Barnstead FB1300 Operation And Repair Manual And Parts List page 21

M S
AINTENANCE AND ERVICING
Note
If the thermocouple touches
metal, this could short out the
signal, causing the control to
display room temperature. This
could cause the furnace temper-
ature to run away, possibly dam-
aging furnace components.
Note
If the furnace temperature
moves downward, the thermo-
couple leads are reversed.
20
5) Disconnect the thermocouple from the
terminal block by removing the screws
on the terminals. Pull the thermocouple
through the hole in the furnace base
and discard.
6) Insert the new thermocouple into the
back of the furnace until the tip extends
1-1/2" into the chamber. Make sure the
porcelain insulator extends through the
steel back plate to prevent the lead
wires from touching metal.
7) Bend the thermocouple sharply so that
it lies flat along the back of the furnace.
8) Thread the thermocouple through the
hole in the base which has a nylon
insulator, replace clamp and screw.
9) Bend the thermocouple sharply toward
terminal block.
10) Secure the two yellow wires marked "+"
together on the terminal block. Secure
the two red wires "-" together on the
adjacent terminal. Make sure connec-
tions are secure to terminal block.
A polarity test of the thermocouple and lead
wire is easily made with the use of a magnet.
On chromel alumel thermocouples and lead
wire, the non-magnetic wire is positive ( + ) and
the magnetic wire is negative ( - ).
11) Replace bottom plate.
12) Replace thermocouple cover.
13) Reconnect furnace to power supply.
14) Test operation of furnace.