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Instruction Manual
245364-V
May 2002
Rosemount Analytical Inc. A Division of Emerson Process Management Operation 3-9
Model 755A
Figure 3-3. Calibration by Pressure Decrease Setup
Standard Procedure: Calibration by
Pressure Decrease
1. Verify that the Pressure
Compensation Option is selected,
i.e., Jumper inserted between E1
and E3 on the Control Board.
2. Connect a compound range
pressure gauge (or mercury
manometer), pressure gauge,
pressure regulator, flowmeter,
needle valves and vacuum pump as
shown in Figure 3-3 above.
3. Open V2, set PR1 to approximately
10 psig (69 kPa) and adjust V1 for a
flow rate of 250 cc/min. into the
sample inlet line. Compound range
pressure gauge (or mercury
manometer) should indicate close to
atmospheric pressure (0.00).
4. Set TEST switch to PRESS CAL 1
and adjust CAL 1 potentiometer R98
(see Table 3-2, page 3-6, and
Figure 3-2, page 3-7) for a reading
of 00.00±5 counts on the display.
5. Set TEST switch to NORM and note
display reading.
6. Start vacuum pump.
7. Close V2 and adjust V3 and V4 to
decrease the pressure on the
sample exhaust by about 3%. (-
12.00 inches of water; -0.4 psi; -23
mm of mercury; -3 kPa).
8. Adjust CAL 2 potentiometer R99
(see Table 3-2, page 3-6, and
Figure 3-2, page 3-7) until reading
on display is the same noted in step
5.
9. Repeat steps 3 through 7 as many
times as necessary to ensure
repeatability of compensation
calibration.
NOTE
Although not mandatory, it is
desirable, in order to obtain
maximum accuracy, that the oxygen
concentration of the gas used during
calibration be close to that of the
process stream which is to be
analyzed.
F1
Compound Range
Pressure Gauge or
Mercury Manometer
Pressure
Gauge
Vacuum
Pump
PR1
Sample
In
Sample In
755A
250
cc/min
V1
V3
10 psig
V2
V4