Understanding the sampling frequency of electronic tensile testing machines:

Customers often mention the sampling frequency of tensile testing machines. Some competitors, when providing specifications, will list a sampling frequency of 2000Hz or even higher. Some customers then use these figures to inquire about pricing. I really want to ask, do they truly understand static testing machines? Can a static tensile testing machine really achieve such a high sampling frequency?

Technical understanding of sampling frequency: 

1. Before 2010, the formal testing of the testing machine's measurement and control system was based on the samples specified in GB/T228 room temperature metal standard, with a sampling frequency of no less than 15Hz. After 2010, the sampling frequency standard is no less than 30Hz. However, it is important to note that the sampling frequency specified in the evaluation standard has quality requirements. It is not the theoretical sampling frequency of the sampling circuit, but a noise-free, stable, and identifiable sampling frequency. In other words, every sampling point, regardless of frequency, must be accurate and reliable. Static testing machines emphasize high reliability and precision. The standard does not give an upper limit to this; the higher the reliable data accuracy for static testing machines, the better. Our system has always exceeded the standard requirements. From power supply design to the unique circuit technology, we have pursued noise-free and zero-point drift-free operation. In particular, the unique technology of multi-channel parallel acquisition ensures that the data from each channel sensor is strictly synchronized, without any time difference. The data can be directly used to accurately evaluate the key parameters of the sample. In addition, the high-precision synchronization clock ensures that the sensors of each channel can achieve long-term synchronization when working simultaneously, and also ensures the repeatability of the test. This is very important for static testing machines!

2. In the field of metals, considering that the stress-strain data of ultra-hard materials at their yield point is non-linear, a higher sampling frequency is required to capture transient data at the yield point, making a higher sampling frequency necessary. However, a higher sampling frequency will inevitably cause a loss of noise-free accuracy, resulting in a larger amount of data. However, the accuracy and reliability of the transient data become unknown, and the data is also unverifiable. Therefore, increasing the sampling frequency is a very cautious matter. After increasing the sampling frequency, the actual impact of the loss of accuracy on the results must be honestly evaluated. In this regard, we adopted a solution that first ensures minimal or no loss of noise-free accuracy, and then strives to increase the sampling frequency with extreme caution.

3. The control frequency is generally the same as the sampling frequency. However, it's important to note that to achieve higher test forces under constant speed loading, static testing machines require increased mechanical strength and a series of deceleration processes in the transmission mechanism. Therefore, a static testing machine is a mechanism with control lag. Any minor adjustment to the motor shaft will inevitably result in progressively increasing backlash and losses as it passes through a series of deceleration mechanisms before reaching the clamping end. The problem arises because an excessively high control frequency cannot provide timely and stable signal feedback on such a mechanical model. It will only lead to more control-end waiting and silence, as the feedback signal generated by each control will be identical, rendering the PID closed-loop control ineffective. Therefore, it is scientifically sound to use a reasonable high-frequency control based on the tonnage of the testing machine. In this case, the machine needs to provide 10 tons of tensile and compressive strength, and a control frequency of around 50Hz is sufficient to ensure a closed-loop control accuracy better than 1%, and within a specified range, it is likely to be better than 0.5%. Achieving a 1% control accuracy is the evaluation standard for an excellent static testing machine.

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