15
Process HILO
1. Process HILO is a fixed value (a fixed high and a fixed low alarm setpoint)
and will not change if the SP temperature value is changed. The purpose
for process HILO is to set the fixed HI and LO value at which to trigger
the alarm relay. Refer to Figure 20. Refer to the Process HI and Process
LO sections for detailed descriptions of the operation of each alarm
setpoint.
ALARM MODE
PROCESS HILO
FIGURE 20. PROCESS HILO SCREEN
2. Select PROCESS - HILO by pressing the MENU key. The following screen
will appear (refer to Figure 21). Set the alarm temperatures by using the
arrow keys. Once the first alarm value is set, press the LEFT arrow key to
adjust for the other alarm variable.
PROCESS ALARM °F
HI XXXX.X LO XXXX.X
FIGURE 21. PROCESS HILO SETTINGS SCREEN
Deviation Alarms
Deviation alarms are offset values relative to the setpoint (SP). The values
change with the SP temperature setting. For example: if an operator sets the
deviation HI alarm to 10 degrees Fahrenheit and the SP temperature is at 50
degrees Fahrenheit, the alarm will trigger when the PV reaches 60 degrees
Fahrenheit. If the operator then changes the previously set SP temperature
to 55 degrees Fahrenheit, then the alarm will trigger at 65 degrees Fahren-
heit. The 10-degree Fahrenheit difference stays the same.
There are four possible deviation alarms settings: DEVIATION LO, DEVIA-
TION HI, DEVIATION HILO, and DEVIATION BAND. Refer to the following
paragraphs.
