Instruction Manual
CON 11/110
73
16 CALIBRATION
TIPS
You only need one calibration for measurement throughout the entire range of the
meter. If a range was not calibrated, the meter automatically detects the closest
range calibrated and uses that calibration information. However, only the ranges that
were calibrated have maximum accuracy.
If you are measuring in ranges near to or greater than 20 mS (10 ppt), or near to or
lower than 100 µS (50 ppm), calibrate the meter at least once a week to get specified
±1% F.S. accuracy.
If you are measuring in the mid-ranges and you washed the electrode in de ionised
water and stored it dry, calibrate the meter at least once a month.
Wet the electrode for 10 minutes before calibrating or taking readings to saturate the
electrode surface and minimise drift. If you make measurements at extreme
temperatures, calibrate the meter at least once a week.
You should only use the conductivity / TDS electrode specified for these meters.
These electrodes have a built-in temperature sensor. If you use a different electrode
without a temperature sensor, you must measure the solution temperature separately
and manually enter the solution temperature (see manual temperature compensation
section on page 21).
17
CALCULATING TDS CONVERSION FACTORS
You can calibrate your meter using TDS calibration standard solutions. The
calibration standard only needs to give the TDS value at a standard temperature
such as 25 °C. To determine the conductivity-to-TDS conversion factor use the
following formula:
Factor = Actual TDS ÷ Actual Conductivity @ 25 °C
Definitions:
Actual TDS: Value from the solution bottle label or as a standard you make using
high purity water and precisely weighed salts.
Actual Conductivity: Value measured using a properly calibrated Conductivity /
Temperature meter.
Both the Actual TDS and the Actual Conductivity values must be in the same
magnitude of units. For example, if the TDS value is in ppm the conductivity value
must be in µS; if the TDS value is in ppt the conductivity value must be in mS.
Check your meter factor by multiplying the conductivity reading by the factor in the
above formula. The result should be in TDS value.
