Only if you get it on the approved list from Tripoli and NAR. NAR doesn't actually certify ANY altimeter for altitude record contests. Tripoli has a fairly short list that leaves a number of commercial altimeters off due to "issues". You'll need to contact Tripoli to see about that.

Warren

Hmm.. I couldn't find anything about altimeters anywhere on the site. But I'll contact one of their people to see what's required.

Hmm.. I couldn't find anything about altimeters anywhere on the site. But I'll contact one of their people to see what's required.

Adrian, the guy in the know is Tom Rouse:

Tripoli Contest and Records Committee
Tom Rouse
7170 Wooded Lake Dr
San Jose Ca. 95120

I don't have his current email address regarding TRA matters, though he is the Rouse Tech guy http://rouse-tech.com/

Also, Warren is exactly right -- there are a few altimeters that have not passed TRA scrutiny. As a current TRA record holder, I can tell you that there is a certain amount of rigidity to their approved list. They ask a lot of questions when you set a record... I have seen records that I thought were solid DQ'd because of altimeter issues.

Hope that helps,

JW

Thanks, John.

I sent Tom an email asking about what I would need to do to get the Parrot certified for official Tripoli records. In the meantime, I'll have fun seeing how high I can go unofficially. I'm looking forward to meeting you at the JWMRL.

-Adrian

Thanks, John.

I sent Tom an email asking about what I would need to do to get the Parrot certified for official Tripoli records. In the meantime, I'll have fun seeing how high I can go unofficially. I'm looking forward to meeting you at the JWMRL.

-Adrian

Adrian, any luck certifying yet? Has TR returned your emails or calls?

FWIW, I'll probably see him at BALLS. You might call him, number is on the Rouse-Tech page...

A week ago, he asked for me to give him all the data I could about the altimeter, and I replied with a bunch of information, data and graphs. I haven't heard back since, so I'll ping him again today.

IIRC he also needs a unit to chamber test, etc. Keep us posted-

J

Adrian,

Let me know what you find about regarding the chamber test. I've built a couple of altimeters that I just messed around with. I would like to find a better and more accurate way of testing.

What I have done is taken a mason jar and attached a vacuum pump(from Harbor Freight to bleed brake lines) to the lid in order to simulate the launch and flight.

You can also fit a couple of altimeters in a quart jar.

I'm sure the mason jar routine would not pass the Tripoli test, but it's a cheap way to test and compare to altimeters.

What I've been using so far is a shop vac hooked up to an airtight container. The Shop Vac pulls the equivalent of 3000 feet of altitude. I have a well-calibrated altitude watch that I put in the same chamber while I'm recording the data with the altimeter.

I'm working out a way to automate the calibration of a batch of altimeters so each board can get its individual, end-to-end calibrations for pressure and acceleration without having to spend an hour on each one. It will involve being able to dial in a pre-selected altitude for the chamber and holding it there for a while. I've been meaning to get a real vacuum pump for vacuum bagging anyway, so I think I'll do that and also put in a bleed valve in the chamber to help hold a constant pressure while the pump is running.

What I've been using so far is a shop vac hooked up to an airtight container. The Shop Vac pulls the equivalent of 3000 feet of altitude. I have a well-calibrated altitude watch that I put in the same chamber while I'm recording the data with the altimeter.

My altitude watch changes *dramatically* with the change in baro pressure. It constantly needs re-calibration. Curious if you have tried tossing in other brands of altimeters into the same chamber at the same time with the Parrot?

My altitude watch changes *dramatically* with the change in baro pressure. It constantly needs re-calibration. Curious if you have tried tossing in other brands of altimeters into the same chamber at the same time with the Parrot?

I'm sure it does; any altimeter or barometer is just measuring the same absolute air pressure, and normal barometric variation from weather systems can cause an equivalent offset of 300 feet or more. Fortunately, all of the rocketry altimeters have a way to re-zero at the pad, and weather systems don't change the barometric pressure enough during a flight to make a difference.

To double-check the calibration of the altimeter I used in Chris's flight, (and my method of using the altimeter watch as a pressure reference) I took the Parrot altimeter on a drive from Denver over Loveland Pass, while it was recording air pressure continuously. When I got back home, I used USGS topo maps and the recorded data to do a direct altitude calibration of the altimeter, and it was within 20 feet of the original calibration via altimeter watch. By the way, later I checked that the barometric pressure was flat during the 1-hour drive. 🙂

Where the calibration issue gets trickier is with temperature. It's easy to find pressure transducers that claim to have built-in temperature compensation, but temperature changes can still have a significant effect on the rest of the electronics in the measurement chain. And while I've seen several altimter web sites talk about how well they deal with the nonlinear variation of pressure with altitude, none of them that I've seen address how they compensate for temperature. Try a fun experiment. Start your altimter recording, and then hold a light bulb near it for a few minutes, and take it away again. I wouldn't be surprised if the recorded data tells you your altitude changed. If the temperature dependence is in the offset part of the measurement, it won't be a problem as long as the temperaure stays constant during the flight. (which it will, more or less, in an enclosed avionics bay) But if it affects the scale factor, then you'll get inaccurate data if you fly when it's warmer or colder than the temperature at which it was calibrated. My alt was reading 128 degrees F inside Chris's avionics bay on the July 21 flight. That's a pretty big temperature delta from a winter day in Hartsel :). One of the reasons I selected the microcontroller that I did was because it has an on-chip temperature sensor, which I'm planning to use for compensation. I know that the accelerometer offset changes significantly with temperature, and I'm going to do some more testing to measure the effect on the pressure and compensate for it, as well. Hopefully the temperature dependence will be similar enough from board to board that I'll be able to use the same temperature factor for all of the boards.