Computer Compass Accuracy

[lucca brassi]

How it is with yours compasses on diving computer , how accuracy are ?

Six iPhones tested, and they can't agree on magnetic north

IMO : computer should not use hall sensor for magnetic field but gyroscope ( i don't know what they really use )

 

[Skulmoski]

Good question; I don't know how accurate my Suunto is and I have not compared its performance with verified accurate compass.

However, I rely mostly on headings in order to find my way to the exit point. So, often follow reciprocal or square patterns. It does not matter to me if the Out pattern takes a 30 or 40 degree heading; I just adjust for 180 degrees.

Regards

GJS

 

[Phil_C]

Provided I have calibrated it the compass on my Cobalt dive computer works fine, and if anything seems less affected by metal objects nearby than my wrist mounted 'traditional' compass.

We did a navigation exercise yesterday where we dropped in off a boat about 700 metres off shore and followed a bearing back to a point on the shore (the dive centre). We surfaced about 40-50 metres from the target, not bad considering we had a slight cross current. I had both my Cobalt and a manual Suunto, was checking both, and they both kept to track fine.

Phil.

 

[RonR]

They technology of small electro-mechanical sensors of all types has been improving incredibly rapidly in recent years.

The electronic compass we put into the Cobalt 1 years back was slow to respond, and probably only accurate to within 5° or so. The current Cobalt 2 compass is fully integrated with the accelerometer in one chip and we reliably get 1° accuracy- note that this is fully 360° tilt compensated, which an analog compass would not be. This is consistent with what the chip manufacturer specifies they see in military applications, where they are used extensively. It is a magnetic sensor. I believe the latest version of these sensors are (depending on the interface and implementation, of course) superior to traditional compasses, if only because they aren’t affected by tilt. But they also respond more rapidly to course changes, can display digital headings, and provide multiple (90°, 120°, 180°) heading offsets.

The iPhone is not a fair comparison, as the implementation is more for general orientation and entertainment, not really navigation. And it isn’t (not mine, anyway) fully tilt compensated.

I do question the article’s methods for testing- the photo shows two iPhones on either side of a magnetic compass- of course the iPhone’s compass would be deflected by the magnet in close proximity. But there is a lot of engineering and firmware behind making an accurate electronic compass, sensors do differ, and it’s very likely that this is not a priority for Apple.

-Ron

 

[Phil_C]

Hi Ron, I'd agree about the accuracy, and be perfectly happy to rely on the Cobalt alone based on what I saw yesterday. It was certainly quicker to settle to the bearing than the analogue one was and less affected by metal distractions.

Yesterdays dive wasn't planned to check the compasses, it was to challenge the student I had with me - by profession he is a soldier from a commando unit and teaches military navigation, and rather (over) confident in his navigation on the usual exercises, so I took him off shore with a sideways current drift and set him a real challenge.

He did well - and I used the opportunity to test the various features of the Cobalt 2 compass against the analogue one.

Now we just need to get GPS to work under water without a towed surface antenna buoy and I will be a truly happy puppy

Phil

 

[dmaziuk]

Now we just need to get GPS to work under water without a towed surface antenna buoy and I will be a truly happy puppy

The accelerometers and gyros are evolving too, they're now often the same chip as the magnetometer. As do CPUs meaning you can potentially run better path fitting algorithms. I think the ratio computers might already have dead reckoning path logging and GPS fix on the endpoints -- or at least their glossy sales brochure says the hardware's there. Once it becomes commonplace it could get "good enough" in very few years.

 

[lucca brassi]

Well when i open that thread i have in my mind my compass Suunto SK7 , lenovo shot z90 phone and asus tablet ASUS ZENPAD S 8 580
with android 5.1 on my desk in my DIY electronic workshop at home.
SK7 shows right direction but in other case both androids devices were confused ...... i have also in my mind those projects
Project Ariadna - the personal underwater navigation technology , Karst Worlds: Underwater cave-mapping sensor ,
also i know that could in correct angle in android compass , but still...

it is known that compass don't work in cave very well (cavers says so ... depends also from geological structure of the caves ) but also wrecks spoil magnetic field.

In other case gyro ( MEMS gyroscope ) should be very accurate and hold position independent from magnetic fields , wrecks....and other anomalies . But should be orientated to north ( with hall ?? ) or in direction you need
In other case hall effect sensor compass ( HES ) senses every near magnetic field .

 

[CapNemo]

My Oceanic OCS's electronic compass seems to be very accurate, and is easy to set both outward and reciprocal headings. I did once question its accuracy on a dive where it seemed to constantly show the same bearing as if it was stuck... however I soon realised that was because my Sunnto analogue compass was cradled alongside it and was disturbing the magnetic field. If you have doubts check it against a trusted analogue compass (and possibly recalibrate), but as stated do not place them in too close a proximity to one another.

 

[lucca brassi]

 

[Jax]

How it is with yours compasses on diving computer , how accuracy are ?

Six iPhones tested, and they can't agree on magnetic north

IMO : computer should not use hall sensor for magnetic field but gyroscope ( i don't know what they really use )

Phones don't use magnetic north, AFAIK. They use GPS and make calculations from that.

Compasses in dive equipment use magnetic north. One should re-calibrate at every dive location. Also, one should input the proper magnetic declination for the location. It is ~10.5 degrees east in SE AZ. It is about 8 degrees east in NW Florida. It is less on the east coast of Florida.

Great site: Magnetic Declination (Variation) | ngdc.noaa.gov

And when it comes down to it, all the compass is at the moment a direction indicator, a point of reference. As long as the point of reference stays steady, the rest doesn't matter.