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3.6 ALARM 3 VALUE
If Alarm 3 is selected to be a Process High alarm, this defines the process variable
value at or above which Alarm 3 will be active; the default value will be Input Range
Maximum. If Alarm 3 is selected to be a Process Low alarm, this defines the process
variable value at or below which Alarm 3 will be active; the default value will be Input
Range Minimum. Its value may be adjusted between Input Range Maximum and Input
Range Minimum. Alarm operation is illustrated in Figure 3-1.
3.7 ALARM 3 HYSTERESIS
This parameter applies a hysteresis band on the “safe” side of the Alarm 3 value. The
effect of the hysteresis value on alarm operation is shown in Figure 3-2.
3.8 PROCESS VARIABLE OFFSET
This parameter is used to modify the actual process variable value (measured at the
input terminals) in the following manner:
Offset PV value = Actual PV value + Process Variable Offset value.
The offset process variable value is used for all PV-dependent functions (display,
alarm, recorder output).
CAU TION: This is, in ef fect, a cali bra tion ad just ment. In ju di cious ap pli ca tion
of val ues to this pa rame ter could lead to the dis played pro cess vari able value
bear ing no mean ing ful re la tion ship to the ac tual pro cess vari able value.
There is no front panel in di ca tion when this pa rame ter is in ef fect (i.e.
has been set to a non- zero value).
The default value is 0.
3.9 INPUT FILTER TIME CONSTANT
The input is equipped with a digital filter which is used to filter out any extraneous
impulses on the process variable. This filtered PV is used for all PV-dependent
functions (alarms etc.). The time constant for this filter may be adjusted in the range 0.0
seconds (filter OFF) to 100.0 seconds in 0.5 second increments. The default setting is
2.0 seconds.
CAUTION: If this parameter is set excessively high, the indication
quality may be significantly impaired. The value chosen should be
sufficiently large to attenuate stray noise but no larger.
3.10 LINEAR INPUT SCALE RANGE MINIMUM
This parameter, applicable only if a linear input is fitted, defines the scaled input value
when the process variable input is at its minimum value. It is adjustable between –1999
and 9999 (with decimal point as defined by Linear Input Decimal Point Position). The
default value is 0. This parameter can be set to a value greater than (but not equal to)
Linear Input Scale Range Maximum, in which case the sense of the input is reversed.
3-4 November, 2000 OM067-3
Sec tion 3
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-DIN Digi tal In di ca tor 59039
Set Up Mode Prod uct Man ual - Vol ume I