Instruction manual

54
MODEL XMT-A-FF/FI SECTION 9.0
CALIBRATION — DISSOLVED OXYGEN
2. Press MENU. The menu screen appears. Choose Calibrate.
3. Choose Oxygen.
4. Choose Zero.
5. The screen at left appears. The top line is the raw sensor current.
6. Once the reading is stable, the screen at left appears. Sensor zero is
complete and the transmitter has stored the zero current. The screen
remains until the operator presses MENU then EXIT to return to the
main display.
NOTE
Pressing ENTER during the zero step will cause the transmitter to
use the present sensor current as the zero current. If the sensor is
zeroed before the current has reach a minimum stable value, sub-
sequent readings will be in error.
7. This screen appears if the zero current is extremely high. See Section
15 for troubleshooting. To repeat the zero step, press EXIT and choose
Zero.
8. This screen appears if the zero current is moderately high. To continue,
choose Yes. To repeat the zero step choose No. See Section 15 for trou-
bleshooting.
9.2 PROCEDURE — ZEROING THE SENSOR
1. Place the sensor in a fresh solution of 5% sodium sulfite (Na
2
SO
3
) in water. Be sure air bubbles are not
trapped against the membrane. The current will drop rapidly at first and then gradually reach a stable zero
value. To monitor the sensor current, go to the main display and press  until the input current screen appears.
Note the units: nA is nanoamps, µA is microamps. The table gives typical zero currents for Rosemount
Analytical sensors.
A new sensor or a sensor in which the electrolyte solution has been replaced may require several hours (occa-
sionally as long as overnight) to reach a minimum current. DO NOT START THE ZERO ROUTINE UNTIL THE
SENSOR HAS BEEN IN ZERO SOLUTION FOR AT LEAST TWO HOURS.
Sensor Zero Current
499ADO <50 nA
499ATrDO <5 nA
Hx438 and Gx448 <1 nA
Cal?
Oxygen
Temp
Cal? AirCal
InProcess
Zero
Live 200nA
Zeroing
Wait
Possible ZeroErr
Proceed? Yes No
Live 0.000ppm
Sensor Zero Done
Sensor Zero Fail
Current too high
Calibrate
Sim. PV
Program Display