Model 755A

Instruction Manual

245364-V May 2002

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.

Rosemount Analytical Inc. A Division of Emerson Process Management

Service and Maintenance

6-3