Science Buddies: "Ask an Expert"

I am helping my son perform the “Conductance as a Water Quality Measurement” experiment for his science class. I noticed that in this experiment you used a DI-194RS. He was interested to perform this experiment however since the DI-194RS required an RS232 connection (which none of our computers have) we purchased the DI-148U which has a USB connection. When converting the voltage output to micro Siemens there was a calculator to perform this conversion. There was a note however, which stated that the calculator will only work for the DI-194RS.
Questions:
1) Do you know what the formula is for converting the voltage output to micro Siemens for the DI-148U?

2) Do you know how we can gain access to a calculator for the DI-148U?

3) Can I use the same calculator as the DI-194RS?

I also noticed the experiment also stated that the tap water voltage readings were around .6-.7 volts – using the DI-194RS. The readings we get using the DI-148U for tap water are around .1 volts. Not sure if this is because of the difference of equipment being used to measure the voltage or the difference of the actual conductivity or resistivity of the water. I think .6 to .1 is a big difference though for the voltage measurement in regards to the conductivity of the water.

Thanks for your help.

Hi,
Welcome to the Ask an Expert forum. I think your best bet is to contact DATAQ. I see the calculator you are talking about (http://www.dataq.com/science-fair/calc- ... ncebuddies) and the note that goes with it ("Because of the hardware inside the data acquisition unit, using an instrument other than the DI-194RS requires a different calculator (not available).") I have never used these particular instruments and I am not sure if there are differences in the electronics that would require a different formula to convert voltage to conductance. If another expert has more info, I hope they will chime in.

Another possibility would be to calibrate the instrument using various solutions with known concentrations of salt. That approach won't give you an exact measurement of conductance, but it would give you a means to assess the relative differences in conductance between water samples.

It sounds like a great project. Good luck!

Regards,
Chris

Thanks for your suggestions.

You're welcome. Please let us know how it goes.