S
ERVICE AND
M
AINTENANCE
7-8
June 1997 Rosemount Analytical 748213-P
Model 755R Oxygen Analyzer
7.4.3 D
ETECTOR
R
EMOVAL
Prior to removal of the detector, remove power from instrument and stop flow of
sample gas.
1. Remove the four screws securing the detector cover plate.
2. Disconnect cable from J12 on the detector assembly.
Note:
Note how the rubber sample lines are looped into a "long coil". When
reinstalling the sample lines they must be configured in the same way. This
precaution isolates the detector from the effects of mechanical vibration.
Otherwise vibration waves could travel upward along the tubing walls,
resulting in noisy readout.
3. Refer to Figure 7-1. Using needle-nose pliers, squeeze the hose clamps to
disconnect the rubber sample lines from the metal inlet and outlet tubes of the
detector assembly.
4. Remove the two screws at the bottom of the detector assembly, slide detector out.
I
NSTALLATION
1. Install replacement detector assembly and connect cable to J12.
2. Seat the detector assembly firmly against the magnet pole pieces and tighten
attaching screws.
3. Reconnect rubber sample lines to metal inlet and outlet tubes on detector
assembly.
4. Apply power to instrument and allow to warm up approximately one hour.
C
ALIBRATION
1. On the Control Board, set the front panel ZERO control (R13) at mid-range (i.e.,
five turns from either end).
2. Connect a digital voltmeter from the slider of R9 to chassis ground. With a steady
flow of 50 to 500 cc/min. of nitrogen gas passing through the instrument, adjust R9
for zero volts.
3. Connect the voltmeter between TP10 and circuit ground (TP7). Adjust front panel
ZERO control (R13) for reading of exactly zero on voltmeter.
4. With all internal adjustments now properly set, the instrument may be calibrated
per Section 3.4.
