Siemens SIMATIC ET 200AL, System Manual

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What you should know about analog technology
2.13 Crosstalk between channels
Analog value processing
34
Function Manual, 06/2014, A5E03461439-AC
2.13 Crosstalk between channels
Origin of the term
The term crosstalk/XT was originally used in the field of telecommunication to denote
unwanted coupling of voice signals between two cable conductors of different subscribers.
Definition
Crosstalk between signal channels denotes the interactive influence between two
independent channels as a result of leakage currents and capacitive or inductive coupling.
Crosstalk between the channels changes the signal by the value of the amplitude of the
crosstalk signal.
Causes
Technically, it is not feasible to totally isolate the module channels from environmental
conditions. This means that it is always possible for leakage currents or disturbance coupling
having an interactive effect.
Figure 2-18 Crosstalk between two channels
The diagram shows the effects of crosstalk for the user with two channels (Ch
1
/Ch
2
) of an
analog module. The crosstalk value is the factor by which the utility signal at a second
channel U
a2
is affected by the signal at the first channel U
e1
. The measuring error (U
a1
) can
be calculated using the following equation: