Edge 520 thermometer error

1209

The fix would be to do an offset calibration of the sensor. But there isn't any way to do that. The difference is always the same so the best you can do is know what the difference is and take it into account.

One thing that I noticed is that when I first start the 520, the temp is a bit higher than it should be but in about 10 to 15 minutes of being on, it seems to correct itself. Even if I have the computer sitting in my AC conditioned home it does this.

The fix would be to do an offset calibration of the sensor. But there isn't any way to do that. The difference is always the same so the best you can do is know what the difference is and take it into account.

That's very disappointing. I just purchased the Edge 520 and also noticed the recorded temperature showing for my ride on Strava is about 5C less than the actual outside temperature according to our Bureau of Meteorology. That's a very big difference and if its due to calibration of the sensor that's a QA issue in my opinion - should not be happening?

I believe the temperature sensing is there in order to compensate for the effect of temperature on the pressure sensing element. It really doesn't need to have a zero offset calibration for that. It is made available as a data field but the additional cost to make a calibration of each unit probably isn't worth it. The offset is constant so you can take that into account. I think it would be possible to allow the user to enter the offset value but that isn't something they did. Maybe if enough people asked they would do that.You can submit ideas here

I believe the temperature sensing is there in order to compensate for the effect of temperature on the pressure sensing element.

I don't think the Edges use the temperature to adjust barometric readings.

https://support.garmin.com/support/searchSupport/case.faces?caseId=%7B53d6ba60-e4d2-11de-d785-000000000000%7D

Yes, this is about the 500 but there is no positive indication that any of the Edges use the temperature to adjust the barometric readings.

It's not to adjust the barometric reading. The characteristics of the pressure sensing element vary with temperature and it is to compensate for that

http://www.additel.com/UploadFiles/WhitePaper/Why-Temperature-Compensation-Really-Matters-for-Pressure-Measurement.pdf.

It's not to adjust the barometric reading. The characteristics of the pressure sensing element vary with temperature and it is to compensate for that

http://www.additel.com/UploadFiles/WhitePaper/Why-Temperature-Compensation-Really-Matters-for-Pressure-Measurement.pdf.

???

Why wouldn't Garmin go all the way and correct the effect of temperature on the barometeric reading?

That link is talking about a 0.15% error at rather cold and hot temperatures.

That's small enough to ignore.

http://www.skybrary.aero/index.php/Altimeter_Temperature_Error_Correction

This seems to say a 4% difference in elevation reading per 10 ' C.

That's 80-100 times as large.

???
That link is talking about a 0.15% error at rather cold and hot temperatures.
That's small enough to ignore.

That link was probably not the best example. They made various types of industrial sensors. It is something I had found it with a quick search and used as an example that pressure sensors are compensated for temperature. The intergraded circuit sensors used in the Edge may have totally different characteristics. I really don’t know for sure. I found a few intergraded circuit pressures sensors and they all say temperature compensation is included.

???

Why wouldn't Garmin go all the way and correct the effect of temperature on the barometeric reading?

www.skybrary.aero/.../QUOTE]I think making that correction would be fairly complicated and it is something that isn’t done. Aircraft altimeters are not corrected. On cold days aircraft fly closer to the ground. The error correction discussed in your link is done by the pilots. That correction is only done when they are flying the minimum safe altitude for a segment. The correction is to fly at a higher altitude as per the altimeter making the actual altitude high enough. The correction is based on the temperature at the airport and they have charts showing the correction values for various temperatures.

Just to be clear. The correction is because the altitude vs pressure relationship is dependent on temperature. Altimeters are calibrated for a temperature of 20 C at sea level. There has been some discussion that temperature correction could be applied to compensate for changes in the temperature at the surface throughout the day. Or that going from inside a building to the outside results in an error. That is not the correct.. The correction is for the pressure to altitude relationship.

I think making that correction would be fairly complicated and it is something that isn’t done.

My point was that those errors may be much larger than the errors due to not temperture compensating the pressure guage.

The correction is easy.

https://allaboutairplanes.wordpress.com/2011/08/31/correction-formula-on-altimeters-in-cold-weather/

(The reason the chart is for colder temperatures is because pilots are more concerned with readings that are higher than accurate.)

I really don’t know for sure. I found a few intergraded circuit pressures sensors and they all say temperature compensation is included.

They don't necessarily allow the read-out of temperature but that could be the case.

Just to be clear. The correction is because the altitude vs pressure relationship is dependent on temperature. Altimeters are calibrated for a temperature of 20 C at sea level. There has been some discussion that temperature correction could be applied to compensate for changes in the temperature at the surface throughout the day. Or that going from inside a building to the outside results in an error. That is not the correct.. The correction is for the pressure to altitude relationship.

measured altitude = f(pressure, temperature)

The altimeters simplify things by assuming temperature is constant.

measured altitude = f(pressure)

This all goes back to the Garmin statement for the 500 that it is not temperature compensated. That can mean different things and there is confusion on what it does mean. I wanted to clarify what I think it means just for the benefit of the overall discussion.

The slope of the pressure/elevation curve is dependent on temperature. Altimeters are set up using the slope for what's called a standard day based on a temperature of 68 deg F at sea level. Pilots dial in a pressure setting that will result in the altimeter reading correctly when at the airport. When the airplane is in the air the altimeter reading will be correct if it is a standard day. If it is not a standard day the altimeter will read high or low. Correction for that error is what I believe Garmin is referring to.

There has been some discussion over the years that the temperature change when going from inside a building to outside affects the elevation reading and that is what they are referring too. That temperature change does not affect the elevation reading so it is not what Garmin is referring too.

I believe that the pressure sensor used in the Edge has a temperature sensor in order to compensate for the effect of temperature on the pressure sensing element. That temperature reading could be easily made available to the Edge. Or maybe the Edge actually makes the correction and needs the temp. If you want the air temperature it would make sense to measure it where the pressure is measured. I can't say for sure but it makes sense to me that is where the OAT reading comes from.