Chromalox PQ404-6 - Manual (Page 9)

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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.
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.
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.
OPTIONAL EQUIPMENT FOR CHROMALOX STEAM BOILERS (cont’d.)
Main Scale
Adjusting Screw
Proportioning Range
Adjusting Screw
Main Scale
Setting
Indicator
Ohmmeter
Setpoint
R
W
B
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
Figure 19 – Five Step Sequencer
Figure 20
Typical Wiring Diagram for 5 Step Motor Driven Sequencer