BW July 2015

7/7: I changed the LabVIEW program so that for now if the temperature is NaN or zero, the hot plate will not turn on or off.

During July, we started calibrating the thermistors using a 2.4 kOhm test thermistor. First Jim calibrated the test thermistor using ice water and boiling water so that we could use it to calibrate the other thermistors. The test thermistor measured a higher temperature than some of the other thermistors, and Dr. Jones explained that the existing fixed thermistors might not have enough length of wire inside the hot air box for the wire to reach the temperature of the air. The wire outside the box could be cooling the short section of wire inside the box. To overcome the cooling effect of the wire outside the box, he instructed Brendan to put old pennies with 95% copper on the thermistors.

Once the pennies were fixed to the thermistors, we put the free thermistor in thermal contact with each of the other thermistors through the pennies and heated the air in the box. Four tests gave us the data we needed to calibrate the fixed thermistors against the free test thermistor.

7/24: We noticed that after running the heater in the hot air box, the air temperature increased at the beginning of the next run even while the heater was off. One possible reason for this heating is that the hot plate remains warm for a while, and when the lid is put on the box, the fans blow air from the hot plate toward the thermistors. Another influence on the air temperature might be warm air trapped under the lid.