2002 by ELTRA GmbH Germany – January 2002 – Service Manual OH 900 / ON 900 / ONH 2000
1.24-1
1.24 Unstable current:
If during power periods the current is unstable, it is an indication for a bad contact. The
power control of the analyser keeps accurately constant power, i.e. current multiplied by
voltage. A possible bad contact having a relatively high resistance will increase the voltage
so that the current will be accordingly reduced in order to keep constant power. However,
this constant power is shared between the crucible and the bad contact that is heating up.
Therefore in this case, although the (total) power is unchanged, the crucible temperature
decreases while a contact area heats up.
Possible places for a poor contact are:
- The surface of the upper electrode that touches the crucible. It can be
a) not clean. Clean with a metal brush or with polishing material, like abrasive foam.
Don’t use pastes. Final cleaning with solvent.
b) worn out . Replace it.
- The upper surface of the electrode and the surface of the furnace where the electrode
should properly touch is not clean or grains are sticking on this surface. Check carefully
and clean as describesd in a) above.
- The holes of the upper electrode, where the four screws are screwed in, are not free, so
that the screws cannot be screwed in deep enough. In this case the electrode will not be
properly pulled by the screws to be pressed on the furnace block surface. Clean properly
the holes of the electrode to make sure that the screws can be screwed deep enough in
the electrode.
- The graphite tip is worn out. Replace it.
- The graphite tip holder is not properly srewed on the lower furnace block. Check and take
same measures for cleaning and for making free the holes for the screws like in case of
the upper electrode as described above.
- The high current braid connecting the furnace with the high current transformer are not
properly connected. Drive properly the big screws connecting the braids to the furnace and
to the transformer (two screws for each braid).
To Next Page
Loading...
Need help?
General
