Class: BE-309
Group: T2
Members: Kathryn Guterl, Lytal Kaufman, Maryam Malik, Andrea Sultenfuss
Date: December 11, 1998
Full Text

Abstract:
A portable, inexpensive conductivity meter was constructed using a signal generating circuit, a wheatstone bridge, and a voltage comparator. The conductivity meter was powered by two 9-volt batteries and conductivity cells were constructed from a mixture of tin and copper wire (bench wire) as well as from pure copper wire. Testing numerous cells, the average optimal conductivity cell measurements that caused the constructed circuit to work effectively were determined. The cell constants of these optimal cells were determined to be 3.0 + 0.16 cm-1 and 1.7 + 0.21 cm-1 for the bench and copper wire cells, respectively. Using these cells, the resistance readings of NaCl solutions (0.05, 0.1, 0.15, 0.2, 0.25, and 0.3 M) were determined. It was found that the measured resistance from the constructed bench wire and copper wire conductivity cells deviated from the expected resistance readings by 165% and 51%, respectively; the average voltage error across the wheatstone bridge was 143 mV and 98 mV; the percent deviation from the expected cell constant was 84.7% and 87.3%.

Four urine samples with specific gravity measurements ranging from 1.0036 g/mL to 1.0257 g/mL were tested using the constructed optimal conductivity cells in conjunction with the circuit thus forming the conductivity meter. The constructed bench wire cells were found to be more effective in determining the difference in concentration of the urine samples, illuminating the LED as expected in 66.7% of the trials. From a regression equation for each individual cell relating the resistance reading to the concentration of the sample tested, it was found that highly concentrated urine samples deviated significantly from estimated concentration values determined from the specific gravity measurements.