30
£
SERVO-MOTOR ADJUSTMENT
Feedback Potentiometer
WARNING: The servo-motor internal feedback potentiometer must be secured within the
servo-motor to ensure that there is no possibility that the potentiometer can become discon-
nected from the motor output shaft.
For each servo-motor, it is necessary to adjust the potentiometer’s position relative to its shaft in
order to obtain the correct open and closed positions on the display. To do this, follow the procedure
below:
1.
Move the valve/damper to its fully closed position and adjust the potentiometer’s position on the
motor shaft so that approximately 2° to 3° is shown on the display.
2.
Move the valve/damper to its fully open position and check that the display reads approximately
85° to 88° or the maximum angular opening required from the servo-motor if this is less than
90°. If the displayed position decreases as the valve is opened, reverse the supply connections
(motor terminals 5 & 7) to the feedback potentiometer. If the displayed position range is incor-
rect, check that the correct potentiometer supply voltage has been selected.
Control Direction
It is necessary to ensure that each motor travels in the correct direction when moved using the UP/
DOWN keys on the keyboard. To do this, follow the procedure below.
1.
Enter commission ratio mode (refer to Commission Ratio Mode page 34).
2.
Check that when the DOWN key is pressed, each motor moves its valve/damper towards the
closed position. If not, reverse drive signals on motor terminals 2 & 3.
3.
With the display showing P00, use the UP/DOWN keys to move each servo-motor. If the dis-
played position decreases as UP is pressed, or increases as DOWN is pressed, reverse the servo-
motor output UP/DOWN connections.
Adjusting microswitch positions
Each time a burner start-up sequence is initiated, the unit will move the fuel and air damper servo-
motors to their closed and purge positions to prove correct servo-motor and potentiometer operation.
Each servo-motor must have microswitches to limit the close and purge positions obtainable during
this proving operation. To set the microswitch positions, follow the procedure below.
1.
Enter commission ratio mode.
2.
Move each servo-motor to approximately 45°, either by hand or using the UP/DOWN keys.
3.
Holding the DOWN key, adjust the low limit microswitch until the servo-motor will no longer
move down.
4.
Holding the DOWN key, gradually slacken off the low limit microswitch until the servo-motor
starts moving down. Continue to slacken off the microswitch until the servo-motor stops with a
reading on the display of approximately 2° to 3°.
5.
Move the servo-motor up and down a few times to check that the servo-motor stops each time at
approximately 2° to 3°, and readjust the microswitch if necessary. This position will allow for
some tolerance in microswitch operation.
6.
Hold the UP key and tighten up the high limit microswitch until the servo-motor will no longer
move up.
7.
Holding the UP key, gradually slacken off the high limit microswitch until the servo-motor starts
moving up. Continue to slacken off the microswitch until the servo-motor stops in the desired
purge position. This position does not have to be 90°, but it is recommended that it is more than
45° and less than 88°.
8.
Move the servo-motor up and down a few times to check that the servo-motor stops each time at
the desired purge position. Repeat steps 3 to 7 if necessary.
