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Operation
OVERRANGE ALARM INDICATES HIGH
CONCENTRATIONS OF NITROGEN (≥ 0.5
PERCENT) IN THE SAMPLE LINE.
On completion of the zero and span calibrations, the Model 2120 is
ready to begin taking readings on the sample gas.
1. Open the valve of the desired sample inlet line.
2. Adjust the flow rate to 2 cfh (940 ccpm).
3. If desired, connect a recorder to the recorder output connector
on the back panel.
4. To proceed with an analysis of another sample line, close the
valve of the current sample line, open the valve of the new
sample line, and adjust the flow rate to 2 cfh (940 ccpm).
4.4 Overrange Protection Circuit
The Overrange Protection Circuit has two main parts:
1. A photodiode that provides a signal proportional to the total
light intensity from the analytical cell.
2. An alarm that takes action if the photodiode signal falls below a
threshold value.
The Overrange Protection Circuit requires no adjustment other than
the initial factory calibration. Even if the photodiode output shifts
substantially, the Overrange Protection Circuit operates properly. No
routine maintenance to this circuit is required, but the following test of
the circuit is recommended after each scheduled analyzer calibration.
To test the Overrange Protection Circuit:
1. While the analyzer is running, shut off sample flow. This causes
the low flow switch to cut off the high voltage to the analytical
cell so that the glow discharge will extinguish. The alarm
circuitry should indicate an overrange condition.
2. The following events should take place:
a.
The red overrange LED turns on and stays on.
b.
The panel meter reads "1" without any figures after
the decimal point.
Teledyne Analytical Instruments
34
Model 2120
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