Fig. 17 Typical Course Of Test Pulses Of The Inputs - Beckhoff EL1904 Operating Instructions Manual

Route the signal cable separately
The signal cable must be routed separately from potential sources of interference, such as motor supply
cables, 230 V power cables etc.!
AC
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 or OpenLoad 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.
Test pulses
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.
The test pulses at the outputs Input 1+ to Input 4+ are generated separately for each channel in order to be
able to detect cross-circuits between the individual channels of a terminal and also between channels of
different terminals. In order to generate test pulses as shown in the diagram, the sensor test active safety
parameter must be set to true for the respective channels. The test cycle for all four channels is typically 4
ms. The times between the test pulses of different channels vary, thus allowing better diagnostic detection.
Fig. 17: Typical course of test pulses of the inputs
If self-testing sensors are to be used on the safe inputs, please refer to chapter Configuration for light
barriers, light grids, light curtains etc [} 44].
EL1904
NOTE
Version: 3.0.0
Operation
35