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Teledyne 7300a - NDIR analyzer User Manual

Page 54

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4 Operation

Model 7300A

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 7300A is usually associated with inability to zero the

instrument with a reasonable voltage differential across the Wheatstone bridge. If
this should ever happen, the 7300A 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.