Onderwerp: Ultrasoon snelheidssensor Airmar ST900/950

I am happy to report that Airmar is now finally shipping the long awaited ST900/950 ultrasonic speed sensor (for either NMEA0183 or NMEA 2000 output). Reading the updated Airmar brochure PDF it sounds all very well and seems especially suited to high speed motorboats. What was even more interesting though was another new paddle-less electromagnetic speed sensor oriented to racing and high-end sailboats, which will be on the market in just a few months. I wasn't the only one impressed as the DX900+ MultiLog won the DAME electronics and software category award. Airmar was confident enough to let me speak to the three French engineers who developed it. It's always a good sign if a company lets you talk directly to the engineers behind the product.

The first thing I liked is that it adapts existing technology to a new use. The core of this same sensor has been used in the fishing market for years to monitor trawls. The sensors are mounted on the net ends because the fishermen want to keep the mesh square so that the trawl has the optimal size and strength, and thus they must measure sideways as well as forward speed. The beauty for sailors is that the DX900+ can measure leeway directly, instead of inferring it from the difference between speed through water and speed over ground. As the sensor is fully symmetrical it can even measure reverse speeds accurately. It's been tested in non-saline waters as well as sea water. It also contains a fast response temperature sensor (I think it's the fifth metal surface you see) and a three-axis accelerometer and gyroscope, outputting heel and trim. Since the technology measures in the boundary layer it does require some calibration, but the engineers have found that one point calibration is good enough for all but high end racing conditions.

Another DX900+ advantage over a paddle wheel speed sensor is its sturdiness. The four speed measuring pins stick out of the epoxy core about 1 mm or so, to ensure a good bond of the epoxy to the alloy. Since they are bonded in completely it should survive being covered by a sling when hauling the boat (it's also retractable), or flotsam passing by whilst sailing.

There will be three models, one with speed and temperature outputting via NMEA 0183, and two with depth, speed and temperature and either 0183 or 2000 output. The latter include a small interface box. All three are calibrated using an application from your smartphone or tablet, and the BlueTooth connection can also be used to view the data. Software updates will be possible using this method as well.

Zou het kunnen zijn dat in bovenstaand plaatje van henkvd ( die van Panbo komt) de 4 metalen kruiselings meten? Dan kun jenk ik daarmee wel verlijering meten?
www.panbo.com/archives/2016/11...ar_and_signal_k.html

Of dat EM log gaat aanslaan in de zeilracerij zal leren of het beter is.

Beide systemen (looptijd en frequency shift) bestaan. Het laatste meetprincipe maakt gebruik van het dopplereffect. Beide meetprincipes gebruiken ultrasone signalen.

Looptijd principe:




Doppler principe:


Nu (ook voor mij inmiddels) de vraag wat Airmar gebruikt.

Edit: En het antwoord staat volgens mij gewoon in de folder:
...Het Transit Time principe dus (en niet het Doppler effect - hoewel dat volgens mij gecombineerd zou kunnen worden: de frequentie van de pulsetreintjes zal ook verschuiven).