CN104267232B - A kind of non-cpntact measurement capacitance sensor lower frequency limit extension system - Google Patents
A kind of non-cpntact measurement capacitance sensor lower frequency limit extension system Download PDFInfo
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- CN104267232B CN104267232B CN201410539060.0A CN201410539060A CN104267232B CN 104267232 B CN104267232 B CN 104267232B CN 201410539060 A CN201410539060 A CN 201410539060A CN 104267232 B CN104267232 B CN 104267232B
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- capacitance sensor
- frequency band
- expanding device
- band expanding
- measurement
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Abstract
The present invention discloses a kind of transformer coil transient process non-cpntact measurement capacitance sensor lower frequency limit extension system.The system includes SMD capacitance sensor, frequency band expanding device, measurement cable, RC compensation match circuit and measuring system output port.High-voltage signal is changed into low-voltage signal by SMD capacitance sensor using the voltage signal of principle of capacitive divider sensor transformer coil wire turn.The expansion of capacitance sensor lower frequency limit is realized in input impedance of the frequency band expanding device by increasing measuring system.RC compensation match circuits can improve the high frequency characteristics of measuring system.Power-frequency voltage and long wave tail voltage in the measurable winding of capacitance sensor after the expansion of lower frequency limit.
Description
Technical field：
The invention belongs to power transformer transient voltage field of measuring technique, more particularly to a kind of non-cpntact measurement electric capacity
Sensor lower frequency limit extension system.
Background technology：
The measuring method of power transformer transient process at present more uses direct method, it is necessary to destroy the insulation system of winding.
Can realize that transformer coil transient process is measured without intervention using the contactless measurement of capacitance sensor.Capacitance sensor
The measurement lower limit frequency of measuring method itself is often hundred Hz.The power frequency electric in measuring transformer coil is difficult to this measuring method
Pressure and wave rear switching overvoltage long.Therefore need to expand the lower frequency limit of capacitance sensor measuring method, realize transformer wire
The broadband measurement of transient process in circle.
The content of the invention：
According to disadvantages described above, the present invention is proposed under a kind of capacitance sensor for measuring transformer coil transient process
Limit frequency extension system, it is characterised in that：The system includes capacitance sensor, frequency band expanding device；Wherein：
The capacitance sensor is used to for the high-voltage signal of transformer coil to be changed into low pressure letter by principle of capacitive divider
Number；
Described frequency band expanding device one end is connected with capacitance sensor, and frequency band expanding device is used to increase the input resistance of the system
It is anti-, expand the lower frequency limit of sensor.
The present invention has advantages below：
(1) present invention realizes that impedance conversion reaches the purpose for expanding lower frequency limit using integrated circuit technique.
(2) present invention increases frequency band expanding device unit using by between capacitance sensor and measurement cable, realizes surveying
The input impedance of amount system, to the transformation of high resistant, so as to increase the time constant of measuring system, has expanded its lower limit frequently from low-resistance
Rate.
Brief description of the drawings：
Fig. 1 is the equivalent circuit of the measuring system for not adding frequency band expanding device, C in figure1It is capacitance sensor high voltage arm capacitor,
C2It is capacitance sensor low-voltage arm electric capacity, RpIt is cable head build-out resistor, Z is measurement cable wave impedance, R0For measuring instrument is defeated
Enter impedance；
Fig. 2 is capacitance sensor measuring system schematic diagram；C in figure1It is capacitance sensor high voltage arm capacitor, C2For electric capacity is passed
Sensor low-voltage arm electric capacity, RpIt is frequency band expanding device front end build-out resistor, R1It is frequency band expanding device front end parallel connection high resistant, Z is measurement electricity
Cable wave impedance, Ri、CiRespectively RC compensation circuits resistance and electric capacity, R0It is measuring instrument input impedance；
Fig. 3 is SMD capacitance sensor schematic diagram；1st, BNC connector；2nd, metal shell；3rd, Kapton；4th, feel
Answer electrode；5th, winding conducting wire d1：Kapton thickness 0.1mm；d2：Induction electrode thickness 0.05mm；
Fig. 4 is the electric capacity schematic diagram with frequency band expanding device；
Fig. 5 is RC compensation circuit structural representations.
Specific embodiment：
Referring to Fig. 1 to Fig. 5, the present invention is realized by following technical proposal.
In one embodiment
Capacitive sensor system of the present invention is made up of capacitance sensor, frequency band expanding device, wherein：
The capacitance sensor is used to for the high-voltage signal of transformer coil to be changed into low pressure letter by principle of capacitive divider
Number；
Described frequency band expanding device one end is connected with capacitance sensor, and frequency band expanding device is used to increase the input resistance of the system
It is anti-, expand the lower frequency limit of sensor.
In another embodiment
The capacitance sensor is SMD capacitance sensor, and the SMD capacitance sensor is by induction electrode, insulation
Film and BNC connector are constituted, and the SMD capacitance sensor periphery is enclosed with metal shell；It is gold in the middle of the BNC connector
Category guide rod, periphery parcel insulating materials, the BNC connector is connected with induction electrode；The induction electrode, insulation film and metal
Shell seal is connected.
Preferably, the induction electrode is made of copper；The insulation film need to increase paster using Kapton
The low-voltage arm electric capacity of formula capacitance sensor.
The frequency band expanding device is needed with high input impedance (more than 10M Ω), low output impedance (50 Ω), broadband (0
~100MHz), voltage amplification factor is 1, and the frequency band expanding device belongs to the voltage feedback type operation amplifier of unity gain stable
Device.
The lower-cut-off frequency of the capacitance sensor measuring system is f=[2 π (Rp+R0)(C1+C2)]-1.If taking R0=
1M Ω, Rp=50 Ω, C1=0.5pF, C2=1.3nF, then f be about 122Hz, it is impossible to meet to power-frequency voltage in transformer coil
The measurement request of (frequency is 50Hz) and switching overvoltage (Hz of equivalent frequency about hundred).To reduce lower-cut-off frequency f, it is necessary to increase
Big R0.The present invention is exactly using frequency band expanding device increase R0So as to meet measurement request.For example frequency band expanding device can be by R0It is increased to
100M Ω, improved measuring system lower-cut-off frequency is 1.22Hz, so as to the measurement request of system can be met.
Preferably, the main circuit of frequency band expanding device is a voltage follower being made up of high speed operation amplifier and resistance.
Accessory circuit is the power circuit of operational amplifier.
Preferably, the operational amplifier can use model 0PA659 type operational amplifiers, and it has 0~650MHz
Bandwidth and unity gain stable characteristic, input resistance is 1012Ω。
Preferably, the circuit element of frequency band expanding device is connected using printed circuit board (PCB), the biography of signal during design
It is defeated to keep straight line as far as possible.The input impedance of frequency band expanding device determines by the input impedance of operational amplifier, 10M Ω with
On.Output impedance should be matched with the cable of rear class, therefore concatenate one 50 Ω resistance in impedance transformer output end.
Preferably, frequency band expanding device uses lithium battery power supply, and cell voltage is ± 6V.Resistance is adopted in RC compensation match circuits
With noninductive resistance, it is 50 Ω that resistance is identical with measurement cable wave impedance.The selection of integrating capacitor needs to consider sensor electricity
Hold and cable length.
The input impedance of frequency band expanding device is relevant with the input impedance of operational amplifier, and output impedance is identical with measurement cable
It is 50 Ω；
Preferably, it is the influence that reduces catadioptric, frequency band expanding device head end can increase build-out resistor Rp, resistance elects 50 as
Ω.Meanwhile, when frequency band expanding device input impedance is excessive, the capacitance sensor induction electrode charge discharging resisting time is more long, measurement weight
There is problem during frequency pulse.It is this in frequency band expanding device front end parallel connection one resistance larger resistance R1, it is preferred that resistance is 500M
Ω；
Preferably, frequency band expanding device circuit is integrally positioned in shielding box, and preferably material is copper.Input/output port can be adopted
With engineering modular connection, such as Q9 joints etc., can be with the superior and the subordinate's circuit good match；
Frequency band expanding device is installed between capacitance sensor and measurement cable, by BNC connection；
In another embodiment
The method that the present invention is provided also includes measurement cable and RC compensation circuits.
Measurement cable one end connection frequency band expanding device, other end connection RC compensation circuits；The measurement cable is used
In connection transformer coli winding and measurement apparatus, such as oscillograph, its wave impedance is 50 Ω.
RC compensation circuits are positioned in copper shield pipe, and first and last end connects head output signal using BNC.
When cable length is more long, the direct-to-ground capacitance of cable can influence measuring system performance.For this cable end piece needs to increase
RC compensation circuits.Compensation resistance is identical with cable wave impedance, elects 50 Ω as.The selection of compensating electric capacity needs to carry out experiment determination.
When cable length is 3m, compensating electric capacity is optimal when being 210pF；
RC compensation circuits two ends use bnc interface, integrally use coaxial configuration, brass shell as framework, while can be with
Influence of the shielding outside electromagnetic interference to integrating circuit.New introducing RC compensation circuits can be reduced using said structure latter aspect
Stray parameter, reduce the new stray capacitance and stray inductance introduced in circuit；On the other hand due to selecting coaxial configuration, can be with
Make compensation circuit impedance and cable Impedance matching；
RC compensation circuits are made up of noninductive resistance and compensating electric capacity；
Preferably, the resistance value of the noninductive resistance is identical with the measurement cable wave impedance；RC compensation match circuits are mended
The selection for repaying capacitance is determined by the electric capacity of capacitance sensor and the direct-to-ground capacitance of measurement cable.
Description of the invention is given for the sake of example and description, and is not exhaustively or by the present invention
It is limited to disclosed form.Many modifications and variations are for the ordinary skill in the art obvious.Select and retouch
State embodiment and be to more preferably illustrate principle of the invention and practical application, and one of ordinary skill in the art is managed
The solution present invention is suitable to the various embodiments with various modifications of special-purpose so as to design.
Claims (9)
1. a kind of capacitance sensor lower frequency limit extension system for measuring transformer coil transient process, it is characterised in that：
The system includes capacitance sensor, frequency band expanding device；Wherein：
The capacitance sensor is used to for the high-voltage signal of transformer coil to be changed into low-voltage signal by principle of capacitive divider；
Described frequency band expanding device one end is connected with capacitance sensor, and frequency band expanding device is used to increase the input impedance of the system,
Expand the lower frequency limit of sensor.
2. system according to claim 1, it is characterised in that the system also includes measurement cable, RC compensation matching electricity
Road；
Measurement cable one end connection frequency band expanding device, other end connection RC compensation circuits；
The RC compensation match circuit is used to compensate the signal distortion caused by the direct-to-ground capacitance of measurement cable, while realizing measurement
The impedance matching of cable, for improving the high frequency response of the system, the RC compensation match circuit first and last ends are connected using BNC
Head output signal.
3. system according to claim 1, it is characterised in that the capacitance sensor is SMD capacitance sensor, institute
State SMD capacitance sensor to be made up of induction electrode, insulation film and BNC connector, the SMD capacitance sensor periphery bag
It is wrapped with metal shell；It is metal guide rod, periphery parcel insulating materials, the BNC connector and induction electrode in the middle of the BNC connector
Connection；The closing connection of the induction electrode, insulation film and metal shell.
4. system according to claim 3, it is characterised in that：The induction electrode is made of copper；The insulation film is needed
Increase the low-voltage arm electric capacity of SMD capacitance sensor using Kapton.
5. system according to claim 3, it is characterised in that：Described frequency band expanding device is by BNC connector and paster electricity
Hold sensor connection, the main circuit of the frequency band expanding device is made up of high speed operation amplifier and resistance；Accessory circuit is computing
The power supply circuit of amplifier, the power supply circuit provides ± 5V power supplys for operational amplifier.
6. system according to claim 5, it is characterised in that the operational amplifier has a high input impedance, broadband,
Using the operational amplifier of model OPA659.
7. system according to claim 5, it is characterised in that：The circuit element of the frequency band expanding device uses printed circuit
Plate is connected, and whole frequency band expanding device is positioned in the shielding shell of brass making, and the frequency band expanding device uses chargeable lithium
Battery is powered.
8. system according to claim 2, it is characterised in that：The RC compensation circuits are by noninductive resistance and compensating capacitance group
Into the resistance value of the noninductive resistance is identical with the measurement cable wave impedance；RC compensates the choosing of match circuit compensating electric capacity value
Take and determined by the electric capacity of capacitance sensor and the direct-to-ground capacitance of measurement cable.
9. system according to claim 2, it is characterised in that：It is described measurement cable be used for connect transformer coli winding and
Measurement apparatus, its wave impedance is 50 Ω.
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| CN108152554B (en) * | 2018-02-02 | 2024-03-19 | 中国工程物理研究院流体物理研究所 | Capacitive voltage divider for measuring pulse voltage of coaxial cable |
| CN108872682B (en) * | 2018-08-30 | 2020-07-28 | 重庆大学 | Microstrip line coupling-based voltage measurement device and method |
| CN115494281A (en) * | 2022-09-19 | 2022-12-20 | 芜湖麦可威电磁科技有限公司 | Wireless induction type capacitive voltage divider |
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