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3.5.3 Adjusting the Hysteresis
The hysteresis is the pH 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 pH7.00, as a “too low” trip point, with a
hysteresis of ±0.10pH, the alarm/control output is switched ON when the reading
goes to pH6.90 (i.e. 7.00 - 0.10). The output is not switched OFF until the reading
goes back up to pH7.10 (i.e. 7.00 + 0.10).
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 ±0.10 pH, as in the example above.
The hysteresis can be increased to as high as ±0.40 pH 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 time. The process
being controlled should then be closely monitored over a time to ensure that the
desired control is being achieved.
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