| CPC G01K 3/08 (2013.01) [G01K 7/16 (2013.01); G01K 2219/00 (2013.01)] | 20 Claims |
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1. A measurement method for a differential proportional temperature measurement circuit based on a bidirectional constant voltage drive, wherein the differential proportional temperature measurement circuit comprises a bidirectional constant voltage source proportional bridge circuit, a differential and single-ended amplifier circuit, an analog-to-digital conversion circuit, a digital filter circuit, a data processing circuit, and an isolated filter power supply circuit;
wherein the bidirectional constant voltage source proportional bridge circuit, the differential and single-ended amplifier circuit, the analog-to-digital conversion circuit, the digital filter circuit, and the data processing circuit are connected in turn; the isolated filter power supply circuit provides power for the bidirectional constant voltage source proportional bridge circuit, the differential and single-ended amplifier circuit, the analog-to-digital conversion circuit, the digital filtering circuit, and the data processing circuit;
wherein the measurement method comprises the following steps:
(1) in a first step, connecting an output pin of a main control chip to a selection control terminal S of an analog switch SW1 through an isolated I/O1, firstly, connecting an A terminal and an O1 terminal, a C terminal and an O2 terminal, at this time, an voltage excitation direction applied by a constant voltage source V1 to a reference resistor Rref and a measurement resistor RT being positive, assuming that a first voltage conversion sensitivity error of the bidirectional constant voltage source proportional bridge circuit is recorded as α1, and recording current flowing through the measurement resistor RT and the reference resistor Rref as I+, amplifying voltages (1+α1) I+RT and (1+α1) I+Rref at both ends of the reference resistor Rref and the measurement resistor RT by three differential amplifiers A1, A2, and A3, recording magnifications of the three differential amplifiers A1, A2, and A3 as G1, G2, and G3, wherein G1=G2, Eθ1 is a first thermal potential of a wire, and a first offset voltage error of the differential amplifier is ΔU1*; wherein an output voltage signal ΔU+=(1+α1) [I+(RT−Rref)+E01−E01]G2G3+ΔU1* of the differential amplifier A3 is a difference between voltages at both ends of the reference resistor Rref and the measurement resistor RT, and an output voltage signal Uref+=(1+α1) (I+Rref+E01)G2+ΔU1* of the differential amplifier A2 is voltages at both ends of the reference resistor Rref, entering the output voltage signal ΔU+ and the output voltage signal Uref+ into an analog-to-digital converter (ADC) after filtering out high-frequency noise by low-pass filtering, and performing an analog-to-digital conversion, then filtering low-frequency noise by a sinc filter and a 32-order finite impulse response (FIR) filter, assuming ΔU1 and ΔU2 as errors caused by a zero drift of 1 channel and 2 channel of the ADC, respectively, finally, obtaining values of ΔU+ and Uref+ and sending the values of ΔU+ and Uref+ to the main control chip for storage by an isolated I/O2, wherein:
ΔU+=(1+α1)[I+(RT−Rref)+Eθ1−Eθ1]G2G3+ΔU1*+ΔU1
Uref+=(1+α1)I+(Rref+Eθ1)G2+ΔU1*+ΔU2
(2) in a second step, passing the output pin of the main control chip through the isolated I/O1 to control the analog switch SW1, and connecting a B end and an O1 end, a D end and an O2 end, at this time, an voltage excitation direction applied by the constant voltage source V1 to the reference resistor Rref and the measurement resistor RT being negative, subjecting voltages at both ends of the reference resistor Rref and the measurement resistor RT to a same differential amplification as the first step, after a process of the low-pass filtering, an A/D conversion, the sinc filter, and the 32-order FIR filter, obtaining voltage values ΔU− and Uref−, sending the voltage values ΔU− and Uref− to the main control chip for storage through the isolated I/O2; when the voltage excitation direction is negative, recording a second voltage conversion sensitivity error of the bidirectional constant voltage source proportional bridge circuit as α2, recording current flowing through the measurement resistor RT and the reference resistor Rref as I−, wherein the magnifications of the three differential amplifiers A1, A2, and A3 are unchanged, recording as G1, G2, and G3, wherein G1=G2, Eθ2 is a second thermal potential of the wire, and a second offset voltage error of the differential amplifier is ΔU2*, assuming ΔU3 and ΔU4 be errors caused by the zero drift of the 1 channel and the 2 channel of the ADC respectively, then:
ΔU−=(1+α2)[I−(RT−Rref)+Eθ2−Eθ2]G2G3+ΔU2*+ΔU3
Uref−=(1+α2)I−(Rref+Eθ2)G2+ΔU1*+ΔU4; and
(3) in a third step, calculating and obtaining an RT resistance of a resistance to be measured in the main control chip by a circuit voltage division theorem:
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