Hardware Manual PCD1.M2110R1 │ Document 27-619 │ Version ENG 04 │ 2018-08-20
Saia-Burgess Controls AG
Watchdog (Hardware Relay)
CPU / Control Process Unit
3-13
3
3.9
Watchdog (Hardware Relay)
PCD1.M2_ CPUs have a hardware watchdog as standard equipment. The watch-
dog relay is at Pins 35 and 36 at Plug X3.
+24V
0V
+
0
1
+
+
+
–
–
–
CO
X3
NO
39
38
37
36
35
34
33
32
31
30
D/
D
PCD1.M21xx
Main switch
Process
e.g. Output modules
Danger:
observe the contact load
of the WD-relay!
(Possibly via power
contactor)
WD Relay
Watchdog-Relais
Power "dangerous" outputs
Functional description
As soon as the watchdog relay is called at the address O 255 by a switch on/off
frequency of < 200ms, the relay contact closes. It remains closed until the pulse
time exceeds 200ms.
If this happens, it can mean the following:
The CPU has stopped
(no longer in RUN mode)
Program execution too long
(AWL program loops, program too large)
