CN111122170A - High-precision resistance signal conditioning circuit and method based on current source - Google Patents
High-precision resistance signal conditioning circuit and method based on current source Download PDFInfo
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- CN111122170A CN111122170A CN201911190374.3A CN201911190374A CN111122170A CN 111122170 A CN111122170 A CN 111122170A CN 201911190374 A CN201911190374 A CN 201911190374A CN 111122170 A CN111122170 A CN 111122170A
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- G—PHYSICS
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M15/00—Testing of engines
- G01M15/04—Testing internal-combustion engines
- G01M15/042—Testing internal-combustion engines by monitoring a single specific parameter not covered by groups G01M15/06 - G01M15/12
- G01M15/048—Testing internal-combustion engines by monitoring a single specific parameter not covered by groups G01M15/06 - G01M15/12 by monitoring temperature
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Abstract
The invention belongs to the field of monitoring of an aeroengine temperature sensor (resistance signal). The circuit and the method solve the problem that the line resistance of a temperature sensor used in an aircraft engine in the signal transmission process and the impedance superposition of a protection circuit influence the temperature acquisition precision, realize accurate measurement of the working temperature of the engine and judge whether the engine works at normal temperature. The lightning protection circuit comprises a lightning protection circuit, an EMI filter circuit, a Wheatstone bridge, a precision current source, a low-pass filter circuit, a differential amplification circuit and a second-order low-pass filter circuit; the invention reduces the system error caused by the cable resistance of the temperature sensor (resistance signal), and realizes the open-circuit detection function of the temperature sensor through the circuit with simple structure on the basis of realizing high-precision temperature signal acquisition. The circuit has the characteristics of simple structure, strong reliability and high practicability.
Description
Technical Field
The invention belongs to the field of monitoring of temperature signals of an aircraft engine, and relates to a high-precision resistance signal conditioning circuit and method based on a current source, which are used for realizing high-precision monitoring of a temperature sensor (resistance signal) in an engine working state in a complex environment of strong vibration and high noise of the aircraft engine.
Background
The temperature state of an engine of the airplane can be reliably monitored in real time in all operating states of the airplane. In actual work, the working temperature of an engine needs to be monitored, the real-time temperature of the engine is obtained with high precision under the complex environment of strong vibration and high noise, the real-time temperature is an important guarantee for safe flight of an airplane, a temperature sensor used for the airplane engine at present is provided, a lead wire from a sensor end to a conditioning circuit usually reaches several meters, the lead wire enters the conditioning circuit and needs to pass through a thunder and EMI filter circuit, and the superposition of a wire resistance and a protection circuit impedance in the signal transmission process can influence the temperature acquisition precision.
In order to be able to accurately obtain the operating temperature of the engine, accurate acquisition of the temperature signal is the basis of the above-mentioned work. The engine is in the course of the work, and its operational environment is comparatively abominable, and interference factor is many, consequently needs to gather through a high accuracy temperature signal conditioning circuit.
Disclosure of Invention
In order to solve the problem that the superposition of the line resistance and the impedance of a protection circuit of a temperature sensor used for an aircraft engine in the signal transmission process influences the temperature acquisition precision, the invention provides a high-precision resistance signal conditioning circuit based on a current source, the circuit conditions the signal of the engine temperature sensor (resistance signal) into a corresponding voltage signal, the superposition of the line resistance and the impedance of the protection circuit is eliminated by adopting a measuring mode of combining the precision current source and a Wheatstone bridge, the resistance value of a three-wire platinum resistor is accurately acquired, the resistance value is processed by a processor after being acquired by an AD (analog-to-digital) acquisition device, and the circuit also realizes the fault detection function of the resistance temperature sensor to be detected. The circuit is applied to a plurality of engine health management monitoring devices, and has stable functional performance and higher test precision.
The technical scheme of the invention is to provide a high-precision resistance signal conditioning circuit based on a current source, which is characterized in that: the lightning protection circuit comprises a lightning protection circuit, an EMI filter circuit, a Wheatstone bridge, a precision current source, a low-pass filter circuit, a differential amplification circuit and a second-order low-pass filter circuit;
the output end of the lightning protection circuit is electrically connected with the input end of the EMI filter circuit, the output end of the EMI filter circuit and the output end of the precision current source are electrically connected with the input end of the Wheatstone bridge, and the output end of the Wheatstone bridge, the low-pass filter circuit, the differential amplification circuit and the second-order low-pass filter circuit are electrically connected in sequence;
the lightning protection circuit is used for realizing lightning protection;
the EMI filter circuit is used for realizing electromagnetic compatibility protection;
the Wheatstone bridge is used for measuring the resistance value of the resistor to be measured;
the output voltage of the precision current source generates high-precision current through a high-precision resistor (the error cannot exceed one thousandth), excitation is applied to a Wheatstone bridge, and a resistance signal to be detected is converted into a voltage signal;
the low-pass filter circuit is used for filtering an input voltage signal;
the differential amplification circuit is used for amplifying the voltage signal after the low-pass filtering;
the second-order low-pass filter circuit is used for filtering the voltage signal output by the differential amplification circuit.
Further, the lightning protection circuit comprises 3 TVS tubes, which respectively correspond to three output signals of the resistor to be tested, and the power of each TVS tube is estimated according to the following formula:
P＝IP×Vc………………………(3)
wherein Z issExciting an output impedance for the signal; v. ofocExciting a peak open circuit voltage for the signal; i isscExciting a peak short circuit current for the signal; i isPIs the transient peak current; vcThe maximum clamping voltage of the TVS tube is obtained; p is the estimated power.
Furthermore, the EMI filter circuit is three paths and respectively corresponds to three output signals of the resistor to be tested, and in order to simplify the design, the EMI filter circuit is an L-shaped EMI filter circuit consisting of an inductor and a capacitor;
the input impedance of the LC filter circuit is as shown in equation (4):
wherein Z isjωThe input impedance of the LC filter circuit is L, inductance, capacitance, cut-off frequency, angular frequency, and imaginary number.
Further, the three resistance values of the wheatstone bridge are equal and are Ra, and Ra is greater than the resistance value R of the resistor to be measuredpt；
The final output voltage U of the Wheatstone bridge32Comprises the following steps:
wherein I is the current output by the precision current source.
Further, the low-pass filter cut-off frequency of the low-pass filter circuitRate fLIt is confirmed that only signals having a frequency band within a limited range are allowed to pass through according to the following formula:
then by choosing the appropriate resistance-capacitance device R56、C78And C6To a low pass cut-off frequency requirement, where R56Is a resistance in an electric circuit, C78Being capacitors in the circuit, C6Is a common capacitance.
Further, a second-order low-pass filter cut-off frequency f in the second-order low-pass filter circuitLConfirmed according to the following formula:
wherein R is89Is a resistance value in the circuit, C90Is the capacitance value in the circuit.
Further, the protection range of the lightning protection circuit is three protection levels.
The invention also provides a conditioning method of the high-precision resistance signal conditioning circuit based on the current source, which comprises the following steps:
firstly, three paths of resistance signals of a resistance to be detected pass through a lightning protection circuit and an EMI filter circuit to realize lightning protection and electromagnetic compatibility protection;
secondly, eliminating a line resistance signal and a protection circuit impedance superposed signal in the transmission process of the resistance signal to be detected by combining the lightning protection circuit and the EMI filter circuit with a Wheatstone bridge; the resistance signal to be detected is converted into a voltage signal through a precise current source and a Wheatstone bridge;
and step three, outputting a voltage signal after passing through a low-pass filter circuit, a differential amplifier circuit and second-order low-pass filtering in sequence.
The invention also provides a method for realizing fault detection of the resistance sensor to be detected by utilizing the high-precision resistance signal conditioning circuit based on the current source, when the output voltage of the operational amplifier of the differential amplification circuit in the high-precision resistance signal conditioning circuit based on the current source is full-biased, the resistance sensor to be detected is considered to have open circuit or short circuit fault; when the output voltages of the operational amplifiers of the differential amplification circuit in the high-precision resistance signal conditioning circuit based on the current source are all in the normal amplification area, the resistance sensor to be measured is considered to work normally.
The invention has the beneficial effects that:
1. the resistance value of the three-wire platinum resistor is accurately obtained by adopting a measuring mode of combining a precise current source and a Wheatstone bridge, the sectional areas and the lengths of 3 wires led out in a three-wire lead mode are the same, the Wheatstone bridge is adopted for measuring, the influence of the resistance of an inner lead can be eliminated during measurement, the error of the resistance of the lead is eliminated, and the lead is converted into a voltage signal through a conditioning circuit;
2. the EMI filter circuit is an L-shaped LC low-pass filter circuit, and aims to eliminate conduction and radiation noise; in order to meet the requirement of EMI protection, proper turning frequency is selected according to the frequency range to be protected
Attenuating noise outside the frequency range;
3. the conditioning circuit selects the reference voltage source chip and the resistor with high precision and low temperature drift, and effectively reduces the measurement error caused by the factors (precision and temperature drift) of the device in the circuit;
4. the high-precision platinum resistance sensor signal conditioning circuit based on the current source simultaneously has the function of detecting the fault of the three-wire platinum resistance temperature sensor.
Drawings
FIG. 1 is a schematic diagram of the operation of a platinum resistance sensor signal conditioning circuit;
FIG. 2 is a schematic diagram of a three wire platinum resistance temperature sensor signal conditioning circuit;
FIG. 3 is an LC passive filter circuit;
FIG. 4 is a three wire platinum resistance measurement principle;
FIG. 5 is a Wheatstone bridge;
FIG. 6 is a schematic diagram of a filter amplifier circuit;
fig. 7 is a simplified depiction of a filter amplifier circuit.
Detailed Description
The invention is further described with reference to the following drawings and specific embodiments.
As can be seen from FIG. 1, the high-precision resistance signal conditioning circuit based on the current source mainly comprises a lightning protection circuit, an EMI filter circuit, a Wheatstone bridge, a precision current source, a low-pass filter circuit, a differential amplification circuit and a second-order low-pass filter circuit; the input end of the lightning protection circuit is connected with a resistance signal to be detected, the output end of the lightning protection circuit is electrically connected with the input end of the EMI filter circuit, the output end of the EMI filter circuit and the output end of the precision current source are electrically connected with the input end of the Wheatstone bridge, and the output end of the Wheatstone bridge, the low-pass filter circuit, the differential amplification circuit and the second-order low-pass filter circuit are electrically connected in sequence.
As can be seen from fig. 2, in this embodiment, 3 sets of bidirectional TVS tubes are adopted, which respectively correspond to three output signals of the resistor to be tested, and are connected in series between the input interface and the chassis ground for lightning protection, and the power requirement estimation formula of the TVS tubes is as follows:
P＝IP×Vc………………………(3)
wherein,
Zs-the signal excites the output impedance;
voc-the signal excites the peak open circuit voltage;
Isc-signal excitation peak short circuit current;
IP-a transient peak current;
Vc-maximum clamping voltage of TVS tube
P-estimated Power.
When the circuit is designed, the TVS tube is selected to meet the following conditions: rated reverse turn-off voltage V of TVS tubewmShould be greater than or equal to the maximum operating voltage of the circuit being protected; the maximum clamping voltage of the TVS tube is less than the damage voltage of the protected circuit; according to the protection grade requirement, the maximum peak pulse power consumption P of the TVS tubePPMShould be greater than the peak pulse power that may occur within the protected circuit.
As can be seen from fig. 3, the EMI filter circuit of this embodiment uses an LC passive filter circuit, where JK _ PT _ IN + is an input terminal. The input impedance of the LC filter circuit is as shown in equation (4):
can be obtained from the formula (4),
where f is the cut-off frequency, ω is the angular frequency, and j is an imaginary number.
After TVS is adopted, a precise current source forms shunt (leakage current) in a TVS tube, meanwhile shunt exists in an LC passive filter circuit of an EMI filter circuit, the impedance of the TVS tube and the impedance of the LC passive filter circuit and the wire resistance in the circuit influence the accuracy of acquired signals. The three-wire system measurement principle is shown in fig. 4:
during measurement, the three wires with the resistance of r1, r2 and r3 adopt the same specification and lengthR1-R2-R3-R, RptFor platinum resistance, measuring terminals Ua, UbThe point measurement circuit uses a high impedance input circuit. To test RptA constant current I is added to the terminal U1. The Ua voltage is then:
Ua＝I×(r1+Rpt+r2)＝I×(Rpt+2r)………………………(6)
due to UbThe measuring terminal is a high impedance input terminal where no current flows through the wire, so:
Ub＝I×r3＝I×r
Rptab point voltage at two ends is Uptab。
Ua-2Ub＝I×(Rpt+2r)-2(I×r)＝Uptab………………………(7)
From the above formula, it can be seen that the influence of the resistance r of the wire on the measurement is eliminated by using the platinum resistance temperature sensor with three wires, and it can be seen that the measurement only needs to provide a constant current I and measure Ua，UbThe voltage of the spot. Therefore, the invention adopts a precise current source to provide a constant current I.
As shown in FIG. 2, the precision current source of this embodiment comprises a precision voltage source N1, a capacitor C12, and a precision resistor R1And (4) forming. Output voltage U of precision voltage source1And R1An output current is determined. The output of the precision current source is as follows:
in FIG. 2, the Wheatstone bridge is composed of R2, R3, R4 and RPTAnd (4) forming. Wherein R2 ═ R3 ═ R4 ═ Ra. The excitation of the wheatstone bridge is the output I of the current source, the wheatstone bridge is simplified as in fig. 5.
As can be seen from formula (12), when R isa>RptWhile, U32>0. Therefore, in order to ensure that the output of the conditioning circuit is always positive, when designing a wheatstone bridge, it is necessary to ensure that the arm resistance Ra is greater than the maximum value of the platinum resistor.
The present embodiment adopts a passive low-pass filter, that is, a low-pass filter with a cut-off frequency designed to be a suitable frequency by using a resistor and a capacitor, and the function of the low-pass filter is to allow only signals with a frequency band within a limited range to pass through.
By simplifying the precision current source and the wheatstone bridge, the circuit is simplified as shown in fig. 6. For convenience of description, symmetrical resistors, inductors, and capacitors are denoted by the same symbols. Namely, L1 ═ L2 ═ L, C1+ C2 ═ C3+ C4 ═ C12，C7＝C8＝C78，R5＝R6＝R56，R8＝R9＝R89，C9＝C10＝C90. The capacitance reactance of the capacitor C is ZCB, carrying out the following steps of; the inductance of the inductor L is ZL. The circuit is shown in fig. 7.
In fig. 7:
is a passive low-pass filter with low-frequency cut-off frequency fLSatisfies the following conditions:
at this time, the following can be obtained:
then by choosing the appropriate resistance-capacitance device R56、C78And C6To the requirement of a low-pass cut-off frequency.
Since the voltage signal output by the wheatstone bridge is relatively small (mV level), amplification is required. The differential amplifier circuit composed of the typical operational amplifier is selected in the embodiment, and has the characteristics of strong output signal and strong anti-interference capability, so that the differential amplifier circuit is suitable for being used in the engine sensor conditioning circuit, and the anti-interference capability of the circuit can be improved. In FIG. 7, the voltage amplifier and the resistor R12An amplifying circuit is formed to realize the millivolt level signal amplification of the sensor with the amplification factor of
The present embodiment uses an active second-order low-pass filter, that is, a low-pass filter with a cut-off frequency of a desired frequency is designed by using a resistor, a capacitor and an amplifier, and the function of the low-pass filter is to allow only signals with a frequency band within a limited range to pass through. In fig. 7:
is an active second-order low-pass filter, low-frequency cut-off frequency:
by selecting suitable resistance-capacitance means R89、C90To meet the requirement of a low-pass cut-off frequency.
The resistance signal can be conditioned by the following processes:
step 1: the resistance signal of the platinum resistance temperature sensor firstly passes through a lightning protection circuit formed by TVS tubes and an L-shaped EMI filter formed by an inductor and a capacitor;
step 2: the resistance signal is converted into a millivolt voltage signal through a precise current source and a Wheatstone bridge, wherein the precise current source and the Wheatstone bridge are composed of a high-precision voltage source, a high-precision resistor and a capacitor;
and step 3: then passing through a passive low-pass filter consisting of a resistor and a capacitor;
and 4, step 4: and amplifying the millivolt-level signal to a proper range by a precise signal amplifier, performing second-order filtering on the signal after amplification, and directly outputting the filtered signal to an analog-to-digital converter to measure an analog value.
Because the working environment of the platinum resistance temperature sensor is generally severe, the lead wire from the lead wire end of the sensor to the conditioning circuit usually reaches several meters, and the protection of the lead wire is very important in the temperature conditioning circuit during design, so as to avoid the phenomena of disconnection and mutual short circuit; under the normal working condition of the sensor, the output voltage of the operational amplifier is in a normal amplification region, a saturation state cannot occur, and the fault detection function of the sensor is realized through the criterion.
Claims (9)
1. The utility model provides a high accuracy resistance signal conditioning circuit based on current source which characterized in that: the lightning protection circuit comprises a lightning protection circuit, an EMI filter circuit, a Wheatstone bridge, a precision current source, a low-pass filter circuit, a differential amplification circuit and a second-order low-pass filter circuit;
the output end of the lightning protection circuit is electrically connected with the input end of the EMI filter circuit, the output end of the EMI filter circuit and the output end of the precision current source are electrically connected with the input end of the Wheatstone bridge, and the output end of the Wheatstone bridge, the low-pass filter circuit, the differential amplification circuit and the second-order low-pass filter circuit are electrically connected in sequence;
the lightning protection circuit is used for realizing lightning protection;
the EMI filter circuit is used for realizing electromagnetic compatibility protection;
the Wheatstone bridge is used for measuring the resistance value of the resistor to be measured;
the precision current source outputs voltage to generate high-precision current through the high-precision resistor, excitation is applied to the Wheatstone bridge, and a resistance signal to be detected is converted into a voltage signal;
the low-pass filter circuit is used for filtering an input voltage signal;
the differential amplification circuit is used for amplifying the voltage signal after the low-pass filtering;
the second-order low-pass filter circuit is used for filtering the voltage signal output by the differential amplification circuit.
2. The current source based high precision resistive signal conditioning circuit of claim 1, wherein: the lightning protection circuit comprises 3 TVS tubes, three paths of output signals of the resistors to be tested respectively correspond to the TVS tubes, and the power of each TVS tube is estimated according to the following formula:
P＝IP×Vc………………………(3)
wherein Z issExciting an output impedance for the signal; v. ofocExciting a peak open circuit voltage for the signal; i isscExciting a peak short circuit current for the signal; i isPIs the transient peak current; vcThe maximum clamping voltage of the TVS tube is obtained; p is the estimated power.
3. The current source based high precision resistive signal conditioning circuit of claim 1, wherein: the EMI filter circuit is three paths and respectively corresponds to three paths of output signals of the resistor to be tested, and the EMI filter circuit is an L-shaped EMI filter circuit consisting of an inductor and a capacitor;
the input impedance of the LC filter circuit is as shown in equation (4):
wherein Z isjωThe input impedance of the LC filter circuit is L, inductance, capacitance, cut-off frequency, angular frequency, and imaginary number.
4. A current source based high precision resistive signal conditioning circuit according to any of claims 1-3, wherein: the three resistance values of the Wheatstone bridge are equal and are Ra, and Ra is greater than the resistance value R of the resistor to be measuredpt；
The final output voltage U of the Wheatstone bridge32Comprises the following steps:
wherein I is the current output by the precision current source.
5. The current source based high precision resistive signal conditioning circuit of claim 4, wherein: low-pass filter cut-off frequency f of the low-pass filter circuitLConfirmed according to the following formula:
wherein R is56Is a resistance in an electric circuit, C78Being capacitors in the circuit, C6Is a common capacitance.
6. The current source based high precision resistive signal conditioning circuit of claim 5, wherein: second-order low-pass filtering cut-off frequency f in the second-order low-pass filtering circuitLConfirmed according to the following formula:
wherein R is89Is a resistance value in the circuit, C90Is the capacitance value in the circuit.
7. The current source based high precision resistance signal conditioning circuit of claim 6, wherein: the protection range of the lightning protection circuit is three-level protection level.
8. A conditioning method of a high-precision resistance signal conditioning circuit based on a current source is characterized by comprising the following steps:
firstly, three paths of resistance signals of a resistance to be detected pass through a lightning protection circuit and an EMI filter circuit to realize lightning protection and electromagnetic compatibility protection;
secondly, eliminating a line resistance signal and a protection circuit impedance superposed signal in the transmission process of the resistance signal to be detected by combining the lightning protection circuit and the EMI filter circuit with a Wheatstone bridge; the resistance signal to be detected is converted into a voltage signal through a precise current source and a Wheatstone bridge;
and step three, outputting a voltage signal after passing through a low-pass filter circuit, a differential amplifier circuit and second-order low-pass filtering in sequence.
9. The method for detecting the fault of the resistance sensor to be detected by using the high-precision resistance signal conditioning circuit based on the current source as claimed in any one of claims 1 to 7 is characterized in that:
when the output voltage of an operational amplifier of a differential amplification circuit in a high-precision resistance signal conditioning circuit based on a current source is full-biased, the resistance sensor to be detected is considered to have an open circuit or short circuit fault;
when the output voltages of the operational amplifiers of the differential amplification circuit in the high-precision resistance signal conditioning circuit based on the current source are all in the normal amplification area, the resistance sensor to be measured is considered to work normally.
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| 席利君 等: "基于TVS管的机载电子设备数据接口雷电防护设计", 《航空电子技术》 * |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114689925A (en) * | 2022-05-31 | 2022-07-01 | 陕西半导体先导技术中心有限公司 | Isolated transient short-circuit current testing system and method |
Also Published As
| Publication number | Publication date |
|---|---|
| CN111122170B (en) | 2022-01-25 |
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