Data Acquisition System Common Terms

Data Acquisition System Common Terms

● Number of channels: The signal that the board can collect several channels is divided into single-ended and differential. Commonly used are single-ended 32-channel/differential 16-channel, single-ended 16-channel/differential 8-channel

● Sampling frequency: The number of data points collected in a unit of time is related to the time required to convert one point of the AD chip. For example, when AD converts one point, T = 10uS, then the sampling frequency f = 1 / T is 100K, that is, every second. The AD chip can convert 100K data points. It uses Hertz (Hz), often 100K, 250K, 500K, 800K, 1M, 40M, etc.

● The difference between the cache and its role: It is mainly used to store the converted data of the AD chip. There is a buffer to set the sampling frequency, and if it is not there is no option. Cache has two kinds of RAM and FIFO: FIFO is used on the data acquisition card to do data buffering, storage is not large, and speed is fast. RAM is an abbreviation for random access memory. Generally used for high-speed capture card, large storage, slower speed.

Resolution: The value of the analog value represented by the lowest bit of the sampled data, often 12-bit, 14-bit, 16-bit, etc. (12-bit resolution, voltage 5000mV) 12 bits can represent the amount of data is 4096 (2 of 12 Power), that is, ±5000 mV voltage range can represent 4096 voltage values in units of (5000 mV)/4096 = 1.22 mV. The resolution has a definite relation with the number of bits of the A/D converter and can be expressed as FS/2n. FS represents the full-scale input value, n is the number of bits of the A/D converter. The more digits, the higher the resolution.

● Accuracy: The error between the measured value and the true value. The accuracy of the nominal data acquisition card is generally expressed as a percentage of the full scale range (FSR). Common examples are 0.05% FSR, 0.1% FSR, etc. If the full-scale range is 0~10V and the accuracy is 0.1%FSR, the difference between the measured value and the true value is within 10mv.

● Range: The amplitude of the input signal, commonly used in ± 5V, ± 10V, 0 ~ 5V, 0 ~ 10V, requires the input signal within the range

● Gain: The amplification factor of the input signal is divided into program-controlled gain and hardware gain. The voltage-amplified chip of the data acquisition card is used to amplify the AD-converted data by a fixed factor. The gain chip consists of two types of PGA202 (1, 10, 100, 1000) and PGA203 (1, 2, 4, 8).