CN0359 Conductivity Measurement Problem


We have been using CN0359 for conductivity measurement. We are trying different types of EC probes and PT100.

Our problem is in the same container when you dip the EC probe and PT100 together the EC value is increasing after 2 seconds. Around 0.3mS.

We have a refferance EC meter from WTW and we are comparing our probe with it.

Our probe is 4 electrode cell.

Ex Volt : 3V

Ex Freq : 1 kHz

Cell Cont : 0.4868

Set up time : %10

Hold time : %1

If we dont put the pt100 in the same container with our EC probe.

The EC measurement is good and very stable. ( Temp of the water and the air is same so temp effect is not the problem here)

But when we put the PT100(stainless steel cased) in to container The EC value is directly increasing around 0.3mS in 2 seconds. And when put back from water its turning to normal.

Do we need speacial pt100 for this measurement ?

In few pt100 We recognized that the metal body of the pt100 has a volta on it. Some of the chinese brand pt100 which are very often in the all markets.

They have like 1V or 2V on their metal case. Maybe this is effecting the measurement.

After that we tried to use good brand pt100 which is italian brand SPT85.

The problem is same.

Can anybody give me the reason of this problem ?