55 | P a g e
Figure 31 – Motor On and Motor Off Times
Fine Tuning With PI Control
When operating in constant pressure mode, if the parameter PROPORTIONAL GAIN is set to a value
less than 1, the keypad displays SIMPLE MODE and the controller uses an algorithm that is not PI
control. Simple Mode requires less fine tuning than PI control, but in some applications may not provide
the control and stability desired. The stability of the constant pressure system (i.e., its tendency not to
exhibit pressure oscillations) is determined by parameters set on the keypad, the flow rate of the pump,
and the volume of the pressure tank. Stability of a system with a large maximum flow rate and a small
pressure tank will be more difficult to control and may require de-tuning the system to accept larger
variations in the system pressure and longer response times. Analog CP systems with PI (proportional
integral) control provide more options to fine tune pressure control than Simple Mode. Systems that are
not adequately controlled with the Simple Mode may require fine tuning by switching to PI control.
Increasing the value of PROPORTIONAL GAIN to any value greater than SIMPLE MODE will initiate PI
control. Pressure control is achieved by adjusting the values of PROPORTIONAL GAIN and
INTEGRAL GAIN. Larger values for PROPORTIONAL GAIN and INTEGRAL GAIN give smaller errors
in the pressure, but also make the system more susceptible to oscillation.
Emergency Over-Pressure Limit Switch
CP systems have the option of connecting an emergency over-pressure limit switch to the AUX2
terminals in case the main pressure control system fails. The emergency over-pressure set-point
should be at least 10 psi higher than the system control pressure to prevent nuisance tripping.
CAUTION: By default, AUX1 and AUX2 are programmed to be always in RUN mode. See
parameters AUX1 SELECT and AUX2 SELECT to change this setting.
SIMPLE MODE Control
When the PROPORTIONAL GAIN parameter is set at the lowest value, the display will read "SIMPLE
MODE". In SIMPLE MODE a set of control equations is used which may not require the user to tune
the system to obtain acceptable performance.
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