conductivity to consistency

garby · Jul 6, 2010

Hi there,

I am using E+H CLD132 sensor to detect the conductivity of both NaOH solution and HNO3 solution, I can only read the conductivity with unit ms/cm, now the end user asked for the data of consistency with unit %, can I change the data of conductivity into consistency in %? how?

i saw some one applied a linear function into this transition, but the result is not satisfied.

thanks and best regards,

nonuke · Jul 6, 2010

Are you reading the 4-20mA output from the CLD 132 with a PLC or a 4-20mA indicator? If you are, you can convert the ms/cm to % with the help from the Lab. The Lab can make a solution with a known % of NaOH etc. If you measure the conductivity of the sample, you know that X ms/cm = Y%. I do this all the time in our CIP's.

garby · Jul 6, 2010

thanks nonuke!

yes i am reading 4-20ma output with s7-300 plc. i've tried the lab, but the result is not satisfied. for example, i measured 204ms/cm for HNO3 with 1.6%,25 centigrade degree, but when I measure the solution with 1%, i got 145ms/cm, according to the calculation, it should be 128ms/cm.

this is also for CIP project for a dairy plant

Christoff84 · Jul 6, 2010

I would try taking 4 or 5 test points with different solutions, you may find out the the ratio isn't linear.

garby · Jul 7, 2010

Yes Chris, you are right, the ratio isn't linear, then how can i program this not linear relationship in the step 7?

nonuke · Jul 7, 2010

In most Dairy plants we build CIP's for, the % of NaOH and HNO3 is kept the same over the years, or than the change is very small so your set point will always have the same % (you will never use a 0-100% scale). You are correct, the change in conductivity is logaritmic not linear.

garby · Jul 7, 2010

Our process is:
NaOH for example,
SP1: normaly 2.0% , above this setpoint, the clean is ok, and the timer is running, below the setpoint, the timer is hold;
SP2: normaly 1.5%, below this setpoint, the solution will be drain, above this setpoint, the solution will go back to the lye tank;
SP3: normaly 0.1%, below this setpoint, the flow will go to the water recover tank to save the water;

current i can only use ms/cm, but customer would prefer %

thanks,
garby

nonuke · Jul 7, 2010

Hi garby: Just ask the Lab to make a sample with 2%, 1,5% and 0,1% of NAOH, than you can insert the conductivity cell in each sample and find out the conductivity for each percentage.

conductivity to consistency

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