Example:
If A1Hi is set to 100 then relay 1 will activate when the display value is 100 or higher.
Display Value
Time
A Hix
A Hi
A HY
x
x
minus
Relay
activates
at this value
or above
Relay
resets
below this
value
A HYx value
Alarm high operation with hysteresis
5.3 Alarm relay hysteresis (deadband)
Display: AxHY
Range: 0 to 9999
Default Value: 10
Displays and sets the alarm relay hysteresis limit for the designated relay x. Note x will be replaced
by the relay number when displayed e.g. A1HY for relay 1. To set a relay hysteresis value go to the
AxHY function and use the ^ or v push buttons to set the value required then press F to accept
this value. The hysteresis value is common to both high and low setpoint values. The hysteresis
value may be used to prevent too frequent operation of the relay when the measured value is rising
and falling around setpoint value. e.g. if A1HY is set to zero the alarm will activate when the
display value reaches the alarm setpoint (for high alarm) and will reset when the display value falls
below the setpoint, this can result in repeated on/off switching of the relay at around the setpoint
value.
The hysteresis setting operates as follows: In the high alarm mode, once the alarm is activated
the input must fall below the setpoint value minus the hysteresis value to reset the alarm. e.g. if
A1Hi is set to 50.0 and A1Hy is set to 3.0 then the setpoint output relay will activate once the
display value goes to 50.0 or above and will reset when the display value goes below 47.0 i.e. at
46.9 or below. In the low alarm mode, once the alarm is activated the input must rise above the
setpoint value plus the hysteresis value to reset the alarm. e.g. if A1Lo is to 20.0 and A1Hy
is set to 10.0 then the alarm output relay will activate when the display value falls to 20.0 or
below and will reset when the display value goes above 30.0 i.e at 30.1 or above. The hysteresis
units are expressed in displayed engineering units.
Example: If A1Hi is set to 100 and A1HY is set to 10 then relay 1 will activate when the
display value is 100 or higher and will reset at a display value of 89 or lower.
PM4IVMAN-2.4-0 19 of 56
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