BECKHOFF EP1908 - Manual (Page 22)

Operation
20 EP1908-0002
Permitted cable length
When connecting a single switching contact via a dedicated continuous cable (or via a non-metallic
sheathed cable), the maximum permitted cable length is 30 m if a sensor test is active.
Attention
Route the signal cable separately
The signal cable must be routed separately from potential sources of interference, such
as motor supply cables, 230 V
AC
power cables etc.!
Interference caused by cables routed in parallel can influence the signal form of the
test pulses and thus cause diagnostic messages (e.g. sensor errors).
The common routing of signals together with other clocked signals in a common cable also reduces the
maximum propagation, since crosstalk of the signals can occur over long cable lengths and cause
diagnostic messages. The test pulses can be switched off (sensor test parameter) if the connection of a
common cable is unavoidable. However, this then leads to a reduction in the degree of diagnostic cover
when calculating the performance level.
The use of contact points, plug connectors or additional switching contacts in the cabling also reduces the
maximum propagation.
The typical length of a test pulse (switching from 24 V to 0 V and back to 24 V) is 350 µs and takes place
approx. 250 times per second.