If the panel meters show that the generator voltage is different from that of the bus, the voltage offset potentiometer may need adjustment. Make sure that the
panel meters are accurate, calibrated, and at operating temperature. Most panel meters are accurate to ±3% and are not temperature compensated.
The speed-signal voltage is compared to the reference voltage at the summing
point. If the speed-signal voltage is lower or higher than the reference voltage, a
signal is sent by the control amplifier calling for an increase or decrease in
speed. The actuator is controlled by this signal, repositioning the fuel valve or
rack until the speed-signal voltage and the reference voltage are equal.
Auxiliary Inputs
Terminals 11 through 17 are used for auxiliary inputs which change the reference
voltage and thus the output of the speed control. These inputs include speed
trim, droop, SPM synchronizer, and the auxiliary input, (usually from a load
sensor and parallel lines).
Failed Speed Signal Circuit
A failed-speed-signal circuit monitors the speed-signal input. When no signal is
detected, it calls for minimum fuel. The minimum-fuel signal is sufficient to cause
the actuator to go to the minimum position. Incorrect linkage adjustments or other
restrictions in the external system may prevent prime-mover shutdown.
For controls with actuator current of 20 to 160 mA, minimum fuel is defined as:
· Actuator current of less than 10 mA for forward-acting controls.
· Actuator current greater than 180 mA for reverse-acting controls.
For controls with actuator current of 40 to 320 mA, minimum fuel is defined as:
· Actuator current of less than 20 mA for forward acting controls.
· Actuator current of more than 360 mA for reverse-acting controls.
A contact to override the failed-speed-signal circuit can be connected in series
with terminal 4 and low voltage dc power. (This power is available on terminal 2
for units supplied with 10 to 40 Vdc power and from terminal 6 on those units
supplied with about 120 V ac or dc power.) Temporarily closing the contact
overrides the failed-speed-signal circuit as required for start-up.
The control must be tuned to each system for optimum performance. The
potentiometers for setting and adjusting these circuits are located in the upper
right corner of the control as shown in Figure 4-2. They include:
