The data acquisition unit is also called the analog input system. Its function is to isolate and regulate the input voltage, and convert the analog input to the digital quantity required by the microcomputer system in order to interface with the CPU. The analog input system is a very important circuit in the microcomputer protection device, and the performance of the protection device's action speed and measurement accuracy are closely related to this circuit.
The data acquisition unit of the digital strong vibration recorder is mainly composed of an analog-to-digital converter (ADC) and a digital signal processing chip (DSP). The analog-to-digital converter is an over-sampling analog-to-digital converter, which converts the analog signal (voltage) input by the sensor into a digital data stream with a high sampling rate after being amplified, and then is processed by a 24-bit digital signal processing chip. False filtering, output the digital data stream of the required sampling rate.
Anti-aliasing filtering is a must-have step in analog-to-digital conversion. According to the sampling theorem, after sampling an analog signal at a certain sampling rate, frequency components greater than 1/2 the sampling rate will become false signals and alias into the effective signal bandwidth, causing errors in the digitized signal. Therefore, such aliasing signals must be filtered out. The oversampling method is to first filter the analog signal. The corner frequency of the analog filter can be very high, which is several tens of times the highest frequency of the signal. The out-of-band slope of the filter does not need to be very large, which greatly reduces the analog filter's corner frequency. Difficulty of production. Then, the pre-filtered signal is digitized with a much larger sampling rate to obtain a digitized signal with a high sampling rate. After the over-sampled data enters the 24-bit digital signal processor, it is filtered by a digital filter to remove frequencies greater than five, and then sampled to obtain the digitized data with the required sampling rate.
The main technical indicators to measure the performance of the data acquisition unit are resolution, sampling rate, noise and dynamic range, etc.
