Omron CRT1 - 10-2008 Operation Manual page 489

Temperature Input Unit Functions
Setting Hysteresis
466
Set values
Comparator Result Flag
(in Analog Status Flags)
ON/OFF
Note When the temperature input value changes faster than the conversion cycle,
the status may go from a Low Limit alarm directly to a High Limit alarm without
having the Normal Flag (pass signal) go ON in between. Write ladder pro-
grams to allow for this.
The Comparator Result Flag turns OFF when the value is lower than the hys-
teresis width (H or HH alarm occurs) or exceeds it (L or LL alarm occurs), as
shown in the following diagram. If the temperature input value fluctuates
around the threshold and the flag repeatedly turns ON or OFF, set hysteresis
to stabilize the flag operation. The setting range is 0 to 16,383.
HH set value or
H set value
HH Alarm Flag or
H Alarm Flag
Note When setting the hysteresis value, allow for the decimal point position or the
1/100 Display Mode for each input. Always correct the hysteresis value after
changing the display mode or replacing the input with one that has a different
decimal point position.
Examples for an Hysteresis of 10 ° C:
• R thermocouple (normal display) setting: 0010 decimal
• T thermocouple (normal display) setting: 0100 decimal
• Setting for any input with 1/100 display: 1000 decimal
HH
H
L
LL
HH alarm
H alarm
Normal Flag
(Pass signal)
L alarm
LL alarm
Hysteresis width
LL set value or L
set value
LL Alarm Flag or
L Alarm Flag
Section 11-5
Hysteresis
width