Teledyne 7120 - NDIR analyzer - Manual (Page 51)

4 Operation Model 7120
4-18 Teledyne Analytical Instruments
4.4.1.2 Manual Mode Zeroing
Scroll to Zero and enter the Zero function. The screen that appears allows
you to select between automatic or manual zero calibration. Use the UP/DOWN
keys to toggle between
AUTO and MAN zero settling. Stop when MANUAL
appears, blinking, on the display.
Select zero
mode: MANUAL
Enter to begin the zero calibration. After a few seconds the first of three
zeroing screens appears. The number in the upper left hand corner is the first-
stage zero offset. The microprocessor samples the output at a predetermined
rate.
####.## % CO2
Zero adj:2048 C—Zero
The analyzer goes through C–Zero, F–Zero, and S–Zero. During C–Zero
and F–Zero, use the UP/DOWN keys to adjust displayed Zero adj: value as
close as possible to zero. Then, press Enter.
S–Zero starts. During S–Zero, the Microcontroller takes control as in Auto
Mode Zeroing, above. It calculates the differences between successive sam-
plings and displays the rate of change as
Slope= a value in parts per million per
second (ppm/s).
####.## % CO2
Slope=#.### S—Zero
Generally, you have a good zero when Slope is less than 0.05 ppm/s for
about 30 seconds.
Once zero settling completes, the information is stored in the analyzer’s
memory, and the instrument automatically returns to the Analyze mode.
4.4.1.3 Cell Failure
Cell failure in the 7100 is usually associated with inability to zero the
instrument with a reasonable voltage differential across the Wheatstone bridge. If
this should ever happen, the 7100 system alarm trips, and the VFD displays a
failure message.
Cell cannot be balanced
Check your zero gas
Before replacing the sensor:
a. Check your zero gas to make sure it is within specifications.