38 Rockwell Automation Publication 440R-UM013G-EN-P - December 2022
Chapter 6 Pulse Testing Functions
Figure 30 - Pulse Test Sequence for DI, DIS, and SI Safety Relays
Pulse Testing for OSSD
Outputs
The DIS safety relay has OSSD transistor outputs. One main transistor supplies current to four
individual transistors (see Figure 31). When the main transistor is pulse tested, the pulse
appears on all outputs. When the individual transistors are tested, the pulse only appears on
that transistor.
Figure 31 - Output Transistor Arrangement
The pulse test pattern is shown in Figure 32. The pulse widths vary from 50…150 µs. The pulse
pattern on terminal 14 is identical to terminal 34, and the pulse pattern on 24 is identical to 44.
The pattern is repeated every 3.371seconds.
Figure 32 - OSSD Output Test Pulses on DIS Safety Relay
Although pulse tests appear on terminals 34 and 44, the DIS safety relay does not detect faults
from A1 to 34, 44 or between 34 and 44 when the outputs are on.
When using a digital voltmeter, S11 measures approximately 14V DC and S21
measures approximately 18V DC when the supply voltage to A1 is 24VDC.
0
24V
0V
S11
S21
24V
0V
3.8
Time (ms)
5.9
4.9 7.2
16 18.1
17.1
02.4
5.9
7.9 12.3 14.6 18.1 20.2
19.4
Main Transistor
Individual Transistors
24V
0V
24V
0V
0 131 524 655 3371 (ms)
262 393
Main Transistor Test
Terminals
14 and 34
24 and 44
Individual Transistor Tests Repeats
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