BECKHOFF EL1904 - Manual (Page 28)

Operation
26 EL1904
Permitted cable length
When connecting a single switching contact via its own continuous cabling (or via a non-metallic
sheathed cable), the maximum permitted cable length is 100 m.
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).
D - Distance between the cable ducts should be as large as possible
Blue arrows - signal line
Red arrows - potential source of interference
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.