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Old 01-29-2014
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Is it useless: NMEA2000 In-line terminator

I just received a bundled Garmin GWS-10 (wind sensor) / GMI-20 (display head), and have a question for folks experienced in NMEA 2000 about the in-line terminator.

In the following diagram an "in-line terminator" is used as a junction between the GWS10 wind sensor and the backbone cable:




What does this do? I buzzed it out with a multimeter and found absolutely no resistance across the pins. It seems to be a direct feed-through for signal and power.

Why can't I just connect the backbone cable directly to the instrument? (The connectors mate just fine.)

The only reason I can think to use the in-line terminator is that it provides some strain relief, but it's a little bulky to mount at the masthead if it's not critical. I have other cables (vhf, anchor light) that will require strain-relief as well, so I figured I'd use 1 clamp to provide strain relief for all the masthead cables.

I'd appreciate insight as to whether or not this thing is really needed.
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Old 01-29-2014
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Re: Is it useless: NMEA2000 In-line terminator

Each end of your network must be terminated to work properly. I would doubt that Garmin or any other nmea2000 manufacturer would specify one if it was not needed.

Exactly how did you test it? Between pins on opposite ends or across pins on the same end?
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Re: Is it useless: NMEA2000 In-line terminator

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Originally Posted by Tim R. View Post
Each end of your network must be terminated to work properly. I would doubt that Garmin or any other nmea2000 manufacturer would specify one if it was not needed.

Exactly how did you test it? Between pins on opposite ends or across pins on the same end?
I tested all 5 pins across opposite ends of the terminator. Unless the resistance is really, really low, (say around 0.1 ohms which is below the sensitivity of my digital multimeter), I'm pretty sure this piece does nothing. I don't have the equipment to check for capacitance, inductance, nor do I believe there are any fuses, internal chips, or circuitry inside this little piece of plastic

I suspect that the true network termination (whatever that really means) occurs at the sensor (GWS10). However, since the NMEA2000 specification states that all networks must be terminated, I suspect this device was generated simply to conform to that language of the specification.

I will set up the network here at home and test it both ways. Unless someone else knows better and chimes in.

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Re: Is it useless: NMEA2000 In-line terminator

There should be a resistance of 60 ohms. Try testing between the pins at the end where the wind sensor connects.

Have you tested an end terminator. Which pins provide the specified resistance?
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Re: Is it useless: NMEA2000 In-line terminator

Quote:
Originally Posted by Tim R. View Post
There should be a resistance of 60 ohms. Try testing between the pins at the end where the wind sensor connects.

Have you tested an end terminator. Which pins provide the specified resistance?
Thank you! You pointed me in the right direction.

Across the network connections pin 4 (data hi) and pin 5 (data lo) in the diagram below there is a resistance of approx 120 ohms in both the end terminator and the in-line terminal.



Now that I can see that it's doing something, it'll get installed. What's one more hole drilled into my mast anyway..
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