Tend monitoring TRD / TRD- :
Measurement principle:
The trend monitoring function is for checking the timed change
of the input signal. The time base tm for the monitoring function
is set up in the menu group PARA section TRDT. The difference
between the start value MW
A
and the end value MW
E
of the
interval is calculated. If the calculated value is higher than the
value set up in
SP the relay is de-energised. The relay switches
on again once the calculated value is less than the value set up
in RESP. The direction of the signal is set by using the prefix. A
new value is calculated every 0.4 seconds (sliding interval).
Example: The display shows a filling level which requires
monitoring. In menu group
LIM1 address MODE the parameter
set is
TRD. The parameter set for the switch point SP is 3, the
reset switch point RESP is set to
-2. The time base tm is set up
in menu group PARA address TRDT.
In this example the relay is de-energised when the level
(MW
E
-MW
A
) change exceeds the value of 3/time units. The
relay is energised again when the level change is 2/time units.
Fault recognition
OC:
If the parameter set in
LIM1 MODE is at OC, relay 1 operates as
an alarm relay. In fault condition the relay is de-energised. This
happens with the following faults:
- Cable open circuit and short circuit with 2 wire transmitters
- Sensor fault with 2 wire transmitters (<3.6mA or >21mA)
- Cable open circuit on RTDs or thermocouples
- Various recognisable hardware and software faults
(Please see fault finding).
Relay
Process display
51
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