62 Rockwell Automation Publication 440R-UM013F-EN-P - July 2021
Chapter 11 Troubleshooting
Figure 66 - Capacitive Effect on Pulse Tests
Long Wire — Resistance Effect
Long input wiring adds resistance and decreases the input signal voltage.
Figure 67
shows the effects on the pulse tests. Notice that the shape of the
pulses has not changed, only the amplitude. If the wiring is too long, the safety
relay does not turn ON.
Figure 67 - Resistance Effect on Input Signal
GSR safety relays have a maximum input resistance of 900 ohms.
Table 16 on page 63
shows the resistance of wire sizes that are typically used to
connect to safety devices. For example, if you used 200 m (656.2 ft) of a 4-wire
cable that contains 0.33 mm
2
(22 AWG) wire, the wire resistance from the relay
pulse test outputs to the safety device and back to the relay inputs, would be:
200 m x 52.94 Ω / 1000 m x 2 directions = 21 Ω
As the example shows, long wires are not a likely cause of safety input issues.
Capacitance causes
deformation of leading edge
Long Wiring adds resistance and
decreases the input signal voltage
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