13
Measurements in Ultrapure Water
Process Calibration
A process calibration is a single-point calibration performed with the probe installed in the process.
This type of calibration allows the user to adjust the measured EC , resistivity, or seawater salinity value so that
it matches the value determined with a calibrated reference meter.
Preparation
• Use a calibrated reference meter and probe to determine the process EC or Salinity value.
• Select measurement unit.
Procedure
1. Press
m
direct key then
CAL
virtual key.
2. Press
Process
when available.
3. Use
ud
directional keys to adjust the process value in agreement with the predetermined value.
4. Press
CFM
to confirm and save calibration.
Note
: For process calibration, input reading must be greater than 0.015 µS/cm (1.0%Sal) and Setpoint value
should not be lower than 0.015 µs/cm (1.0%Sal).
11. 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)
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.
6. Press
m
direct key then
CAL
virtual key.
