Unit
Manual
3.4
THE SCU'S METHOD OF OPERATION
3.4.1 MEASUREMENT AND EVALUATION
The SCU 800 retrieves temperatures from the sensors in defined intervals (measuring cycles). During a
measuring cycle all sensors are addressed, temperature values retrieved and evaluated. In auto-
configured mode a new measuring cycle is started every 10 seconds.
The checksum of each retrieved data is tested and the value checked for plausibility. Discrepancies will
re-initiate the measurement. If three consecutive measurements are invalid, a fault alarm is set. (
All valid measurements are evaluated against two alarm criteria.
Maximum temperature
Differential temperature
Default value [°C]
50°C
2,8°
Alarm trigger
The measured temperature is
higher than the maximum value.
The differential value is higher
than the threshold.
The differential temperature is calculated according to an algorithm, which compensates for natural
temperature variations (e.g. day, night, seasons).
Note
: An alarm is only triggered if a pre-alarm was set in the previous measuring
cycle.
In case of an alarm the following LED and relay assignment applies for the SCU 800-03, irrespective of
the operation mode (
or
OPERATION ):
Alarms on sensor cable port K1 set LED A and alarm relay REL1
Alarms on sensor cable port K2 set LED B and alarm relay REL2
Note
: Alarms can only be reset once the values fall 0.5°C below the respective
threshold.
3.4.2 COMMUNICATION INTERFACES
The SCU 800 has one serial port, which is switchable between RS232 and RS485.
Switching takes place on ST4 of the main board (
60T023-04 / 30.04.2014
LISTEC GmbH
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