135 Measuring with EC Probes
5. Press CFM when displayed to confirm and save the calibration.
“Wait” is displayed followed by “Calibration DONE” when the process calibration is confirmed and saved.
The controller returns to the menu.
22.4.4. Measurements in ultrapure water
Resistivity is the reciprocal of conductivity and their scales emphasize different areas of the measurement range.
Resistivity is commonly used in ultrapure water while larger amounts of contaminants are best measured in
conductivity (EC) Meas.Mode. The user can subsequently change Meas.Mode to RES to measure in resistivity
units (MΩ
•cm).
Ultrapure water self ionizes into H
+
and OH
‑
ions and has a conductivity of 0.055 μS/cm or a resistivity of
18.18 MΩ
•cm at 25 °C. The self‑ionization of water is highly temperature dependent.
Recommended temperature compensation setting for these type of measurements taken with HI7630‑28 probes
only is "Standard" as it utilizes the correct compensation algorithm.
Calibration recommendations
• Remove the probe from the process and shake all the water from the probe.
• Wait for moisture to evaporate off the probe before calibration.
• Suspend the probe in the air and use 0.000 μS/cm or 0.0 μS/cm as first calibration point.
• Use 84 μS/cm standard for the best calibration.
Process calibration (with conductivity calibration completed only)
To enter resistivity process calibration, the resistivity input value should be greater than 50 Ω•cm (k ≈ 0.1/cm)
or 15 Ω•cm (k ≈ 1.0/cm).
1. Place the cleaned probe in line, in a flowing, gas‑free water.
2. Allow the probe to acclimate to the water and temperature of the water.
3. Return the Meas.Mode back to RES.
4. Verify Temp.Comp. is set to Standard.
Verify temperature agrees with the reference measurement.
5. Use Temp. Offset to adjust temperature.
The cell may be calibrated using a reference measuring system on site or a traceable plant standard.
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