4-9
SIMATIC PC RI25/45, Technical Description
C79000-G7076-C808-01
4.5
Relay Output
An external unit (for example, a call device, a horn or a signal lamp) can be
informed about the PC’s current system status via the relay output.
After switching ON or resetting the PC, the relay output starts operating (no
error occurs); that is, the relay coil is energized and the switch makes contact,
which means it switches to an active working position.
The relay is deactivated if the watchdog has been executed or excess
temperature occured. The coil is then de-energized and the switch breaks
contact (fail-state); that is, it switches to a de-energized position.
The relay output can also be controlled via bit 1 in the I/O cell base a
0Dh.
Switching the relay from fail-state to error-free status via the software is
impossible if a fail-state occurs (that is temperature error or watchdog
executed).
The following table shows you the operating status occuring and the
corresponding switch position.
State
Switch
position
Normal operation
Working
condition
Watchdog executed
De-energized
position
User cancels bit 1 in register base a 0Dh
De-energized
position
User sets bit 1 in register base 0Eh
Working
condition
Temperature error
De-energized
position
Power failure
De-energized
position
In order to secure the recognition of a fail-state via an interrupt-evaluating
unit which is connected to the relay interface, the SafeCard guarantees an
error hold time of at least 500 ms This also applies if the PC is, for example,
reset after the watchdog das been executed.
The following table lists the technical specifications of the relays:
Switching voltage DC
max. 60V
Switching current DC
max. 1 A
Switching capacity DC
max. 30 W
Limiting continuous current DC
max. 1 A
Switching ON/OFF
Conditions
State Diagram
Technical
Specifications of
the Relays
Monitoring Module