CN203241168U - Platinum resistor non-linear correction temperature transmitter - Google Patents

Abstract

The utility model relates to a platinum resistance non-linear correction temperature transmission circuit, which comprises a temperature measuring bridge and a programmable gain amplifier PGA. The output end of the electric bridge is connected with the input end of the programmable gain amplifier PGA, and a non-linear compensation resistor Rf is connected between the positive input end of the programmable gain amplifier PGA and its output end to form a positive feedback; the temperature measuring bridge is composed of a platinum resistance RT A single-arm bridge as one arm of a bridge. The utility model adopts the common-mode matching resistance and the non-linear compensation resistance, and converts the resistance value of the platinum resistance changing with the temperature into a voltage signal through the temperature measuring bridge and the programmable gain amplifier, utilizes the method of hardware linear correction, and uses digital adjustment Zero position and full scale avoid the disadvantages of debugging errors and poor stability caused by potentiometers or resistors, and realize low-cost, high-precision temperature measurement.

Description

Platinum resistance nonlinear correction temperature transmission circuit

technical field

The utility model relates to the field of detection technology and automatic control technology, in particular to a temperature transmission circuit.

Background technique

Temperature is an important physical quantity related to industrial and agricultural production, scientific research, environmental protection, meteorology, and even daily life. How to achieve accurate measurement is of great significance. Especially for temperature measuring instruments used in the process industry, it is required to have high temperature measurement accuracy, good reliability, and low cost.

In the past, temperature transmitters were realized by using analog technology and single-chip microcomputer technology. Although the cost of temperature transmitters using analog technology is not high, they use potentiometers (or resistors) to adjust zero and full scale. , so it is difficult to achieve high debugging accuracy, and the potentiometer will drift with time, and the reliability and stability are not good. The direct result is that the measurement accuracy is difficult to improve; Linearity correction, zero position and full scale are adjusted by software, with high measurement accuracy and good reliability, but the cost is high, which is not conducive to mass production, and its application is limited.

At present, platinum resistance thermometers are the most commonly used temperature sensors in industrial production processes. Platinum resistance thermometer has the characteristics of wide measurement range, high precision, good stability and oxidation resistance, so it has been widely used in medium and low temperature areas.

The relationship of platinum resistance with temperature changes follows the formula:

R _t =R ₀ [1+A _t +Bt ² +Ct ³ (t-100)] -200℃～0℃

R _t =R ₀ (1+At+Bt ² ) 0℃～600℃

In the formula,

R _t is the resistance value of the platinum resistance element at temperature t;

R ₀ is the resistance value of the platinum resistance element at 0°C;

A, B, C are graduation constants;

t is the temperature of the measured medium.

It can be seen that there is a nonlinear relationship between the resistance value of the platinum resistance and the temperature. In the application process of the platinum resistance sensor, the unbalanced bridge circuit is usually used to convert the resistance change of the platinum resistance sensor into a voltage. When the platinum resistance After connecting to the temperature measuring bridge circuit, due to the nonlinear relationship between the bridge arm resistance and the bridge output voltage, the nonlinearity between the voltage output by the bridge and the temperature will increase, and the nonlinear and unbalanced measurement of the platinum resistance The inherent nonlinearity of the temperature bridge brings a large nonlinear error to the temperature measurement. Therefore, it is necessary to modify it nonlinearly.

Utility model content

The utility model aims at the above-mentioned problems such as large nonlinear error, low precision and poor stability existing in the temperature measurement of the existing temperature transmitter, and provides a platinum sensor with small nonlinear error, high measurement accuracy, good stability and low cost. Resistance non-linear correction temperature transmission circuit.

The technical scheme of the utility model: a platinum resistor non-linear correction temperature transmission circuit, including a temperature measuring bridge and a programmable gain amplifier PGA, the negative end of the power supply of the temperature measuring bridge is connected to the signal ground through a common mode matching resistor Rc , the output end of the temperature measurement bridge is connected to the input end of the programmable gain amplifier PGA, and a non-linear compensation resistor Rf is connected between the positive input end of the programmable gain amplifier PGA and its output end to form a positive feedback; the temperature measurement bridge is based on Platinum resistance RT is used as a single-arm bridge with one arm of the bridge.

Preferably, the temperature transmission circuit also includes a V/I conversion circuit, the power supply of the temperature measuring bridge is positively connected to the reference voltage terminal of the V/I conversion circuit, and the output terminal of the programmable gain amplifier PGA is connected to the V /I conversion circuit input connection.

Preferably, the temperature transmission circuit further includes an excitation voltage source Vr, and the excitation voltage source Vr is connected to the positive terminal of the power supply of the temperature measuring bridge.

Preferably, the platinum resistor RT adopts a two-wire or three-wire platinum resistor.

Preferably, the programmable gain amplifier PGA adopts a programmable gain amplifier with adjustable zero and full scale.

Beneficial effects of the utility model: the utility model utilizes the hardware linear correction method to adjust the zero position and the full scale digitally, avoiding the shortcomings of debugging errors and poor stability caused by potentiometers or resistors, and realizing low cost and high precision temperature measurement; the negative end of the power supply of the temperature measuring bridge is connected to the signal ground through the common-mode matching resistor Rc, which makes it possible for the programmable gain amplifier to be used for signal amplification of the temperature measuring resistance, and the positive input end of the programmable gain amplifier is connected to the output There is a non-linear compensation resistor Rf connected between the terminals, and the non-linear change signal of the resistance value that changes with temperature is amplified by the programmable gain amplifier, and part of its output is fed back to the positive input terminal of the programmable gain amplifier through the non-linear compensation resistor Rf, and then connected with After the temperature measuring resistance signal is superimposed, the non-linear correction of the temperature measuring resistance is realized. As long as the range of the temperature measuring resistance is determined, the error of the output signal at the midpoint of the range can be checked by adjusting the zero position and the full scale to determine the size of the compensation resistance, that is Under the condition that other parameters remain unchanged, the non-linear compensation resistor is only related to the range, easy to mass-produce, and can achieve non-linear error ≤ 0.025% FS. Temperature measuring resistance refers to a resistor with a positive temperature coefficient. The utility model adopts a platinum resistor as a temperature measuring resistor, and can realize low-cost and high-precision temperature measurement within the temperature measuring range of the platinum resistor.

Description of drawings

Accompanying drawing 1 is the schematic circuit diagram of the first embodiment of the utility model.

Accompanying drawing 2 is the schematic circuit diagram of the second embodiment of the utility model.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is further described.

Embodiment 1: As shown in Figure 1, a platinum resistance nonlinear correction temperature transmission circuit includes a temperature measuring bridge, a programmable gain amplifier PGA and a V/I conversion circuit, and the power supply of the temperature measuring bridge is positively terminated At the reference voltage end of the V/I conversion circuit, the temperature measurement bridge is powered by the V/I conversion circuit, and the negative end of the power supply of the temperature measurement bridge is connected to the signal ground through the common-mode matching resistor Rc, so that the programmable gain amplifier PGA It is possible to amplify the signal of the temperature measuring resistance. The output end of the temperature measuring bridge is connected to the input end of the programmable gain amplifier PGA, and the output end of the programmable gain amplifier PGA is connected to the input end of the V/I conversion circuit; programmable A nonlinear compensation resistor Rf is connected between the positive input terminal of the gain amplifier PGA and its output terminal to form positive feedback and realize the nonlinear compensation function. The temperature measuring bridge is a single-arm bridge with a platinum resistance RT as one arm of the bridge. The platinum resistance RT is used as a temperature measuring resistance to achieve low-cost, high-precision temperature measurement within the temperature measurement range of the platinum resistance.

The above-mentioned platinum resistor RT adopts a two-wire or three-wire platinum resistor.

The programmable gain amplifier PGA realizes amplifying the signal of the platinum resistance RT at the same time, in order to realize the digital adjustment of zero position and full scale, the above-mentioned programmable gain amplifier PGA adopts a programmable gain amplifier with adjustable zero position and full scale.

The output current of the above-mentioned V/I conversion circuit is 4mA-20mA.

The resistance value of the common-mode matching resistor Rc is selected by adjusting the zero position and full scale to see whether the output signal of the programmable gain amplifier PGA is normal, and its resistance value is usually greater than the critical value.

The resistance value of the non-linear compensation resistor Rf is determined by adjusting the zero position and full scale to see if the signal error value at the midpoint of the range is the smallest. The resistance value at this time is the non-linear compensation resistance value under the range.

The platinum resistance nonlinear correction temperature transmitter adopting the platinum resistance nonlinear correction temperature transmission circuit of this embodiment, the test result of using the resistance box instead of the platinum resistance in the range of 0°C-100°C, the maximum error is ≤0.025%FS.

The platinum resistor non-linear correction temperature transmitter circuit of this embodiment is suitable for output current type temperature transmitters.

Working principle: The V/I conversion circuit supplies power to the temperature measuring bridge. Through the common mode matching resistor Rc, the programmable gain amplifier PGA realizes the nonlinear correction of the temperature measurement of the platinum resistor RT, and the resistance value of the platinum resistor RT changes nonlinearly with temperature. The signal is amplified by the programmable gain amplifier PGA, and a part of the nonlinear signal output by the programmable gain amplifier PGA is fed back to the positive input terminal of the programmable gain amplifier PGA through the nonlinear compensation resistor Rf, and then superimposed with the platinum resistor RT signal to realize the platinum resistor Non-linearity correction for RT.

Embodiment 2: As shown in Figure 2, a platinum resistor non-linear correction temperature transmission circuit, including a temperature measuring bridge, a programmable gain amplifier PGA and an excitation voltage source, the positive terminal of the power supply of the temperature measuring bridge and the excitation voltage Source connection, the temperature measuring bridge is powered by the excitation voltage source, the negative end of the power supply of the temperature measuring bridge is connected to the signal ground through the common mode matching resistor Rc, which makes it possible for the programmable gain amplifier PGA to be used for signal amplification of the temperature measuring resistor , the output end of the temperature measuring bridge is connected to the input end of the programmable gain amplifier PGA; the non-linear compensation resistor Rf is connected between the positive input end of the programmable gain amplifier PGA and its output end to form positive feedback and realize the nonlinear compensation function . The temperature measuring bridge is a single-arm bridge with a platinum resistance RT as one arm of the bridge. The platinum resistance RT is used as a temperature measuring resistance to achieve low-cost, high-precision temperature measurement within the temperature measurement range of the platinum resistance.

The above-mentioned platinum resistor RT adopts a two-wire or three-wire platinum resistor.

The programmable gain amplifier PGA realizes amplifying the signal of the platinum resistance RT at the same time, in order to realize the digital adjustment of zero position and full scale, the above-mentioned programmable gain amplifier PGA adopts a programmable gain amplifier with adjustable zero position and full scale.

The resistance value of the common-mode matching resistor Rc is selected by adjusting the zero position and full scale to see whether the output signal of the programmable gain amplifier PGA is normal, and its resistance value is usually greater than the critical value.

The resistance value of the non-linear compensation resistor Rf is determined by adjusting the zero position and full scale to see if the signal error value at the midpoint of the range is the smallest. The resistance value at this time is the non-linear compensation resistance value under the range.

The platinum resistance nonlinear correction temperature transmitter adopting the platinum resistance nonlinear correction temperature transmission circuit of this embodiment, the test result of using the resistance box instead of the platinum resistance in the range of 0°C-100°C, the maximum error is ≤0.025%FS.

The platinum resistor non-linear correction temperature transmitter circuit in this embodiment is suitable for output voltage type temperature transmitters.

Working principle: The excitation voltage source supplies power to the temperature measuring bridge, and the programmable gain amplifier PGA realizes the non-linear correction of the temperature measurement of the platinum resistance RT through the common-mode matching resistance Rc, and the signal of the non-linear change of the resistance value of the platinum resistance RT with the temperature change Amplified by the programmable gain amplifier PGA, a part of the nonlinear signal output by the programmable gain amplifier PGA is fed back to the positive input terminal of the programmable gain amplifier PGA through the nonlinear compensation resistor Rf, and then superimposed with the platinum resistor RT signal to realize the platinum resistor RT. Non-linear correction.

The above are the basic principles and features of the present utility model. The specific implementation of the present utility model cannot be limited to this. For those skilled in the art, other similar changes can also be made without departing from the idea of the present utility model. , and this should all be regarded as the scope of protection required by the claims of the present invention.

Claims (5)

1. A platinum resistor non-linear correction temperature transmission circuit, characterized in that: comprising a temperature measuring bridge and a programmable gain amplifier PGA, the negative end of the power supply of the temperature measuring bridge is connected to the signal ground through a common-mode matching resistor Rc, The output terminal of the temperature measuring bridge is connected to the input terminal of the programmable gain amplifier PGA, and the non-linear compensation resistor Rf is connected between the positive input terminal of the programmable gain amplifier PGA and its output terminal to form a positive feedback; the temperature measuring bridge is made of platinum Resistor RT acts as a single-arm bridge with one arm of the bridge. 2. The platinum resistance nonlinear correction temperature transmission circuit according to claim 1, characterized in that: the temperature transmission circuit also includes a V/I conversion circuit, and the power supply of the temperature measuring bridge is positively connected to V The reference voltage terminal of the /I conversion circuit and the output terminal of the programmable gain amplifier PGA are connected with the input terminal of the V/I conversion circuit. 3. The platinum resistance nonlinear correction temperature transmission circuit according to claim 1, characterized in that: the temperature transmission circuit also includes an excitation voltage source Vr, and the excitation voltage source Vr is connected to the power supply of the temperature measuring bridge Positive. 4. The platinum resistor non-linear correction temperature transmission circuit according to claim 1, characterized in that: the platinum resistor RT adopts a two-wire or three-wire platinum resistor. 5. The platinum resistance nonlinear correction temperature transmission circuit according to claim 1, characterized in that: the programmable gain amplifier PGA adopts a programmable gain amplifier with adjustable zero position and full scale.

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