Using Alarms - Watlow 945 Series User Manual

Using Alarms

The Series 945 has two alarm types, Process or Deviation. A Process alarm sets
an absolute temperature. When the process exceeds that absolute temperature
limit an alarm occurs. The Process alarm set points may be independently set high
and low.
A Deviation alarm alerts the operator when the process strays too far from set
point. The operator can enter independent high and low alarm settings. The
reference for the deviation alarm is the set point. Any change in set point causes a
corresponding shift in the deviation alarm. Example: If your set point is 100°F,
and a deviation alarm set at +7°F as the high limit, and -5°F as the low limit, the
high alarm trips at 107°F, and the low alarm at 95°F. If you change the set point to
130°F, the alarms follow the set point and trip at 137°F and 125°F.
Both process and deviation alarms can be latching or non-latching. When the
alarm condition is removed a non-latching alarm automatically clears the alarm
output. You must manually clear a latching alarm before it will disappear.
Flashing 'LO" or "HI" in the lower display indicates an alarm. The lower display
alternately shows information from the current parameter and the "LO" or "HI"
alarm message at one second intervals. The alarm output is de-energized and the
A1 or A2 LED is lit.
To clear an alarm...
• First correct the alarm condition, then...
• If the alarm is latching...
Clear it manually; press AUTO/MAN once as soon as the process temperature
is inside the alarm limit according to the HYSX parameter.
• If the alarm is non-latching...
The alarm will clear itself automatically as soon as the process
temperature is inside the alarm limit according to the HYSX parameter.
Alarm Silencing for alarm output A1 is available with the deviation alarm. This
overrides alarm A1 during power up. The non-latching mode automatically
enables alarm output A1 on initial power up. In the latching mode, manually
disable the alarm by pressing AUTO/MAN once. In both cases alarm silencing
disables the A1 alarm output relay, but the A1 LED displays the alarm condition
until the process value is within the "safe" region of the deviation alarm band.
Once the process value crosses into the "safe" region, both a latching or a non-
latching alarm is ready. Any future deviation outside this safe band triggers an
alarm.
Tuning and Operating, Chapter 5
Press once -
Clear
a latched
and
corrected
alarm.
Alarms
Figure 35 -
Alarm Display
Examples
WATLOW Series 945 User's Manual
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