Accurate conductivity, resistivity, salinity and TDS measurements

Achieve consistent readings of a range of related parameters using conductivity meters and probes. HACH,Orion and Hanna bench conductivity meters, portable conductivity meters and conductivity probes are suitable for wastewater, drinking water, water quality lab applications requiring ultrapure or deionized water, manufacturing processes including clean-in-place, industrial wash and rinse water, power generation, mining, healthcare including water for injection and other uses such as aquaculture and food and beverage.

Tips for accurately measuring conductivity, resistivity, TDS and salinity

Although conductivity measurements are generally simple and easy to take, mistakes can still affect the validity of the data generated. By understanding and avoiding the most common measurement mistakes, you can help ensure you are on the path to accurate and reproducible readings.

10 factors to consider when measuring conductivity

1.Use a suitable conductivity sensor. Sample composition, location (i.e. need for durability in the field), and the purity of the water sample can all influence the type of conductivity sensor you choose. Select the right conductivity probe ›

2.Understand and anticipate the effects of temperature. Conductivity measurements are strongly affected by the temperature of the sample.

3.Accurately use the temperature compensation (TC) function. Temperature compensation (TC) will calculate and display the conductivity at the chosen reference temperature. If TC is off, the displayed value is the actual conductivity at that temperature.

4.Carefully set the temperature compensation settings. Whether to apply a TC or not, or what type of TC selected, can affect the accuracy of your readings.

5.Take a conductivity reading only after temperature equilibrium is achieved. Conductivity is temperature-dependent, so time must be allowed for the conductivity sensor to equilibrate to the same temperature as the sample.

6.Minimize the use of elaborate multi-point calibrations. According to ASTM, a one-point calibration of the cell constant at a representative conductivity is sufficient for accurate conductivity readings. If the samples cover a large range of conductivity levels, one or more points can be made.

7.Use additional care and caution when handling low-level conductivity samples. The stability and purity of the sample and how it is handled can affect the accuracy of the sample reading. Low-level samples can be easily affected by contamination, CO2 absorption, and degassing.

8.Avoid setting calibration standards that are too low. Low-level standards are prone to contamination and difficult to use successfully. Tighter accuracy can be achieved by calibrating at 100 µS/cm or above.

9.Follow storage and maintenance guidelines for your conductivity sensor. Improper long-term and short-term storage of conductivity sensors can change the surface and adversely affect their performance.

10.Understand how to calculate resistivity, total dissolved solids (TDS) or salinity factors. Conductivity readings can be used to determine an estimate of these parameters in a sample by applying the related function through the meter setup. The meter will provide accurate conductivity and resistivity measurements, but the TDS and salinity values are an estimate as the true TDS is determined by gravimetric testing.