FDC DIN Controls - Alarm Logic
A Process alarm has a specific SP set within the configured operating span of the instrument. When the process exceeds this SP an alarm occurs. The process alarm SP is independent from primary control setpoint [output #1].
A Deviation alarm has a positive or negative SP relative to the primary control [output #1] SP.
Example: SP = 100F with deviation alarm set at +20F. When process exceeds 120F an alarm is triggered.
A Deviation Band alarm presents two reference levels to SP [output #1].
Example: SP = 100F with deviation band alarm of 20F. When process is within 20F of SP no alarm.
Non-Latching: Alarms clear when PV is no longer within alarm setting
Latching: Alarms do not clear until PV is no longer within alarm setting AND operator depresses the scroll key
[Note: The L Series FM approved High Limits output #1 is always latching. The L Series optional 2nd relay output is configurable as either latching or non-latching.]
High: Alarm relay closes when PV exceeds alarm SP
Low: Alarm relay closes when PV is lower than alarm SP
A Holding alarm prevents alarm conditions on power up.
The alarm is enabled only when the process reaches SP [output #1].
After PV reaches SP the alarm functions as a normal alarm.
Alarms are configurable to close or open on control failure.
One alarm may be configured as a dwell timer alarm. Once configured the dwell time is measured in minutes - the maximum number of minutes vary by control series with the longest being the 300 Series at 6,553 minutes. Once the process reaches setpoint the dwell timers starts to count down from zero until time out. The dwell timer alarm relay will remain unchanged until time out. The dwell timer is reset by power up sequence.
[Note: The 300 Series event input may be configured to reset the dwell timer]
A Current Transformer [CT; 0-50A] is connected to Input #2.
An alarm is configured as a process alarm. Alarm occurs when current draw exceeds alarm SP.
Loop Break Conditions are detected during a time interval of 2 x TI1 [double the integral time but 120 seconds maximum]. Hence there is a delay for the alarm to respond to actual Loop Break. If the process variable doesn't increase (or decrease) while the control output has reached its' maximum (or minimum) value within the detecting time interval a Loop Break Alarm occurs [when an alarm is configured as Loop Break Alarm].
Sensor Break: [applicable to 300 Series only]
Alarm may be configured as a sensor break alarm and is activated as soon as failure mode occurs. Note that A-D failure also creates a sensor break alarm.
B Series.htm (board level control)
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