Model 755R

Instruction Manual

748213-S April 2002

a.Source Lamp

The simplest check of the source lamp is to verify that it is lit. Another check is done by removing the housing cover and viewing the lamp through the photocell alignment hole (see Figure 6-3, page 6-4). If the photocell is not illuminated, test the voltage across TP2 to TP5 (ground). This voltage should be 2.2 V ±0.2 VDC. If reading is correct, the lamp may be burned out; also inspect the cable for continuity. If voltage reading is not 2.2 V

±0.2 VDC, the Power Supply Board must be replaced.

b.Photocell

If the photocells are on, observe through the photocell alignment hole. The image should be steady. Disconnect the line power and observe the image when you reconnect the power. It should come up from the side and seek a position that equally illuminates the photocells.

c.Suspension

Turn electrical power to instrument OFF. Remove optical bench assembly (see Figure 6-1A, page 6-3). With 100% nitro- gen flowing through the analyzer, note position of the suspension. Then admit air and note response of the suspension. It should rotate clockwise as viewed from the top, and to the right as viewed though the window. Failure to rotate indicates that the suspension has been damaged and detector assembly must be replaced. See Section 6-5c, page 6-7.

If the suspension has been changed, the cause may be improper operating condi- tions.

6-5 REPLACEMENT OF DETECTOR/MAGNET COMPONENTS

a.Source Lamp

Removal/Installation

The source lamp is held in the optical bench assembly by a set screw (see Fig- ure 6-1B, page 6-3). The two lamp leads are connected to J12.

The red line on the lamp base must align with the set screw (see Figure 6-4A). The base of the lamp should extend from the hole approximately 1/4 inch. Tighten set screw when lamp is aligned.

Realign the photocell per Section 6-5b, page 6-5.

b.Photocell

Removal/Installation

Refer to Figure 6-1B, page 6-3. Note lo- cation of photocell leads in connector J12. Remove leads. Remove photocell lock screws (2), slide photocell out.

Reverse the removal procedure for in- stallation. Align photocell (see below).

Alignment

The adjustments in this procedure are made on the Control Board. With zero gas flowing:

1.Place a digital voltmeter between the wiper of zero potentiometer (R13) and TP7 (ground). Adjust for 0 VDC.

2.Remove the voltmeter from R13 and place on R10 (see Figure 6-4B, page 6-6). Adjust R9 for 0 VDC.

3.Remove the voltmeter from R10 and place on TP8. Move the photocell to obtain a DC voltage as close to 0 mV as possible, but no more than ±750 mV.

Rosemount Analytical Inc. A Division of Emerson Process Management

Maintenance and Service

6-5