Replacement of the TH 43 board:
once the TH 43 board has been replaced, it is necessary to perform the above adjustments, to
avoid errors due to the tolerance of any component in the furnace.
4.10.2 Furnace regulation board TH 43 / TH 44
Description of its function:
: Furnace regulation board TH 43/TH 44
The TH 43 or TH 44 control board regulates the furnace power, first by comparing the
temperature set point with the actual furnace temperature, then by sending the appropriate
signal to the thyristor drive unit.
The output voltage of the thermocouple (actual furnace temperature) can be read at TP1. Its
range is about 13 mV at 1300°C.
The output voltage versus temperature characteristic of a thermocouple is not perfectly linear. A
linearisation unit therefore, has been included in the above circuit.
Once linearized and amplified, the furnace temperature voltage can be read on TP10. The
temperature set point, which is adjustable with the potentiometer on the furnace, is compared
with the actual furnace temperature voltage.
The resultant voltage (on TP12) is then fed to the thyristor drive unit, thus increasing or
decreasing the furnace voltage.
A current limitation circuit keeps the furnace current within safe limits.
Either the temperature set point or the actual temperature can be digitally displayed, depending
on the switch setting on the furnace.
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