Universal tensile testing machine can stretch, compress, bend and tear rubber, plastic, film, textile, fiber, polymer materials, composite materials, belts, tapes, alloy materials and other non-metallic materials and metal materials. ? Stripping, pull-out force, elongation elongation and other tests. At present, data acquisition of analog signals is realized by an A/D converter. There are many types of A/D converters, but the ∑-Δ type A/D converter is used in the electronic universal testing machine. These converters are flexible and can be dynamically adjusted at conversion rates for high-speed, low-accuracy conversion and low-speed, high-precision conversion. In the test machine, since the data acquisition rate requirement is not too high, generally tens to hundreds of times per second can meet the demand, so generally lower conversion rate is adopted to achieve higher measurement accuracy. However, in some test machines produced by some manufacturers, in order to pursue higher sampling resolution and extremely high data display stability, the sampling speed is lowered very low, which is not desirable. Because when the sampling speed is very low, the signal that changes at high speed cannot be accurately collected in real time. For example, in the performance test of metal materials, when the material yields and the force value fluctuates up and down, the signal changes so much that the upper and lower yield points cannot be accurately determined, resulting in failure of the test, resulting in the loss of watermelon and sesame seeds. Improper use of universal testing machine control method The relationship between stress and strain when yielding a material. The control mode recommended by the national standard is constant strain control, and the elastic phase control mode before yielding is constant stress control, which is difficult to accomplish in most testing machines and some tests. Because it requires changing the control mode when the yielding phenomenon occurs, and the purpose of the test itself is to ask for the yield point. How can the unknown result be used as the control condition of the measurement and control link of the electronic universal testing machine? Therefore, in reality, the same control mode is generally used to complete the whole test (even if different control modes are used, it is difficult to switch at the upper yield point, generally choose a point ahead). For the test machine using constant displacement control (speed control), since the stress rate of the material in the elastic phase is proportional to the strain rate, as long as the appropriate test speed is selected, the speed control in the whole process can be compatible with the control characteristics of the two stages. However, for an electronic universal testing machine that only controls one mode, if the response of the testing machine is particularly fast (this is the purpose that the automatic control strives to achieve), the process time of yielding will be very short, if the speed of data acquisition is fast. If it is not high enough, the yield value will be lost (the reason is explained in point 2), and the excellent control performance becomes the cause of the error. Therefore, when choosing an electronic universal testing machine and control method, Zui should not choose a single load control mode. Universal testing machine sensor amplifier band is too narrow Since the force detecting elements used in the current testing machine are basically load sensors or pressure sensors, both of which are analog small signal output types, signal amplification must be performed in use. It is well known that in our environment, there are a variety of electromagnetic interference signals that are coupled to the measurement signal through a number of different channels and amplified together, with the result that the useful signal is flooded by the interference signal. In order to extract a useful signal from the interference signal, a low-pass filter is generally provided in the amplifier for the characteristics of the material testing machine. By properly setting the cutoff frequency of the low-pass filter and limiting the frequency band of the amplifier to an appropriate range, the measurement control performance of the test machine can be greatly improved. However, in reality, people tend to see the stable display of data very important, while ignoring the authenticity of the data, the filter cutoff frequency is set very low. In this way, while the interference signal is fully filtered out, the useful signal is often filtered out together. In daily life, our common electronic scales, the data is very stable, one of the reasons is that its frequency band is very narrow, the interference signal can not basically pass. The reason for this design is that the electronic scale weighs the steady-state signal, the symmetrical amount of the transition process is not concerned, and the material testing machine measures the dynamic signal, its spectrum is very wide, if the frequency band is too narrow, higher The frequency signal is attenuated or filtered out, causing distortion. This distortion is not allowed for the case where the yield is expressed as the force value fluctuating many times. As far as the universal material testing machine is concerned, the author believes that this band should be smaller than 10HZ, and Zui should reach 30HZ. In practice, although the frequency band of the amplifier sometimes reaches this range, the bandwidth of the A/D converter is often neglected, so that the actual frequency bandwidth is smaller than the set bandwidth. Take AD7705, AD7703, AD7701, etc. selected by many test machine data acquisition systems as examples. When the A/D converter operates at "zui high output data rate 4KHZ", its analog input processing circuit achieves a large bandwidth of 10 Hz. When operating at the output data rate of 100 Hz commonly used by the test machine, the actual bandwidth of the analog input processing circuit is only 0.25 Hz, which will give a lot of useful signals to the loss, such as the fluctuation of the force value of the yield point. Of course, the correct test results cannot be obtained with such a circuit. 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The data acquisition rate of the universal testing machine is too low.