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.
Pressure vs Temperature
104
y = 0.0013x3 - 0.0725x2 + 1.2656x + 94.068
103.5
From this graph, we can see that pressure readings
are fairly accurate on the interval [15,25]
degrees centigrade
103
102.5
Pressure (Kilopascals)
Function (Green)
102
------------Safe Zone ----------101.5
Static Pressure (Red)
101
h
100.5
Subtracting h from future barometric
readings will compensate for temperature
errors.
h=P(T)-101.3
100
Collected Data (Blue)
99.5
99
5
10
15
20
Temperature (Centigrade)
25
30
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
99.266
kPa
100.504
kPa
101.057
kPa
101.552
kPa
102.666 kPa
103.375 kPa
Temperature
5.809 C
9.213 C
12.451 C
27.003 C
30.17 C
31.766 C
Height h
-2.074
kPa
-.7112
kPa
-.2062 kPa
+.3268 kPa
+.65764
+1.4816
Actual Pressure
101.3
kPa
101.3 kPa
101.3 kPa
101.3 kPa
101.3 kPa
101.3 kPa
Corrected
Pressure
101.34
kPa
101.215
kPa
101.2632
kPa
101.2252
kPa
102.008 kPa
101.89 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:
Barometer 1 vs Barometer 2
105.25
104.75
This is the line we got
104.25
Barometer 2
103.75
103.25
This is the line we wanted
102.75
102.25
101.75
101.25
101.25
101.75
102.25
102.75
103.25
Barometer 1
NOTE: In this test, Barometer 2 was under a heat lamp
103.75
104.25
104.75
105.25
The Exponential Pressure Model
P  P e
h
a
P
 a  ln
h
Po
• 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 (Po )
• The pressure where we want to know the
altitude at (P)
• Derivation:
BaBAR Flight!
Babar in Box