E classic GPS position selection logic

[lotharjt]

Hello, I have a dual E120 installation with a network switch, DSM300 and a S3G course computer pilot. It appears that the plotter is receiving GPS position data from the RS125 sensor via either Seatalk1 or view the NMEA 0183 output from the pilot. Short of tracing the wires, can I tell via the menu selections at the plotter?

I've also noted that the GPS sensor page at the plotter never shows any status info at all, all fields are blank. So I'm wondering what that means.


And now, I've recently added a third party Class B AIS. The AIS data is interfaced tot he NMEA port of the slave plotter. Everything is working fine in display of AIS data but I have noticed that with the AIS on, the plotter appears to be using the GPS position from the AIS, as that position data is also on the NMEA output from the AIS.

So, it appears the plotter will select in a priority scheme which input port it looks at for GPS position data, true? What is that scheme? The net results seems to be that I now have some redundancy built into my installation. The AIS position will be used if available and if that fails, then the RS125 data will be used.

Oh, I should also say that when the AIS is on, the GPS status page does show some data, HDOP, Fix status, Lat - Long position but no satellite status.

Thanks in advance.

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum Lothar,

Q1. It appears that the plotter is receiving GPS position data from the RS125 sensor via either Seatalk1 or view the NMEA 0183 output from the pilot. Short of tracing the wires, can I tell via the menu selections at the plotter?,

A1. Should the Raystar 125 GPS Sensor be interfaced to the system via SeaTalk, then the SeaTalk devices list (MENU->SYSTEM DIAGNOSTICS->EXTERNAL INTERFACES->SEATALK->DEVICES) would list this GPS Sensor. As this command sometimes produces a partial list of SeaTalk devices, it is recommended that it be executed a few times and that each time that the list be inspected for the Raystar 125 GPS Sensor.

Should the Raystar 125 GPS Sensor be interfaced to the MFD via its Port 1 (NMEA 0183_, then changing the MFD's Port 1 setting from its present setting to any other setting would temporarily break communications via the port and should trigger the MFD to report NO GPS after about three minutes. One ill advised practice for interfacing a GPS sensor support 4800 BAUD communications was to interface it to the NMEA 0183 input port of an autopilot to then permit the autopilot to bridge the GPS data to SeaTalk. Switching OFF power to the autopilot and then determining whether the system reported loss of GPS FIX would be a means of determining whether a GPS sensor may have been interfaced to the autopilot course computer.

Other than these suggestions, it can only be advised that the wires be traced.

Q2. I've also noted that the GPS sensor page at the plotter never shows any status info at all, all fields are blank. So I'm wondering what that means.

A2. See the response above concerning how a GPS sensor may have been interfaced to the autopilot's NMEA 0183 input port. In such cases, the autopilot would often not bridge GPS satellite and date/time information.

Q3. So, it appears the plotter will select in a priority scheme which input port it looks at for GPS position data, true? What is that scheme? The net results seems to be that I now have some redundancy built into my installation. The AIS position will be used if available and if that fails, then the RS125 data will be used.

A3. Products of this generation are not designed to support integration with more than one source of system data (i.e. GPS, depth, wind, speed through water, time, etc.). Should the system be interfaced to more than one such source, then it should either be disconnected from the system or a physical switch should be installed to control whether data will or will not be transmitted to the Raymarine system.

Unfortunately, it is often necessary to trace connections between the electronics which have been installed onboard in order to ascertain how they have been interfaced to the system. Maintaining a system diagram of the marine electronics systems, as well as the vessel other circuits and systems is considered a best practice. The assistance a Certified Raymarine Installer may be of value in creating such a system diagram.

[lotharjt]

All good info and background. Thanks Chuck. And I concur, a system diagram is gold in today's complex systems.

[Chuck - Raymarine - Moderator]

You're welcome.