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3.5.3 Adjusting the Hysteresis
The hysteresis is the Dissolved Oxygen 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 10.00 ppM, as a “too low” trip point, with a
hysteresis of ±0.10 ppM, the alarm/control output is switched ON when the
reading goes to 9.90 ppM(i.e. 10.00 - 0.10). The output is not switched OFF until
the reading goes back up to 10.10 ppM (i.e. 10.00 + 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 aerators, pumps, solenoid valves etc.
The factory-set hysteresis is approximately ±0.10 ppM, as in the example above.
The hysteresis can be increased to as high as ±2.00 ppM with the
HYSTERESIS
trimmer in the terminal area. For units set up for % Saturation, the factory-set
hysteresis is approximately ±1.0 % Saturation, which can be adjusted to ±20.0 %
Saturation.
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.
