CN111623954B - A method for fault detection of a balance bridge in a wind tunnel - Google Patents

Abstract

The invention belongs to the technical field of wind tunnel testing, and provides a wind tunnel balance bridge fault detection method. The method comprises the steps of respectively measuring the resistance between every two outer leads of the four electric bridges in a normal state and after a fault of the balance, obtaining six equation sets according to a resistance calculation formula of a series-parallel circuit, solving a numerical solution of the nonlinear equation sets by using a least square method, obtaining the variation of a strain gage on each electric bridge in the normal state and after the fault of the balance, and determining the fault position of the electric bridges of the balance.

Description

A method for fault detection of a balance bridge in a wind tunnel

technical field

The invention relates to a fault detection method for a balance bridge in a wind tunnel, and belongs to the technical field of wind tunnel testing.

Background technique

When the strain gauge is deformed after being loaded, it will cause a change in the electrical resistance value, which is converted into an electrical signal through the measuring bridge.

The measuring bridge used in strain balances is a Wheatstone bridge. The Wheatstone bridge of the strain balance generally uses a DC power supply and a constant voltage power supply to convert the resistance change value of the strain gauge into a voltage change value. The Wheatstone bridge has the advantages of high sensitivity, wide measurement range, simple circuit structure, high measurement accuracy and easy compensation.

The large impact on the balance in the transient wind tunnel, the large vibration amplitude and high frequency of the model balance system, and the excessive load during the test may cause damage to the strain gauge on the balance bridge, such as the adhesive layer or strain. The chip has irreversible damage, the quality of solder joints, and the surface damage of the enameled wire leads to a decrease in the insulation of the entire bridge. The zero point of the balance changes greatly, even beyond the range of the data acquisition system, so that the balance cannot accurately measure the load it receives. When the balance bridge fails, the balance maintenance personnel need to check each position of the entire bridge one by one to determine the fault location. The work is difficult, takes a long time, and takes up a lot of valuable wind tunnel test time.

In order to solve the problems of high difficulty and low efficiency in detecting the fault of the balance bridge in the traditional way, the invention proposes a method for detecting the balance bridge fault in a wind tunnel, which realizes the fast and accurate positioning of the fault position of the balance bridge.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the prior art, the present invention provides a method for detecting the fault of a balance bridge in a wind tunnel, which simplifies the way of troubleshooting and improves the efficiency.

The technical solution adopted by the present invention to solve the technical problem is as follows: a wind tunnel balance bridge fault detection method, the wind tunnel balance bridge includes four bridge arms, and strain gauges are pasted on each bridge arm; the method steps are as follows :

When the balance is in a normal state, connect the balance body to the ground with a wire, and measure the resistance between every two of the four outer leads; six equations are obtained according to the formula for calculating the resistance of the series-parallel circuit, and the numerical solution of the nonlinear equations is obtained. The resistance value of the strain gauge on each bridge arm when the balance is in normal state;

After the balance fails, the balance body is also connected to the ground with wires, and the electrical resistance value between each two of the four outer leads is measured; six equations are obtained according to the resistance calculation formula of the series-parallel circuit, and the nonlinear equations are solved. Numerical solution to obtain the resistance value of the strain gauge on each bridge arm when the balance is in fault state;

According to the change of resistance value of each bridge arm strain gauge in the fault state of the balance and the normal state, the bridge arm where the faulty strain gauge is located is determined.

Preferably, it is assumed that the four outer leads of the balance are respectively a and b, c and d; the resistances at both ends of the measured outer leads a and b, a and c, a and d, b and c, b and d, c and d are respectively R _ab , R _ac , _Rad , R _bc , R _bd , R _cd ; then according to the calculation formula of series and parallel circuit resistances,

Preferably, the least squares method is used to solve the numerical solution of the nonlinear equation system.

Further, when there are multiple strain gauges pasted on the faulty bridge arm, each strain gauge on the bridge arm is disconnected from the bridge, and then the specific resistance value of each strain gauge is measured separately, so as to determine the occurrence of the fault. Faulty strain gauge.

Further, the failure of the balance is eliminated by checking the quality of the strain gauge and the paste process of the strain gauge for the failed strain gauge.

The advantages of the present invention are:

The invention only needs to measure the resistance value between each two of the four outer leads of the bridge when the balance is in normal and fault states, and then calculate the resistance value of the strain gauge on each bridge arm by using the calculation program written The amount of change can determine the bridge arm where the faulty strain gauge is located, avoiding the trouble of maintenance personnel to determine the bridge arm where the faulty strain gauge is located by manually testing various positions of the entire bridge. It reduces the labor intensity of the balance maintenance personnel and saves valuable time for wind tunnel tests.

Description of drawings

Figure 1 is a schematic diagram of a typical conventional wind tunnel balance;

Figure 2 is a schematic circuit diagram of a Wheatstone full bridge.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings:

The invention provides a fault detection method for a balance bridge in a wind tunnel. As shown in Figure 1, it is a typical conventional wind tunnel balance with six components, namely six bridges, including strain gauge 1, terminal 2, balance inner lead 3, balance body 4, balance outer lead 5 resistance value Wait. As shown in Figure 2, each bridge consists of four bridge arms, and each bridge arm consists of several strain gauges, usually one or two, depending on the specific structure of the balance. When the balance bridge fails, the balance maintenance personnel need to check each position of the entire bridge one by one to determine the fault location. Due to the limitation of the working environment on the wind tunnel, the troubleshooting is difficult, takes a long time, and takes up a lot of valuable. Wind tunnel test time.

In this method, the resistance value between every two outer leads of the bridge is measured separately when the balance is in the normal state and the fault state, and then the least squares method is used to solve the numerical solution of the nonlinear equation system to obtain the strain on each bridge arm. The amount of change in the resistance value of the gauge can be used to determine the bridge arm where the faulty strain gauge is located.

A wind tunnel balance bridge fault detection method, the measurement principle and detection steps are as follows:

Two of the balance outer leads 5 are power lines, which are used to connect with the power supply during operation, and the other two are signal lines, which are used to connect with the data acquisition system during operation. When the balance is in a normal state, use a wire to connect the balance body to the ground. As shown in Figure 2, measure the resistances R _ab , R _ac , R _ad , R _bc , R _bd at both ends of the outer leads a and b, a and c, a and d, b and c, b and d, c and d respectively , R _cd . According to the formula for calculating the resistance of series and parallel circuits, we can get

The numerical solution of the above nonlinear equation system is solved by the least square method, and the solution is realized on matlab, and the numerical solutions of R ₁ , R ₂ , R ₃ and R ₄ are obtained as a result.

After the balance fails, the main body of the balance is also connected to the earth with a wire. Again, measure the resistances R' _ab , R' _ac , R' _ad , R' _bc , R' _bd at both ends of the outer leads a and b, a and c, a and d, b and c, b and d, c and d, respectively , _R'cd . According to the formula for calculating the resistance of series and parallel circuits

The numerical solution of the above nonlinear equation system is also solved by the least square method, and the numerical solutions of R ₁ ', R' ₂ , R ₃ ' and R' ₄ are obtained as a result.

The difference between the resistance value of each bridge after the fault and the resistance value of each bridge in the normal state is:

ΔR ₁ =R' ₁ -R ₁

ΔR ₂ =R' ₂ -R ₂

ΔR ₃ =R' ₃ -R ₃

ΔR ₄ =R' ₄ -R ₄

When the resistance change ΔR of a strain gauge exceeds the reasonable change range specified by the manufacturer, it can be determined that it is a faulty strain gauge. According to the number in advance, the position can be quickly found, the strain gauge can be re-pasted and replaced, and the balance failure can be eliminated. For the faulty strain gauge, check the quality of the strain gauge and the pasting process of the strain gauge to eliminate the balance failure.

The parts not described in detail in the present invention belong to the common knowledge of those skilled in the art.

Claims (3)

1. a wind tunnel balance bridge fault detection method, described wind tunnel balance bridge comprises four bridge arms, and each bridge arm is pasted with a strain gauge; it is characterized in that the method steps are as follows: When the balance is in a normal state, connect the balance body to the ground with a wire, and measure the resistance between every two of the four outer leads; six equations are obtained according to the formula for calculating the resistance of the series-parallel circuit, and the numerical solution of the nonlinear equations is obtained. The resistance value of the strain gauge on each bridge arm when the balance is in normal state; After the balance fails, the balance body is also connected to the ground by wires, and the resistance value between each two of the four outer leads is measured; six equations are obtained according to the formula for calculating the resistance of the series-parallel circuit, and the numerical value of the nonlinear equations is solved. Solve the resistance value of the strain gauge on each bridge arm when the balance is in fault state; Determine the bridge arm where the faulty strain gauge is located according to the resistance value change of each bridge arm strain gauge in the balance fault state and normal state; Assume that the four outer leads of the balance are respectively a and b, c and d; the resistances at both ends of the outer leads a and b, a and c, a and d, b and c, b and d, c and d are measured as R _ab , R _ac , _Rad , R _bc , R _bd , R _cd ; then according to the calculation formula of series and parallel circuit resistances,

When there are multiple strain gauges pasted on the faulty bridge arm, each strain gauge on the bridge arm is disconnected from the bridge, and then the specific resistance value of each strain gauge is measured individually to determine the faulty strain piece. 2. The method according to claim 1, characterized in that: the least squares method is used to solve the numerical solution of the nonlinear equation system. 3 . The method according to claim 1 , wherein the failure of the balance is eliminated by checking the quality of the strain gauge and the gage sticking process for the failed strain gauge. 4 .

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