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General pH Information
integral action to affect the process. The integral control action is disabled by setting it to
zero. Note that the integral time is in minutes.
Derivative
Derivative control is used to adjust the control output level based upon the rate at which
the process value is approaching or passing the setpoint. Derivative control action would
be used in cases where the process value can rapidly ramp up and overshoot the setpoint.
The derivative setting is in minutes. The output action of the derivative control is equal to
the rate of change of the process (in pH units per minute) times the derivative time, divided
by the proportional band, times negative one. For example, if the process pH is changing
at a rate of pH 0.20 per minute, the derivative time is set to 3.0 minutes, the proportional
band is set to pH 0.80, and the action is “direct” the derivative control output action will be
approximately equal to: (–0.20 pH/minute X 3.0 minute) /0.80 pH = –75%.
During calibration, the analog outputs can remain active, be held, or be transferred to a
preset mA value.
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