Emerson 7003M - Manual (Page 58)

Operator Manual
748223-K
June 2002
5-2 Routine Servicing and Troubleshooting Rosemount Analytical Inc. A Division of Emerson Process Management
Model 7003M
d. Interfering Gases
Gases that are reduced or oxidized in the
range of 0.5 to 0.8VDC contribute to
sensor current and can cause a readout
error. Only a few gases have this
characteristic. Common gases that
should be avoided include SO
2 , Cl 2 , and
oxides of nitrogen (NO
X
). Low-level
concentrations of hydrogen sulfide tend to
contaminate the sensor, but may not
seriously affect oxygen measurement.
If you suspect that any stream
components are affecting the operation of
the sensor, contact Rosemount Analytical
Technical Services.
If contaminated, the rechargeable sensor
must be rejuvenated and the disposable
sensor must be replaced. Refer to the
instructions supplied with the sensor.
5-3 CIRCUIT DESCRIPTIONS
a. Signal Board
The Signal Board is configured to match
the type of sensor ordered with the
analyzer. If the type of sensor is
changed, or the Signal Board is repaired
or replaced, verify the rocker switch
position (SW1):
Rechargeable Sensor: Close positions
1,4, and 5
Disposable Sensor: Close positions 2,4,
and 6
b. Power Supply Board
The Power Supply Board provides:
• ±12V (non-isolated) for analog
signaling function
• +5V (non-isolated) for
microprocessor and associated
logic
• +24V (non-isolated) for the
isolated current function
• +5V (isolated) for other functions
for that circuit
There are isolated and non-isolated
grounds on the Power Supply Board.
TP1 is the non-isolated ground and
should be used with TP6 and TP7.
c. Microprocessor Board
The Microprocessor Board is the
functional center of the instrument. With
the exception of the program chip, no
user serviceable functions are on this
assembly. If the Microprocessor Board is
to be repaired or replaced, note the
positions of the configuration jumpers for
setting jumpers on replacement board.
An instrument timer circuit monitors
instrument power for a power failure,
power surge or other outside condition
interfering with the microprocessor
operation. When conditions return to
normal, the circuit will attempt a system
restart. If the microprocessor is still
capable of operating, both alarm relays
will be put into alarm condition, the screen
will clear, and the output current will drop
to 0 mA. Then the instrument will go
through a normal power-up routine and
will eventually return to routine operation
with alarms and output restored to their
normal conditions. The appropriate error
code (E-0, etc.) will be displayed until the
ACK button is pressed.
d. Alarm Circuits
Each alarm activation setpoint is designed
to be at a different level from the
deactivation setpoint:
• To prevent relay contacts from
chattering if the oxygen level stays
around the setpoint.
• To indicate to the microprocessor
whether alarm is HIGH or LOW.
• To allow for a time lag between the
time the alarm is activated and the
time it is deactivated for ON/OFF-
Control purposes.