Siemens SIMATIC ET 200AL, System Manual

Page: 2066 / 2255

What you should know about analog technology
2.13 Crosstalk between channels
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
35
Example of crosstalk attenuation
The "crosstalk between inputs" value in the technical specifications is defined as a value of
>-100 dB at a measuring range of -10 V to +10 V on channel 1 of an eight-channel analog
input module. The voltage at the input has an amplitude of 10 V. What is the error caused by
crosstalk at channel 0 (measuring range ±10 V) and channel 2 (measuring range ±80 mV)?
100 dB are equal to a factor of 100,000. The measured values at channels 0 and 2 to 7 are
therefore affected by 10 V / 100,000 = 100 μV. This distortion is added to or subtracted from
the pending measuring signal and its effect depends on the selected measuring range.
●
Channel 0: 100 μV / 10 V = 0.001 %
● Channel 2: 100 μV / 80 mV = 0.125 %
A voltage of 10 V set at channel 1 distorts the measured value at channel 0 by 0.001% and
the measured value at channel 2 by 0.125%. The measuring error resulting from crosstalk in
this example is therefore 0.001 % or 0.125 %. The basic error limit already includes the error
generated as a result of crosstalk between the channels.
Calculating measuring error
You calculate the measurement error at channel 1 in this example based on a change in the
measurement voltage of 10 V at channel 2. The crosstalk (XT [dB]) value is defined in the
technical specifications in the manual of the analog module that you are using.
A change in the measurement voltage of 10 V at channel 2 causes a measurement deviation
of 0.001 V at channel 1.