62 | P a g e
The analog CP system uses an analog pressure transducer connected to the analog input on the
control terminals (see Figure 19 for one-line and wiring diagrams). A normally-closed emergency over-
pressure switch connected to the AUX2 terminals is also recommended. These are used in conjunction
with the internal firmware of the drive to implement a CP water system.
When using an analog pressure transducer for control in CP systems, it is very common for the system
controller to use a proportional-integral (PI) or proportional-integral-derivative (PID) controller in the
feedback loop. This type of controller has a gain adjustment which must be tuned by the user to obtain
optimum performance for each particular application. Phase Technologies has also developed a
proprietary controller, SIMPLE MODE, which requires minimal tuning. 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 usually requires minimal tuning of the
system to obtain acceptable performance. A well-tuned PI or PID controller will give smoother pressure
control and may be necessary to control unstable systems. When the controller is in SIMPLE MODE,
the only parameters which affect the pressure control loop are psi SETPOINT, STARTUP RAMP,
SHUTDOWN RAMP and BOOST AMOUNT.
In PI control mode the analog signal from the pressure transducer is compared to the parameter psi
SETPOINT, which controls the motor speed to maintain CP in the system. In this control scheme, the
error signal between the pressure transducer and the internal signal determined by the psi SETPOINT
value is multiplied by the PROPORTIONAL GAIN. This signal is then used to determine the motor
frequency. If the pressure transducer signal and the internal set-point value were the same, then the
motor speed would be zero. High PROPORTIONAL GAIN and INTEGRAL GAIN values give smaller
error in the pressure, but also make the system more susceptible to oscillation.
Additional adjustable parameters found in the CONSTANT PRESSURE menu help to optimize the
performance of the system. The use of these parameters was discussed in the previous section. The
unit is shipped with default settings which will work in many applications with no adjustment. As with all
systems of this type there are tradeoffs between maintaining a tightly controlled set-point, achieving
high motor efficiency, and maintaining system stability.
7.4 Pre-Charge Mode
When filling a large plumbing system with water, it may be desirable to fill at a slow pump speed so that
when the system reaches the full point, water hammer does not cause damage such as sprinkler head
blow-off or burst pipes. To achieve this, the drive is equipped with a pre-charge feature.
This feature is disabled if the PRECHARGE TIME parameter is set to zero. The frequency of the pump
will not exceed the value set by the PRECHARGE FREQ parameter during the pre-charge interval.
The pre-charge interval will terminate when the system pressure exceeds the setting of the PRECHRG
psi parameter. In this case, the PRECHRG psi must be lower than the psi SETPOINT.
The pre-charge interval occurs whenever the drive is switched from OFF to AUTO or MANUAL > RUN.
To Next Page
Loading...
