CN110646018B - High-frequency current source Wheatstone bridge detection circuit realized by low-speed operational amplifier - Google Patents
High-frequency current source Wheatstone bridge detection circuit realized by low-speed operational amplifier Download PDFInfo
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- CN110646018B CN110646018B CN201910864158.6A CN201910864158A CN110646018B CN 110646018 B CN110646018 B CN 110646018B CN 201910864158 A CN201910864158 A CN 201910864158A CN 110646018 B CN110646018 B CN 110646018B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
- G01D5/16—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying resistance
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R17/00—Measuring arrangements involving comparison with a reference value, e.g. bridge
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Abstract
The invention discloses a high-frequency current source Wheatstone bridge detection circuit realized by a low-speed operational amplifier. The circuit of the invention has simple design and easy realization, and the operational amplifier processes direct current signals, thereby reducing the bandwidth requirement on the operational amplifier, facilitating the selection of devices and reducing the cost of using high-speed operational amplifier. The invention replaces the voltage source as the external power supply of the Wheatstone bridge, can improve the linearity of the output signal of the Wheatstone bridge; meanwhile, the low-frequency output signal of the Wheatstone bridge can be modulated to reduce the coupling of signals in the same frequency band, thereby improving the measurement precision.
Description
Technical Field
The invention relates to the technical field of sensor measurement systems and Wheatstone bridge output detection signals, in particular to a high-frequency current source Wheatstone bridge detection circuit realized by low-speed operational amplifier.
Background
In 1883, the british inventor, clissi, invented a wheatstone bridge with a high-precision measuring circuit consisting of four resistors. The four resistors are respectively called bridge arms of a bridge, and the bridge utilizes bridge arm electricityThe change in resistance measures the change in some physical quantity. As shown in FIG. 2, the resistance strain gauge (formed by adhering resistance wire in grid shape between two layers of thin paper or plastic film) is adhered to the object, and when the object is deformed, R is1、R3To R + DeltaR, R2、R4If the voltage is not changed, the output of the bridge under the condition of the power supply of the direct current voltage source is (as shown in fig. 2):
wherein, Delta R is the change of resistance value when the strain gauge is subjected to external stress, R1、R2、R3、R4Four arms (provided with R) constituting a Wheatstone bridge1＝R2＝R3＝R4R), Δ V is the output signal obtained by the detection terminal. From the above formula, under the condition of voltage source, the bridge only detects the tiny change, and the resistance value of the strain gauge itself is far larger than the resistance value output changed under the external excitation, and the output can be approximate to linearity.
If the current source is used to supply power to the bridge, the output signal of the bridge is (as shown in fig. 3) when the same external stress stimulates the strain gauge:
the equations (1) and (2) show that the linearity of the output signal of the bridge is better than that of the power supply of the voltage source under the condition of the power supply of the current source.
For the processing of the wheatstone bridge detection signal, on one hand, the linearity is improved by using a current source, and on the other hand, the modulation of the signal is also considered to reduce the coupling between the signals, so that a high-frequency current source signal needs to be generated, the high-speed operational amplifier needs to amplify the reference current, and the bandwidth and the slew rate of the operational amplifier need to be considered, and the selection range of the operational amplifier is greatly limited.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention provides a high-frequency constant-amplitude Wheatstone bridge detection circuit realized by low-speed operational amplifier.
The technical scheme is as follows: in order to solve the technical problem, the high-frequency current source Wheatstone bridge detection circuit realized by the low-speed operational amplifier comprises a reference current source module, an H bridge and a detection module which are sequentially connected; the reference current source module is used for providing constant current for an H bridge, and the H bridge is used as a load of a current source and converts constant current input into constant amplitude alternating current; the detection module is used as a load of the H bridge and outputs a detection signal; the detection module is a Wheatstone bridge.
Wherein the reference current source module comprises a voltage source and a resistor R0One output end of the voltage source is connected with the anode input of the low-speed operational amplifier, and the other end of the voltage source is grounded; resistance R0One end of the output of the low-speed operational amplifier is connected with the negative input of the low-speed operational amplifier, and the other end of the output of the low-speed operational amplifier is grounded; the output end of the operational amplifier is connected with an H bridge and returns to the voltage-dividing resistor R through the H bridge0Negative feedback is constructed.
The H-bridge comprises four voltage control type switches S1, S2, S3 and S4 and four high-frequency signal sources C1, C2, C3 and C4; one end of a high-frequency signal source C1 is connected with the positive electrode of a switch S1 power supply, the other end is grounded, one end of a high-frequency signal source C2 is connected with the positive electrode of a switch S2 power supply, the other end is grounded, one end of a high-frequency signal source C3 is connected with the positive electrode of a switch S3 power supply, the other end is grounded, one end of a high-frequency signal source C4 is connected with the positive electrode of a switch S4 power supply, and the other end is grounded; one end of the switch S1 is connected with the switch S2, the other end is connected with the switch S4, one end of the switch S2 is connected with the switch S1, the other end is connected with the switch S3, one end of the switch S3 is connected with the switch S2, the other end is connected with the switch S4, one end of the switch S4 is connected with the switch S3, and the other end is connected with the switch S1; the connection points of the switch S1 and the switch S2 are connected with the output end of the low-speed operational amplifier, the connection points of the switch S2 and the switch S3 are connected with the positive electrode of a power supply of the Wheatstone bridge, and the connection points of the switch S1 and the switch S4 are connected with the negative electrode of the power supply of the Wheatstone bridge.
Wherein, the output signal of the H bridge is used for carrying out high-frequency modulation on the detection signal of the Wheatstone bridge.
Wherein the Wheatstone bridge comprises two variable resistors R1、R3And two constant value resistors R2、R4(ii) a Constant value resistanceR4One end of is connected with a variable resistor R3And the other end is connected with a variable resistor R1Variable resistance R1One end is connected with a constant value resistor R2The other end is connected with a fixed value resistor R4Constant value resistance R2One end of is connected with a variable resistor R3And the other end is connected with a variable resistor R1Variable resistance R3One end is connected with a constant value resistor R2The other end is connected with a fixed value resistor R4(ii) a Constant value resistance R2And a variable resistor R1The connecting point of the resistor is connected with the positive electrode of the bridge power supply and the constant value resistor R4And a variable resistor R3The connecting point of the power supply is connected with the negative electrode of the bridge power supply.
Has the advantages that: the invention has the following beneficial effects:
(1) the circuit design is simple and easy to realize.
(2) Because the operational amplifier processes the direct current signal, the bandwidth requirement on the operational amplifier is reduced, the selection of devices is convenient, and the cost of using the high-speed operational amplifier is reduced.
(3) The current source circuit replaces a voltage source to serve as an external power supply of the Wheatstone bridge, and the linearity of output signals of the Wheatstone bridge can be improved.
(4) The low-frequency output signal of the Wheatstone bridge is modulated by using the circuit of the invention, so that the coupling of signals in the same frequency band can be reduced, and the measurement precision is further improved.
Drawings
FIG. 1 is a block diagram of the system of the present invention;
FIG. 2 is a circuit diagram of the output voltage of the bridge under DC voltage source conditions;
FIG. 3 is a circuit diagram of bridge output voltage under DC current source conditions;
FIG. 4 is a diagram of an embodiment of the present invention;
fig. 5 is a timing diagram of the operation of the high frequency signal source and the H-bridge four-way switch, in which: t is tposPositive half period, tnegA negative half cycle.
Detailed Description
The invention will be further explained with reference to the drawings.
As shown in fig. 1, 4 and 5, a high for low speed op-amp implementationThe frequency current source Wheatstone bridge detection circuit comprises a reference current source module, an H bridge and a detection module, wherein the detection module is a Wheatstone bridge. The reference current source module comprises a voltage source and a divider resistor R0One output end of the voltage source is connected with the anode input of the low-speed operational amplifier, and the other end of the voltage source is grounded; voltage dividing resistor R0One end of the output of the low-speed operational amplifier is connected with the negative input of the low-speed operational amplifier, and the other end of the output of the low-speed operational amplifier is grounded; the output end of the operational amplifier is connected with an H bridge and returns to the voltage-dividing resistor R through the H bridge0Negative feedback is constructed. The H-bridge comprises an H-bridge formed by four voltage control type switches S1, S2, S3 and S4, and four high-frequency signal sources C1, C2, C3 and C4, wherein one end of the high-frequency signal source C1 is connected with the anode of a switch S1 power supply, the other end of the high-frequency signal source C2 is grounded, one end of the high-frequency signal source C2 is connected with the anode of a switch S2 power supply, the other end of the high-frequency signal source C3 is connected with the anode of a switch S3 power supply, the other end of the high-frequency signal source C4 is grounded, one end of the high-frequency signal source C4 is connected with the anode of a switch S4 power supply, and the other end of the high-frequency signal source is grounded; one end of the switch S1 is connected with the switch S2, the other end is connected with the switch S4, one end of the switch S2 is connected with the switch S1, the other end is connected with the switch S3, one end of the switch S3 is connected with the switch S2, the other end is connected with the switch S4, one end of the switch S4 is connected with the switch S3, and the other end is connected with the switch S1; the connection point of the switches S1 and S2 is connected with the output end of the low-speed operational amplifier, the connection point of the switches S2 and S3 is connected with the positive electrode of the power supply of the Wheatstone bridge, and the connection point of the switches S1 and S4 is connected with the negative electrode of the power supply of the Wheatstone bridge.
And for the direct current quantity of the high-frequency constant-amplitude alternating current source, the direct current quantity is generated by the reference current source module and provides constant current for the H bridge.
As shown in fig. 4, for an H-bridge, the signal source outputs a high frequency square wave signal. In order to reduce the demodulation phase shift, the modulation frequency is preferably higher between 1k and 100MHz, and in order to avoid the influence of the high-frequency signal on the circuit, the frequency range of the high-frequency signal output module is set to be 1M to 10 MHz.
The direct current generated by the reference current source module is loaded on the H bridge, and the high-frequency signal source drives the H bridge periodically, so that a high-frequency oscillation waveform with constantly changing current direction is formed. The four-way voltage control type switches constituting the H-bridge are S1, S2, S3, and S4, respectively. S1, S2, S3 and S4 are connected as shown in FIG. 4, and the working mechanism of the four switches is that when the voltage of the positive electrode of the switch is higher than the voltage of the negative electrode of the switch, the switch is closed; the voltage of the positive electrode is lower than that of the negative electrode, the switch is disconnected, and the on-off of the switch is controlled by four high-frequency signal sources C1, C2, C3 and C4. The frequencies of C1, C2, C3 and C4 are the same, at the same time, the polarities of C1 and C3 are the same, the polarities of C2 and C4 are the same, and the polarities of C1 and C2 are opposite, so that the four-way switches S1 and S3, S2 and S4 are closed and interrupted alternately, and a high-frequency square wave with the same period as a high-frequency signal source is formed. The closing/interrupting timings of the switches S1, S2, S3, S4 are shown in fig. 5.
The principle of the power supply of the H bridge is as follows: when the positive half-cycle is output by the C2 and the C4, the switches S2 and S4 are turned on, the switches S1 and S3 are turned off, the current is input from S2 and flows through the bridge to the S4, the voltage at the point a is higher than the voltage at the point b, when the positive half-cycle is output by the C1 and the C3, the switches S1 and S3 are turned on, the switches S2 and S4 are turned off, the current is input from S1 and flows through the bridge to the S3, and the voltage at the point a is lower than the voltage at the point b; the two states repeat continuously and thus oscillate at the same frequency as the signal source.
When the strain gauge resistance of the Wheatstone bridge receives external excitation to change, the output voltage of the bridge is as follows:
ΔV＝KI(R+ΔR)-KIR (3)
＝KI·ΔR
ΔV＝KIR-KI(R+ΔR) (4)
＝-KIΔR
in the formula, K is the amplification factor of the operational amplifier, and I is the output current of the reference current source.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (3)
1. A high frequency current source Wheatstone bridge detection circuit that low-speed operational amplifier realized which characterized in that: the device comprises a reference current source module, an H bridge and a detection module which are connected in sequence;
the reference current source module is used for providing constant current for the H bridge and comprises a voltage source and a resistor R0And a low-speed operational amplifier, wherein one output end of the voltage source is connected with the low-speed operationPositive input, another end connected to ground, and resistor R0One end of the output of the operational amplifier is connected with the negative input of the low-speed operational amplifier, the other end of the output of the operational amplifier is grounded, the output end of the operational amplifier is connected with an H bridge, and the H bridge is connected back to the voltage-dividing resistor R0Forming negative feedback;
the H bridge is used as a load of a current source and converts constant current input into constant amplitude alternating current, and comprises four voltage control type switches S1, S2, S3 and S4 and four high-frequency signal sources C1, C2, C3 and C4; one end of a high-frequency signal source C1 is connected with the positive electrode of a switch S1 power supply, the other end is grounded, one end of a high-frequency signal source C2 is connected with the positive electrode of a switch S2 power supply, the other end is grounded, one end of a high-frequency signal source C3 is connected with the positive electrode of a switch S3 power supply, the other end is grounded, one end of a high-frequency signal source C4 is connected with the positive electrode of a switch S4 power supply, and the other end is grounded; one end of the switch S1 is connected with the switch S2, the other end is connected with the switch S4, one end of the switch S2 is connected with the switch S1, the other end is connected with the switch S3, one end of the switch S3 is connected with the switch S2, the other end is connected with the switch S4, one end of the switch S4 is connected with the switch S3, and the other end is connected with the switch S1; the connection points of the switch S1 and the switch S2 are connected with the output end of the low-speed operational amplifier, the connection points of the switch S2 and the switch S3 are connected with the positive electrode of a power supply of the Wheatstone bridge, and the connection points of the switch S1 and the switch S4 are connected with the negative electrode of the power supply of the Wheatstone bridge;
the detection module is used as a load of the H bridge and outputs a detection signal;
the detection module is a Wheatstone bridge.
2. The high frequency current source Wheatstone bridge detection circuit realized by the low speed operational amplifier as claimed in claim 1, wherein: the output signal of the H bridge is a high-frequency modulation for the detection signal of the Wheatstone bridge.
3. The high frequency current source Wheatstone bridge detection circuit realized by the low speed operational amplifier as claimed in claim 2, wherein: the Wheatstone bridge comprises two variable resistors R1、R3And two constant value resistors R2、R4(ii) a Constant value resistance R4One end of is connected with a variable resistor R3And the other end is connected with a variable resistor R1Variable resistance R1One end is connected with a constant value resistor R2The other one isTerminating a constant value resistor R4Constant value resistance R2One end of is connected with a variable resistor R3And the other end is connected with a variable resistor R1Variable resistance R3One end is connected with a constant value resistor R2The other end is connected with a fixed value resistor R4(ii) a Constant value resistance R2And a variable resistor R1The connecting point of the resistor is connected with the positive electrode of the bridge power supply and the constant value resistor R4And a variable resistor R3The connecting point of the power supply is connected with the negative electrode of the bridge power supply.
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