Sensorex Dissolved Oxygen

Conductivity is used to measure the amount of dissolved solids in a solution or the concentration of acid or base.

This can be a somewhat complex answer. A conductivity sensor has a known AC voltage passed from a "sending" side through the solution being measured and out to the "receiving" side. The current in the circuit is measured. Using Ohm's Law V = IR R the "Resistance" across the water is calculated. Conductivity is = 1/R.

Depending on the range, conductivity is expressed in µS (microSiemens) or mS (milliSiemens). When very low conductivity is measured, (if <0.1µS) it is often expressed as resistivity (Megaohms) rather than conductivity. In the past, conductivity was expressed as in micromhos or millimhos. The mhos units are now expressed in Siemens or fractions of Siemens.

Conductivity is greatly affected by temperature. An error of 2 - 5% per degree Centigrade is common and depends on the range of conductivity being measured. Generally, 2% error is most common for above 500uS. Lower conductivity especially values expressed as resistivity (ultra-pure water = 18.2 Megaohms = 0.055 uS) have up to 5% error. Your conductivity instrument will make these corrections automatically if a temperature sensor is used.

This can be a daunting question, but can be simplified greatly to make choosing easier.

Use mild cleaning agents such as detergents or 5% HCl (removes scaling deposits). Always soak electrodes in chemicals and do not use toothbrush or wire brushes to clean since these will effect electrode performance.