Emerson Rosemount5081, Инструкция по эксплуатации, Страница: 110 / 152

3. Is the zero solution fresh and properly made? Zero the sensor in a solution of 5%
sodium sulfite in water. Prepare the solution immediately before use. It has a shelf
life of only a few days.
4. If the sensor is being zeroed with nitrogen gas, verify that the nitrogen is oxygen-
free and the flow is adequate to prevent back-diffusion of air into the chamber.
5. The major contributor to the zero current is dissolved oxygen in the electrolyte
solution inside the sensor. A long zeroing period usually means that an air bubble is
trapped in the electrolyte. To ensure the 499ADO or 499ATrDO sensor contains no
air bubbles, carefully follow the procedure in the sensor manual for filling the sensor.
If the electrolyte solution has been replaced, allow several hours for the zero current
to stabilize. On rare occasions, the sensor may require as long as overnight to zero.
6. Check the membrane for damage and replace the membrane if necessary.
Zero reading unstable
1. Is the sensor properly wired to the transmitter? Verify that all wiring connections are
tight.
2. Readings are often erratic when a new or rebuilt sensor is first placed in service.
Readings usually stabilize after an hour.
3. Is the space between the membrane and cathode filled with electrolyte solution,
and is the flow path between the electrolyte reservoir and the membrane clear?
Often the flow of electrolyte can be started by simply holding the sensor with the
membrane end pointing down and sharply shaking the sensor a few times as though
shaking down a clinical thermometer. If shaking does not work, perform the checks
below. Refer to the sensor instruction manuals for additional information.
• For 499ADO and 499ATrDO sensors, verify that the holes at the base of the
cathode stem are open (use a straightened paper clip to clear the holes). Also
verify that air bubbles are not blocking the holes. Fill the reservoir and establish
electrolyte flow to the cathode. Refer to the sensor instruction manual for the
detailed procedure.
• For Gx438 and Hx438 sensors, the best way to ensure that there is an adequate
supply of electrolyte solution is to simply add fresh electrolyte solution to the
sensor. Refer to the sensor instruction manual for details.
Sensor current different from below
Sensor nA/ppm
499ADO 1,800 - 3,100
499ATrDO 3,600 - 6,100
Hx438 and Gx448 4.8 - 9.8
1. Is the sensor properly wired to the sensor? Verify that all connections are tight.
Diagnostics and troubleshooting
100 Rosemount 5081