BaBAR Vernier Barometers By Marshall Rogers

The BaBAR Experiments The first one was finding the correlation between Temperature and Pressure readings in Vernier Barometers. The second one was using Vernier Barometers to estimate altitudes using two pressure measurements.

About the first Experiment In order to find the correlation between Temperature and Pressure, I had to subject the Barometers to a controlled temperature/pressure environment. I did this by placing the Barometers in my fridge and under a heat lamp. After I recorded data, I compiled the fridge and lamp data together, and graphed the pressure versus the temperature. Then, I used Microsoft Excel to obtain a function that followed the graph

Details on Procedure When one of the Barometers was placed in the fridge, the fridge door was left open, so the pressure would be equal between the Barometers outside of the fridge and the one inside of the fridge. I recorded the temperature of the Barometer in the fridge/under the lamp. The Barometer under the lamp was also at the same pressure as the Barometers not under the lamp. The Barometers were left to record data in the different temperature environments for about half an hour each.

Function (Green) Collected Data (Blue) Static Pressure (Red) From this graph, we can see that pressure readings are fairly accurate on the interval [15,25] degrees centigrade Safe Zone h Subtracting h from future barometric readings will compensate for temperature errors. h=P(T)-101.3

Using P(T) We must know distance h. By subtracting h from barometric readings, we can get a good estimate of the actual pressure. Example: Recorded Pressure kPa kPa kPa kPa kPa kPa Temperature5.809 C9.213 C C C30.17 C C Height h kPa kPa kPa kPa Actual Pressure101.3 kPa Corrected Pressure kPa kPa kPa kPa kPa kPa Difference from Actual Pressure.04 kPa.085 kPa.0368 kPa.0748 kPa.708 kPa.59 kPa

Predicted/Wanted Results Before I performed the experiment, I was fairly sure that temperature affected the pressure readings given by the Barometers. I was also hoping that temperature wasn’t affecting the Barometers, but that would have left me with some other variable. If the Barometers weren’t affected by temperature, a graph of a barometer outside of the controlled temperature versus the barometer at room temperature would look like a y=x line, or rather a P1=P2 line. Instead, the graph was much more extreme and looked like this:

This is the line we wanted This is the line we got NOTE: In this test, Barometer 2 was under a heat lamp

The Exponential Pressure Model We can use the Exponential Pressure Model to use our barometric readings to get height measurements. To use the EPM we must have two pressure measurements. One Reference pressure (P o ) The pressure where we want to know the altitude at (P) Derivation:

BaBAR Flight! Babar in Box