Paddle wheel sensors - what is ouput?

dgadee

dgadee

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There have been a few posts about paddle wheel sensors, but I'm a bit lost about how they operate. I have a Nexus Server on my boat (from a decade ago) which is no longer used (the wind sensor always seemed to be knackered and then the multidisplay went). I put in a new depth sensor and display which is not connected to the Nexus Server, but didn't bother about speed since I always just use SOG from the gps.

I have no interest in complex navigation systems onboard (which is what the Nexus Server was). However, I still have the paddle wheel in the hull and am wondering whether to remove it and fill in the hole or whether it would function external to the Nexus Server. Would this paddle wheel sender send out pulses which can be counted or does it send out NMEA sentences? Is there some way I could take output and wireless/input it to a PC or tablet?

My understanding is that most of these paddle wheel sensors were made by one manufacturer (Airmar). I have not been able to find any technical information on how they operate.
 
It will send out nominally squarewave pulses related to the speed the paddle is turning and the magnet on the wheel is flipping past the sensor. Usually around 20,000 pulses per mile I think.

I'm sure you could process the signal. Perhaps even my standard ST60 could transmit the speed derived from the paddlewheel over the Seatalk bus and it could then be converted to NMEA but I've never tried that. I am sure there will be paddlewheel to NMEA purpose-built converters available if you Google it. Once it's converted to NMEA then the wifi bit is easy with another gizmo :)

Richard
 
Thanks for that. Just looked for converters and they seem to work the other way around (so that GPS output can be fed in as pulses). Maybe take out the sender and fill in the hole is the best idea - the simplest, certainly.
 
dgadee said:
Thanks for that. Just looked for converters and they seem to work the other way around (so that GPS output can be fed in as pulses). Maybe take out the sender and fill in the hole is the best idea - the simplest, certainly.
Click to expand...

Indeed. I just looked and there are pulse to NMEA converters but they seem to be designed for large ships and accept very low pulse rates. Probably horrendously expensive. :(

Richard
 
just came across this log speed wiring diagram in case anyone i interested now or from a google later.. Looks similar to my ST40 but with the green and screen wires swapped.
So you should be able to tee off into an arduino to get speed data without having to hack into seatalk somehow??

VEvvf3A.png
 
Depth is frequency of response or length of response? Not quite sure what I am looking at.
 
GHA said:
On a raymarine st40 speed looks like this.. (about 0.8Kt, last of the tide)
29VmTkT.png


and depth like this...(About 3.5m below the sensor)
i3i7fQy.png
Click to expand...
Do we know what happens at a standstill - would the speed trace still give an indication of whether the transducer’s working or not?

Guessing the pulses get further and further apart ‘til were at a steady DC. Would we be expecting a steady High, so a steady Low indicates a fault?

Am working with an electromagnetic log, so there’s no paddlewheel you can flick to simulate boat speed.

(Hoping the picture will be visible - it wasn't until I started the reply.)

Cheers
 
Problem with these - usually comes down to physical size of the through hull - not its output.

I have a cracked Echopilot Speed log - not the mount - its the actual log item itself ..

I have a new Nasa Dual unit in box - and was hoping I could just swap out the log ... but they are different diameters. Which would mean removal and reducing the through hull hole to fit the Nasa unit.

I have also noticed that some paddle wheels have two magnets - each 180 deg oposed. While others have only the one. The cable and plug may differ as well ...

They don't make it easy !!
 
Yes, that's the one RivalRedwing, only mine's the blue box one with the simulated paddle pulse output.

They certainly don’t make it easy Refueler! Changing to the NASA transducer had to replace hull fitting of course, chissling away rock hard sealant on the old one. Now it’s just a case of getting the EM log and Raymarine display to play nicely together.

So tricky narrowing down faults when there’s multiple units that all need work and interface properly.
 
Hi Roger Jolly ....

Don't know what image provider you are using - but every image you post is RED X and not seen.

I used to use Photobucket - still pay the sub because I have a huge archive there and it would be a real work-up to get all back again ... and downloads come back as tiny files instead of the high res I uploaded.
For forums etc. - I now use IMGUR ... but I see that recently they changed the upload sequence ... now its a pain ... but the link system is still good.
 
Refueler said:
Hi Roger Jolly ....

Don't know what image provider you are using - but every image you post is RED X and not seen.

I used to use Photobucket - still pay the sub because I have a huge archive there and it would be a real work-up to get all back again ... and downloads come back as tiny files instead of the high res I uploaded.
For forums etc. - I now use IMGUR ... but I see that recently they changed the upload sequence ... now its a pain ... but the link system is still good.
Click to expand...
Hi Refueler

I was just quoting ‘GHA’ from further up the thread.

As mentioned in previous post, when I was writing the post, with the quote, I could see the image. As soon as I posted, the image changed to red cross.

Seems like the picture is on IMGUR:

https://imgur.com/VEvvf3A

So not sure what’s going on here. Does it need to be flagged up as a problem somewhere?
 
...well, above image appeared automatically on posting, replacing the image address text that I typed in (having got the URL from GHA's post, using right-click > 'Copy Link Address'.)
 
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