Especially in case of resistance furnace operation, the peak of hard-to-burn samples starts
coming up quite late. In such cases, the minimum analysis time should be set to about 60
seconds.
If after prolongation of the minimum analysis time to a reasonable value, a peak still doesn't
appear, possible reasons for the fault are:
– No combustion. See chapter “No combustion”.
– There is no gas flow. See chapter “No flow”.
– There is gas flow, but bypassing the furnace. See chapter “Sample burns but no peak
on the screen“.
– The IR cell is faulty. See chapter “Check base lines“.
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3.32 Chopper motor doesn‘t rotate
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The rotation of the chopper motor needs to be checked in case of problems only, like when
there are no combustion peaks on the screen or the IR signals are minus -10V (take care,
minus) displayed on the PC screen in the window “inputs”.
In order to check whether the chopper motor is rotating, the easiest way is to remove an IR
path. See chapter “IR-paths, cleaning and replacing”. Mostly, the easiest path to remove is
the shortest one. Then, the chopper blade can be seen thru the hole of the chopper housing,
which becomes free (open) after removing the path.
The reason of failure can be a faulty motor but also the controlling electronics of the motor may
have become defective. If so, the motor or the IRC board has to be replaced. Before replacing,
check at least the voltages on the board, mainly the supply voltage of 24VDC. See chapter
“Infrared cell adjustments”.
For replacing the chopper see chapter “Chopper”.
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3.33 Sample burns but no peak on the screen
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When the analysis cycle is carried out normally and the sample is burned but no peak on the
screen, possible reasons are the following:
- The IR cell could be faulty. Check the base lines. See chapters “Check base lines” and
“Infrared cell adjustments”. If the base lines look normal, the IR cell can be regarded as
ruled out. If the base lines are practically at zero volts, the cell is faulty or without power.
(24VDC). See chapter “Bad combustion”.
- The plunger of bypass valve V4 jams. See chapter “Cleaning solenoid valves”.
This is related to induction operation only:
This may happen in case of induction furnace operation. There is gas flow, but bypassing the
furnace, so that there is gas flow shown on the flow meter and by the flow sensor on the screen,
but no gas flow thru the induction furnace. In this case the bypass valve V4 jams, causing the
oxygen flow to bypass the furnace like in case of open furnace. See chapter “Gas flow
system”.
The furnace has though oxygen pressure but without having oxygen flow. Due to oxygen being
present, the metal sample and accelerator(s) burn, because there is availability of oxygen in the
furnace, coming thru the chamber valve V3 and/or thru the lance valve V2. In case of metal
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