EFHSS Questions and Answers - Answer to Question Q00512

Like some other departments that use RO water feed for the disinfection rinse stage of a wash cycle we have a problem in conforming to certain guidance. It recommends the conductivity of the RO water should be 30μS/cm or less. Our problem is, we are achieving this value at the plant but the washers say it’s higher. The RO water is being circulated at 60°C and I am confident the temperature is having an effect on the reading at the washers. The manufacturers say not because they inform us the sensors have temperature compensation built in. So when we perform a ‘debug’ of the system (raise the temperature to 90°C), why does the conductivity value at the washers rise with an increase in temperature? Has any one else noticed this? I have come across a conductivity verses temperature chart and this tie’s up the two different readings.

Temperature dramatically affects the conductivity of water. Therefore, conductivity measurements are internationally referenced to 25 degrees C. With normal water supplies, temperature changes the conductivity an average of 2% degrees C which is relatively easy to compensate for. RO water are much more difficult to read, and automatic compensation for temperature inside the machine is a chalange.

Yaffa Raz

I would like to add some information to my previous answer:

Basically, conductivity expresses a stream's ability to transport electricity. This parameter can be further defined as "the reciprocal of resistance." Measured in microSiemens, conductivity relates to the amount of total dissolved solids (TDS). Higher TDS values generate higher conductivity counts. For example, pure water possesses a minute conductivity, as the ability increases with rising charged ion concentration in the water. Conductivity receives a slight increase effect by increasing temperature. As a whole, warmer substances allow for great dissolving capabilities, in turn boosting the presence of TDS. A multiplied TDS value will directly heighten the conductivity of a solution. On average, a one percent rise in temperature results in a three percent rise in conductivity. However, effects from slight temperature change will remain insignificant.

I hope it helps,
Yaffa Raz