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The effect of electronic tensile testing machine sensor on force value measurement
The force measurement of the electronic tensile test machine is measured by a load cell, an amplifier and a data processing system. The commonly used load cell is a strain gauge sensor.
The so-called strain gauge sensor is a device that can change a certain mechanical quantity into a power output by strain gauges, elastic components and some accessories (compensating components, protective covers, wiring sockets, and loading components).
Strain gauge type pull and pressure sensors are available at home and abroad, mainly including cylindrical force sensors, spoke-type force sensors, S double-connected sensors, and cross-beam sensors.
It is known from the material mechanics that under small deformation conditions, the strain ε at a certain point of an elastic element is proportional to the force received by the elastic element and also proportional to the elastic deformation. Taking the S-type sensor as an example, when the sensor is subjected to the pulling force P, since the strain gauge is attached to the surface of the elastic member, since the strain of the elastic member is proportional to the magnitude of the external force P, the strain gauge is connected to the measuring circuit. The magnitude of the force is measured by measuring its output voltage.
For the sensor of the electronic tensile testing machine, the differential full bridge measurement is generally adopted, that is, the attached strain gauges form a bridge, and R1, R2, R3, and R4 are actually four (or eight) strain gauges with equal resistance values. That is, R1=R2=R3=R4. When the sensor is subjected to external force (tension or pressure), the elastic element of the sensor generates strain and changes the resistance values. The change values ​​are ΔR1△, R2, △R3, △R4. As a result, the original balanced bridge is now unbalanced, and the bridge has voltage output, setting △E
Then â–³E=[R1R2/(R1+R2)2]â–³R1/R1-â–³R2/R2+â–³R3/R3-â–³R4/R4) U is the voltage of the external power supply bridge in U
â–³E=[R2/4R2](â–³R1/R-â–³R2/R+â–³R3/R-â–³R4/R)U
Put △Ri/Ri=Kεi on the above formula
Then there is △E=[UK/4](ε1-ε2+ε3-ε4)
In simple terms, the external force P causes deformation of the strain gauge in the sensor, resulting in imbalance of the bridge, which causes the change of the output voltage of the electronic tensile tester sensor. We can know the magnitude of the force by measuring the change of the output voltage.
In general, the output signal of the sensor is very weak, usually only a few mV, if we directly measure this signal, it is very difficult, and can not meet the high-precision measurement requirements. Therefore, the weak signal must be amplified by the amplifier, and the amplified signal voltage can reach 10V. The signal at this time is an analog signal, and the analog signal is converted into a digital signal by the multiplexer and the A/D conversion chip, and then the data is processed. At this point, the measurement of the force of the electronic tensile test has come to an end.