Calibration 50
10.2. DO CALIBRATION
Guidelines
• Rinse the probe with purified water.
• Shake any remaining solution off the probe. No droplets should remain on the DO sensor sensing surface.
•
For measurements across a temperature gradient (when water temperature is drastically different from
the standard), allow the probe to reach thermal equilibrium before conducting calibrations or making
measurements.
Calibration protocol
Slope and Offset use two‑point calibration data. During calibration users adjust the sensor’s Offset at both 100%
and 0% saturation.
Automatic Calibration
The following options are available for the Dissolved Oxygen calibration:
• Single or two point calibration at 100 or 0% saturation
• Single or two point calibration at 8.26 or 0 ppm (or mg/L)
When automatic calibration is performed it is assumed that the standard value is 100% water saturated air.
Two‑Point Calibration
With the probe correctly plugged in:
1. From Measurement screen, tap
(Measurement Menu icon).
2. Tap on Temperature tab and configure Temperature Source.
3. Tap Calibration tab and configure Standard Entry Type as Automatic.
4. Tap Calibrate to start the process.
5. Tap Clear Calibration to start a fresh calibration and clear all previous calibrations.
If using a new probe, it is recommended to clear all standards and start new.
• At 100 % saturation (8.26 mg/L)
Optical probe
` Place a moistened sponge in the bottom of the calibration beaker.
` Place the calibration beaker on the probe body. Do not tighten the calibration beaker on the probe threads.
` Wait at least 15 minutes for the air to become saturated with water vapor. This condition
corresponds to 100 % air saturated water at the temperature of measurement.
` Allow for the reading to stabilize. The standard value is automatically recognized.
Polarographic probe
` Suspend probe with membrane just over beaker of water. Do not put the sensor in an sealed container.
• At 0 % saturation (0 mg/L)
` Fill the calibration beaker 2/3 full with HI7040 Zero Oxygen solution and slowly place the probe in
the solution.
` Dislodge bubbles that may adhere to the sensor.
` Stir gently for 2‑3 minutes.
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