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NORA Oilheat Technicians Manual

Second generation cad cell primary controls Second generation cad cell primary controls have the same basic features as first generation controls, but steady advances in technology have led to a number of improvements. For example, second generation cad cell primary controls have electronic reset mechanisms which are not spring loaded. The reset button on these controls does not “pop-up” when the unit shuts off on safety, and the reset doesn’t have a thermal component, so there’s no cooling time required before the control can be reset. To bring the control out of safety lockout, you simply depress the reset button for three seconds. Typical second generation cad cell primary controls include: Safety monitoring circuit This circuit monitors the contacts of two separate, redundant motor relays. Safety lockout occurs if the contacts of either motor relay are found closed when they should be open, thus ensuring shutdown even if one motor relay fails. Interrupted duty ignition These controls have an additional wire that is connected to the transformer or igniter. With interrupted duty ignition: • Electrodes and igniters/transformers last longer • Electrical consumption, operational noise and NOx emissions are reduced • Combustion problems leading to dirty boilers and running saturations are minimized Recycle-on-flame-failure Recycle-on-Flame-Failure means that instead of shutting off on safety on loss of flame during the run cycle, the burner will shut off within approximately 1.5 seconds. After a wait of 60-90 seconds, the control will attempt to restart the oilburner. Operation Second generation cad cell primary controls operate similarly to first generation controls. If all components are functioning properly, the control is in stand-by mode until— • Power is applied through the limit control to the black wire, AND the circuit between T and T is closed. Then assuming that the cad cell does NOT sense light— • The control is energized and the orange and blue wires are powered. • The ignition and motor start. • After the cad cell senses flame, the ignition stays on for another 10 seconds, then shuts off. As long as the cad cell senses flame, the oilburner continues to run until the thermostat or limit control is satisfied. If the control does not sense flame within the control’s safety timing, lockout occurs. Pressing the reset button for 3 seconds resets the control. Third generation cad cell primary controls Third generation primary controls Chapter 11 Primary Controls 11-12 Primary Controls


NORA Oilheat Technicians Manual
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