Rosemount 755, Instruction Manual

Page: 78 / 94

M
ODEL
755 O
XYGEN
A
NALYZER
7-4
748183-H
Rosemount Analytical December 1997
SUSPENSION
LOOP
P12
PHOTOCELLS
4
5
6
A
B
D
C
CURRENT TO VOLTAGE OP AMPS
ON CONNECTOR BOARD
F
IGURE
7-2. V
OLTAGE
T
EST
P
OINTS
7.3 DETECTOR COMPONENT CHECKOUT
7.3.1 D
ETECTOR
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.
7.3.2 S
OURCE
L
AMP
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 7.4.2.
7.3.3 P
HOTOCELL
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 Figures 7-3, 7-4.
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.
If photocell readings not correct, replace photocell per Section 7.4.3.