Engineering Manual o.. - HVAC.Amickracing

ELECTRIC CONTROL FUNDAMENTALSDPDTSWITCH,RELAY, ORTHERMOSTATHEATINGCOOLINGTHERMOSTATW R BUNISON CONTROLFigure 32 illustrates a circuit for controlling up to sixSeries 90 actuators in unison from one Series 90 controller.The B to W terminals of the controller are shunted with theappropriate value resistor, depending on the number ofactuators in the circuit. This method can control a large bankof dampers requiring more torque than can be provided froma single actuator.W R BTRANSFORMERCONTROLLERT1T2ACTUATORLINEVOLTAGEC2531W R BSHUNTINGRESISTORCONTROLLERW R BFig. 30. Circuit Used for ReversingHeating and Cooling Control.Transferring Controller fromOne Actuator to AnotherFigure 31 illustrates a circuit which allows a single controllerto control two Series 90 actuators, one at a time. With the 3pdtswitch in the Cooling (C) position, the circuit connects thecontroller to the cooling actuator with B to W and W to B. Thecooling actuator operates under normal control of the controller.At the same time, the manual switch causes R to W to connectat the heating actuator, positively closing it. With the switch inthe Heating (H) position, the controller is connected B to Band W to W to the heating actuator which operates normallyand the cooling actuator is positively closed by a R to Wconnection at the actuator.SPDT SWITCHHW R BT1T2W R BT1T2W R BT1T2ACTUATOR ACTUATOR ACTUATORFig. 32. Actuators Controlled inUnison from One Controller.MANUAL MINIMUM POSITIONINGOF OUTDOOR AIR DAMPERTRANSFORMERLINEVOLTAGEC2533Figure 33 illustrates a circuit for a typical outdoor air dampercontrol system with a manual potentiometer for minimumpositioning. Adjusting the potentiometer so that the wiper is atW shorts the potentiometer coil out of the circuit and the outdoorair damper actuator operates normally. The damper closescompletely if commanded by the controller. Moving thepotentiometer wiper toward B increases the resistance betweenB on the controller and W on the actuator to limit the travel ofthe actuator toward closed. The damper remains at the setminimum position even though the controller is trying to closeit completely.CMINIMUM POSITIONPOTENTIOMETER CONTROLLER135 135W R BT1T2HEATINGACTUATORTRANSFORMERLINEVOLTAGEW R BT1T2COOLINGACTUATORTRANSFORMERFig. 31. Circuit for Transferring Controllerfrom One Actuator to Another.LINEVOLTAGEC2532W R B B R WDAMPERW R BT2T1ACTUATORTRANSFORMERLINEVOLTAGEC2534Fig. 33. Manual Minimum Positioningof Outdoor Air Damper.ENGINEERING MANUAL OF AUTOMATIC CONTROL 113