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Thermometer
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bflentje
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Joined: 29 May 2006

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PostPosted: Wed Apr 23, 2008 12:32 pm    Post subject: Thermometer Reply with quote

There allegedly is a thermometer built into the Garmin GPSMAP60CSx, which I would guess is used with the barometric pressure to calculate altitude. Does anyone know if the actual temperature is visible as a data field ANYWHERE on ANY screen in this unit? The owners manual mentions temperature a few times but says nothing about using it as a stand alone thermometer.

There's a chance I am looking right at it but can't see it... kind of like caching.
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NeoAddict
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PostPosted: Wed Apr 23, 2008 3:59 pm    Post subject: Reply with quote

Really? Sounds neat if someone could find it. I should do some sleuthing on mine. Surprised
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Pear Head
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PostPosted: Wed Apr 23, 2008 4:44 pm    Post subject: Reply with quote

The thermometer is in most Garmin units for sure, if not most units of all brands. It's used to correct for drift of the GPS's clock (as the crystal is affected by temp). Some units also use it to adjust the contrast of the display (which is also affected by temp).

It can usually be viewed from the diagnostics screen, which isn't accessible while the unit is in a normal operating state.

PROCEED AT YOUR OWN RISK:

Using Garmin's secret keystrokes can have unintended consequences on your unit. If you toast your unit doing what I describe below or any other keystrokes then don't come crying to me.


As far as I know (which is very little), the only thing that going into diagnostics will do is possibly force the unit to do a cold-start the next time it's powered up (looking for satellites). If something else happens then you're on your own and I'm not responsible.

Accessing the diagnostics screen varies by model. For the 76CSx (which I have), and I'm guessing it applies to the 60CSx as well, you need to hold the enter key down and then hold down the power key. Hold those keys down until you see diagnostics. It takes about 1 second to come into diagnostics. If you get to the normal first "welcome" screen that you're used to seeing then you're doing it wrong.

The temp is displayed in Celsius.
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spinowner
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PostPosted: Wed Apr 23, 2008 9:30 pm    Post subject: Reply with quote

Keep in mind that it's going to register the temperature inside the receiver, not the ambient air temperature. Therefore it's not going to be very useful, which I'm sure is why the screen is not normally set up to display the reading. Altitude is determined strictly by satellite signals in exactly the same way that latitude and longitude are determined.
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Pear Head
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PostPosted: Wed Apr 23, 2008 9:35 pm    Post subject: Reply with quote

spinowner wrote:
Altitude is determined strictly by satellite signals in exactly the same way that latitude and longitude are determined.


In the CSx models I believe it's determined by barometer.
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spinowner
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PostPosted: Wed Apr 23, 2008 9:39 pm    Post subject: Reply with quote

I'm not familiar with how that particular unit works. I would think that satellite signals would be more accurate because barometric pressure is so variable.

Edited to add: My eTrex displays the altitude accurately in a pressurized jet airplane cabin. If barometric pressure is used the receiver would tell you you were on the ground.
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Last edited by spinowner on Wed Apr 23, 2008 9:44 pm; edited 1 time in total
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Pear Head
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PostPosted: Wed Apr 23, 2008 9:42 pm    Post subject: Reply with quote

spinowner wrote:
I'm not familiar with how that particular unit works. I would think that satellite signals would be more accurate because barometric pressure is so variable.


I'm not 100% sure of what the theory is behind it (maybe someone here can explain it?).

The unit gives you your altitude even with no signal lock.
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bflentje
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PostPosted: Wed Apr 23, 2008 9:46 pm    Post subject: Reply with quote

We spend $300 to $500 on a device to talk to a multi-billion dollar satellite system and they can't add the $.37 external thermometer circuit? I guess I can't have it all.

Thanks for the note about diagnostics. Sounds pretty cool. Will have to borrow a GPS during the next weeknight event and try it on someone else's unit.
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LucidOndine
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PostPosted: Wed Apr 23, 2008 10:59 pm    Post subject: Reply with quote

To my knowledge, the CSx models determine altitude by barometer alone, but I'll test it the next time I can sneak it on an airplane without scaring the flight attendants, or Jambro.
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spinowner
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PostPosted: Thu Apr 24, 2008 5:10 am    Post subject: Reply with quote

Even though determination of altitude by barometric pressure wouldn't be as accurate as by satellite it still can be used to monitor changes in altitude. This could be useful for climbers, for example. It's also better than nothing if you are in a location where satellite signals are blocked, such as in a cave or under dense tree cover.
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Arcticabn
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PostPosted: Thu Apr 24, 2008 7:51 am    Post subject: Reply with quote

Pear Head wrote:
spinowner wrote:
Altitude is determined strictly by satellite signals in exactly the same way that latitude and longitude are determined.


In the CSx models I believe it's determined by barometer.


This is incorrect. In order for a barometer to work correctly it has to be calibrated initially for the location it is at. That is why when an airplane flies it sets the barometer for takeoff and when it gets to its destination it is provided the barometric pressure at ground level there.

It take a minimum of 3 sats to get lat/long and a min of 4 sats to get elevation.
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LucidOndine
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PostPosted: Thu Apr 24, 2008 9:27 am    Post subject: Reply with quote

Assuming you've calibrated your barometer (which I hope anyone with a CSx model has calibrated both barometer and digital compass already) it should work just fine. You're right though, to get altitude by satellites alone you need 4 or more.
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bflentje
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PostPosted: Thu Apr 24, 2008 9:47 am    Post subject: Reply with quote

LucidOndine wrote:
Assuming you've calibrated your barometer (which I hope anyone with a CSx model has calibrated both barometer and digital compass already) it should work just fine. You're right though, to get altitude by satellites alone you need 4 or more.


In response to calibrations... I believe that doesn't mean just the first time out. You have to calibrate both frequently to be accurate.
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Pear Head
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PostPosted: Thu Apr 24, 2008 9:51 am    Post subject: Reply with quote

Arcticabn wrote:
Pear Head wrote:
spinowner wrote:
Altitude is determined strictly by satellite signals in exactly the same way that latitude and longitude are determined.


In the CSx models I believe it's determined by barometer.


This is incorrect. In order for a barometer to work correctly it has to be calibrated initially for the location it is at. That is why when an airplane flies it sets the barometer for takeoff and when it gets to its destination it is provided the barometric pressure at ground level there.

It take a minimum of 3 sats to get lat/long and a min of 4 sats to get elevation.


This is incorrect.

Read the users manual:

http://www8.garmin.com/manuals/GPSMAP76CSx_OwnersManual.pdf

For the 76CSx it's on page 37, under "Calibrating the Altimeter":

Quote:
Because the GPSMAP76CSx relies on the barometric pressure to determine the elevation and the pressure at any elevation can fluctuate, calibrate the altimeter to increase its accuracy.


On units without a barometer it does use a satellite fix to determine altitude, although this method is actually less accurate than a pressure fix (that's why those with the "S" model of Garmins paid more for the pressure sensor).
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Marsha and Silent Bob
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PostPosted: Thu Apr 24, 2008 11:29 am    Post subject: Reply with quote

Pear Head wrote:
On units without a barometer it does use a satellite fix to determine altitude, although this method is actually less accurate than a pressure fix (that's why those with the "S" model of Garmins paid more for the pressure sensor).

If you ever plot your tracks with altitude from a GPS that uses the sats for altitude, you will notice large (100s of feet) fluctuations in altitude over the course of several miles.
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