Air Pressure Sensor for Kite

Comments

• dre Posts: 106

  2009-06-05 16:05 edited 2009-06-05 16:05

  Would this link help?
  
  http://www.rocket-roar.com/rap/alt.html
  
  cheers, David
• sylvie369 Posts: 1,622

  2009-06-05 16:55 edited 2009-06-05 16:55

  There are quite a few options for barometric pressure sensors with the appropriate range, but precision may be an issue. Here is a nice little $11 sensor that detects from 15 to 115 kPa (2.2 lbs/in sq to 16.7 lbs/in sq)
  
  http://www.freescale.com/files/sensors/doc/data_sheet/MPX4115A.pdf
  
  and a site that will give you a quick reference for how pressure corresponds to altitude:
  
  http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html
  
  It'd be nice to have one whose entire range covered just the lower altitudes, though the last time I flew an barometric altimeter it did go to 94,000 feet (in a balloon), which would have maxed out that 4115 sensor. We flew a Honeywell ASDX015A24R, which is a bit pricier ($32) but can measure right down to a nearly pure vacuum.
  
  Anyway, they put out a nice linear voltage over all the altitude and temperature range you're likely to need. However, the +/-1.5% looks like it translates to a couple of hundred feet of error at sea level, which would be a real problem.
  ·
• Ken Gracey Posts: 7,386

  2009-06-05 17:13 edited 2009-06-05 17:13

  humanoido!
  
  Got the solution for you. Parallax is in the final stages of a small module based upon the http://www.vti.fi/en/products/pressure-sensors/pressure_sensors/ SCP1000 pressure sensor: sold by the manufacturer as the most precise pressure sensor in the world! The version we have designed into a module is functional from 0 to 120 kPA (you can figure out the elevation).
  
  Today Josh is doing the final code testing and we are sending it to production next week. I could send you one of the prototypes to try out. Being that you live in a high-rise building, you can easily test it from ground level to the 20th floor. Send me an e-mail to remind me and I'll take care of the request next week.
  
  Sincerely,
  
  Ken Gracey
• Humanoido Posts: 5,770

  2009-06-06 03:55 edited 2009-06-06 03:55

  @ dre
  Thank you for the link. This method determines rocket altitude based on accelerometer and time readings. If you have a constant rate of acceleration over time, this equates into distance. An interesting novel approach, but it does not work on kites, which are slow to reach altitude - the rate of climb is not constant or significant enough to register on the accelerometer.
  
  @ sylvie369
  Thank you for the links. The chart with air pressure versus altitude is especially helpful. The sensor looks like a good one, for thousand foot altitudes and above. Accuracy is a consideration. Ken has come up with exactly what I'm looking for - a very good sensor with amazing accuracy that looks perfect for the application. Your near space balloon project sounds very exciting. Do you have a web site? It would be interesting and useful to see Earth/Space photos at 94,000 feet!
  
  @ Ken
  Thanks!!!
• sylvie369 Posts: 1,622

  2009-06-06 10:25 edited 2009-06-06 10:25

  Photos of the workshop, launch, and recovery are at
  
  www.tinyurl.com/balloonworkshop
  
  Unfortunately, I don't have the onboard video yet.
  
  Very good news about the Parallax sensor. I was going to spend today searching for more precise sensors, but I guess now I don't have to. Man, this is a good company.
• dre Posts: 106

  2009-06-06 13:32 edited 2009-06-06 13:32

  Oops, sent the wrong link. See if this helps:
  
  http://geocities.com/SiliconValley/Orchard/6633/altimeter.html
  
  cheers, David