Altimeter accuracy

[captain1976 0]

I suspected my hand altimeter to be inaccurate for some time but today I took another one to cross check and the attached pictures show what they each read at pull time and just a couple seconds later when opened.

Pretty much the same thing on 3 jumps. Just wondering if anyone else has the same issues with the digital units.

You live more in the few minutes of skydiving than many people live in their lifetime

[theplummeter 14]

I recently had to take a King Air up unpressurized for a maintenance flight to check the Cabin Altitude light and a few other systems. Boredom got the best of me, so I wore my Viso II on my wrist for the ride up. We took off from 3200msl and climbed to 10000msl to check the light. My Viso read 6800 even at 10k, so if the King Air pitot static system is accurate, my Viso is as well.

I realize this isn't all that scientific, but it's something.

[Remster 24]

When's the last time you had the Alti calibrated?

Remster

[BigMikeH77 0]

Good point... I heard that Alti-2 offers free calibration at certain "events" but I can't seem to find a schedule of where they are going to be... does anyone know?

[LouDiamond 1]

The acceptable tolerance +/- for ANALOG altimeters is 250 ft. With that said, have Alti-2 chamber check your analog altimeter to see if it is within tolerance. Based on the pictures you provided, I am going to say it will come back as "within tolerances" as the digital altimeters are balls on accurate.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[LouDiamond 1]

theplummeter

I recently had to take a King Air up unpressurized for a maintenance flight to check the Cabin Altitude light and a few other systems. Boredom got the best of me, so I wore my Viso II on my wrist for the ride up. We took off from 3200msl and climbed to 10000msl to check the light. My Viso read 6800 even at 10k, so if the King Air pitot static system is accurate, my Viso is as well.

I realize this isn't all that scientific, but it's something.

I'm going to go out on a limb here and say that the aircraft altimeter was calibrated to the Hg for that day which was for 3200msl and your altimeter was zeroed to the ground, so the offset seen is expected. 6800 +3200 msl= 10,000. You are right, not scientific at all.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[captain1976 0]

Remster

When's the last time you had the Alti calibrated?

I just got it back from a new face place install. I assume it was calibrated then but am not positive they do it automatically on units in for service

You live more in the few minutes of skydiving than many people live in their lifetime

[Fast 0]

captain1976

***When's the last time you had the Alti calibrated?

I just got it back from a new face place install. I assume it was calibrated then but am not positive they do it automatically on units in for service

Mike we have an altitude chamber that you can put it in and test it. Talk to Mary or Brian about it.

~D
Where troubles melt like lemon drops Away above the chimney tops That's where you'll find me.
Swooping is taking one last poke at the bear before escaping it's cave - davelepka

[df8m1 19]

If you take a close look at your hand while in free fall you will notice that the digital altimeter is not seeing any air at all, where as the analog altimeter is getting some given it's slight angle, ( I do not recall if the vent on that is on the top or the bottom on that altimeter).

I wear two analog altimeters on one arm, a wrist mounted and a hand mounted, along with a chest mounted one, (I make them and am still cycling the original prototypes for grins).

Depending on where the wrist mount one is clocked on my wrist compared to the hand mounted one, I can make the readings vary by as much as 1K if I put the wrist one in the some air and have my hand flat blocking the other one.

Now comparing a digital pressure transducer with possible temperature compensating software trying to keep up with the fast changes things can get interesting...

Altimeters need to be checked in a controlled environment, and a jump is not a controlled environment lol...

[hackish 8]

I did some testing with my Altitrack and a series of precision MEMS barometer sensors plus a couple of old school analog units. I believe that the digital altimeter will be most accurate over the largest range. I actually have an altimeter rigged up with a raspberry pi that can read approx 1' of altitude change. It's not very useful as it takes about 3 seconds per measurement...

-Michael

[captain1976 0]

Fast

******When's the last time you had the Alti calibrated?

I just got it back from a new face place install. I assume it was calibrated then but am not positive they do it automatically on units in for service

Mike we have an altitude chamber that you can put it in and test it. Talk to Mary or Brian about it.

Will do since I just happen to be here for a week, but I'm going to look into the static thing anyway as I have seen these digitals actually stay at the same altitude on occasion while in freefall. I'm also going to do some research on the subject and report on it.

You live more in the few minutes of skydiving than many people live in their lifetime