Remove the panel by loosening the four fixing screws (behind plastic caps) at the left-
hand end of the furnace; do not remove the screws. Lift the panel about 15 mm and
then pull off to the side.
8.4
Thyristor Replacement and Adjustment
Replacement
To replace the thyristor unit, isolate the furnace from the electrical supply and remove
the left-hand side cover. See section 8.3. Make a note of all wiring to the thyristor, then
disconnect it. Replace the unit and connect the wiring again.
Note that the thyristor unit requires replacement if changing from, or to, a 208 V
supply.
If the thyristor unit has been replaced because of a change of voltage, the correct
transformer tapping should also be set. See section 8.10 for panel removal instructions.
Adjustment
After any thyristor unit replacement, or any change of voltage or
transformer tapping, the potentiometer on the thyristor must be
adjusted to give the correct element current. This should be done by a
qualified person, as there are dangerous voltages inside the control
compartment. It also requires a calibrated non-intrusive clip-on
ammeter.
Before connecting the electrical supply, turn the potentiometer on the
thyristor fully to the left (anti-clockwise). This sets the output current of
the thyristor to 'off'.
Connect the electrical supply with the side cover off. TAKE CARE! Set the furnace
temperature to maximum. Allow the furnace to start heating up.
Measure the current through the element circuit. This is carried out with the clip-on
meter around one pair of thick cables on the left-hand side of the transformer (as seen
when facing the control side of the furnace).
Adjust the potentiometer on the face of the thyristor unit. Adjust it slowly to the right
(clockwise) to increase the current, pausing to allow the time for response at the meter.
Keep adjusting to obtain an ammeter reading of between 149 to 150 A for the HTF
1700 or 139 to 140 A for theHTF 1800. This adjustment should be set up within the first
5 minutes of heat up from ambient and should finally be checked when the furnace
temperature is approximately 100 °C below its maximum temperature. Make further
adjustments if necessary at this temperature.
Disconnect the electrical supply to ensure safe replacement of the side panel. See
section 8.1
8.5
Temperature Controller Replacement
Refer to the controller instructions for more information on how to replace the
temperature controller.
53
8.0 Repairs and Replacements
Summary of Contents for CARBOLITE GERO HTF 18/4
Page 7: ...Caution Double Pole Neutral Fusing 7 1 0 Symbols and Warnings ...
Page 37: ...Power Limit View 37 4 0 3508 Dual Loop Cascade ...
Page 59: ...59 8 0 Repairs and Replacements ...
Page 63: ...GR Y Green Yellow 63 10 0 Wiring Diagrams ...
Page 67: ...Notes Service Record Engineer Name Date Record of Work ...
