Instruction manual

MODEL XMT-A-FF/FI SECTION 9.0
CALIBRATION — DISSOLVED OXYGEN
4. Press MENU. The main menu screen appears. Choose Calibrate.
5. Choose Oxygen.
6. Choose AirCal.
7. To continue air calibration, choose EnterPress and go to step 8. To
change the stabilization criteria for air calibration or to enter a salinity dif-
ferent from the default value (0.0 parts per thousand), choose Setup and
go to step 12.
8. Enter the barometric pressure.
NOTE
Be sure to enter the actual barometric pressure. Weather forecast-
ers and airports usually report barometric pressure corrected to sea
level; they do not report the actual barometric pressure. To estimate
barometric pressure from altitude, see Appendix A.
9. The display changes to the screen shown at left. The live reading is the
concentration of dissolved oxygen based on the previous calibration.
Wait flashes until the reading meets the stability criteria programmed in
step 12.
10. The screen at left appears once calibration is complete. The concentra-
tion of oxygen in the display is the equilibrium solubility of atmsopheric
oxygen in water. The transmitter automatically calculates the solubility
from the measured temperature and the barometric pressure entered by
the user. The transmitter also assumes that the sensor is in water-satu-
rated air when the calibration is done. To return to the main display press
MENU then EXIT.
11. This screen appears if the sensitivity (sensor current divided by concen-
tration) is much higher or lower than expected. See Section 15 for trou-
bleshooting. To repeat the calibration step, choose No. To continue
choose Yes.
Procedure continued on following page.
9.3 PROCEDURE - CALIBRATING THE SENSOR IN AIR
1. Remove the sensor from the process liquid. Use a soft tissue and a stream of water from a wash bottle to clean
the membrane. Blot dry. The membrane must be dry during air calibration.
2. Pour some water in a beaker and suspend the sensor with the membrane about 0.5 inch (1 cm) above the wa-
ter surface. To avoid drift caused by temperature changes, keep the sensor out of the direct sun.
3. Monitor the dissolved oxygen reading and the temperature. Once readings have stopped drifting begin the cal-
ibration. It may take 5-10 minutes for the sensor reading to stabilize. Stabilization time may be even longer if
the process temperature is appreciably different from the air temperature. For an accurate calibration, the tem-
perature measured by the sensor must be stable.
Cal?
AirCal
InProcess Zero
AirCal?
EnterPress
Setup
Calibrate
Sim. PV
Program Display
Air Calibrate
Press
7
60.0mmHg
Live 8.00ppm
AirCal
Wait
Live 8.00ppm
Air Cal Done
Air Cal Failure
Check sensor
Cal?
Oxygen
Temp
55