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3 Operation Model OT-2 System
3-8
Teledyne Analytical Instruments
NOTE: This procedure is more critical on the 0-10 ppm range and
less critical on the 0-100 or 0-1000 ppm range.
3.3.2 Setting the Span Pot
1. Switch the system from zero gas to span gas and allow
time for stabilization.
Figure 3-6: Span Pot Location
NOTE: The span gas should have an O
2
concentration of 80% -
100% of full scale. For example, if the range is set at 0-100
ppm, the span gas should be a certified grade gas of
about 90 ppm O
2
in N
2
or Argon.
2. If 90 ppm gas is used, adjust the span pot (Figure 3-6)
to read 90.0 ppm on the LCD display. The output to
the Elsag Baily Total Flow
TM
computer will have a
signal of 4.6VDC (into a >10K ohm load).
The formula for this is:
Span Gas % F.S. x 4
Output in VDC
+=
100
1
Display
Span
Span Pot