Electronic tensile testing machine is the product of the combination of modern electronic technology and mechanical transmission technology. It is a large-scale precision testing instrument composed of electromechanical advantages. It can carry out tensile, compression, bending and other performance tests on various materials, and has the characteristics of wide measurement range, high precision and fast response. It has reliable operation and high efficiency, and can display, record and print the test data in real time.

Electronic tensile testing machine is composed of measuring system, driving system, control system, computer and other structures.

1、 Measuring system

1. Measurement of force value

The measurement is realized by force measuring sensor, amplifier and data processing system. The most commonly used force measuring sensor is strain gauge sensor.

The so-called strain gauge sensor is a device that can turn a certain mechanical quantity into electric output by strain gauge, elastic element and some accessories (compensation element, protective cover, wiring socket and loading part).

There are many kinds of strain gauge tension and pressure sensors at home and abroad, mainly including cylindrical force sensor, spoke force sensor, s double hole sensor, cross beam sensor and so on.

It is known from the mechanics of materials that the strain at a certain point of an elastic element under the condition of small deformation ε It is directly proportional to the force on the elastic element and also directly proportional to the elastic deformation. Taking the S-type sensor as an example, when the sensor is subjected to the action of tensile force P, because the surface of the elastic element is pasted with a strain gauge, because the strain of the elastic element is directly proportional to the size of the external force P, the output voltage can be measured by connecting the strain gauge to the measuring circuit.

For the sensor, differential full bridge measurement is generally adopted, that is, the pasted strain gauges form a bridge, R1, R2, R3 and R4. In fact, they are 4 (or 8) strain gauges with equal resistance, 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 each resistance value, and the change values are △ R1 △, R2, △ R3 △ R4, as a result, the original balanced bridge is now unbalanced, and the bridge circuit has voltage output. Set △ E

Then △ e = [r1r2 / (R1 + R2) 2] △ R1 / R1 - △ R2 / r2 + △ R3 / R3 - △ R4 / R4) u, where u is the voltage of the external power supply bridge, which is further cylindrical

△E=[R2/4R2]（△R1/R-△R2/R+△R3/R-△R4/R）U

Set △ RI / ri = K ε I generation upper formula

Then △ e = [UK / 4]（ ε 1- ε 2+ ε 3- ε 4）

In short, the external force P causes the deformation of the internal variable plate of the sensor, resulting in the imbalance of the bridge, resulting in the change of the sensor output voltage. We can know the size of the force by measuring the change of the output voltage.

Generally speaking, the output signal of the sensor is very weak, usually only a few MV. If we measure this signal directly, it is very difficult and can not meet the requirements of high-precision measurement. Therefore, the weak signal must be amplified by the amplifier. The amplified signal voltage can reach 10V. At this time, the signal is an analog signal. The analog signal is transformed into a digital signal through the multi-channel switch and a / D conversion chip, and then the data is processed. So far, the force measurement has come to an end.

2. Deformation measurement

It is measured by the deformation measuring device, which is used to measure the deformation of the sample during the test.

There are two chucks on the device, which are connected with the photoelectric encoder installed on the top of the measuring device through a series of transmission mechanisms. When the distance between the two chucks changes, it drives the shaft of the photoelectric encoder to rotate, and the photoelectric encoder will have pulse signal output. Then the signal is processed by single chip microcomputer, and the deformation of the sample can be obtained.

3 measurement of cross beam displacement

The principle is roughly the same as that of deformation measurement. The displacement of the beam is obtained by measuring the output pulse number of the photoelectric encoder.

2、 Drive system

It is mainly used for the movement of the beam of the testing machine. Its working principle is that the servo system controls the motor, and the motor drives the screw rod to rotate through a series of transmission mechanisms such as reducer, so as to control the movement of the beam. By changing the speed of the motor, the moving speed of the beam can be changed.

3、 Control system

As the name suggests, it is a system that controls the operation of the testing machine. People can control the operation of the testing machine through the console, and can know the status and various test parameters of the testing machine through the display screen. If the machine is equipped with a computer, it can also realize various functions, process and analyze data and print test results. The communication between the testing machine and the computer generally uses RS232 serial communication mode. It communicates through the serial port (COM number) behind the computer. This technology is relatively mature, reliable and easy to use.

4、 Computer

It is used to collect and analyze data. After entering the test interface, the computer will continuously collect all kinds of test data, draw the test curve in real time, and automatically calculate each test parameter and output report.