Carbolite MTT 12/38/850 - Manual (Page 9)

MTT
MF38 – 3.07
9
5.5 Thermocouple Replacement
Disconnect the furnace from the supply.
It is necessary to separate the furnace from its base or stand. Remove the back panel of the control
base and remove the bolts which hold the furnace terminal cover to the base.
Remove the self-tapping screws which hold the terminal cover to the cylindrical furnace body.
Make a note of the thermocouple connections. The negative leg of the thermocouple is marked
blue. Compensating cable colour codings are:
negative positive (type N)
white pink
Disconnect the thermocouple from its terminal block.
Withdraw the thermocouple from its sheath (the narrow-bore wound-in tube) and remove any
broken bits of thermocouple.
Bend the new thermocouple carefully to match the shape of the original (working from the
terminal end). Should the length differ from that of the original this will usually not be important
provided that the thermocouple tip is within a tube diameter's distance from the zone centre. In this
furnace the thermocouple tip should be approximately 215mm from the end of the ceramic
worktube.
Insert the new thermocouple into position, and reconnect.
Re-assemble the furnace.
5.6 Element Replacement
Please see safety note 5.2 - please wear a face mask.
Disconnect the furnace from the supply.
It is necessary to separate the furnace from its base or stand. Remove the back panel of the control
base and remove the bolts which hold the furnace terminal cover to the base.
Remove the self-tapping screws which hold the terminal cover to the cylindrical furnace body.
Disconnect all electrical leads from the terminal blocks on the furnace case. Note the colours and
positions of the connecting leads to enable correct reassembly. Take care not to crack porcelain
terminal blocks - use two spanners where appropriate.
Remove the thermocouple.
Lay the furnace body horizontally with the split in the cylindrical case uppermost. Remove the two
metal end-caps from the body.
Use a sharp knife to cut right through the insulation down to the wire-wound tube element along
the whole length of the body, but do not cut either of the ceramic board end discs. The knife cut
must be in line with the element lead wires. Slide the element gently out through the end of the
furnace body.
Check the cylindrical case and clean out as appropriate.
Remove any insulation sleeving from the tails of the old element and fit to the replacement
element.
Slide in the new element. Close up the furnace again, refitting the end-caps. Any cut made in the
insulation should close up completely: if the insulation appears loose or damaged in any way,
please contact our service division.
Reverse the rest of the disassembly process. Take care to make all connections to the correct
terminals. Do not overtighten the connectors in porcelain terminal blocks.