Model 755R

Instruction Manual

748213-S April 2002

c.Detector

Removal

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.

Calibration

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 ni- trogen gas passing through the in- strument, 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, page 3-1.

3.Refer to Figure 6-1, page 6-3. Using needle-nose pliers, squeeze the hose clamps to disconnect the rubber sam- ple lines from the metal inlet and out- let tubes of the detector assembly.

4.Remove the two screws at the bottom of the detector assembly, slide de- tector out.

Installation

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 detec- tor assembly.

4.Apply power to instrument and allow to warm up approximately one hour.

6-6 CONTROL BOARD SETUP

a.Power Supply Test

1.TP7 (circuit ground) is ground point for all voltage tests.

2.Counterclockwise end of front panel ZERO potentiometer (R13 on Control Board): -15 VDC ±0.5 VDC.

3.Clockwise end of ZERO potentiome- ter: +15 VDC ±5 VDC.

4.Set ZERO potentiometer to obtain a reading of .0 VDC ±10 mV at slider.

5.Measure TP19: +5 VDC ±0.25 VDC.

b.Detector zero

1.Flow 250 cc/min nitrogen.

2.Monitor TP8, adjust R9 for 0 VDC

±2mV.

Rosemount Analytical Inc. A Division of Emerson Process Management

Maintenance and Service

6-7