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birger75

B&g h5000 motion sensor spec

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Anyone know the accuracy on this sensor, it’s not specified on their website. Just thinking, I get reliable heel and pitch data from my Maretron ssc220 compass. So what is the best sensor to correct twa

/B

 

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I don't believe they've ever published a spec. Without understanding the whole data flow, from sensor accuracy and bandwidth to sampling rate and number of bits, to algorithm loop rate and math precision, the individual numbers actually don't tell you much. That's made worse when the data flows across something like a CAN bus, and introduces more sampling and delay uncertainty and more data formatting conversions.

I can't find any documentation for the SSC220, but the SSC200 (discontinued) and the SSC300 only output heading, roll & pitch angles and yaw rate. The Motion module also generates roll & pitch angles plus roll, pitch & yaw rates (but no heading). B&G doesn't document which of those they use to stabilize their wind triangle computations.

To the best of my knowledge, there is no NMEA2000 standard for exchanging 3D rates, only rate-of-turn, so getting the information the H5000 wants isn't possible from a standard product offered by the likes of Maretron, etc. There have been a variety of work arounds for this in the past with H2000 and WTP systems that are a bit more open than the H5000. If you have an H5000 and want the best wind information, I believe you need to stick with the Motion.

Nice mess, huh?

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Take a look at the websocket on the H5000.

Was looking today for other reasons, recall that precision is multiple (4?) decimal, accuracy ? 

A few minutes dockside with a bubble level, ruler and some large friends would answer. 

The heading sensor (Precision-9) only claims 2 degree & You need at least Hercules level software for it to be used.

 The effective accuracy in terms of correcting TWS and TWA would also depend on accuracy of the lever arms.

While it may know the mast height, it doesn’t ask the X,Y,Z offset from mast base/datum , or centers of bouyancy and gravity or which masthead wand.

 

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Expedition,

I've always found that heading accuracy loss due to roll is the result of soft iron issues, not the heading unit. The real problem is that there's no way to do a 3D spin for compensation. Have you found that replacing a heading unit with another brand has lessened the problems with heading vs. roll?

LR,

XYZ offset are usually inputs to the IMU, not the instrumentation system, and they have fairly negligible effects in the grand scheme of things. Can't decipher your comments on precision, which has nothing to do with accuracy.

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13 hours ago, Moonduster said:

LR,

XYZ offset are usually inputs to the IMU, not the instrumentation system, and they have fairly negligible effects in the grand scheme of things. Can't decipher your comments on precision, which has nothing to do with accuracy.

Agreed on precision not having much to do with accuracy in a formal sense, (statistical repeatability vs mean offset) though to the user, both are important, especially if the precision is affected by any hysteresis vs strictly random.  I was surprised to see that the readings were displayed to 4 decimals, which implied a sensitivity greater than I would have expected. No idea what the integral and differential linearity is, hence comment on bubble level and friends to evaluate. 

Correcting out the motion of the masthead, you can decide it's essentially a 1-D problem due to the mast height >> any practical offset location of the Inertial unit near the mast base, though to be more accurate you would want to characterize the observed sensor motion and determine the effective center of motion, then correcting to the location/motion of the MHU.  

My sensor is about 1 meter behind mast,  1 meter outboard and 0.5 meter above mast step, with a ~16 meter arm on the MHU. 

 Roll/pitch/yaw will track, but knowing where the boat/mast will pivot would be needed to describe the linear motion of the masthead. 

Most sloops will have a center of motion somewhere near the mast base/keel root. 

 

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What are they trying to do with these inputs?  I have seen where some systems correct for the wind measurements with heel measurements, then correct the heading for leeway, then updraft using wind speed and direction along with boat speed.  All this to get wind direction, basically a single term. Fine from a theoretical standpoint but good luck measuring these things independently.  Updraft dominates, leeway is opposite to updraft and almost impossible to measure, and heel vs wind direction is small but I guess easily calculated.  But all of these errors are due to the wind. In other words, the wind causes the boat to heel.  The wind causes leeway, and obviously the wind causes the updraft errors.  Why not just characterize everything vs wind inputs and leave out these other noisy data terms and things that cannot be measured.  One linearization equation instead of three or four.

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