Magnetic vs Electronic Compass

[tinped]

Thanks Tanglewood for the great post. Interesting how the poster who feels he knows so much, invents a word called "gps maps". Thought I was going to have to reopen my books

 

[Northern Spy]

You're right, I miss-spoke. I meant some sort of electronic compass.

Or maybe you meant Transmitting Heading Device. (THD).

 

[Seevee]

Thanks Tanglewood for the great post. Interesting how the poster who feels he knows so much, invents a word called "gps maps". Thought I was going to have to reopen my books

Tinped,

I'm sure you're referring to me so I'll respond.
Sorry I speak with confusing terms, and it is confusing.
Gps Map is a term, you might call it made up, but it's printed right on the face of most of Garmin's chart plotters.... guess they made it up.

But, chart plotter is probably a better term in marine use. They also use the term gps map, multifunction display (MFD), and perhaps others. The same type of box in aviation is called an MFD, flight deck, Gsp nav/com, and in the automotive they are called GPS or GPS navigation.... and then the manufacturers add their own names....

They all have one thing in common. They all have a GPS (or Glonass) and a map, and they are all used basically for the same purpose... to get from one point to another.

I'll try to use the term Chart Plotter for marine use. Sorry for the confusion.

 

[danderer]

Silly question: What is a rate compass? Is that a fluxgate with some form of integrated AHRS?

Not exactly. Here is an excerpt from the Simrad Autopilot Compass Manual.

"The Simrad Rate Compass is in principle a combination of a solid state rate sensor and a fluxgate sensor, where the rate sensor is slaved to the fluxgate sensor.

The extract from the Simrad manual makes it sound to me like a rate compass is indeed a fluxgate with some form of integrated AHRS. What is the difference/subtlety that I'm missing?

Not arguing, just still unclear.

 

[twistedtree]

The extract from the Simrad manual makes it sound to me like a rate compass is indeed a fluxgate with some form of integrated AHRS. What is the difference/subtlety that I'm missing?

Not arguing, just still unclear.

I think it's just got accelerometers so it can better detect rate of turn, heave, pitch, roll. And probably give a more stable heading.

 

[LarryM]

The extract from the Simrad manual makes it sound to me like a rate compass is indeed a fluxgate with some form of integrated AHRS. What is the difference/subtlety that I'm missing?

Not arguing, just still unclear.

As I looked at this again, I think you are right, there is an AHRS (Attitude Heading and Reference System) or AHRS-Like feature in a marine Rate Compass. I was only taking into account the NMEA sentences from the compass that I have seen used by autopilots, chartplotters, radars etc., which is limited to Heading and sometimes Rate of Turn. When I examined the available information transmitted by the Rate Compass, I found the following:

Over a NMEA 0183 Interface
HDG Heading, Deviation, and Variation
ROT Rate of Turn

Over a NMEA 2000 Interface
PGN 127250 Vessel Heading
PGN 127257 Attitude (Pitch and Roll)
PGN 127251 Rate of Turn

That is 3-axis AHRS in my book. I do believe your initial post was correct, and stand corrected, thanks for the good catch

 

[danderer]

Thanks for helping me understand. So now I've learned two new terms recently: "rate compass" and "allision". Cool.