Watlow MLS - Manual (Page 100)

88 MLS User’s Guide
Setup
Alarm Types
The MLS has three different kinds of alarms: failed sensor alarms,
global alarms, and process alarms.
Failed Sensor Alarms
Failed sensor alarms alert you to T/C breaks and these RTD open or
short failures:
• Open + or - input.
• Short between + and - input.
When the loop is in Automatic or Tune mode and a failed sensor alarm
occurs, the MLS sets the loop to Manual control at the failed sensor
percentage you set in the Setup Loop Outputs menus.
Global Alarms
Global alarms occur when a loop alarm, set to Alarm (not Control), is
unacknowledged, or when there are any unacknowledged failed sensor
alarms. (If an alarm occurs, the MLS front panel displays an appropriate
alarm code--see Chapter 4: Using the MLS for an explanation of these
codes.) Even if the alarm condition goes away, the global alarm stays on
until you use the Alarm Ack key (or ANASOFT) to acknowledge it.
Process Alarms
Process alarms include high and low deviation and high and low process
alarms. You can set each of these alarms to Off, Alarm, or Control, as
shown here.
• High process and high deviation alarms activate when the process
variable goes above a value you set. They remain active until the
process variable goes below that value minus the deadband. (See
the diagram on the next page.)
• If you don’t use a digital output for PID control, you can assign it to
one or more process variable alarms. The output is active if any of
its alarms are active. All alarm outputs are active Low or active
High, depending on the global alarm output polarity setting.
• Low process and low deviation alarms activate when the process
variable goes below a value you set. They remain active until the
process variable goes above that value plus the deadband. (The dia-
gram below shows these alarms.)
Function Description
Off No alarm or control function
Alarm Standard alarm function
Control Normal alarm function, except that you
don’t have to ackowledge alarms