Chromalox PQ404-6 Optional Equipment for Chromalox Steam Boilers cont’d, Boiler Sequencer 5 Step

OPTIONAL EQUIPMENT FOR CHROMALOX STEAM BOILERS (cont’d.)

5.Connect the ohmmeter between controller terminals W and R and raise the set point of the controller above the actual pressure being measured. The ohmmeter should read the full value of the poten- tiometer measured in step 4 (135 ohms for an L91B).

6.Slowly lower the set point of the controller while observing the ohmmeter reading. The resistance should drop to zero at some set point below the actual pressure.

7.An approximation of the proportioning range can be made by observing the change in set point required for a resistance change from zero to full value.

8.When the controller is operating properly, reconnect the wires, replace the cover. tighten the cover screw, and reset the controller to the desired value.

9.Reconnect power to the controlled motor.

Main Scale
Adjusting Screw	Proportioning Range
	Adjusting Screw
Main Scale	R
Setting	W
Indicator	B
Ohmmeter	Setpoint
	W R B
	Increases
	to 15 Ohms

Note: Terminals are not labeled, but screw-heads are color-coded red (R), white (W) and blue (B).

Figure 18

BOILER SEQUENCER (5 STEP)

RECYCLE FEATURE (See Figure 19)

The step control is designed to drop out all contactors when con- trol circuit is interrupted. On resumption of power, the camshaft rotates to the counter-clockwise (ccw) limit, opening all the load switches. The recycle relay then energizes, pulling in the load contact, and final- ly the camshaft rotates clockwise (cw) to the position called for by the pressure controller energizing, in sequence, the required load stages.

TESTING OPERATION OF SEQUENCER (See Figure 20)

1.With boiler off, remove wiring from pressure control on sequencer low voltage terminal board.

2.Turn on boiler to supply the voltage to sequencer. Short terminal R and B for counter-clockwise rotation and terminal R and W for clockwise rotation.

3.If sequencer operates under this test procedure, but when rewired to pressure controller, does not function, check pressure control. Note that wiring is W-B and B-W-R-R between sequencer and pressure control.

Figure 20

Typical Wiring Diagram for 5 Step Motor Driven Sequencer

SEQUENCE REVERSER (See Figure 21)

GENERAL:

Sequence Reverser is an automatic switching device which is interposed on an electric boiler between the proportional sequence controller and the heating element contactors. The device is periodi- cally actuated to alter the operating sequence of each of the heating elements, thereby increasing the overall reliability of the boiler.

DETAILS:

The Sequence Reverser consists of an eight-day timer set up for four days on and four days off which energizes and de-energizes dou- ble throw relays which are wired to reverse the “firing” order of the heating element contactors with each operation of the timer.

Figure 19 – Five Step Sequencer

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