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3.5.3
Adjusting the Hysteresis
The hysteresis is the Redox range over which the alarm/control output remains
switched on, once the trip point has been exceeded.
For example, if the limit is set to 700 mV, as a “too low” trip point, with a
hysteresis of ±10 mV, the alarm/control output is switched ON when the reading
goes to 690 mV (i.e. 700 - 10). The output is not switched OFF until the reading
goes back up to 710 mV (i.e. 700 + 10).
The hysteresis stops the relay “chattering” around the set point, by providing a
buffer between the points at which the output is switched ON and OFF. This
feature can significantly increase the life of pumps and solenoid valves.
The factory-set hysteresis is approximately ±10 mV, as in the example above. The
hysteresis can be increased to as high as ±40 mV with the
HYSTERESIS
trimmer in the terminal area. Turning the
HYSTERESIS
clockwise increases the
hysteresis and turning it anti-clockwise decreases the hysteresis.
TPS DOES NOT recommend that this setting be altered, unless it is absolutely
necessary.
The
HYSTERESIS
trimmer should only be adjusted a little at a time. The
process being controlled should then be closely monitored over a time to ensure
that the desired control is being achieved.
