Honeywell UMC800 Reference Guide

Function Blocks
3/99 Function Block Reference Guide 19
2.6 ALM Function Block
Description
The
ALM
label stands for the
Analog Alarm function.
This block is part of the
Alarms/Monitor
category.
It looks like this graphically on the Control Builder.
Function
The analog alarm block accepts an analog signal as a process variable and compares it to a limit value
(setpoint) to determine an alarm condition. The setpoint may be entered by the user or be another analog
signal in the controller.
Alarm actions may be high, low or high deviation, low deviation or band deviation. For deviation alarming, a
second analog signal provides the reference and setpoints represent deviation from the reference.
The alarm output may be inverted to create normally active digital output. A user selection for latching until
acknowledged or automatically reset is provided.
A user-specified hysteresis value in the engineering units of the process variable is provided.
An on-delay time value up to 240 seconds is available to prevent momentary alarm actions. A digital reset
input is available to disable alarm actions.
Alarm Type Function
(PV>SP) High Process Variable/Local Setpoint
•
OUT = ON If the PV is greater than the local Setpoint
•
OUT = OFF If the PV is less than the Local Setpoint minus Hysteresis
(PV>CV) High Process Variable/Compare Value
•
OUT = ON If the PV is greater than the Compare Value (CV) i.e. Alarm Setpoint
•
OUT = OFF If the PV is less than the Compare Value minus Hysteresis
(PV<SP) Low Process Variable/Local Setpoint
•
OUT = ON If the PV is less than the Local Setpoint
•
OUT = OFF If the PV is greater than the Local Setpoint + Hysteresis
(PV<CV) Low Process Variable/Compare Value
•
OUT = ON If the PV is less than the Compare Value (CV)
•
OUT = OFF If the PV is greater than the Compare Value + Hysteresis
[(PV-CV)>SP]High Deviation Alarm
•
OUT = ON If the PV input minus the CV input is greater than the Local Setpoint
•
OUT = OFF If the PV input minus the CV input is less than the Local Setpoint minus Hysteresis
[(CV-PV)>SP]Low Deviation Alarm
•
OUT = ON If the CV input minus the PV input is greater than the local Setpoint
•
OUT = OFF If the CV input minus the PV input is less than the Local Setpoint minus Hysteresis



PV-CV



>SP Band Deviation Alarm
•
OUT = ON If the absolute value of (PV-CV) is greater than the Local Setpoint
•
OUT = OFF If the absolute value of (PV-CV) is less than the Local Setpoint minus Hysteresis

Honeywell UMC800 Specifications

General

Brand	Honeywell
Model	UMC800
Category	Controller
Language	English