Spectral Characteristics of the Noise Voltage of Analog Sensors and Computer Interfaces Vernier

The article dwells upon the analysis results of spectral characteristics of Vernier analog sensors noise voltage connected to the BTA input of SensorDAQ interface. Several types of interferences varying in frequency and their dependedce on the sampling rate were detected. Namely in the signal of the temperature sensor there appears a periodic interference with spectral peaks at mains frequency 50 Hz and multiples of its frequences. The level of this interference has different values depending on the type of the computer (desktop PC, laptop) and connection to or disconnection from the laptop adapter. Also, two more types of periodic interference were detected, which registered frequency depended on the sampling rate. The given behavior of the interference was a result of the <;<;aliasing>> effect. The author offered an algorithm of evaluation of interference frequency. As a result of applying the proposed algorithm, the generation band of this interference was determined. It was located in the range of 610 - 650 kHz. The hypothesis of the relationship between the interference and operation of the pulse frequency converter was proved by means of registering the emission spectrum of the data acquisition unit with the spectral analyzer R&S FSH8 and the direct measurement of the impulse signal with the help of the oscilloscope. A similar interference was found in the data acquisition unit NI USB 6009, that has the scheme decision similar to SensorDAQ. The frequency of the second periodic interference, which occurs when the current probe and the differential voltage probe are operating, turned out to be 24.86 kHz. Its source also turned to be the voltage convertor. In order to reduce the noises mentioned it may be viable to avoid choosing sampling frequencies converting the interference into the zero frequency range and to use the averaging-out of signal readings.