LaMotte 5 Series TDS Meter - Manual (Page 36)

Conductivity measurements are very dependent on temperature. The ability of
the ions to move through the solution, and conduct the current, is related to
the temperature of the solution. As the temperature of the solution rises, the
ions move more quickly through the solution, increasing the conductivity. As
the temperature decreases the ions move more slowly and the conductivity
decreases. Since the conductivity of the same solution can change by as much
as 2 percent per
°C, accurate temperature measurements must be made
simultaneously to with the conductivity reading. The CON 6/TDS 6 has a
temperature sensor within the probe that will measure the temperature of the
solution.
To make conductivity readings taken at different times and places comparable,
measurements are often converted to what the conductivity of the solution
would be at 20
°C or 25°C. The CON 6/TDS 6 automatically applies this
conversion before displaying a reading.
Because it is a quick, reliable, and inexpensive way of monitoring the ionic
content of a solution, conductivity measurements are widely used in many
areas of water testing from environmental monitoring to municipal water
supplies to many industrial applications.
APPENDIX 1: CALIBRATION TIPS
Only one calibration point is needed to measure solutions throughout the
entire range of the meter. If a range was not calibrated, the meter will
automatically detect the closest range calibrated and use that calibration
information. However, only the ranges that were calibrated will have
maximum accuracy.
If the solutions being measured are near to or greater than 20 mS (10 ppt), or
near to or lower than 100 µS (50 ppm), the meter should be calibrated at least
once a week to get the specified ±1% F.S. accuracy.
If the solutions being measured are in the mid-ranges and the probe was
washed in deionized water and stored dry, the meter should be calibrated at
least once a month.
Wet the probe for 10 minutes before calibrating or taking readings to saturate
the probe surface and minimize drift. If measurements are made at extreme
temperatures, the meter should be calibrated at least once a week.
Use only the conductivity/TDS probe specified for the CON 6/TDS 6 meters.
This probe has a built-in temperature sensor. If a probe without a temperature
sensor is used, the temperature of the solutions must be measured and manually
entered into the meter. (see Manual Temperature Compensation section 5.2)
36