Teledyne 7120 - NDIR analyzer - Manual (Page 32)

Photometric Analyzer Start-up and Operation
3-9 Teledyne Analytical Instruments
3.8 AUTOMATIC FUNCTION
The events talking place during a zero cycle are as follows:
l. The zero cycle starts with activation of the calibration contact. The
analyzer outputs are held during the zero cycle.
2. The Auto Zero solenoid valve is activated and zero gas replaces the
sample. (This valve may be internal or external to the Model 7100
enclosure).
3. At about minute one in the cycle. The Auto Zero board then begins its
zeroing function, adjusting the processing circuitry of the analyzer to develop
a zero signal output. During this period, the analyzer display may swing
from below zero to above fullscale several times before it finally settles to
zero output. The “hold” feature prevents these wide output excursions from
affecting the analog output and trigger alarms. The Auto Zero circuit board
function takes about 6 minutes to complete. It is important that zero gas is
continually purging the cell during this time.
4. At around the 5th minute, the Auto Zero solenoid valve is deactivated and
sample replaces the zero gas.
5. The hold feature is deactivated and the display starts reading the sample
again, and the analog output soon starts tracking.
This concludes the zero cycle.
The time between zero cycles, may be programmed to last from one (1) to 23
hours.
For “Purity Measurements” typical zeroing is performed every 3 hours. This
may increase or decrease depending upon the complexity of the application
involved.