Analog modules
6.3 Analog input module SM 331; AI 8 x 16 bit; (6ES7331-7NF00-0AB0)
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
317
Measuring errors as a result of CMV
SM 331; AI 8 x 16 Bit is capable of taking measurements, irrespective of the presence of any
CMV in the AC or DC range.
With AC CMV values of a multiple of filter frequency settings, noise is suppressed as a result
of ADC integration time and common mode suppression at the input amplifiers. With AC
CMV < 35 V
RMS
, the noise suppression of > 100 dB results in negligible measurement errors.
The influence of
DC CMV can only be reduced to minimum using the noise suppression
function of the input amplifier unit. A certain degradation of measuring accuracy in proportion
to CMV must be expected. The worst case error is generated at 50 VDC between one
channel and the remaining seven channels. The calculated worst case error is 0.7% at 0 °C
to 60 °C, while the measured error usually lies at ≤ 0.1% at 25 °C.
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