# Garmin external temp sensor



## Harold (Dec 23, 2003)

https://buy.garmin.com/shop/shop.do?pID=107335

check this little guy out!

also look at the compatibility list. Looks like a bunch of older models with ANT+ capability are getting updates to work with this unit. Oregons, Dakota 20, Rino 650, Montanas, eTrex 30, 62/78 series, and the new fenix

Lots of folks have wanted temp on their receivers - well here you go!


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## OneTimeCRX (Aug 7, 2008)

Looks cool, too bad it doesn't show any Edge units as being compatible. I've always wished that my Edge 305 had a temp sensor!


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## TobyGadd (Sep 9, 2009)

Cool. Thanks!


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## ghettocruiser (Jun 21, 2008)

OneTimeCRX said:


> Looks cool, too bad it doesn't show any Edge units as being compatible. I've always wished that my Edge 305 had a temp sensor!


The internal temperature reading of the Edge 500 is of suspect accuracy, since (1) it's enclosed in a black case in the sun (maybe I should have bought the silver one) and (2) I suspect the unit itself generates measurable internal heat as it operates.

It always reads a few degrees high, much more on sunny days.

I guess with a separate ANT+ sensor you could hide it under a seat or a seat bag. Or at least paint it white.


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## Harold (Dec 23, 2003)

OneTimeCRX said:


> Looks cool, too bad it doesn't show any Edge units as being compatible. I've always wished that my Edge 305 had a temp sensor!


The Edge 500 and 800 already have an onboard temp sensor. Only 3 Edge models are currently supported by Garmin, so you cannot reasonably expect them to issue updates for models that are no longer supported by bug fixes.


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## Harold (Dec 23, 2003)

ghettocruiser said:


> The internal temperature reading of the Edge 500 is of suspect accuracy, since (1) it's enclosed in a black case in the sun (maybe I should have bought the silver one) and (2) I suspect the unit itself generates measurable internal heat as it operates.
> 
> It always reads a few degrees high, much more on sunny days.
> 
> I guess with a separate ANT+ sensor you could hide it under a seat or a seat bag. Or at least paint it white.


Any temp sensor exposed to the sun is of suspect precision. High end weather instruments are almost always enclosed in a white ventilated housing to shield from the sun and reflect its energy away.

The accuracy, or repeatability, of those measurements is something else entirely. I find them to be pretty good, and with enough use, I can usually predict how far off they are. The temp sensor at my house is a good example. When it's not sunny, it's pretty good. When it's been baking in the sun all day, it seems as though it is about 5-6deg high.


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## ghettocruiser (Jun 21, 2008)

See I still get this wrong 20 years later. 

Wouldn't the instrument have high precision (since it always measures the temperature in the black case to one tenth of a degree and we think that's "right") but low accuracy (since the temperature in the the case is always 5 degrees higher than than the target parameter which is the ambient air temp?


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## Harold (Dec 23, 2003)

ghettocruiser said:


> See I still get this wrong 20 years later.
> 
> Wouldn't the instrument have high precision (since it always measures the temperature in the black case to one tenth of a degree and we think that's "right") but low accuracy (since the temperature in the the case is always 5 degrees higher than than the target parameter which is the ambient air temp?


no, you're right. I flipped the terms. I looked it up. accuracy is closeness to the "true" value and precision is the repeatability of the measurement.

at any rate, if the measuring device is consistently off, then I'm not terribly concerned if the margin is relatively small. In this case, it's useful for temp to be recorded along with other training data to see how performance changes with changes in temp so a super accurate measurement isn't too necessary.


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## OneTimeCRX (Aug 7, 2008)

I'm not so sure that you'd get high precision (repeatability) in this case either, since the device wouldn't be uniformly off - it would be highly dependent on the cloudiness of the weather, which is a variable that is not directly tied to the actual temperature.


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## ghettocruiser (Jun 21, 2008)

I'd still hit the thing with some white paint. What has been seen in 3rd year meteorology cannot be unseen.


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## Harold (Dec 23, 2003)

OneTimeCRX said:


> I'm not so sure that you'd get high precision (repeatability) in this case either, since the device wouldn't be uniformly off - it would be highly dependent on the cloudiness of the weather, which is a variable that is not directly tied to the actual temperature.


it is a variable that can be accounted for. If you wanted to be technical about it, you could very easily measure it. Take two temp sensors. Put one in the sun, and put the other under a deeply shaded canopy. temp differences can be recorded.

for additional improvement in prediction, you can measure variations in cloud coverage and how they affect the differences measured between temp sensors. you could do the same thing for the Edge models. put the edge outside in the sun and use an adequately shaded thermometer known to be accurate as the control.

with the external sensor, not a problem. put it in a pack (but not next to your bladder)


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## Diesel~ (Feb 17, 2008)

Where would you mount it? To one of the seat rails?

-D


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## Harold (Dec 23, 2003)

Diesel~ said:


> Where would you mount it? To one of the seat rails?
> 
> -D


should work fine in a pack. did you read where Garmin suggests where to put it?

It looks like a little oval thing that's sitting in a cradle/clip of some kind. I have a Garmin Chirp transmitter and it looks identical to that in shape, minus the cradle it's in (the chirp also has a little notch in the housing which looks like it would allow it to be clipped into the same housing). Which would make sense. It'll have a coin cell battery in the back and a little battery door. The chirp comes with a little velcro disc to attach it to things. This clip looks like it would easily attach to a pack strap.

And FYI, the battery in this chirp has been running for more than a year.

But do expect that if you're using this external sensor that it will reduce battery life in the handheld.


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