Altimeter Fenix 5

Returned my watch after talking to Garmin about the altimeter problem. Got a new one no questions asked. The new one worked like a charm up until now. I connected it to the computer to charge it and it automatically loaded and upgraded the wifi driver to «WIFI A2 Firmware version 2.40», and now the altimeter on the new one has started to go nuts. Anybody know how to roll back the WIFI firmware?

Hi,

Look here : http://gawisp.com/perry/fenix_D2_tactix/ in zip files, beta also, you show find your wifi driver. ;-) Put it in the good folder into your watch.

Noticed the same thing, maybe coincidence in my car: changes in ambient conditions (from warm to cold) or sudden weather changes (rapid drop in baro) seem to correlate with these altimeter weird readings. Would be good to know whether this is a hardware issue. As a side note I'm curious what inputs are used for elevation formula.

Noticed the same thing, maybe coincidence in my car: changes in ambient conditions (from warm to cold) or sudden weather changes (rapid drop in baro) seem to correlate with these altimeter weird readings. Would be good to know whether this is a hardware issue..

As I have already written earlier in the thread: Look at Ambient Pressure on the watch, not Barometric Pressure.

Ambient Pressure comes from the pressure sensor. So a hardware problem will be very obvious if you look at Ambient Pressure. I have written an explanation on Page 2 of this thread: https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-5-5s/155092-?p=1285883#post1285883

Barometric Pressure comes from pressure sensor + watch guesswork + watch calculations. Just as Altitude does. If you use those for troubleshooting your pressure sensor, your troubleshooting will be much more indirect, and you need a better understanding of everything to arrive at the correct conclusion.

As a side note I'm curious what inputs are used for elevation formula.

I am pretty certain that the formula looks like this:
Elevation = c1 * (Barometric Pressure - Ambient Pressure)

The parameters in this equation: Elevation:
Your current altitude above Mean Sea Level

c1:
A(n almost) constant which describes the ratio between ambient pressure reduction and elevation increase.
This constant will change slightly with altitude (google "ISA atmosphere").
At my altitude, when doing the calculation backwards from displayed data, I can see that the watch uses c1 = 8,6 meter/millibar.
In the Garmin forums, there are also claims that the watch will use measured temperature to make a correction of this altitude/pressure ratio, because hot air has lower density. I have however not been able to reproduce this, and I believe that it would be silly to do it because the temperature in the watch is not a very reliable indication of the temperature of the outdoor air.

Barometric Pressure:
The ambient pressure at Mean Sea Level. This pressure changes all the time depending on weather, so the watch needs to know the current value when it does the calculation. However, the value is not and cannot be measured by the watch. Consequently, the watch will have to do a lot of guesswork to arrive at the Barometric Pressure, depending on how much information the watch had available when deciding on a value to be used.

Ambient Pressure:
The ambient pressure measured by the pressure sensor in the watch.

As can be seen from this, calculating a correct elevation is impossible without knowing the current barometric pressure. If you want a usable barometric pressure in the watch, the altimeter in the watch will have to be calibrated to a known altitude every time you need it. The calibration will force the watch to do the above calculation in reverse and set the barometric pressure in the watch. The calibration will only be valid for some hours.

The watch does have some functionality to attempt to keep the barometric pressure calibrated without user interaction, for example by using GPS information before starting an activity, or by guessing if changes in ambient pressure were caused by weather changes or by altitude changes. But as a user, you will have to at least keep an eye on altimeter and check that it hasn't strayed in a wrong direction. It is not something which Just Works, and it can never be, unless the watch starts getting barometric pressure information from a remote source or starts relying much more on the GPS (which is also problematic).

I went out to mailbox and the elevation started rising. Now it's showing 8600m and baro pressure was constant around 1030 mb, ambient pressure started dropping, now around 320 mb. If baro pressure is computed then should follow closely the ambient pressure which in my case does not.

Wiyh regards to temp role in elevation, you can check an online elevation calculator based on baro and temp. The temp variations it seems more like a correction maybe +-10 m with 20 degrees temp variation or so. I see thousands of meters variations in my case.

It seems my watch has a hardware issue, otherwise a lot of people would have hit this and complained. I'm on FW 7.0.

Regardless my main scenario is hiking. I expect elevation reading in +-30 m error range. I think I will return this one.

As a side note Fenix5X forum does not seem to have threads about altimeter problems. Different hardware maybe?

I went out to mailbox and the elevation started rising. Now it's showing 8600m and baro pressure was constant around 1030 mb, ambient pressure started dropping, now around 320 mb.

A change from 1030 to 320 millibars is a very clear sign of a sensor error. And the change is so large that it can't even be explained with a plugged air opening to the sensor.

If baro pressure is computed then should follow closely the ambient pressure which in my case does not.

No, the barometric pressure shown on the watch should not follow ambient pressure if the watch thinks that the ambient pressure change was caused by an altitude change. A lot of people apparently draw this faulty conclusion, and this is one of my reasons to recommend looking at ambient pressure instead.

Wiyh regards to temp role in elevation, you can check an online elevation calculator based on baro and temp.

The online calculator just shows that the density of the air depends on temperature and that you can get a more precise result if you know the actual temperatures in the air column between your position and Mean Sea Level. The question is whether the temperature measured by the watch is used or should be used for such a calculation. I think not, because the watch can be measuring a lot of other temperatures: Your skin temperature, or the indoor temperature.

I am experiencing the very same issues. Garmin has replaced two watches already and the third is not working properly neither. The first worked well for nearly 3 months. I start to have the feeling it may be software/firmware related.

I am a owner of a F5 WiFi/sapphire.

I wonder if the same issue occurs with the standard F5 model?

Mine (5 sapphire) is behaving a bit strange since the last update, up and down in altimeter but not as much as reported in this thread.

I have F5 Sapphire edition SN starts with 539. This is my first one but I will return it. I consider getting F5X but I may give F5 another chance.

The fact that some people hit 3 watches with the same issue after RMA (as reported above) worries me: is Garmin aware and acknowledged the issue? This seems like a basic functionality issue.

If this issue appears after the watch is out of warranty then what?? To me will be pretty much useless in my main scenario hiking.

I own several other Garmin products that work fine and lasted beyond warranty. I thought that Garmin values quality and brand.

My 3rd Fenix 5 sapphire started doing this yesterday, this one didn't even last a week. I don't think there will be a 4th, a watch this expensive needs to be more reliable. In all the years I've had my Forerunner 620 it's been so reliable, I expected more from the Fenix. I've not even managed to get a weeks worth of running stats on one, what with all of the resets and swaps. That and the fact that even now Garmin don't have cloud backup for these devices so you lose half of your stats each reset. Can you imagine if you had to start from scratch with your mobile phone each time you got a new one or reset one!