Carbolite CTF Series - Manual (Page 9)

MTF, CTF
MF03 3.13
9
5.5 Thermocouple Replacement
The coverings and guards which must be removed to gain access to the thermocouple depend on
the model, its orientation (horizontal or vertical), and possibly other options and fittings. It will
usually be necessary to separate the furnace from its base or stand. On horizontal CTF models one
outer end-cap will need to be removed, and on MTF and vertical CTF models the terminal cover.
On MTF 10/ models the thermocouple lies inside the furnace body; the body must be removed
from the control base, and the end-cap and insulation ring removed from one end.
Disconnect the furnace from the supply, and separate the furnace body and/or remove covers and
guards as necessary.
Make a note of the thermocouple connections. The negative leg of the thermocouple is marked
blue. Compensating cable colour codings are:
negative positive (type K) positive (type N)
white green pink
Disconnect the thermocouple from its terminal block.
Withdraw the thermocouple from its sheath 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 furnace centre.
Insert the new thermocouple into position, restoring any removed porcelain spacers, and ensuring
correct polarity.
Re-assemble the furnace.
5.6 Element Replacement
Please see safety note 5.2 - please wear a face mask.
The coverings and guards which must be removed to enable replacement of the wound tube
element depend on the furnace model, its orientation (horizontal or vertical), and other options and
fittings. The general procedure is:
Disconnect the furnace from the electrical supply.
Remove all outer guards, meshes and terminal covers from the furnace body. For a horizontally
mounted furnace remove the furnace body from its base; to reach the bolts or screws which fix the
body to the base, remove the back panel from the base.
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. For MTF 10/ models this must be done after removing the end-cap and
ceramic fibre disc adjacent to the thermocouple terminal - see below.
Lay the furnace body horizontally with the split in the cylindrical case uppermost. Remove the two
metal end-caps from the body. In the case of the CTF models undo the self-tapping screws which
hold the terminal strip to the case join. The case will spring open slightly. Remove the ceramic
board disc from one end (the thermocouple end in the case of MTF 10/ models).
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.