2002 by ELTRA GmbH Germany – January 2002 – Service Manual OH 900 / ON 900 / ONH 2000
2.5-2
The opposite happens when the temperature in the laboratory goes higher. The
IR-cell heaters need less power to keep the temperature constant, so that the
voltage will become lower.
■ The adjustment of the IR-cell should be done, if possible, when the laboratory has the
average temperature of the year. The set point of the IR-temperature should then
be adjusted with P1 so that the voltage in stable condition measures 6 volts.
■ For readjusting, turn P1 clockwise when the voltage to is too low; when the voltage is
too high turn counter clockwise.
■ Caution: After you have turned P1 several times, the voltage will be out of range.
This is normal. When turning P1, you enter a new set point of the IR-cell temperature
which is at that moment different to the actual temperature of the cell.
■ The temperature control circuit will give full power to the heaters ( in case you
have set a higher temperature ) or the circuit will completely shut down the power to
the heaters, if you have adjusted a lower temperature set point than the actual
temperature.
■ After about 10 minutes the temperature will reach the new adjusted level, and the
voltage will come back to remain stable at the new level.
■ This is the voltage level which corresponds to the power to keep the
IR-temperature stable at the new level.
■ If the LED still doesn’t start blinking , adjust P1 on the TH 61, until there is about
5.35 VDC present between TP2 and TP3.
If the fault still remains, despite adjusting the TH 61, then check the board NR 32,
according to the following instructions.
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