Teledyne 7120 - NDIR analyzer - Manual (Page 57)

4 Operation Model 7120
4-24 Teledyne Analytical Instruments
Note: If all three ranges are currently defined for different applica-
tion gases, then the above screen does not display (because
mode must be manual). Instead, the VFD goes directly to the
following screen.
If above screen displays, use the UP/DOWN arrow keys to Select MANU-
AL, and press Enter.
Select range to run
—> Ш1 Ш2 Ш3 CAL<—
Use the UP/DOWN keys to select the range: 01, 02, 03, or CAL. Then
press Enter.
Gas use: CO2
Range: Ø — 10 %
Use the ENTER key to move the range to low-end field. Use ENTER
key to move the range to high-end field. Use the UP/DOWN keys to change
the values of the fields.
Press Escape to return to the previous screen to select or define another
range.
Press Enter to return the to the Analyze function.
4.6.2 Auto Screen
Autoranging will automatically set to the application that has at least two
range setup with the same gases.
In the autoranging mode, the microprocessor automatically responds to
concentration changes by switching ranges for optimum readout sensitivity. If the
upper limit of the operating range is reached, the instrument automatically shifts
to the next higher range. If the concentration falls to below 85% of full scale of
the next lower range, the instrument switches to the lower range. A correspond-
ing shift in the DC concentration output, and in the range ID outputs, will be
noticed.
The autoranging feature can be overridden so that analog output stays on a
fixed range regardless of the contaminant concentration detected. If the concen-
tration exceeds the upper limit of the range, the DC output will saturate at 1 V dc
(20 mA at the current output).
However, the digital readout and the RS-232 output of the concentration
are unaffected by the fixed range. They continue to read beyond the full-scale
setting until amplifier saturation is reached. Below amplifier saturation, the over