HJ309A-based platinum resistor temperature signal demodulation circuit

Abstract

The utility model belongs to the field of temperature sensor design, and particularly relates to a platinum resistor temperature signal demodulation circuit based on HJ309A, and resistance signals directly output by a platinum resistor are large in nonlinearity and not easy to directly measure. The platinum resistor temperature signal demodulation circuit based on the HJ309A comprises an acquisition circuit, a compensation amplification circuit and a V / I conversion circuit which are connected in sequence according to a signal processing process, the compensation amplification circuit is constructed based on an HJ309A chip and outputs a voltage signal after performing nonlinear compensation on an electric signal output by the acquisition circuit, and the HJ309A chip also provides constant voltage excitation for the acquisition circuit; and a current signal of the platinum resistor temperature signal is obtained through conversion of the V / I conversion circuit. Loss in the transmission process can be avoided, nonlinear compensation can make up for the characteristic of the nonlinear difference of the platinum resistor, and the measurement precision of the sensor is improved.

Description

Technical Field

[0001] The utility model belongs to the field of temperature sensor design, and in particular relates to a platinum resistance temperature signal demodulation circuit based on HJ309A, which is used for demodulating a temperature signal into a current signal. Background Art

[0002] When using a temperature sensor, in order to accurately and conveniently observe the temperature changes of the system, it is necessary to convert the system's temperature signal into an electrical signal output. The resistance signal directly output by the platinum resistance is highly nonlinear and not easy to measure directly. Utility Model Content

[0003] The purpose of this utility model is to propose a platinum resistance temperature signal demodulation circuit based on HJ309A, which can perform nonlinear compensation on the resistance signal output by the platinum resistor and convert the resistance signal into a current signal, thereby reducing the accuracy loss caused by the transmission process and realizing the measurement of the temperature signal.

[0004] The technical solution of the utility model is: a platinum resistance temperature signal demodulation circuit based on HJ309A, which includes an acquisition circuit, a compensation amplifier circuit and a V / I conversion circuit connected in sequence according to the signal processing process, wherein the compensation amplifier circuit is built based on the HJ309A chip, performs nonlinear compensation on the electrical signal output by the acquisition circuit and then outputs a voltage signal, and the HJ309A chip also provides constant voltage excitation to the acquisition circuit; the current signal of the platinum resistance temperature signal is converted by the V / I conversion circuit.

[0005] Advantageously, the acquisition circuit includes a voltage divider circuit and a filter circuit. In the voltage divider circuit, the power supply is connected to resistor R1, a platinum resistor and resistor R4 in sequence and grounded; in the filter circuit, the high-voltage end of the platinum resistor is grounded through resistor R2, capacitor C1 and capacitor C3, and the high-voltage end of the platinum resistor is also grounded through capacitor C2, and the low-voltage end of the platinum resistor is connected to the electrode between capacitor C1 and capacitor C3 after passing through resistor R3.

[0006] Advantageously, the acquisition circuit is used to convert the temperature signal into a mV level voltage signal.

[0007] Advantageously, the resistance of the resistor R1 and the resistor R4 is 3.3 kΩ.

[0008] Advantageously, the resistance of resistors R2 and R3 is R, the capacitance of capacitors C1 and C3 is C, the common mode cutoff frequency is 1 / (2πRC), and the differential mode cutoff frequency is 1 / (2π2R(0.5C+C2)).

[0009] Advantageously, the output end of the HJ309A chip outputs a compensated voltage signal via the resistor R5, and the output end is also grounded via the capacitor C7.

[0010] Advantageously, the V / I conversion circuit includes an operational amplifier and a switching transistor connected in series, and the static operating current of the operational amplifier is required to be less than 1 mA, and the switching transistor is in an amplifying state.

[0011] The beneficial effects of the present invention are as follows: when the measurement temperature range is wide and the transmission signal line is long, the current signal can avoid loss during the transmission process, and the nonlinear compensation can make up for the nonlinear difference characteristics of the platinum resistor itself, thereby improving the measurement accuracy of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the architecture diagram of the platinum resistance temperature signal demodulation circuit;

[0013] Figure 2 Design diagram for acquisition circuit;

[0014] Figure 3 This is the design diagram of the compensation amplifier circuit;

[0015] Figure 4 This is the schematic diagram of the V / I conversion circuit. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings and implementation examples:

[0017] See also Figure 1 The architecture diagram of the platinum resistance temperature signal demodulation circuit shown in the figure is mainly composed of an acquisition circuit, a compensation amplifier circuit and a V / I conversion circuit. The acquisition circuit is used to convert the temperature signal into an mV-level voltage signal. The compensation amplifier circuit provides a constant voltage excitation to the acquisition circuit and compensates the mV-level voltage signal output by the acquisition circuit, and outputs the compensated voltage signal to the V / I conversion circuit. The V / I conversion circuit converts the voltage signal into a current signal and outputs it to achieve temperature measurement.

[0018] The detailed introduction of each circuit module is as follows:

[0019] 1) Acquisition circuit

[0020] See also Figure 2 The acquisition circuit consists of a voltage divider circuit and a filter circuit. The voltage divider circuit uses resistors R1 and R4 connected in series across a platinum resistor to divide the voltage, controlling the voltage across the resistor within an appropriate range. The filter circuit uses resistors R2, R3, capacitors C1, C2, and C3 to create an RC filter circuit to suppress interference signals.

[0021] Resistors R1 and R4 are used for voltage division. The constant voltage excitation provided by the compensation amplifier circuit is 4.096V. The appropriate full-scale output range of the platinum resistor is 40mV to 50mV. When the measurement range of the platinum resistor is -55℃ to 150℃, to meet the output range of the platinum resistor, the resistance of resistors R1 and R4 is selected to be 3.3kΩ. The resistance of resistors R2 and R3 is required to be R, and the capacitance of capacitors C1 and C3 is required to be C. The common-mode cutoff frequency is 1 / (2πRC), and the differential-mode cutoff frequency is 1 / (2π2R(0.5C+C2)). The components can be selected based on the high-frequency interference in the actual use environment.

[0022] (2) Compensation amplifier circuit

[0023] See also Figure 3 The compensation amplifier circuit is built around the HJ309A chip, resistors, and capacitors. The HJ309A chip provides constant voltage excitation for the acquisition circuit and performs nonlinear compensation on the output signal. Resistor R5 is an output protection resistor.

[0024] Usually the maximum nonlinear point of the acquisition circuit output is at V 50％ At this point, when calibrating, you can choose V 0％ 、V 50％ 、V 100％ Compensation at three points can minimize the nonlinearity of the output.

[0025] (3) V / I conversion circuit

[0026] See also Figure 4 The V / I conversion circuit is built based on an operational amplifier, a switching transistor, and a resistor. The voltage signal output by the HJ309A chip needs to be converted to V / I. This is achieved through the operational amplifier and the switching transistor. It is necessary to ensure that the switching transistor is in the amplification state.

[0027] Since the minimum output current of a typical temperature sensor is as low as 4mA, the op amp's quiescent operating current must be less than 1mA. The calculation yields: I = R7 / (R6+R7)*U / R11. After selecting specific values for resistors R6, R7, and R11, the output current I depends solely on U. The output current can be adjusted by changing U during calibration.

Claims

1. A platinum resistance temperature signal demodulation circuit based on HJ309A, characterized by: The signal processing process includes an acquisition circuit, a compensation amplifier circuit, and a V / I conversion circuit connected in sequence. The compensation amplifier circuit is built based on the HJ309A chip, which performs nonlinear compensation on the electrical signal output by the acquisition circuit and then outputs a voltage signal. The HJ309A chip also provides constant voltage excitation to the acquisition circuit; the current signal of the platinum resistance temperature signal is converted through the V / I conversion circuit.

2. The platinum resistance temperature signal demodulation circuit according to claim 1, characterized in that: The acquisition circuit includes a voltage divider circuit and a filter circuit. In the voltage divider circuit, the power supply is connected to resistor R1, a platinum resistor and resistor R4 in sequence and grounded; in the filter circuit, the high-voltage end of the platinum resistor is grounded through resistor R2, capacitor C1 and capacitor C3, and the high-voltage end of the platinum resistor is also grounded through capacitor C2. The low-voltage end of the platinum resistor is connected to the electrode between capacitor C1 and capacitor C3 after passing through resistor R3.

3. The platinum resistance temperature signal demodulation circuit according to claim 2, characterized in that: The acquisition circuit is used to convert the temperature signal into a mV level voltage signal.

4. The platinum resistance temperature signal demodulation circuit according to claim 2, characterized in that: The resistance of the resistor R1 and the resistor R4 is 3.3 kΩ.

5. The platinum resistance temperature signal demodulation circuit according to claim 4, characterized in that: The resistance values of the resistors R2 and R3 are R, the capacitance values of the capacitors C1 and C3 are C, the common-mode cutoff frequency is 1 / (2πRC), and the differential-mode cutoff frequency is 1 / (2π2R(0.5C+C2)).

6. The platinum resistance temperature signal demodulation circuit according to claim 1, characterized in that: The output end of the HJ309A chip outputs a compensated voltage signal via a resistor R5, and the output end is also connected to ground via a capacitor C7.

7. The platinum resistance temperature signal demodulation circuit according to claim 1, characterized in that: The V / I conversion circuit includes an operational amplifier and a switching transistor connected in series. The static operating current of the operational amplifier is required to be less than 1mA, and the switching transistor is in an amplifying state.

Images