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Eltra has changed the IR cell design. This modification makes the cells less
susceptible to contamination problems and makes the calibration more stable. The
changes are:
The IR-4 board is modified so that now the output voltage of the cell is adjusted at
8V instead of zero as it was till now.
The voltage of each source remains unchanged at 1.75 volts as it used to be.
After this modification the peaks you see on the screen and the output voltage of
the IR cell are two different things.
The Peaks on the screen look the same way like they used to look before starting
from zero (base line) and going up positive.
The outputs of the IR cells (IR base lines) are factory set at 8V when the paths are
new and clean. The peaks come down starting from 8V coming down to a
minimum voltage (at the peak maximum) and they go back to the 8V baseline after
completion of combustion. The 8V IR-base line is obtained through preamplifier
adjustment only. The fine adjustment pots are not available in the cell box anymore
because they are now not necessary.
In real operation, with growing contamination resulting in gradually weakened
radiation reaching the detector, the IR cell output base lines will move down to
levels below 8V depending on the grade of contamination. The (negative output)
peaks of the cell will also change to smaller amplitude.
The base line is not regulated any more.
Due to a recalculation formula, the base lines on the screen are always zero volts,
the peaks are positive and they are always of equal amplitude and surface (for
same sample and same weight) regardless the path contamination, regardless
the cell base line level, and regardless the cell output peak amplitude.
Consequently the integrated value (of the peak on the screen) remains the same
and of course also the analyses results remain constant at any grade of
contamination.
• When loading the UNI software select from now on "New cell" mode.
NOTICE
Due to the fact that the cell base line is not regulated, the microcontroller UNI
boards don’t contain the D/A converter any more, therefore they will not work in
case you may install such UNI boards in previous analyzers having IR cells which
need their base line to be automatically set to zero.
For testing the functionality of this system the source voltage was gradually
reduced from normal 1.75V down to 0.5V during an experiment in order to simulate
radiation reduction like it happens due to path contamination during real lab
operation. When gradually reducing the IR source voltage from 1.75V down to 0.5V
the cell base line came from +8V down to minus 3V and the peak amplitudes
became smaller. In all stages of the IR source voltage, the results of the same
samples remained stable and linear. On the PC screen was no difference to see.
All peaks started from zero going up to the same maximum and come back to zero
again. Therefore all results were equal regardless how low the source voltage was.
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