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Why does a compass have to be calibrated?


Insp Gadget
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Simple answer : the electronic sensor varies its output voltage according to where it is pointing. When the input voltage changes, you need to recalibrate so that it knows the processor knows the range of output voltage to expect.

 

If you don't recalibrate, it won't point correctly.

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Can someone explain why an electronic compass has to be calibrated every time you change the batteries?

Because, for reasons I have never understood, Garmin is too cheap to provide regulation to the compass chip, so the output of the chip varies with battery voltage. This problem still remains in current models after being there for quite a number of years.
What happens if you don't calibrate?
You get an error in the direction your compass is pointing. The error can be huge if the voltage has shifted much.
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Should I recalibrate the electronic compass built into my JEEP every time I replace the battery?

Only if you install a GM battery with side terminals. :P

 

Actually, I have them in my Jeeps and I have no idea on how to recalibrate them. :huh:

 

I think you press a button and then drive around in a circle! :P

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Should I recalibrate the electronic compass built into my JEEP every time I replace the battery?

Not sure if you're serious - but yes, that might be necessary. The electronic compass (dash or mirror) must be programmed with declination information. The auto manufacturers supply a map in the owner's manual to identify a magnetic 'zone' to account for the difference between magnetic and true north, give or take. If that data isn't being stored in flash memory (or some other sort of non-volatile memory), then it would need to be reprogrammed after power is lost. I have no idea what Chrysler/Jeep does in that regard.
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Should I recalibrate the electronic compass built into my JEEP every time I replace the battery?

Only if you install a GM battery with side terminals. :P

 

Actually, I have them in my Jeeps and I have no idea on how to recalibrate them. :huh:

 

I think you press a button and then drive around in a circle! :P

 

Odd, but true. According to Dodge (on my Ram '11 hemi)...

 

Compass calibration

This compass is self calibrating which eliminates the need to manually set the compass. When the vehicle is new, the compass may appear erratic and the CAL symbol will be displayed. Complete three 360 degree turns in an area free from large metal or metallic objects in not less than 48 seconds. The CAL symbol will turn off and the compass will function normally.

 

Manual compass calibration

If the compass appears erratic and the CAL symbol does not appear, you must manually put the compass into the Calibration Mode. To put into a calibration mode: turn on the ignition and set the display to comp/temp. While pressing the US/metric button, press the comp/temp button for at least 10 seconds until the cal symbol appears. Release both buttons and complete three 360 degree turns in an area free from large metal objects in not less than 48 seconds. The cal symbol will turn off and the compass will function normally.

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I have a Garmin 62s and I calibrated the compass when I first powered it up. I've replaced the batteries many times since then and have never re-calibrated anything. The compass works fine. Who says you have to re-calibrate the compass at every battery change?

Did you check against a good magnetic compass to verify that the direction it is pointing to doesn't change?

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I have a Garmin 62s and I calibrated the compass when I first powered it up. I've replaced the batteries many times since then and have never re-calibrated anything. The compass works fine. Who says you have to re-calibrate the compass at every battery change?

Did you check against a good magnetic compass to verify that the direction it is pointing to doesn't change?

I have the compass calibrated to true north and, for geocaching purposes, east is still east and south is still south, nothing has changed between battery replacements.

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Should I recalibrate the electronic compass built into my JEEP every time I replace the battery?

Only if you install a GM battery with side terminals. :P

 

Actually, I have them in my Jeeps and I have no idea on how to recalibrate them. :huh:

 

I think you press a button and then drive around in a circle! :P

 

Odd, but true. According to Dodge (on my Ram '11 hemi)...

 

Compass calibration

This compass is self calibrating which eliminates the need to manually set the compass. When the vehicle is new, the compass may appear erratic and the CAL symbol will be displayed. Complete three 360 degree turns in an area free from large metal or metallic objects in not less than 48 seconds. The CAL symbol will turn off and the compass will function normally.

 

Manual compass calibration

If the compass appears erratic and the CAL symbol does not appear, you must manually put the compass into the Calibration Mode. To put into a calibration mode: turn on the ignition and set the display to comp/temp. While pressing the US/metric button, press the comp/temp button for at least 10 seconds until the cal symbol appears. Release both buttons and complete three 360 degree turns in an area free from large metal objects in not less than 48 seconds. The cal symbol will turn off and the compass will function normally.

Ok, I know the 3 circle tricky, two of my Grand Cherokees are like that, the third one has the indash nav and I think it uses the mag compass & odometer as sensors to dead recon when in parking structures and tunnels as the map still updates without a GPS signal. Better cal it out with some parking lot donuts :)

Edited by coggins
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I have a Garmin 62s and I calibrated the compass when I first powered it up. I've replaced the batteries many times since then and have never re-calibrated anything. The compass works fine. Who says you have to re-calibrate the compass at every battery change?

Did you check against a good magnetic compass to verify that the direction it is pointing to doesn't change?

I have the compass calibrated to true north and, for geocaching purposes, east is still east and south is still south, nothing has changed between battery replacements.

Answering your original question, Garmin says you should recalibrate the compass at every battery change. See page 13 of the owner's manual.

 

However, I have to admit that I don't bother with that myself with my Oregon 300. I find it good enough.

 

What batteries do you use? Some claim that they need less recalibration when using NiZn batteries due to its higher voltage.

Edited by Chrysalides
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I have a Garmin 62s and I calibrated the compass when I first powered it up. I've replaced the batteries many times since then and have never re-calibrated anything. The compass works fine. Who says you have to re-calibrate the compass at every battery change?

Did you check against a good magnetic compass to verify that the direction it is pointing to doesn't change?

I have the compass calibrated to true north and, for geocaching purposes, east is still east and south is still south, nothing has changed between battery replacements.

luvvinbird,

If you don't calibrate your compass, you may well find that it points approximately to magnetic north. (It's probably unlikely to be out by more than say 10 to 15 degrees or so.) If all you want to know is which way is north(ish), its probably fine. However, if you need to set a navigation course to (say) 27 degrees east of true north and walk that course for 5 km, you had better calibrate before heading off - or you could miss your destination by a couple of km!

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What batteries do you use? Some claim that they need less recalibration when using NiZn batteries due to its higher voltage.

Not sure if it's related but I noticed I needed to calibrate my compass less with NiMh batteries (1.2v) than with Alkaline (1.5v)!!

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What batteries do you use? Some claim that they need less recalibration when using NiZn batteries due to its higher voltage.

Not sure if it's related but I noticed I needed to calibrate my compass less with NiMh batteries (1.2v) than with Alkaline (1.5v)!!

I also use NiMh rechargeable batteries.

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Simple answer : the electronic sensor varies its output voltage according to where it is pointing. When the input voltage changes, you need to recalibrate so that it knows the processor knows the range of output voltage to expect.

 

If you don't recalibrate, it won't point correctly.

 

I've read this several times now and it's pretty much wrong.

 

An electronic ompass works with 2 (or sometimes 3) magnetometers. So it can detect a magnetic field along two or three axes.

 

See e.g. this device: klein_kompass_german_pin.gif

 

The two 8 pin chips on theleft and below are two magnetometers. And one is placed 90 degrees to the other to be able to measure two axes.

 

Now these two magnetometers output voltages in return to the magnetic field applied. Due to metal parts in the remaining device and due to limited absolute accuracy of such devices, you cannot determine the exact heading just from these two values. But once the device has been rotated and the CPU monitoring it has seen e.g. the max values returned by the magnetometers when each of them pointed exactly north/south, then the CPU is able to calculate the heading quite precise.

 

However, if the device is switched off, it usually looses the calibration data. Also after some time the sensors behavior may change as different battery voltage levels may cause different megnetic fields to be generated by other parts in your device etc etc ...

 

So it's not because they are supplying unregulated battery power directly to the chip.

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What batteries do you use? Some claim that they need less recalibration when using NiZn batteries due to its higher voltage.

It's not the higher voltage of the NiZn cells that avoids the problem .. it's the flat discharge profile that avoids it. Rather than slowly dropping in voltage, these puppies kinda fall off a cliff when depleted, but hold voltage very well during use. If you don't get voltage drift with use or when you replace depleted cells, you don't have compass issues. The voltage is similar to that of lithium cells. The only downside is that when that first bar drops on the display, you'd better have another pair of cells ready, because you have only a few minutes left!

 

The bad news is that PowerGenix never got enough traction in the consumer market to continue with their production of NiZn AA cells, and have reverted back to being exclusively a manufacturer of automotive batteries. Not sure if it was lack of marketing skills or marketing budget. I only found out about them by accident as it was. Before they stopped production, I invested in some more cells and a 2nd charger. They're still be available on Amazon, though, and the web page is still functional http://www.powergenix.com/?q=products

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What batteries do you use? Some claim that they need less recalibration when using NiZn batteries due to its higher voltage.

Not sure if it's related but I noticed I needed to calibrate my compass less with NiMh batteries (1.2v) than with Alkaline (1.5v)!!

That's because there's somewhat less 'margin for error' in NiMH that already start out at a very low voltage than there is with alkaline that can potentially drift all the way down from 1.5 to about 1.1 before the unit shuts down. Less voltage variation between fresh cells and depleted cells means less compass error. You'll find, of course, that the NiMH cells come off the charger a good bit hotter than the nominal 1.2V. 1.45 volts wouldn't be at all unusual. That drops down to something more reasonable pretty quickly in use in your GPS, but if you calibrate your unit with a 'hot' set of NiMH installed, you'll find yourself less accurate as they start to deplete. Edited by ecanderson
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As has been said, voltage levels/magnetic fields change with new batteries. I have Magellans and Garmins w/ 3-axis compass and many times no calibration is needed after a change.....if they read perfect, why bother. At other times after a change they are way off and must be calibrated.

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An electronic ompass works with 2 (or sometimes 3) magnetometers. So it can detect a magnetic field along two or three axes.

You will find that this device is replaced by a single chip in the GPS. Take a look at chips like the Honeywell HMC5843.

 

The data that is returned by the device you show depends upon a well regulated 5V (also not something you'll find in the GPS). So there's a bit of apples and oranges here.

 

Now these two magnetometers output voltages in return to the magnetic field applied.
Which is in turn delivered digitally to the GPS processor over an I2C bus using the part you show.

 

The problem is that the values created by pointing the device (both analog, and then converted to digital) are voltage dependent. If the input voltage is not well regulated, the output will vary. Take a look at the specs for the chip shown above. Note that while the device can be calibrated with an AVdd anywhere between 2.5V and 3.3V per the device specification, it must be regulated to avoid variation in the output signal.

 

9595317ba898bc2fcd52c778f94809e14c75ef0740fbcf7515d5adf158f65a196g.jpg

Edited by ecanderson
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I use the NiMH batteries in my Garmin 550T. I never recalabrate as it has ALWAYS been more than accurate enough for my purposes. I've checked it many times agaist my Silva compass and its always within a couple of degrees. I just checked it and my 550T was 1 degree off. The only reason I would ever recalibrate is if it was acting weird or I needed extreme percision (which you really cannot get with a GPS-in a case when I need extreme percision, I would use the site on my Silva compass). To get a reading any more accurate than a couple of degrees, you really need a compass with a site. My CO never needed recalabration either-but my 60CSX and all GPS before it did.

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The only reason I recalibrate mine is not due to the accuracy as I only use mine when near to a cache. The issue I have that it often complains about not holding it level (as it's 2 axis), but after calibration it doesn't complain so much.

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Should I recalibrate the electronic compass built into my JEEP every time I replace the battery?

Only if you install a GM battery with side terminals. :P

 

Actually, I have them in my Jeeps and I have no idea on how to recalibrate them. :huh:

 

I think you press a button and then drive around in a circle! :P

 

Maybe that's why Jeep invented this thing? :P

 

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With my Colorado 300, I definitely need to calibrate the compass with every battery change or it is almost 90 degrees off, I even often calibrate it one other time during a full day of use as the batteries run down. However with my Oregon 450, the calibration is much better and is accurate to within a couple degrees even after battery changes.

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However, if you need to set a navigation course to (say) 27 degrees east of true north and walk that course for 5 km, you had better calibrate before heading off - or you could miss your destination by a couple of km!

For that situation, I'll project a waypoint from my current position and navigate to it. Much easier and less error prone.

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My experience has been that when a gps compass is off calibration, it is way OFF! As in walking within .10 of a mile and it starts pointing 5 miles away or it can't figure out which way it wants to point you to walk. That way? No this way! that way, this way, even though you are keeping a steady pace.

 

I've never seen one be just kinda almost off. In the last few years most systems seem to do better. So, you can take your chances but personally I find calibration fun to do.

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I've read this several times now and it's pretty much wrong.

That was an excellent explanation, thank you for the correction.

Unfortunately, so was the correction. Without a regulated AVdd, there's no stable analog reference for the internals of the compass chip - whether calibration has been performed or not.
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However, if you need to set a navigation course to (say) 27 degrees east of true north and walk that course for 5 km, you had better calibrate before heading off - or you could miss your destination by a couple of km!

For that situation, I'll project a waypoint from my current position and navigate to it. Much easier and less error prone.

Having an accurately calibrated compass has the advantage that your GPS can effectively project a course line between your start point and your projected end point, and it will tell you how far off the course line you are - left or right - as you progress along the line.

 

E.g. suppose you are traversing some very heavily wooded country; you come to a clearing (or climb a tree), calibrate your compass, and project a course line to the next visible waypoint (e.g. a hilltop, shelter, or whatever), which you estimate might be about 2 km away (but it could easily be 1.5 km, or 2.5 km or ...). With a calibrated compass and using the course line feature, you can navigate across country, staying as close as practical to your projected course line, moving back on line after you have had to deviate to negotiate the terrain, and have a chance of coming up to your target. If your compass is not calibrated properly you could be several degrees off track, and end up missing your target by several hundred metres, which may make it impossible to find in heavy scrub.

 

All of the above may have zero relevance for navigation where you have full topo maps installed, or where you have accurate coordinates for all your waypoints (e.g. geocaching), but it can be vital in back-country hiking with limited topo mapping detail. Whatever works for your needs is fine.

Edited by julianh
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It's also very handy for caching. While standing still, you can shoot a bearing to the cache and sort out the best approach to the location. The more accurate the compass reading, the better idea you get. Backcountry caching is sometimes a whole lot more 'entertaining' than the urban variety when it comes to needing a heading.

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Should I recalibrate the electronic compass built into my JEEP every time I replace the battery?

Only if you install a GM battery with side terminals. :P

 

Actually, I have them in my Jeeps and I have no idea on how to recalibrate them. :huh:

 

I think you press a button and then drive around in a circle! :P

 

Odd, but true. According to Dodge (on my Ram '11 hemi)...

 

Compass calibration

This compass is self calibrating which eliminates the need to manually set the compass. When the vehicle is new, the compass may appear erratic and the CAL symbol will be displayed. Complete three 360 degree turns in an area free from large metal or metallic objects in not less than 48 seconds. The CAL symbol will turn off and the compass will function normally.

 

Manual compass calibration

If the compass appears erratic and the CAL symbol does not appear, you must manually put the compass into the Calibration Mode. To put into a calibration mode: turn on the ignition and set the display to comp/temp. While pressing the US/metric button, press the comp/temp button for at least 10 seconds until the cal symbol appears. Release both buttons and complete three 360 degree turns in an area free from large metal objects in not less than 48 seconds. The cal symbol will turn off and the compass will function normally.l1.jpg

Ok, I know the 3 circle tricky, two of my Grand Cherokees are like that, the third one has the indash nav and I think it uses the mag compass & odometer as sensors to dead recon when in parking structures and tunnels as the map still updates without a GPS signal. Better cal it out with some parking lot donuts :)

 

Lol there's some amazing info on here I get a feeling I'm gonna be learning a lot from this forum, thank god for the search feature hehe :)

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Lately, I am leaning towards a different take. A two axis sensor gives two voltages. To get a magnetic field, you convert the volts by making two field strength vectors and adding the two right angle vectors. There are two problems. Converting from hall effect volts to field strength is not linear. A curve needs to be generated by calibration. Second, the curve changes over time as sensor ages. I think saying calibrate with battery change has to do with time, not voltage. Much like changing smoke detector batteries at DST change has nothing to do with the sun's orbit.

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I think saying calibrate with battery change has to do with time, not voltage.

Except for the fact that it's an easily repeatable experiment. Charge 4 cells to same voltage. Load one pair of fresh cells. Calibrate immediately after loading. Use unit until cell voltage drops to some significantly lower level. Observe compass behaving very badly. Install second pair of fresh cells with same voltage as the original pair you installed. (All done over the course of one day). Compass behaves well.

 

It's a shame that PowerGenix got out of the consumer AA business with their NiZn cells. They have a VERY flat discharge profile, so there was little voltage drop over the course of using the cells to near depletion. I'll keep using the ones I bought (I stocked up when I heard they were ceasing production) until they're all toast some day. I NO LONGER calibrate my Oregon at all during the course of using these cells to a nearly depleted state. With NiMH or other battery chemistries, it was inevitable. It's been over a least a year since I starting using these and haven't calibrated since.

 

Without a well regulated voltage on the reference pin of the chip, one would expect this exact set of symptoms. I'm still astounded that I find this in newer units. It's easy enough to provide the necessary regulation for a few cents.

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I did the hall effect experiment in college. You pass a current through a doped semiconductor and the current splits into holes and electrons, which causes a voltage at right angles to the current. The voltage is proportional to current and field strength. So you need a known current source that is not dependant on voltage. I still think the battery voltage may be a red herring.

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