Watlow Series 920 Microprocessor-Based Ramping Control - Manual (Page 58)

Alarm function is either “latching” or “non-latching.” Latching is a means of
“saving” indication of an alarm event for the operator to clear manually. A
latching alarm requires the operator to manually clear it with the ENTER key
when ACTUAL returns to within the limits. A non-latching alarm clears itself
automatically when ACTUAL returns to within the limits. It’s your choice.
Here again is the "LAT” information from the Operating Parameters:
LAT Defines Alarm Function:
NLAT = Non latching. Alarm relays are automatically energized when
ACTUAL temperature returns to within the operating band (as defined
by ALTYP X, AXL and AXH).
LAT = Latching. Requires the ENTER key to manually energize alarm
relays after ACTUAL temperature returns to within the operating band
(as defined by ALTYP X. AXL and AXH).
Alarms have a 3°F/1.7°C switching differential.
Clearing An Alarm Message
When a latched alarm condition occurs, the ACTUAL display will flash an alarm
code. You can clear the latched alarm when the ACTUAL display value returns
to within the operating band.
While in either the RUN or HOLD mode, press the ENTER key to stop the
alarm code from flashing for 5 minutes. This will not clear the alarm. The
alarm must be cleared in the SYSTEM menu within the 5 minutes, or the alarm
code will flash in the display again.
To clear an alarm, return to the SYSTEM prompt. Press ENTER; SP XXXX will
be displayed. Press the MODE key until the CLR ALRM parameter is dis-
played. Press ENTER to clear the alarm.
A non-latching alarm cannot be cleared. A non-latching alarm clears itself
when the ACTUAL display value returns to within the operating band.
An Alarm And The State Of The Alarm Relay
Simply stated, a flashing alarm on the 920 alphanumeric display indicates the
state of the alarm relay contacts. A flashing alarm means when an alarm
condition is present (ACTUAL beyond an alarm limit), then the alarm relay is
de-energized.
58 WATLOW Series 920 User’s Manual