SECTION 3
OPERATION
ACTUATOR UNIT
The electric capacity control actuator unit operates on 115v., 60-Hz, single-phase electrical service. Power is supplied to
the actuator through an interconnecting control cable (not furnished). The actuator is driven by a gearmotor at 0.8 rpm.
A system of toothed pulleys and belts converts rotary motion into linear motion that actuates the pump capacity control
spool. Complete travel from zero to 100 percent capacity is accomplished in less than one minute.
Normally, the actuator is direct acting (pump capacity increases with increasing input signal to controller). To convert the
actuator to reverse acting (pump capacity decreases with increasing input signal to controller), reverse interconnecting
leads to the actuator terminal strip only (leads 8 & 9, 4 & 6, and, if applicable, 1 & 3).
A 250-ohm potentiometer (pot) driven by the pulley system provides the resistance signal to feed back the actuator
position to any one of the control units. Limit switches, which prevent overtravel of the actuator beyond 100 or 0 percent
capacity adjustments, are located at fixed distances and actuated by an extension of the rigid mechanical link between
the pulley system and the pump control spool.
The location of the limit s-witch mounting plate is set with respect to the actuator mechanism. This correlates the
calibration-settings between the limit switches and the pump capacity control mechanism positions. These adjustments
have been properly set at the factory and will require no attention in normal service.
CONTROLLERS
Model RMI Controller (Figure 7)is provided with a single-pole, double-throw switch that, when operated manually,
energizes the actuator motor in either the forward or reverse direction. This adjusts the capacity setting, which is
indicated as a percentage of stroke on the meter on the face of the control box. A 250-ohm potentiometer furnished with
the actuator provides the resistance signal feedback that controls the indicating meter on the control station. The meter,
calibrated by factory adjustment, is connected to a trim pot that is accessible for field recalibration if necessary.
Model PRRA Controller (Figure 8) is a bridge balancing relay utilizing a fully transistorized amplifier. Maximum power
consumption is 3.5 watts. This unit can be controlled by a process controller having a transmitting potentiometer with a
value between 135 and 1000 ohms. The sensitivity adjustment controls dead band of the instrument. Factory
adjustment will be made for nominal sensitivity.
Model PRRA-MA Controller (Figure 9) is a solid-state, electronic-proportioning relay. Power consumption is
approximately 6.5 watts. This unit can be controlled from an electronic instrument with 1-5, 4-20, or 10-50 ma DC output
ranges. Since the milliamp rating must agree with the DC input signal being applied, the rating on the control should be
checked before wiring the circuit. The various ranges are attained by using different values of resistors R1 and R2.
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