Instruction Manual

245364-V May 2002

Model 755A

6-2 DETECTOR COMPONENT CHECKS

a.Detector

Before concluding that the detector is defective and must be replaced, verify that all components and circuits that could cause erratic readings are operating properly.

To isolate the detector as a source of a problem, the source lamp, photocells and suspension should be checked for proper operation.

b.Source Lamp

To verify that the source lamp in operating properly:

1.Verify that lamp is lit.

2.Voltage at U7 pin 2 should be 2.2±0.2 VDC.

If lamp is not operating properly, replace per instructions in Section 6-4 on page 6- 5.

If photocell readings not correct, replace photocell per Section 1-1a on page 6-7.

d.Suspension

If the suspension has been damaged, the cause may by improper operating conditions.

Maximum permissible operating pressure for the detector is 10 psig (69 kPa gauge pressure). To ensure against over- pressurization, a pressure relief valve may be inserted into the sample inlet line. In addition, a check valve should be inserted into the vent line, if connected to a manifold associated with a flare or other outlet that is not at atmospheric pressure. If the detector is over-pressurized, the suspension could break.

To verify correct operation:

1.Turn electrical power to analyzer OFF.

2.Remove optical bench assembly (see Section 6-4 on page 6-5, steps 1 through 4.)

c.Photocell

To verify that photocell is operating properly, perform the following steps:

1.Keeping power source ON, disconnect the leads of the photocell from connector J12. See Figure 6-1 on page 6-4.

2.Note the current measurement between the gray and orange wires (between 300 to 450 mA).

3.Measure between the orange and red wires. The reading should be approximately the same as step 2.

3.With 100% nitrogen flowing through the analyzer, note the position of the suspension.

4.Admit air and note response of suspension. It should rotate clockwise (as viewed from the top) and to the right (as viewed through the window).

Failure to rotate indicates that the suspension has been damaged and that the detector assembly must be replaced. See Section 6-3a on page 6-3.

6-2

Service and Maintenance

Rosemount Analytical Inc. A Division of Emerson Process Management