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Old 11-09-2021, 14:48   #76
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Re: Wind Instrument

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Originally Posted by Tehani View Post
And do not think that this lasts a long time, there can be a delay of 1-2mS from the reception of each NMEA0183 sentence until the complete transmission in its NMEA2000 equivalent with the applied calibration.
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And do not think that this lasts a long time, there can be a delay of 1-2mS from the reception of each NMEA0183 sentence until the complete transmission in its NMEA2000 equivalent with the applied calibration.
I think one of the issues with the CV7 is that it has corrections inside it's circuit board that are applied during calibration and saved in non-volatile memory. These are not the calculations to compute the TWD and TWS but to correct for velocity, angle, etc. The problem is that the network device which receives the signals from the CVB7 would need to be able to set those corrections and therefore would have to have the UI and programming to do so. OP alludes to this being an issue.
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Old 11-09-2021, 15:42   #77
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Re: Wind Instrument

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Originally Posted by wingssail View Post
I think one of the issues with the CV7 is that it has corrections inside it's circuit board that are applied during calibration and saved in non-volatile memory. These are not the calculations to compute the TWD and TWS but to correct for velocity, angle, etc. The problem is that the network device which receives the signals from the CVB7 would need to be able to set those corrections and therefore would have to have the UI and programming to do so. OP alludes to this being an issue.
Interesting manual and solution:

https://r-p-r.co.uk/downloads/windsy...Manual-CV7.pdf

From it it can be deduced that the CV7 output data is always in raw format (without processing) on RS422 / NMEA0183.

Then we have the options of digital conversion to NMEA2000, without calibration (Windyplug box) and with fine calibration (CANBUS-RM box).

And sine / cosine analog conversions for use with Raymarine and B&G instruments with the optional STBG module.
As stated in the manual, if this STBG module is used, the calibration is carried out by the Raymarine or B&G device.
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Old 11-09-2021, 15:53   #78
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Re: Wind Instrument

I like this topic but it is too late here in Spain.
I hope you are here tomorrow too ...
Good Night.
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Old 11-09-2021, 16:12   #79
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Re: Wind Instrument

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Originally Posted by Tehani View Post
Interesting manual and solution:

https://r-p-r.co.uk/downloads/windsy...Manual-CV7.pdf

From it it can be deduced that the CV7 output data is always in raw format (without processing) on RS422 / NMEA0183.

Then we have the options of digital conversion to NMEA2000, without calibration (Windyplug box) and with fine calibration (CANBUS-RM box).

And sine / cosine analog conversions for use with Raymarine and B&G instruments with the optional STBG module.
As stated in the manual, if this STBG module is used, the calibration is carried out by the Raymarine or B&G device.
Yes, Interesting manual. Reading it we see that the only fine adjustment is the mast head alignment which, in the case of B&G displays, is set by pressing a couple of buttons on the STBG module which are then remembered by the CV7 (or STBG). So it is raw data with the mast head alignment correction applied which is delivered to the display system. Further calibration would apparently be made in the B&G system according to the manual. That is not surprising, my B&G Hercules system works that way. I wonder where OP got the idea it could not be calibrated by B&G. The wiring diagram shows the output of the STBG module going right to the B&G MHU connectors. So the B&G system must think its got a B&G MHU. Right? It should be able to apply calibration adjustments same as with any B&G MHU.

If the accuracy, precision, and speed are as advertised, there is no reason not to use this with a B&G system, or Ray Marine or any other of the ones listed as compatible.
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Old 11-09-2021, 19:59   #80
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Re: Wind Instrument

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Can bus is not derived From RS422

Can bus has indeed a low level protocol on top of an electrical interface

Rs232 and RS422 is just a electrical interface

As a result NMEA 0183 has virtually no ability to error check or Re transit , but can has several low level data integrity checks.

As a 30 year embedded system engineer I’ve never heard the term
“ electrical protocol “ used. The correct term would be electrical interface
The protocol is the metaphysical aspect and the interface the physical connection.

The basic difference is RS232 requires 3 wires, positive, negative and earth. Rhe RS 422 and 485 are two wire systems.

The difference between 422 and 485 is in the transceiver chip. RS-422 can be either a talker, such as a GPS putting NMEA 0183 or a listener, an autopilot receiving NMEA 0183 sentences, it's usually not both. It's a one way system whereas RS-485 is a two way system and each device can be both a talker and a listener whatever the tranceiver chip decides.
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Old 11-09-2021, 22:29   #81
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Re: Wind Instrument

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The protocol is the metaphysical aspect and the interface the physical connection.

The basic difference is RS232 requires 3 wires, positive, negative and earth. Rhe RS 422 and 485 are two wire systems.

The difference between 422 and 485 is in the transceiver chip. RS-422 can be either a talker, such as a GPS putting NMEA 0183 or a listener, an autopilot receiving NMEA 0183 sentences, it's usually not both. It's a one way system whereas RS-485 is a two way system and each device can be both a talker and a listener whatever the tranceiver chip decides.
I’m just jumping in here without knowing the context of this, but I designed many circuits around these interfaces and can tell for sure that:

- RS232 is a single ended transmission line: there is one signal conductor and one ground conductor, i.e. Tx and Gnd or Rx and Gnd.

- RS422 is a double ended or differential, not referenced to ground, i.e. Tx+ and Tx- or Rx+ and Rx-.

Both use a shield as well. This means that a typical full duplex RS-232 only has 4 conductors: Tx, Rx, Gnd, Shield while a RS-422 has 5 conductors: Tx+, Tx-, Rx+, Rx-, Shield. The Tx and Rx pairs should be twisted, which creates a solid medium for transmission over long distances. Also, opto isolation is very easy.
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Old 11-09-2021, 23:06   #82
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Re: Wind Instrument

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Originally Posted by RaymondR View Post
The protocol is the metaphysical aspect and the interface the physical connection.

The basic difference is RS232 requires 3 wires, positive, negative and earth. Rhe RS 422 and 485 are two wire systems.

The difference between 422 and 485 is in the transceiver chip. RS-422 can be either a talker, such as a GPS putting NMEA 0183 or a listener, an autopilot receiving NMEA 0183 sentences, it's usually not both. It's a one way system whereas RS-485 is a two way system and each device can be both a talker and a listener whatever the tranceiver chip decides.
Why are you bringing rs-485 into the picture? Neither nmea0183 or n2k is based on it.
The practical difference between rs232 and rs422 is that 422 is a differential signal, so the two data lines are marked + and - and the signal state is the difference between these. Rs232 uses a signal line with a ground reference. Still two lines. 422 is more resilient to noise.
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Old 12-09-2021, 01:29   #83
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Re: Wind Instrument

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Why are you bringing rs-485 into the picture? Neither nmea0183 or n2k is based on it.
The practical difference between rs232 and rs422 is that 422 is a differential signal, so the two data lines are marked + and - and the signal state is the difference between these. Rs232 uses a signal line with a ground reference. Still two lines. 422 is more resilient to noise.
RS 422 and 485 are solely physical layer specs, CAN and it's descendant N2K add a software layer.

RS-232 being referenced to ground you don't actually need the third wire as it's inferred that all devices have a 0 volt ground.
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Old 12-09-2021, 02:13   #84
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Re: Wind Instrument

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RS 422 and 485 are solely physical layer specs, CAN and it's descendant N2K add a software layer.

RS-232 being referenced to ground you don't actually need the third wire as it's inferred that all devices have a 0 volt ground.
Maybe it's a language issue, but you are really misstating what these standards reference. The CAN bus, which Nmea 2000 is layered on, has absolutely nothing to do with rs232 or 422 or 485. It is a completely different animal at the hardware level.
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Old 12-09-2021, 06:27   #85
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Re: Wind Instrument

I think we're getting caught up in a pretty sterile discussion ...
In any case, abundant and good documentation of these standards can be found on the internet.

At this point, I think it is interesting to take a look at the history of the methods that the most well-known manufacturers have used in the last 30-35 years:

Raymarine: Implemented the Seatalk1. It is not electrically compatible with any standard, but it was a great advance in connecting different devices (receivers / transmitters) to a single data wire referenced to ground. It uses voltage levels of 0-12v, with 0v being the dominant value, and 12v (logical 1) the recessive value. In this way collisions are not dangerous, each device "listens" to its own transmission, and if it does not match, it retries after a few mS. This concept is similar to the current CAN BUS and there is no master device.
Seatalk uses 9 bits for each asynchronous transfer, which also makes it similar to the "multiprocessor" method used in some RS485 networks, but used differently. Here, the ninth bit indicates the start of the message when it is equal to 1. The length of data in a stream is variable, but always very short.

RS485 networks:
They are electrically sensitive to collisions (There are serious problems if two devices "talk" at the same time). That is why there must be a "master" device that establishes control on the network.
B&G and Simrad: They have evolved using different data structures (Fastnet, Robnet, Robnet2), on a RS485 physical support forming a network. The identification of the devices (number) is assigned by the one we call "processor" and who is the master.
Here you have a very interesting link about B&G fastnet:
https://www.oppedijk.com/bandg/fastnet.html

NKE also uses RS485 on its "topline" network. I have not investigated the protocol in depth yet.

All this has been prior to the implementation of CAN BUS and NMEA2000.
In both RS485 and RS422 it is possible to electrically isolate the devices because there is no "0" reference.
The galvanic isolation in NMEA2000 has been done in another way: The network drivers (understand buffer chips, etc.) are fed from the network. If they also consume little energy and are not connected to anything else (Displays, sensors, etc.), they also take all the power from the N2k network. This is not the case with MFDs, APs, Radios and AIS; these devices consume a lot of energy and must be powered separately. In these cases there is internal isolation between the power supply of the network chip drivers and the rest of the electronics in these devices. (If anyone is interested, I can give the references of quite a few specialized chips).
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Old 12-09-2021, 07:55   #86
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Re: Wind Instrument

All this is well known, but when we talk about the design of a product, the engineer seeks that it is good and sufficient for the function to be performed, and also that its implementation is as cheap as possible.

Years ago, CPUs were expensive and required a lot of additional circuitry. Stowe Robertson, B&G and others chose to bring analog signals directly to a single central computer. B&G still provides that option with its analog inputs.
In this way, one sensor can be isolated from another. But only partially because there is only one internal A / D converter for the sensor array.

The option offered by other sensor manufacturers is to carry out this conversion work in a distributed way, and individually on each sensor, then using an individual RS422 channel with opto-isolation, which is a very safe and cheap way using current microcontrollers. This is the case of LCJ-Capteurs, ADVANSEA, NASA, VDO and others. Some in NMEA0183 format, and others in proprietary format.
The NMEA0183 option is a good way to make devices compatible with other manufacturers.

I find it interesting to study in depth the need and how a wind sensor should be calibrated.
Everyone knows that sails create turbulence around them, which alters the angle and speed reading, and is different for each angle and wind speed. That is minimized by separating the sensor as much as possible, but it may not be enough for some. I do not know B&G products as a user, and I would like to know how the calibration is done because I think it must be difficult to do it right. (Where should you put a calibrated reference sensor?)

As a simple sailor, I often trust small variations in heel and rudder force more than I do instantaneous reading of the wind. As an engineer I am interested in how the devices perform the calibration task.
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Old 12-09-2021, 08:54   #87
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Wind Instrument

The drop cable length isn’t a function of voltage drop by the way it’s a function of signal propagation timing and the way CAN bus does collision and bus arbitration. In reality the 6m is very conservative for a 250 KB/s CAN system that NNEA 2000 uses. you’d get away with 12m drops in reality
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Old 12-09-2021, 09:06   #88
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Re: Wind Instrument

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I really really want to have valid true wind data.

Anyone have any advice?
You can install a high end system but between upwash, shear and gradient it's impossible to really know. We've experienced shear where the top of the main sets to starboard and the bottom sets to port. Granted that's extreme but it happens to some degree all the time. And just because the MHU reads 10 knots doesn't mean the wind speed at other elevations will be 10 knots.

I think the best you can do is know your target boat speeds for the wind your MHU indicates and try to sail to them. Do you need the very best MHU to achieve this? IDK but suspect the very best system is no better then any other system unless you want to spend hours upon hours calibrating. I certainly don't want to invest the time and energy to develop downwind upwash correction tables. I would rather go scuba diving or hiking.
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Old 12-09-2021, 09:36   #89
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Re: Wind Instrument

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Originally Posted by Tehani View Post
...I find it interesting to study in depth the need and how a wind sensor should be calibrated.
Everyone knows that sails create turbulence around them, which alters the angle and speed reading, and is different for each angle and wind speed. That is minimized by separating the sensor as much as possible, but it may not be enough for some. I do not know B&G products as a user, and I would like to know how the calibration is done because I think it must be difficult to do it right. (Where should you put a calibrated reference sensor?)

As a B&G user, (not a professional or very sophisticated one, just a sailor), what I observe is that the adjustments to angle and speed readings because of turbulence, angle of heel, and wind speeds, etc, are performed in software in the B&G CPU or Performance CPU, not in the sensors. This is what makes some sensors a special issue when connected to a B&G display system. There is not sufficient UI or options in the B&G display system to send calibration commands to the sensor (such as alignment for the CV7) although the fastnet protocal would seem to provide the flexibility and capability if B&G decided to implement the various commands.

B&G has spent years developing the algorithms to do this.


As a simple sailor, I often trust small variations in heel and rudder force more than I do instantaneous reading of the wind. As an engineer I am interested in how the devices perform the calibration task.

Of course I also sail as much by the seat of my pants as I do by the instruments. However at the top end of the sport the skippers and tacticians rely on very precise pieces of information to make their tactical decisions.
In this video (if you can bear the tiresomeness of it) you will hear the guy (I think he is "steve") who is holding a tablet with displays from the B&G system and feeding information to Terry Hutchinson, the tactician. For example you will hear frequent phrases such as "4,5" meaning how many minutes to each layline, upwind or downwind. This is dependent on accurate and precise true wind information in addition to accurate and precise polars and current actual performance.

Top end racers find this essential and pay plenty for that level of information. The OP apparently wants this level also.

On my boat we make a feeble attempt to do this, but it requires a very talented tactician and very good instrument information, and we have weakness in both areas, so we do more by the seat of our pants. However I am in the process of upgrading my system to get better data.
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Old 12-09-2021, 11:16   #90
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Re: Wind Instrument

We never could get our old Raymarine wind speed gauge calibrated. But, we found if we took the recorded speed, and multiplied it times two, it was pretty close. I found I could live with that.
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