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controlled is not in this list, select OTHER. Press ENTER to proceed. If OTHER is
selected, MOTOR PHASE ANGLE must be manually changed in OPERATING
PARAMETERS.
7. ENABLE RESTARTS - YES(ENTER)/NO(HOME) – enabling restarts controls the
ability of the drive to automatically restart after a power failure. The drive will initialize
in AUTO mode after power is restored if YES is selected. If NO is selected, the drive
will remain OFF when power is restored.
8. DISABLE MANUAL MODE – Selecting YES disables manual operation of the drive
through the keypad.
9. OVERCURRENT LIMIT – Setting for motor overload protection (service factor amp
rating for the motor).
This quick setup of constant pressure should provide good pressure control in most
situations. It is advisable to read the entire section on constant pressure control for a
complete explanation of constant pressure control methods. Refer to Table 13, Constant
Pressure Parameters, for expanded menu options to fine tune the constant pressure
system.
7.5 Analog Constant Pressure Systems
Controlling the Essential Drive using analog constant pressure requires an additional I/O
board. The analog CP system uses an analog pressure transducer connected to the analog
input (I+ and I-) on the Control Terminals (see Figure 8 and Figure 20 for wiring diagram
and one-line diagram). A normally-closed emergency overpressure switch connected to the
AUX2 terminals is also recommended. If an overpressure switch is used, AUX2 SELECT
must be changed to 0. These are used in conjunction with the internal firmware of the drive
to implement a constant pressure water system.
The drive uses a proportional-integral (PI) or proportional-integral-derivative (PID) controller
in the feedback loop for constant pressure control. 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 constant pressure 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, in the Constant Pressure menu, can 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 any system, there are tradeoffs between maintaining a tightly
controlled set-point, achieving high motor efficiency, and maintaining system stability.
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