13 August, 2003

Jason's Thermometer

In preparation for the trip, one of my students from last year, Jason Hunter, has been constructing a thermometer to put aboard one of the first few balloons that will be launched in August.

Jason works during the day so we meet in the evenings in my classroom at school. He has worked four nights trying to get the electronic thermometer to work. We are using a specialty chip designed to go to -55 °C. We expect temperatures in the polar stratosphere to drop even colder than that so we are curious if this chip will give reliable results at colder temperatures. The chip produces a voltage that is converted into a frequency and then those pulses are counted by an on-board computer. This frequency will be relayed back by radio to the ground station at McMurdo. This is how all the data is sent, including the actual thermometer that is used. It will be interesting to see how well Jason's thermometer will match the data from the one on-board the balloon.

Tonight we finally have had success! A quick trip to Baskin's and Robins and we have some dry ice to test the thermometer. Jason says CO2 becomes solid at negative 78 degrees C. Through some trickery with the batteries we are able to read negative temperatures. Now all we have to do is package the device.

Jason is curious if the battery will change its voltage as it gets cold. This is a common problem in electronic circuits and engineers spend a lot of time making sure circuits work at different temperatures. To test this, Jason has built another board that will dangle a battery out in the air and record the voltage. Most of the electronics carried by the balloon is insulated with Styrofoam and a tin can of water keeps the batteries warm for the duration of the flight.

Well, hope it all works!

Jason working on thermometer.

Testing the thermometer.

Close-up of the electronics.