CN206488794U - A kind of high precision electro bridge circuit of resistance strain type sensor - Google Patents

Abstract

The utility model belongs to the field of process detection, in particular to a high-precision electric bridge circuit of a resistance strain sensor. The circuit consists of a single-arm bridge, four instrumentation amplifiers G1, G2, G3 and G4, DC power supplies U _S and V _CC and current limiting resistor R ₀ , analog-to-digital converter ADC, and two analog multiplexers C1 and C2 , Processor MCU composition. _The input voltage of G1 is the unbalanced output voltage of the bridge, the input voltage of G2 is the voltage difference between the two ends of the resistor R4, the input voltage of G3 is the voltage difference between the _two ends of the resistor R2, and the input voltage of G4 is the voltage difference between the two ends of the bridge. The processor MCU selects a group of signals for analog-to-digital conversion by controlling the CTL signal, and uses the ratio as the output value N of the measurement result. N has a linear relationship with the sensor resistance change ΔR, and can eliminate the influence of temperature. The circuit of the utility model has high accuracy.

Description

A High Precision Bridge Circuit for Resistance Strain Sensor

technical field

The utility model relates to the field of process detection, in particular to a high-precision electric bridge circuit of a resistance strain sensor.

Background technique

Resistance strain sensors play an important role in non-electrical measurements such as pressure, displacement, strain, and acceleration. They have the advantages of simple structure, stable performance, and high sensitivity, and some are also suitable for dynamic measurements. However, there is a disadvantage of the resistance strain type, that is, its resistance value and sensitivity change with temperature. The resistance change of the resistance strain sensor due to the change of the ambient temperature and the resistance change due to the strain have almost the same order of magnitude. Piezoresistive sensors use semiconductor materials, which are sensitive to temperature. Therefore, temperature compensation must be considered when using resistance strain type and piezoresistive sensors for measurement, otherwise there will be a large error.

In addition, when using resistance strain type and piezoresistive sensors for measurement, in order to linearize the output of the system, improve the sensitivity and temperature compensation of the system, a full bridge circuit is usually used. The full-bridge circuit requires that the resistance change coefficients and temperature coefficients of the four sensors be as completely consistent as possible; two of the sensors are required to be under pressure, and the other two are under tension, and the degree and direction of tension and compression are as consistent as possible. This has high requirements on the manufacturing process and installation conditions of the sensor

Therefore, in order to reduce the influence of the differences in the sensor manufacturing process on the system measurement results and reduce the requirements for the installation conditions of the sensor on the measurement system, and at the same time eliminate the influence of ambient temperature changes, the utility model proposes a method based on the ratio method. The high-precision bridge circuit of the resistance strain sensor, the circuit only uses two resistance strain sensors, and only one resistance strain sensor is subjected to force, which reduces the cost of the sensor and reduces the dependence on the sensor installation conditions and The requirements of the sensor manufacturing process; and the effect of linearization of the full bridge circuit can be achieved.

Utility model content

The technical scheme adopted in the utility model is:

A high-precision bridge circuit for resistance strain sensors consists of a single-arm bridge, four instrumentation amplifiers G1, G2, G3 and G4, DC power supplies U _S and V _CC , current limiting resistor R ₀ , and an analog-to-digital converter ADC , two analog multiplexers C1 and C2, and a processor MCU;

The four bridge arms of the single-arm bridge are composed of two high-precision resistors with resistance values R ₂ and R ₄ respectively and two identical resistance strain sensors with resistance values R ₁ and R ₃ ; R ₁ is for measuring pressure The resistance strain sensor of R ₃ is the resistance strain sensor of system temperature compensation;

The DC power supply U _S of the bridge power supply is the power supply voltage U _of the bridge after being divided by the current _- limiting resistor R0 _; The negative terminal of the power supply U _S , the in-phase terminals of the instrumentation amplifier G1 and the instrumentation amplifier G3 are connected in the middle of the two resistors; the positive terminal of the power supply voltage U is connected in series with a high _- precision resistor R4 and a resistance strain sensor _R3 , and then connected to the DC The negative terminal of the power supply U _S , the inverting terminal of the instrumentation amplifier G1 and the inverting terminal of the instrumentation amplifier G2 are connected in the middle of the two resistors; the non-inverting terminal of the instrumentation amplifier G2, the inverting terminal of the instrumentation amplifier G3 and the The inverting terminal is connected to the positive terminal of the power supply voltage U of the bridge, and the non-inverting terminal of the instrument amplifier G4 is connected to the negative terminal of the DC power supply U _S ;

The output terminal of the instrument amplifier G1 is connected to the CH1 channel of the analog multiplexer C1, the output terminal of the instrument amplifier G2 is connected to the CH2 channel of the analog multiplexer C1; the output terminal of the instrument amplifier G3 is connected to the analog multiplexer The CH1 channel of the selector C2, the output terminal of the instrument amplifier G4 is connected to the CH2 channel of the analog multiplexer C2;

The output terminal OUT of the analog multiplexer C1 is connected to the AIN+ input terminal of the analog-to-digital converter ADC, the output terminal OUT of the analog multiplexer C2 is connected to the REF IN+ reference input terminal of the analog-to-digital converter ADC, and the analog-to-digital converter The AIN-end, REFIN-end and GND end of the ADC are connected to the negative terminal of the DC power supply U _S , and the power supply terminal VCC of the analog-to-digital converter ADC is connected to the DC power supply _VCC ;

The power supply terminal VCC of the processor MCU is connected to the DC power supply V _CC , the chip select signal CTL is connected to the CTL terminals of the analog multiplexers C1 and C2, and the GND terminal of the processor MCU is connected to the negative terminal of the DC power supply U _S .

The working process is: the input voltage _U01 of the instrumentation amplifier G1 is the unbalanced output voltage of the bridge, the input voltage _U02 of the instrumentation amplifier G2 is the voltage difference between the two ends of the resistor R4, and the input voltage _U03 of the instrumentation amplifier _G3 is the resistance The voltage difference at both ends of R ₂ , the input voltage U ₀₄ of the instrumentation amplifier G4 is the voltage difference at both ends of the bridge. After passing through the analog multiplexer, U ₀₁ and U ₀₃ are used as a group of analog-to-digital conversion signals, U ₀₂ and U ₀₄ are used as another group of analog-to-digital conversion signals, and the processor MCU selects one of the signals for analog-to-digital conversion by controlling the CTL signal convert. When U ₀₁ and U ₀₃ are selected, the result of analog-to-digital conversion is N ₁ , and when U ₀₂ and U ₀₄ are selected, the result of analog-to-digital conversion is N ₂ . After the conversion of N ₁ and N ₂ is completed, the processor MCU performs a division operation, and takes the ratio of N ₁ and N ₂ as the output value N of the measurement result.

The beneficial technical effects of the utility model are: N has a linear relationship with sensor resistance change ΔR, which can achieve the effect of full-bridge circuit linearization; N has nothing to do with resistance change ΔR _t caused by ambient temperature changes, and can eliminate the influence of temperature. If a high-accuracy instrumentation amplifier is used in the system, the system has high accuracy and can easily adjust the sensitivity of the system, which has strong practical value.

Description of drawings

Accompanying drawing 1 is the high precision bridge circuit of resistance strain type sensor.

detailed description

The specific implementation of the device of the present invention will be further described below in conjunction with the accompanying drawings.

In attached drawing 1, R ₁ and R ₃ are the same resistance strain sensor, R ₁ is the resistance strain sensor for measuring pressure, R ₃ is the system temperature compensation resistance strain sensor, R ₂ and R ₄ are high-accuracy resistance . _U01 is the unbalanced output voltage of the bridge, _U02 is the voltage difference across the resistor _R4 , _U03 is the voltage difference across the resistor R2, and _U04 is the voltage difference _across the bridge. In general, the initial value of resistance strain sensor R ₁ in the bridge is R, the variation of resistance strain is ΔR, and the variation of resistance after temperature changes is ΔR _t ; R ₂ =R ₃ =R ₄ =R, then:

U ₀₄ = U (4)

U ₀₁ and U ₀₂ are respectively amplified G ₁ and G ₂ times by instrument amplifiers G1 and G2, and then used as the analog input of the analog-to-digital converter ADC, U ₀₃ and U ₀₄ are respectively amplified by instrument amplifiers G3 and G4 G ₃ and G ₄ After multiplying, it is used as the reference voltage of the analog-to-digital converter ADC. After passing through the analog multiplexer, U ₀₁ and U ₀₃ are used as a group of analog-to-digital conversion signals, U ₀₂ and U ₀₄ are used as another group of analog-to-digital conversion signals, and the processor MCU selects one of the signals for analog-to-digital conversion by controlling the CTL signal convert. When U ₀₁ and U ₀₃ are selected, the result of analog-to-digital conversion is N ₁ , and when U ₀₂ and U ₀₄ are selected, the result of analog-to-digital conversion is N ₂ . Assuming the resolution of the analog-to-digital converter ADC is n bits, we can get:

After the conversion of N ₁ and N ₂ is completed, the processor MCU performs a division operation, and takes the ratio of N ₁ and N ₂ as the output value N of the measurement result.

It can be seen from formula (7) that N has a linear relationship with the sensor resistance change ΔR, indicating that the effect of full-bridge circuit linearization can be achieved; N has nothing to do with the resistance change ΔR _t caused by ambient temperature changes, indicating that the influence of temperature can be eliminated. If a high-accuracy instrumentation amplifier is used in the system, the system has high accuracy and can easily adjust the sensitivity of the system, which has strong practical value. In addition, the system only uses two sensors, and only one sensor is subjected to force, which reduces the cost of the sensor, and reduces the dependence on the sensor installation conditions and the sensor manufacturing process requirements.

The above are only preferred implementations of the utility model, and the utility model is not limited to the above examples. It can be understood that other improvements and changes directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present utility model shall be considered to be included in the protection scope of the present utility model.

Claims (1)

1. a high precision electric bridge circuit of resistance strain sensor, it is characterized in that, circuit is made of single-arm electric bridge, four instrumentation amplifiers G1, G2, G3 and G4, DC power supply U _S and V _CC and current-limiting resistor R ₀ , analog-to-digital converter ADC, two analog multiplexers C1 and C2, and processor MCU; the four bridge arms of the single-arm bridge are composed of two high-precision resistors with resistance values R ₂ and R ₄ respectively It is composed of two same resistance strain sensors with resistance values R ₁ and R ₃ ; R ₁ is a resistance strain sensor for pressure measurement, and R ₃ is a resistance strain sensor for system temperature compensation; the bridge power supply DC power supply U _S passes through The current-limiting resistor R ₀ is divided into the power supply voltage U of the bridge; the positive end of the power supply voltage U of the bridge is connected in series with a high-precision resistor R ₂ and a resistance strain sensor R ₁ , and then connected to the negative end of the DC power supply U _S for instrument use The non-inverting terminals of the amplifier G1 and the instrument amplifier G3 are connected in the middle of the two resistors; the positive terminal of the power supply voltage U is connected in series with the high _- precision resistor R4 and the resistance strain sensor _R3 , and then connected to the negative terminal of the DC power supply U _S. The inverting terminal of the amplifier G1 and the instrument amplifier G2 is connected in the middle of the two resistors; the non-inverting terminal of the instrument amplifier G2, the inverting terminal of the instrument amplifier G3 and the inverting terminal of the instrument amplifier G4 are connected to the power supply of the bridge The positive terminal of the voltage U, the non-inverting terminal of the instrumentation amplifier G4 is connected to the negative terminal of the DC power supply U _S ; the output terminal of the instrumentation amplifier G1 is connected to the CH1 channel of the analog multiplexer C1, and the output terminal of the instrumentation amplifier G2 is connected to the analog The CH2 channel of the multiplexer C1; the output terminal of the instrumentation amplifier G3 is connected to the CH1 channel of the analog multiplexer C2, and the output terminal of the instrumentation amplifier G4 is connected to the CH2 channel of the analog multiplexer C2; the analog multiplexer The output terminal OUT of the selector C1 is connected to the AIN+ input terminal of the analog-to-digital converter ADC, the output terminal OUT of the analog multiplexer C2 is connected to the REF IN+ reference input terminal of the analog-to-digital converter ADC, and the AIN of the analog-to-digital converter ADC - terminal, REF IN- terminal and GND terminal are connected to the negative terminal of the DC power supply U _S , the power supply terminal VCC of the analog-to-digital converter ADC is connected to the DC power supply V _CC ; the power supply terminal VCC of the processor MCU is connected to the DC power supply V _CC , and the chip select signal The CTL is connected to the CTL terminals of the analog multiplexers C1 and C2, and the GND terminal of the processor _MCU is connected to the negative terminal of the DC power supply US.