Emerson 755A - Manual (Page 71)

Instruction Manual
245364-V
May 2002
Rosemount Analytical Inc. A Division of Emerson Process Management Service and Maintenance 6-3
Model 755A
6-3 DETECTOR COMPONENT REPLACEMENT
a. Detector Replacement
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 6-1 on page 6-4.
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.
5. Install replacement detector assembly
and connect cable to J12.
6. Seat the detector assembly firmly
against the magnet pole pieces and
tighten attaching screws.
7. Reconnect rubber sample lines to
metal inlet and outlet tubes on
detector assembly.
8. Apply power to instrument and allow
to warm up approximately one hour.
9. Set the front panel ZERO control
(R13) at mid-range (i.e., five turns
from either end).
10. Refer to Table 3-2 on page 3-6,
Figure 3-2 on page 3-7 and Figure
6-3 on page 6-5. Connect a digital
voltmeter (four digit resolution) from
the slider of Coarse Zero
potentiometer (R9) to chassis ground.
With a steady flow of 50 to 500
cc/min. of nitrogen gas passing
through the instrument, adjust Coarse
Zero (R9) for zero volts.
11. Connect the voltmeter between TP10
and circuit ground. Adjust front panel
ZERO control (R13) for reading of
exactly zero on voltmeter.
With all internal adjustments now properly
set, the instrument may be calibrated in
the normal manner.