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[CA] [CA11] EV-1 Sensor ROT Data - Printable Version

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[CA11] EV-1 Sensor ROT Data - rsqunit - 06-04-18 01:18 AM

In addition to the RayMarine MFDs, I also use an iPad with iNavX. It gets NMEA 0183 data from a wireless gateway from Yacht Devices.

While doing some testing, I see that the EV-1 is sending ROT data ranging from -2.8° to +2.5°... that's over a 5° range. The ROT data changes frequently (every second at least) and falls somewhere within this range.

Here's the issue... the boat is stationary on the dock!

Why would the EV-1 be reporting that large of an ROT range on a non-moving boat?

In order to ensure this was not an issue with the wireless gateway and translation to NMEA 0183, I also captured raw NMEA 2000 PGNs and the data in those packets matches the info provided by the wireless gateway.

EV-1 is running firmware version 2.18, which is the latest. All other RayMarine components also updated to the latest firmware.

Attaching network design in case it helps figure this out.

Image showing the deviation info on the p70s:

Video 1: This is the ROT on the Master Axiom Pro 12 RVX (v 3.4.66) - Notice how the ROT changes very rapidly:

Video 2: This is the ROT on the Slave Axiom Pro 12 RVX (v 3.4.66)- Notice how the ROT changes less rapidly than on Master. Next I move the camera to the i70s, configured to show ROT. Notice how it stays at 0. STRANGE!

The numbers on the iNavx app change like the numbers on the slave MFD.

Any ideas on how to troubleshoot this further?


RE: [CA11] EV-1 Sensor ROT Data - Chuck - Raymarine - Moderator - 06-06-18 09:12 AM


I have verified the reported behavior within the Data Master MFD both a system running MFDs with LightHouse II v19.03 software as well as a system with MFDs running LightHouse 3 v3.4.66. The EV-1/EV-2 CCU transmit ROT data in units of degrees per second and is displayed as this on the i70/i70S instruments and p70/p70S/p70R/p70RS autopilot control heads. In contrast, LightHouse II v19.03 and LightHouse 3 v3.4.x software are both displaying ROT in units of degrees per minute. Our examination of the EV-1/EV-2 hardware verified that it was producing a static yaw rate of +/- 0.04 Degrees per second (2.4 degrees per minute (almost exactly the same as reported issue)). The problem here is the difference in displayed units by the Raymarine products rather than an issue with the EV-1/EV-2 ROT data. A static noise floor of 0.04 degrees / second is deemed reasonable for the types of rate sensing components components used within the EV-1 CCU.

A feature change request will be submitted to consider use of degrees per second units for roll, pitch, and yaw rate data items displayed within LightHouse 3 software. If using a third party monitoring application, you may want to determine whether the units used in displaying ROT data may be changed to degrees per second.

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RE: [CA11] EV-1 Sensor ROT Data - rsqunit - 06-06-18 11:15 AM


Thank you for the details. It all makes complete sense that based on that level of accuracy (+/- 0.04° per second) the units will be displaying data that is changing fast if they are displaying degrees per minute from the degrees per second data. :-)

However, I don't think having the MFD display degrees per second is the right answer. I don't think the i70/i70S instruments and p70/p70S/p70R/p70RS control heads should display degrees per second either.

Based on all the information I have seen, it appears the rate of turn standard is degrees per minute. Example:

Displaying degrees per second would be contrary to the established standard (if we can call it a standard).

I can see the benefit of faster data (degrees per second), but as we already know... if the MFD or other units are simply doing the math to convert to degrees per minute (degrees per second * 60 seconds), given the +/- 0.04° per second accuracy, then we can get +/- 2.4° as we are seeing, which is bad.

I see two options (maybe there are more):

Option 1. Have the MFDs and other units round the rate of turn per second data to the nearest 0.1° then do the math to convert to minutes for display purposes. This would take into account accuracy of +/- 0.04° "issue" and provide a more "stable" number.

If you think about it, even though you said the i70/i70S instruments and p70/p70S/p70R/p70RS heads are displaying degrees per second, they are only displaying to 1 decimal place (nearest 0.1), which is why we don't see the +/- 0.04° noise does not affect it.

Of course, this introduces the issue that the best you will ever display is 6° per minute.

Option 2. Have the EV-1 report in degrees per minute instead of degrees per second and have the displays (MFDs, and display heads) all display degrees per minute.

Doing this on the EV-1 would probably give more accurate data, and this has the benefit of having non-RayMarine equipment understand the data as per an established "Rate of Turn Per Minute" value.

Thanks again for the follow-up Chuck!

RE: [CA11] EV-1 Sensor ROT Data - Chuck - Raymarine - Moderator - 06-06-18 12:45 PM


Thanks for your additional input on this subject. For very large power drive displacement vessels (note that the SOLAS requirement that you have referenced is for vessels having displacements of 50,000 gross tons or greater) having slow ROT, units expressing amount of angle turned per minute may be more meaningful. Others such as myself, who are owners of highly maneuverable vessels such as planing hulls and sailing craft, find ROT data expressing amount of angle turned per second to be of far greater value. I believe that the NMEA 2000 standard expects that ROT will be transmitted in radians per second and the EV-1 / EV-2 CCUs appear to adhere to the that standard. That said, your comments have been noted according.

RE: [CA11] EV-1 Sensor ROT Data - rsqunit - 06-06-18 02:40 PM

Thank you Chuck. I'm trying to understand the NMEA standards better and every reference I have found is to NMEA 0183. They all say degrees per minute. I have read no less than 10 references on this.

For my knowledge, are you able to point me to any docs that talk about about the NMEA 2000 standard and it being degrees per second?

Thanks again. I really appreciate your thoroughness.

RE: [CA11] EV-1 Sensor ROT Data - Chuck - Raymarine - Moderator - 06-06-18 03:59 PM


I couldn't locate units in the NMEA 2000 standard. I used a NMEA 2000 analyzer with Actisense NMEA Reader to inspect the data. Irrespective of what the standards use for communications of data, the recreational marine electronics are free to express data in whichever units the manufacturers deems most applicable to the needs of its customers.

RE: [CA11] EV-1 Sensor ROT Data - rsqunit - 06-06-18 04:17 PM

Thanks Chuck. I'll do some more research and post back what I find.

The nice thing about using a standard, such as NMEA 0183 or NMEA 2000, is interoperability across multiple vendor devices, so I'm sure the spec has to define this somewhere. :-)

One clear definition I did find, which does not apply to recreational vessels per se but is interesting nonetheless and makes a case for a standard unit, is Class A AIS transponders, which do need to report ROT in a specific manner and not as a particular vendor sees appropriate. Otherwise other ships would not have an understanding of the data being reported.

Anyway, thanks again. I'll post back there when I find out more.

RE: [CA11] EV-1 Sensor ROT Data - Chuck - Raymarine - Moderator - 06-07-18 08:06 AM