Rockwell Automation Publication 440R-UM010C-EN-P - September 2016 33
Chapter 6
Pulse Testing Functions
Pulse Testing for Inputs
Pulse testing for the inputs is always active. The pulses are generated at
terminals S11 and S21. These test pulses must be used with devices that have
mechanical contacts.
S11 is typically connected to one contact and the other side of the contact is
connected to S12. S21 is typically connected to the second contact, and the
other side of the second contact is connected to S22.
The test pulses are used by the GLT safety relay to detect three short circuit
conditions:
1. Between the input terminals and +24V
2. Between the input terminals and 24V common
3. Between the two input terminals
Figure 24
shows the timings of the two test pulses. The pulse on S21 occurs
shortly after S11. The pulses are repeated every 15 ms.
Figure 24 - Pulse Test Signals
Pulse Testing of Outputs
When the GLT safety relay configuration process starts from Logic Switch
setting 0, the 14, 24, 51, and L61 outputs are pulse tested. The purpose of the
pulse testing is to detect short circuits to 24V, to 24V common, and short
circuits between the output terminals. The use of pulse testing allows the GLT
safety relay to be used in PLe and SIL 3 applications. Without pulse testing,
the GLT safety relay can only be used in applications up to PLd and SIL 2.
The outputs have built in redundancy. A main transistor supplies power to
individual transistors for each output terminal as shown in Figure 25
.
Figure 25 - Output Transistor Arrangement
Terminal S21
Terminal S11
24V
15 ms575 to 775µs
350 µs
0
0V
24V
0V
Main Transistor
Individual Transistors
2414
L6151
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