62 Rockwell Automation Publication 440R-UM013G-EN-P - December 2022
Chapter 11 Troubleshooting
Figure 68 - Capacitive Effect on Pulse Tests
Long Wire - Resistance Effect
Long input wiring adds resistance and decreases the input signal voltage. Figure 69 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 69 - Resistance Effect on Input Signal
GSR safety relays have a maximum input resistance of 900 ohms.
Table 17 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 mm² (22 AWG) wire, the wire resistance from the safety relay pulse test outputs to the
safety device and back to the safety relay inputs, would be:
200 m x 52.94 Ω / 1000 m x 2 directions = 21 Ω
Capacitance causes
deformation of leading edge
Long Wiring adds resistance and
decreases the input signal voltage
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