9
8
4. Calibration
Conductivity/TDS calibration
This instrument is capable of up to three-point calibration to ensure accuracy across
the entire range of the meter. You need only one calibration for measurement of the
entire range of the meter. If a range is not calibrated, the meter automatically detects
the closest range calibrated and uses the calibration information. However, only
the ranges that have been calibrated have maximum accuracy.
Calibrate to all
ranges to ensure highest accuracy throughout all measurement ranges.
When to calibrate
If you are measuring in solutions with conductivity lower than 100 µS or TDS lower
than 50 ppm, calibrate the meter at least once a week to get specified ±2% full scale
accuracy. If you are measuring in the mid ranges and you wash the probe in deion-
ized water and store it dry, calibrate the meter once a month. If you take measure-
ments at extreme temperatures, calibrate at least once a week
Use only the supplied conductivity/TDS probe or replacement probe WD-35606-50.
NOTE
: Do not reuse solutions after calibration. Contaminants in the solution can
affect the calibration, and the accuracy of the measurements.
Preparing for calibration
Select a conductivity or TDS standard near the sample value you are measuring. If
this is not possible, choose a calibration solution value that is approximately 2/3
the full scale (F.S.) value of the measurement range. For example, in the 200 to 1999
µS range, use a 1413 µS solution for calibration. Note: the Acorns will not accept
calibration values less than 40 µS (20 ppm).
Wet the probe for 10 minutes prior to calibration to saturate the probe and
minimize drift.
It is not necessary to reset the meter before calibration. All new calibrations will
automatically override existing calibration.
Calibrating for Conductivity or TDS
1.
Pour approximately 3 cm of the chosen Conductivity / TDS standard into
two separate containers.
2.
Gently stir the probe in one of the containers of your standard. This standard
acts as a rinse solution, removing contami-
nants that offset the calibration.
3.
Dip the rinsed probe into the other container
of your standard.
4.
Turn meter on. Meter will automatically enter
Conductivity/TDS mode.
5.
Tap probe on the bottom of the container to
remove air bubbles. Let the probe stabilize to
the solution temperature.
6.
Press the CAL key. The meter will blink with
the factory calibrated value.
See figure
7.
Press
▲
(up) or
▼
(down) key until the
displayed value matches your standard
solution.
8.
Press enter key to confirm. The meter will exit
calibration, and return to measurement mode.
Repeat for all ranges for maximum accuracy.
4.1
m
S
A
B
A
B
Range
Resolution
Accuracy
0.0 to 199.9 µS*
0.1 µS
±4 µS
Conductivity
200 to 1999 µS
1 µS
±40 µS
2.00 to 19.99 mS
0.01 mS
±0.4 mS
0.0 to 99.9 ppm*
0.1 ppm
±2 ppm
TDS
100 to 999 ppm
1 ppm
±20 ppm
1.00 to 9.99 ppt
0.01 ppt
±0.2 ppt
*Minimum calibration value 40 µS (20 ppm).