JP2012112849A - Highly accurate bridge circuit type detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate bridge circuit type detector having simple structure and capable of reducing errors in measurement of a fine resistance change.SOLUTION: The detector using a bridge circuit having a resistance displacement part Rto be displaced correspondingly to a measurement sensor part on at least one side of a quadrilateral includes a power supply part connected between a point A and a point B facing each other in the bridge circuit, an output voltage measurement part for detecting voltage outputted between the other points C and D facing each other and a net bridge voltage measurement part for measuring voltage between the points A and B to calculate a fine resistance change of the resistance displacement part Rby an output voltage value measured by the output voltage measurement part and a net bridge voltage value measured by the net bridge voltage measurement part.

Description

  The present invention relates to a bridge circuit type detector capable of accurately measuring a minute resistance change.

  A Wheatstone bridge circuit is employed for various sensors such as a temperature sensor and a pressure sensor that measure resistance changes by connecting to a strain gauge, or measure changes in physical quantities such as temperature and pressure as resistance changes.

A configuration example of a conventional bridge circuit type detector is shown in FIG.
A resistance displacement part _RS for detecting resistance displacement, such as a strain gauge, and known resistors R ₁ , R ₂ , R ₃ are connected in a quadrilateral shape, and a power supply voltage E between points A and B facing each other in the bridge circuit. And the output voltage between other opposing points C and D is measured.
Here, R ₁ and R ₂ are known fixed resistors, and R ₃ is a variable resistor, so that the resistance value of R ₃ is calculated by _obtaining the resistance value of R ₃ at which the output voltage becomes zero ( Zero method) and R ₁ , R ₂ , R ₃ as fixed resistors, and a method of detecting an output voltage caused by an unbalanced bridge circuit.
When the resistance displacement part _RS is a strain gauge, the change in resistance is extremely small, so the output voltage generated by the unbalance of the bridge circuit is amplified and measured.

However, in the conventional bridge circuit type detector, since the distortion is measured using the value of the power supply voltage E and the measured output voltage V _CD , the measurement error is caused by the length of the connection cord or some internal resistance r. There was a problem that occurred.
Further, an expensive current control device for stabilizing the current value is required.
Patent Document 1 discloses a technique in which a bridge-type detection circuit is provided. The bridge voltage detection circuit disclosed in the same publication is used for a gas chromatograph or the like, and a resistance value change in the bridge circuit due to self-heating is zero. A complex computer program dedicated to the correction was necessary.
Further, since the resistance value in the bridge circuit changes not only with self-heating but also with changes in the measurement environment such as ambient temperature, pressure, and magnetic field, the above-described correction only with self-heating is not sufficient.

JP 2004-93321 A

  An object of the present invention is to provide a high-accuracy bridge circuit type detector having a simple structure and a small error with respect to measurement of a minute resistance change.

A bridge circuit type detector according to the present invention is a detector using a bridge circuit having a resistance displacement part _RS that is displaced corresponding to a measurement sensor part on at least one side of a quadrilateral, and is a detector that has a facing A of the bridge circuit. A power supply unit between the point B and the point B, and an output voltage measurement unit that detects a voltage output between the other opposing points C and D, and further measures the voltage between the points A and B A net bridge voltage measurement unit is included, and a minute resistance change of the resistance displacement unit _RS is calculated from the output voltage value measured by the output voltage measurement unit and the net bridge voltage value measured by the net bridge voltage measurement unit. It is characterized by being.

  Here, the output voltage measurement unit may include an amplifier as necessary.

The detector according to the present invention measures the net bridge voltage directly applied between the points A and B each time, and can measure the output voltage between the points C and D at this time, so these values are used. Therefore, a minute resistance change can be measured with high accuracy.
For example, even if the length of the connection cord between the power supply unit and the detector changes or the measurement environment such as temperature, pressure, magnetic field, etc. in the measurement system changes, it is truly applied to the bridge circuit at every measurement. Since the net bridge voltage and the output voltage at that time are measured, the change in the measurement environment can be eliminated, and the measurement error can be greatly reduced. In the case of strain measurement, the measurement error has a high standard deviation of 10 ⁻⁶ or less. .
Since the detector according to the present invention directly measures the voltage V _AB between the points A and B and detects a minute resistance change using the voltage V _AB , it is sufficient to have a power supply device. Such a constant current control device is not necessarily required.

The structural example of the bridge circuit type detector which concerns on this invention is shown. The structural example of the conventional detector is shown. The comparison data of the distortion measured using the conventional detector and the detector based on this invention are shown.

A configuration example of a detector according to the present invention is shown in FIG.
The example shown in FIG. 1 is a bridge circuit in which known fixed resistors R ₁ , R ₂ , R ₃ and a resistance displacement portion _RS are connected in a quadrilateral shape, where R _S is a strain gauge, a temperature sensor, It is a resistor that changes in accordance with a change in a physical quantity to be measured in a physical quantity measurement sensor unit such as a pressure sensor.
A power source E is provided between the points A and B of the bridge circuit.
Between the point C and point D has an output voltage measuring unit V _CD.
The measurement of the output voltage _{V CD,} measures the net bridge voltage _{V AB} between the points A and B.

Next, an example in which strain (tensile strain, compressive strain, etc.) is measured using a strain gauge on the resistance displacement portion _RS will be described.
<Example 1>
If R ₁ = R ₂ = R ₃ = R _{S in the} initial equilibrium state and the resistance R _S changes when a strain ε occurs in the strain gauge, the output voltage V _CD (strain ε is less than the net bridge voltage V _AB . As for the relationship of the voltage that has changed due to the occurrence, the approximate expression of ε = 4 / K _S × V _CD / V _AB is obtained because the resistance change of R _S is very small when the gauge factor of the strain gauge is K _S. To establish.
<Example 2>
Active gage affected by external field, such as R strain to the _S and the temperature, pressure and magnetic field, strain using a dummy gauge affected by external field only, such as temperature, pressure, magnetic field R ₃ (tensile strain, compressive strain Etc.), if R ₁ = R ₂ , R ₃ = R _S in the initial equilibrium state, and the resistance R _S changes when the strain ε occurs in the active gauge, then the net bridge voltage V _AB relationship between the output voltage V _{CD (voltage} changed by strain epsilon occurs), when the gauge factor of the strain gauge and K _S, R _S, since the change in resistance of R ₃ is small epsilon = 4 / K An approximate expression of _S × V _CD / V _AB is established.
<Example 3>
When strain (tensile strain, compression strain, etc.) is measured using strain gauges for R _S and R ₁ , R ₁ = R ₂ = R ₃ = R _{S in} the initial equilibrium state, and strain ε is generated in the strain gauge. resistance R _S when _the, if R ₁ is changed, the relationship between the output voltage with respect to the net bridge voltage V _AB V _{CD (voltage} changed by strain ε occurs) is the gauge factor of the strain gauge and K _S Then, since the resistance change of R _S and R ₁ is minute, an approximate expression of ε = 4 / (1 + ν) K _S × V _CD / V _AB is established.
Here, ν is a parameter determined by the direction of distortion of R _S and R ₁ .
<Example 4>
When measuring strain (tensile strain, compressive strain, etc.) using strain gauges for R _S and R ₃ , R ₁ = R ₂ and R ₃ = _{RS in} the initial equilibrium state, and strain ε is generated in the strain gauge. resistance R _S when _the, if R ₃ is changed, the relationship between the output voltage with respect to the net bridge voltage V _AB V _{CD (voltage} changed by strain ε occurs) is the gauge factor of the strain gauge and K _S Then, since the resistance change of R _S and R ₃ is minute, an approximate expression of ε = 4 / (1 + ν) K _S × V _CD / V _AB is established.
Here, ν is a parameter determined by the direction of distortion of R _S and R ₃ .
<Example 5>
When measuring strain (tensile strain, compressive strain, etc.) using strain gauges for R ₁ , R ₂ , R ₃ , and _RS , R ₁ = R ₂ = R ₃ = R _{S in} the initial equilibrium state, Assuming that ΔR ₁ , ΔR ₂ , ΔR ₃ , and ΔR _s are resistance changes when strain ε is generated in the gauge, and ΔR ₁ = ΔR ₃ = −ΔR ₂ = −ΔR _S , the net bridge voltage V _{AB is obtained.} relationship Te output voltage V _{CD (strain} epsilon voltage changed by occurs), when the gauge factor of the strain gauge and K _S, R _S, since the change in resistance of R ₁ is small epsilon = K _S The approximate expression of × V _CD / V _AB is established.
Graph of Figure 3 takes the temperature (K) of the measuring system on the horizontal axis, relative to a detector according to the present invention used on the vertical axis, the strain was calculated from the value of V _AB, V _CD in accordance with the above Example 2 epsilon, The difference when the strain ε ₀ calculated from the value of V _{CD with} a conventional detector is δε is represented by δε, and the value of δε / ε ₀ is represented by%.
As a result, there was a difference of about 0.3% around the temperature of 20-30K.
That is, the measurement error becomes smaller as the strain is calculated using the net bridge voltage V _AB .

As the strain gauge, any of a foil strain gauge, a linear strain gauge, and a semiconductor strain gauge can be used.
Gauge factor K _S is a coefficient representing the sensitivity of the strain gauge, copper nickel based or nickel-chromium-based alloys are used in strain gauge OTC is approximately 2 values.
Therefore, if K _S = 2 at ε = 4 / K _S × V _CD / V _AB and V _AB = 2 [V] × the reciprocal α of the change rate is set, ε = αV _CD is obtained. in it is possible to calculate the reciprocal of the rate of change of voltage α as the product of the output voltage change [Delta] V = V _CD.
The detector according to the present invention may have an automatic calculation unit that automatically calculates the value of V _AB and V _CD only by inputting the value of K _S.

Claims (1)

A detector using a bridge circuit having a resistance displacement part _RS that is displaced corresponding to the measurement sensor part on at least one side of the quadrilateral,
A power supply unit between the A and B points facing each other in the bridge circuit, and an output voltage measuring unit that detects a voltage output between the other C and D points facing each other. A net bridge voltage measurement unit that measures the voltage between
A bridge characterized in that the minute resistance change of the resistance displacement portion _RS is calculated from the output voltage value measured by the output voltage measurement unit and the net bridge voltage value measured by the net bridge voltage measurement unit. Circuit type detector.