NMEA Network

[s/v Jedi]

Originally Posted by colemj

I'm led to believe that the Airmar transducers accept and keep an offset locally.

They do. Sensors have become smart. Soon our transducers will have web servers where we can calibrate, look at statistics of data collected etc. etc.

ciao!
Nick.

[MarkSF]

I'd love to be able to interrogate my wind sensor from home. See if it's worth driving over there to go sailing!

[CarinaPDX]

I stand corrected. I looked at the brochure and the user manual (downloaded yesterday) and there was no reference to a calibration input PGN or any calibration procedure. On second look, the brochure lists only the output PGNs, and the user manual doesn't have any mention of PGNs at all. However, the output of the depth clearly includes the offset (the speed is not so clear). So where did you get a reference guide for this? I am interested as I would like to put the calibrations into the sensors of my system. I have an ST850 Speed/temp sensor and a P79 depth sounder. None of the documentation I have for either one has any mention of calibration.

BTW one way to read the N2K data is to use Airmar's Weathercaster (free download from site). This (Windows) software includes the latest firmware updates for Airmar's weather stations, and can be used to update their other N2K sensors' firmware as well. It works with the Actisense N2K-USB bridge.

[MarkSF]

Originally Posted by CarinaPDX

I stand corrected. I looked at the brochure and the user manual (downloaded yesterday) and there was no reference to a calibration input PGN or any calibration procedure. On second look, the brochure lists only the output PGNs, and the user manual doesn't have any mention of PGNs at all. However, the output of the depth clearly includes the offset (the speed is not so clear). So where did you get a reference guide for this? I am interested as I would like to put the calibrations into the sensors of my system. I have an ST850 Speed/temp sensor and a P79 depth sounder. None of the documentation I have for either one has any mention of calibration.

BTW one way to read the N2K data is to use Airmar's Weathercaster (free download from site). This (Windows) software includes the latest firmware updates for Airmar's weather stations, and can be used to update their other N2K sensors' firmware as well. It works with the Actisense N2K-USB bridge.

Here you go. I stumbled across it when looking for info. See pages 23 to 25 for the paddle speed stuff.

http://www.airmartechnology.com/uplo...serlManual.pdf

[CarinaPDX]

First, thank you MarkSF for the manual. Now give me a second for the vertigo to end...

The manual covers the 200 series products, not the 800 series that we have been discussing, but it seems likely that they have the same or similar firmware. The 2010 date would indicate that it is current thinking at Airmar. Of course it is marked "Proprietary and Confidential" for a reason - it is certainly not info for the novice. The info of interest is located in Airmar proprietary PGNs protected by access level control. We probably shouldn't be doing this, so let's slog ahead.

The calibration for the depth sounder is for the Speed of Sound in water used to calculate the depth. The speed differs based on salinity and I suspect this is for correcting salt water vs. fresh water. There is no keel offset function that I can find in the document, so for the depth info I will return to my earlier statement: keel offset must be done in the MFD.

The speed calibration described is a piece-wise linear calibration. While it is possible to manually calibrate the knotmeter using these PGNs and a computer and N2K bridge, it would be preferable to use purpose-built software if one could find it. There is a PGN for gathering the raw data (pulses/sec) that could be used to collect the pulse rate for each GPS speed, then graphed and fit with the appropriate piece-wise linear "curve". This is pretty cool, but not something that many users could do manually. Press ahead if you like - it would make me a bit nervous though. The typical user calibration is simply a multiplier, and again I have to conclude that this should be in the MFD.

There is a simple temperature offset available as well.

I checked out the Lowrance manual and agree that the only calibrations are found by selecting the device list. Have you tried to calibrate depth? I would be interested in knowing if that calibration is an offset in the MFD or the speed-of-sound in the sensor. I am not surprised that Lowrance is not supporting the sensor's proprietary calibration, but they should have offered a scaling correction. I find it a little hard to get excited by an offset for the temperature, but what the h... Lowrance seems to be coming up short.

What is interesting is that the Simrad MFDs do have depth and temperature offsets as well as a speed calibration (which appears to be a multiplier). Simrad is in the same Navico portfolio as Lowrance; the difference is that Simrad tailors their products for ocean sailors and Lowrance for fishermen. Along these lines my old Lowrance digital depth sounder lacked keel offset, to my continued annoyance. Apparently not needed for fishing boats?

I just checked and my Furuno NN3D does have keel offset, speed correction, and temperature offset.

If I were in your shoes I guess I would either return the Lowrance if possible, and maybe get a Simrad unit. Or work out how to calibrate the sensor directly. Otherwise the lack of calibration would drive me crazy(ier).

[CarinaPDX]

Apparently the Maretron DSM250 display with firmware 1.4.9 or newer can calibrate the DST800.

[MarkSF]

Apparently the 200 and 800 are pretty similar, as the 800 is actually recognised and described as a 200 by the chartplotter.

[CarinaPDX]

That is good confirmation. BTW somewhere I ran into a reference by Airmar to displays that support their proprietary calibration system. So it seems that they are providing the calibration software routine to display vendors, presumably at a price. It seems that is included in the Maretron agreement, but the only manual I found for the DSM250 was for v.1.4.8, which is prior to the agreement. It would be nice to know which other displays support this calibration. Maybe I should start working on a manual approach...

[s/v Jedi]

Originally Posted by CarinaPDX

Apparently the Maretron DSM250 display with firmware 1.4.9 or newer can calibrate the DST800.

I think it was on page 1 that I wrote that...

I disagree that it is better to have the displays do the calibration offsets and multipliers locally, because it means that every single display must be configured fir every calibeation of every sensor and every change made for that. The risk of error is huge.

When I enter the offset for transducer depth, I want that active on all displays incl. the little ones in the cockpit and incl. on the connected computer with nav software.

The weakness of N2K is that they did not standarize this.

ciao!
Nick.

[CarinaPDX]

Agreed that it would be best to make a single calibration to the sensor rather than applying corrections at each display - seems rather obvious. The problem here is how to accomplish that. The DST800 has a powerful speed calibration, but there seem to be few displays capable of supporting it. I am not of a mind to buy another display. One could get one's tail in a knot trying to do it manually. Still, I might try once the engine is in. I have not been able to identify a depth offset function, so a keel offset would have to be done in the display (unless someone finds something I missed - always possible). I'm not going to lose any sleep over the temperature calibration...

But I am losing sleep now, so off to bed...

[CarinaPDX]

Oh, and this is only one of many things that the standard failed to spec. As I said earlier, how about a standard method of updating firmware? But the failings of N2K would need a whole web site to handle...

[s/v Jedi]

Originally Posted by CarinaPDX

Agreed that it would be best to make a single calibration to the sensor rather than applying corrections at each display - seems rather obvious. The problem here is how to accomplish that. The DST800 has a powerful speed calibration, but there seem to be few displays capable of supporting it. I am not of a mind to buy another display. One could get one's tail in a knot trying to do it manually. Still, I might try once the engine is in. I have not been able to identify a depth offset function, so a keel offset would have to be done in the display (unless someone finds something I missed - always possible). I'm not going to lose any sleep over the temperature calibration...

But I am losing sleep now, so off to bed...

For other readers, it should be clear that any display supports calibrated sendors; the discussion is about which displays support performing that calibration.

My view is a simple one: frak the manufacturers that only care to support their own (branded) sensors, or hold agenda's that are not in line with their customers interests. Consumers should choose to buy equipment from manufacturers that try to bring good, innovative products that will integrate with gear from other manufacturers and help make life easier for consumers. Supporting the calibration in Airmar and Maretron sensors should be obvious. Supporting a standard like N2K should also be obvious, yet there is still much trouble with AIS over N2K and the excuses have been invalidated years ago (yes you Simrad, Furuno etc.!)

For all that is wrong with boat electronics, NMEA is not on top of that list IMHO.

ciao!
Nick.

[colemj]

Again, I set the Airmar DT800 keel offset using the Simrad autopilot control head and that offset appears on the Furuno MFD and the computer charting program with no further work. It also appears as a property of the Airmar transducer itself when I poll the transducer with Maretron and Actisense software.

I am led to believe that this offset value resides locally in the Airmar transducer and not just in the MFD that set it.

Mark

[DotDun]

FWIW, I started a new thread to discuss what's wrong with N2K....


http://www.cruisersforum.com/forums/...tml#post876618

[MarkSF]

Originally Posted by CarinaPDX

That is good confirmation. BTW somewhere I ran into a reference by Airmar to displays that support their proprietary calibration system. So it seems that they are providing the calibration software routine to display vendors, presumably at a price. It seems that is included in the Maretron agreement, but the only manual I found for the DSM250 was for v.1.4.8, which is prior to the agreement. It would be nice to know which other displays support this calibration. Maybe I should start working on a manual approach...

I would be quite interested in seeing that reference. I would like to make sure that my NEXT display will perform the calibration!