isolator, amplifier, AD conversion unit, controller, D/A conversion unit and electronic switch, isolator is connected with thermopair, the output terminal AD conversion unit of amplifier, the output terminal connection control device of AD conversion unit, it is characterized in that: the earth terminal of isolator outwards draws ground interface while ground connection, the voltage output end of isolator outwards draws two interfaces simultaneously, be respectively the first voltage output interface and the second voltage output interface, controller according to the signal obtained by AD conversion unit to D/A conversion unit output feedback signal, the output terminal of D/A conversion unit outwards draws output interface, by the action of electronic switch, the in-phase input end of amplifier is connected with the first voltage output interface, the inverting input of amplifier is connected with ground interface simultaneously, or the in-phase input end of amplifier is connected with output interface, the inverting input of amplifier is connected with ground interface simultaneously, or the in-phase input end of amplifier is connected with output interface, the inverting input of amplifier is connected with the second voltage output interface simultaneously.
Preferably, described amplifier is programmable operational amplifier.
Preferably, described electronic switch has two, is single-pole double-throw (SPDT) electronic switch.
Preferably, described AD conversion unit and described D/A conversion unit select the converter of 12 precision.
Another technical scheme of the present invention there is provided a kind of high-precision thermopair input measurement method, and adopt above-mentioned thermocouple input module, its basic ideas are:
The enlargement factor of step-down amplifier, is divided into small-range scope by the bound range reference point of temperature from the section of super large range ability after prediction actual measurement temperature value.Controller utilizes digital to analog converter to form a closed loop as feedback end and input end, and the reference data value of adjustment amplifier is to overcome the composition error of input end and feedback end.Increase substantially the enlargement factor of amplifier, in conjunction with the reference data value of corrected amplifier, the temperature value calculating high-precision thermocouple signal corresponding through controller is characterised in that, concrete steps are:
The first step, operation electronic switch, the in-phase input end of amplifier is connected with the first voltage output interface, the inverting input of amplifier is connected with ground interface simultaneously, the enlargement factor of amplifier is set to A, controller obtains the initial value by the output voltage Vp of AD conversion unit, according to the initial value of output voltage Vp and the temperature Tp of correspondence thereof, the upper limit range value of thermocouple input module is defined as Tp+A DEG C, lower limit range value is defined as Tp-A DEG C, tables look-up find the thermopower V0 corresponding with Tp+A DEG C according to Graduation Number;
Second step, operation electronic switch, the in-phase input end of amplifier is connected with output interface, the inverting input of amplifier is connected with ground interface simultaneously, the feedback voltage V f of adjustment controller, make the reference voltage Vref=V0+ Δ 1 on output interface, Δ 1 is the input composition error of amplifier and AD conversion unit;
3rd step, operation electronic switch, the in-phase input end of amplifier is connected with output interface, the inverting input of amplifier is connected with the second voltage output interface simultaneously, the enlargement factor of amplifier is set to B, B is much larger than A, now, reference voltage Vref on the in-phase input end of amplifier=V0+ Δ 1, voltage on the inverting input of amplifier is the output voltage Vi of isolator, end difference is V0+ Δ 1-Vi, after deducting the input composition error Δ 1 of amplifier and AD conversion unit, the output voltage Vp=V0+ Δ 1-Vi-Δ 1=V0-Vi of final AD conversion unit, the temperature Ti that this thermopower is corresponding, then final temperature value is Tp+A-Ti.
Advantage of the present invention is: ensure that the overall absolute precision of thermocouple signal is at 0.1 ~ 0.2 DEG C, relative accuracy can reach 0.005 ~ 0.01%, can meet the real needs of industrial control process.
Accompanying drawing explanation
Fig. 1 is the high-precision thermocouple input module schematic diagram of one provided by the invention.
Embodiment
For making the present invention become apparent, hereby with preferred embodiment, and accompanying drawing is coordinated to be described in detail below.
As shown in Figure 1, the high-precision thermocouple input module of one provided by the invention, comprise isolator, amplifier, AD conversion unit ADC, controller, D/A conversion unit DAC and electronic switch, isolator is connected with thermopair, the output terminal AD conversion unit ADC of amplifier, the output terminal connection control device of AD conversion unit ADC, it is characterized in that: the earth terminal of isolator outwards draws ground interface 4 while ground connection, the voltage output end of isolator outwards draws two interfaces simultaneously, be respectively the first voltage output interface 1 and the second voltage output interface 3, controller according to the signal obtained by AD conversion unit ADC to D/A conversion unit DAC output feedback signal, the output terminal of D/A conversion unit DAC outwards draws output interface 2, by the action of electronic switch, the in-phase input end SA of amplifier is connected with the first voltage output interface 1, the inverting input SB of amplifier is connected with ground interface 4 simultaneously, or the in-phase input end SA of amplifier is connected with output interface 2, the inverting input SB of amplifier is connected with ground interface 4 simultaneously, or the in-phase input end SA of amplifier is connected with output interface 2, the inverting input SB of amplifier is connected with the second voltage output interface 3 simultaneously.
Amplifier is programmable operational amplifier.
Electronic switch has two, is single-pole double-throw (SPDT) electronic switch.
AD conversion unit ADC and described D/A conversion unit DAC selects the converter of 12 precision, and those skilled in the art also can select the converter of other precision as required.
Utilize the thermopair input measurement method of above-mentioned module, the steps include:
The first step, operation electronic switch, the in-phase input end SA of amplifier is connected with the first voltage output interface 1, the inverting input SB of amplifier is connected with ground interface 4 simultaneously, the enlargement factor of amplifier is set to A, controller obtains the initial value by the output voltage Vp of AD conversion unit ADC, according to the initial value of output voltage Vp and the temperature Tp of correspondence thereof, the upper limit range value of thermocouple input module is defined as Tp+A DEG C, lower limit range value is defined as Tp-A DEG C, tables look-up find the thermopower V0 corresponding with Tp+A DEG C according to Graduation Number;
Second step, operation electronic switch, the in-phase input end SA of amplifier is connected with output interface 2, the inverting input SB of amplifier is connected with ground interface 4 simultaneously, the feedback voltage V f of adjustment controller, make the reference voltage Vref=V0+ Δ 1 on output interface 2, Δ 1 is the input composition error of amplifier and AD conversion unit ADC;
The derivation of above-mentioned second step is:
If the feedback voltage V f of adjustment controller is thermopower V0, then Vref reference voltage=V0-Δ 2, Δ 2 is feedback integration error, then output voltage Vp=Vref-Δ 1=V0-Δ 2-Δ 1.To make output voltage Vp=V0, then by backwards calculation, need the output feedack voltage Vf of controller to be adjusted to V0+ Δ 2+ Δ 1, now, Vref=Vf-Δ 2=V0+ Δ 2+ Δ 1-Δ 2=V0+ Δ 1.
3rd step, operation electronic switch, the in-phase input end SA of amplifier is connected with output interface 2, the inverting input SB of amplifier is connected with the second voltage output interface 3 simultaneously, the enlargement factor of amplifier is set to B, B is much larger than A, now, reference voltage Vref on the in-phase input end SA of amplifier=V0+ Δ 1, voltage on the inverting input SB of amplifier is the output voltage Vi of isolator, end difference is V0+ Δ 1-Vi, after deducting the input composition error Δ 1 of amplifier and AD conversion unit ADC, the output voltage Vp=V0+ Δ 1-Vi-Δ 1=V0-Vi of final AD conversion unit ADC, the temperature Ti that this thermopower is corresponding, then final temperature value is Tp+A-Ti.
The present invention is further illustrated below in conjunction with data.
High-precision signal generator is utilized to export 27.025mV (this thermopower is corresponding 650 DEG C of K Graduation Number) to the first passage of thermocouple input module, the course of work of thermocouple input module is following (for ease of understanding, during computation and measurement value, enlargement factor is left in the basket):
The first step, operation electronic switch, the in-phase input end SA of amplifier is connected with the first voltage output interface 1, the inverting input SB of amplifier is connected with ground interface 4 simultaneously, the enlargement factor arranging amplifier is 50, obtain the initial value 26.856mV of Vp, according to the initial value 26.878mV of Vp and the temperature Tp (646.53 DEG C) of correspondence, its upper limit range value is defined as 28.984mV (696.53 DEG C), and lower limit range value is defined as 24.758mV (596.53 DEG C).
Second step, operation electronic switch, the in-phase input end SA of amplifier is connected with output interface 2, the inverting input SB of amplifier is connected with ground interface 4 simultaneously, the feedback voltage V f of controller is 28.984mV, the Vp obtained by input end is 28.704mV, by backwards calculation, to make Vp be 28.984mV, then the feedback voltage V f of controller is set as 29.264mV.
3rd step, operation electronic switch, the in-phase input end SA of amplifier is connected with output interface 2, and the inverting input SB of amplifier is connected with the second voltage output interface 3 simultaneously, and the enlargement factor arranging amplifier is 500, now, the actual input 27.025mV of Vref to be 29.131mV, Vi be signal generator, end difference is 2.106, finally obtaining Vp is 1.959mV, the thermopower of converting final measured signal is 27.025, and corresponding temperature is 650 DEG C, and measuring error is 0%.
Claims (3)
1. a high-precision thermocouple input module, comprise isolator, amplifier, AD conversion unit (ADC), controller, D/A conversion unit (DAC) and electronic switch, isolator is connected with thermopair, the output terminal of amplifier connects AD conversion unit (ADC), the output terminal connection control device of AD conversion unit (ADC), it is characterized in that: the earth terminal of isolator outwards draws ground interface (4) while ground connection, the voltage output end of isolator outwards draws two interfaces simultaneously, be respectively the first voltage output interface (1) and the second voltage output interface (3), controller according to the signal obtained by AD conversion unit (ADC) to D/A conversion unit (DAC) output feedback signal, the output terminal of D/A conversion unit (DAC) outwards draws output interface (2), by the action of electronic switch, the in-phase input end of amplifier (SA) is connected with the first voltage output interface (1), the inverting input (SB) of amplifier is connected with ground interface (4) simultaneously, or the in-phase input end of amplifier (SA) is connected with output interface (2), the inverting input (SB) of amplifier is connected with ground interface (4) simultaneously, or the in-phase input end of amplifier (SA) is connected with output interface (2), the inverting input (SB) of amplifier is connected with the second voltage output interface (3) simultaneously,
Described amplifier is programmable operational amplifier;
Described electronic switch has two, is single-pole double-throw (SPDT) electronic switch.
2. a kind of high-precision thermocouple input module as claimed in claim 1, is characterized in that: described AD conversion unit (ADC) and described D/A conversion unit (DAC) select the converter of 12 precision.
3. a high-precision thermopair input measurement method, adopt thermocouple input module as claimed in claim 1, it is characterized in that, step is:
The first step, operation electronic switch, the in-phase input end of amplifier (SA) is connected with the first voltage output interface (1), the inverting input (SB) of amplifier is connected with ground interface (4) simultaneously, the enlargement factor of amplifier is set to A, controller obtains the initial value of the output voltage Vp of AD conversion unit (ADC), according to the initial value of output voltage Vp and the temperature Tp of correspondence thereof, the upper limit range value of thermocouple input module is defined as Tp+A DEG C, lower limit range value is defined as Tp-A DEG C, table look-up according to Graduation Number and find the thermopower V0 corresponding with Tp+A DEG C,
Second step, operation electronic switch, the in-phase input end of amplifier (SA) is connected with output interface (2), the inverting input (SB) of amplifier is connected with ground interface (4) simultaneously, the feedback voltage V f of adjustment controller, make the reference voltage Vref=V0+ Δ 1 on output interface (2), Δ 1 is the input composition error of amplifier and AD conversion unit (ADC);
3rd step, operation electronic switch, the in-phase input end of amplifier (SA) is connected with output interface (2), the inverting input (SB) of amplifier is connected with the second voltage output interface (3) simultaneously, the enlargement factor of amplifier is set to B, B is much larger than A, now, reference voltage Vref=V0+ Δ 1 on the in-phase input end (SA) of amplifier, voltage on the inverting input (SB) of amplifier is the output voltage Vi of isolator, end difference is V0+ Δ 1-Vi, after deducting the input composition error Δ 1 of amplifier and AD conversion unit (ADC), the output voltage Vp=V0+ Δ 1-Vi-Δ 1=V0-Vi of final AD conversion unit (ADC), the temperature Ti that this thermopower is corresponding, then final temperature value is Tp+A-Ti.
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| US5121051A (en) * | 1988-09-22 | 1992-06-09 | U.S. Philips Corporation | Method and apparatus for measuring small electrical signals |
| CN202018345U (en) * | 2011-03-07 | 2011-10-26 | 济南大学 | Novel thermocouple temperature measurement module |
| CN102426066A (en) * | 2011-09-26 | 2012-04-25 | 天津成科自动化工程技术有限公司 | Switching detection circuit using multi-channel PT100 thermistors as temperature sensor |
| CN202814584U (en) * | 2012-09-26 | 2013-03-20 | 深圳市华煜芯科技有限公司 | Temperature measuring system of temperature control device |
| CN203672507U (en) * | 2013-10-10 | 2014-06-25 | 上海发电设备成套设计研究院 | High-precision thermocouple input module |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5121051A (en) * | 1988-09-22 | 1992-06-09 | U.S. Philips Corporation | Method and apparatus for measuring small electrical signals |
| CN202018345U (en) * | 2011-03-07 | 2011-10-26 | 济南大学 | Novel thermocouple temperature measurement module |
| CN102426066A (en) * | 2011-09-26 | 2012-04-25 | 天津成科自动化工程技术有限公司 | Switching detection circuit using multi-channel PT100 thermistors as temperature sensor |
| CN202814584U (en) * | 2012-09-26 | 2013-03-20 | 深圳市华煜芯科技有限公司 | Temperature measuring system of temperature control device |
| CN203672507U (en) * | 2013-10-10 | 2014-06-25 | 上海发电设备成套设计研究院 | High-precision thermocouple input module |
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Address after: 200240 Shanghai city Minhang District Jianchuan Road No. 1115 Patentee after: SHANGHAI POWER EQUIPMENT Research Institute Address before: 200240 Shanghai city Minhang District Jianchuan Road No. 1115 Patentee before: SHANGHAI POWER EQUIPMENT Research Institute |