Problems

1. Calculate the steady state current output from the DO sensor that we have made in the lecture when it is placed in air saturated water. Assume that we used 25 m thick Teflon FEP membrane. Use the table given below for the permeability data.

2. Suppose we use two 25 m Teflon membranes to cover the cathode.

(a) What will be the output current under the same condition as in Problem 1?

(b) Comment on the response time. Will this sensor become slower? By how much? Take diffusivity of oxygen in water as 2x10-5 cm2/s.

3. Suppose you place the DO sensor in a stagnant liquid which has a magnetic stirrer in it. Qualitatively show the sensor output current as you increase the stirring rate.

4. Flow dependency of DO sensor is a big problem in actual measurement. The flow dependency can be reduced by placing a silicone membrane over the Teflon membrane. Explain why this reduces the flow sensitivity.

5. Suppose we measure DO concentration in (a) dense aerobic culture, and (b) low cell density aerobic culture. In which case the accuracy will be better. Explain why. What can you do to improve the accuracy?