Electronic tensile testing machine commonly used working principle


A. Tensile testing machine measuring system

1. Force measurement

Measured by force sensors , amplifiers, and data processing systems, the most commonly used force sensors are strain gauge sensors.

The so-called strain gauge sensor is a device that can convert a mechanical quantity into a power output by strain gages, elastic elements, and certain accessories. There are a wide variety of strain gauge and pressure sensors at home and abroad, including cylindrical force sensors, spoke type force sensors, S double hole type sensors, and cross beam type sensors.

From the material mechanics, it is known 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 is also proportional to the change of elasticity. Take the S-type sensor as an example. When the sensor is subjected to a pulling force P, a strain gauge is attached to the surface of the elastic element. Since the strain of the elastic element is proportional to the magnitude of the external force P, the strain gauge is inserted into the measurement circuit. By measuring its output voltage, the force is measured.

For sensors, differential full-bridge measurements are generally used, ie, the bonded strain gauges are used to form bridges.

In simple terms, the external force P causes deformation of the strain gage in the sensor, resulting in imbalance of the bridge, which causes a change in the output voltage of the sensor. We can know the magnitude of the force by measuring the change in 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, this weak signal must be amplified by an amplifier, and the amplified signal voltage can reach 10V. The signal at this time is an analog signal. This analog signal is converted into a digital signal through a multi-way switch and A/D conversion chip, and then data processing is performed. At this point, the measurement of force came to an end.

2. Measurement of deformation

Measured by a deformation measuring device, it is used to measure the deformation of the specimen during the test.

There are two chucks on the device, which is connected to the photoelectric encoder mounted on the top of the measuring device through a series of transmission mechanisms. When the distance between the two chucks changes, the axis of the photoelectric encoder is driven to rotate. The encoder will have a pulsed signal output. The signal is processed by the processor to determine the amount of deformation of the sample.

3. Measurement of beam displacement

The principle is almost the same as the deformation measurement. The displacement of the beam is obtained by measuring the number of output pulses of the photoelectric encoder.

Second, the tensile testing machine drive system

It is mainly used to move the cross beam of the testing machine. Its working principle is that the servo system controls the motor, and the motor drives the screw rod through a series of transmission mechanisms such as a gear box to achieve the purpose of controlling the movement of the cross beam. By changing the speed of the motor, you can change the speed of the beam.

Three. Tension testing machine control system

As the name implies, it is the system that controls the operation of the testing machine. People can control the operation of the testing machine through the console. Through the display screen, the status of the testing machine and various test parameters can be known. If the computer is equipped with a computer, it can also be realized by the computer. Item functions and data processing analysis, test results print. The communication between the testing machine and the computer generally uses the RS232 serial communication mode. It communicates through the serial port (COM port) behind the computer. This technology is mature, reliable, and easy to use.

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