Engine monitoring via NMEA 2000 (N2K) and an ActiSense EMU-1

[geoffschultz]

My boat, BlueJacket, was struck by lightning while on the hard in Guatemala. I'm in the process of replacing just about everything electrical on it, which includes installing B&G autopilot system, which is NMEA 2000 based. While I'm at it, I want to monitor the engine oil pressure, temp, etc on the MFD, so I'm looking at using an ActiSense EMU-1 to do this. Note that the engine is a Yanmar 3JH series, which is about 20 years old.

I still want to have my analog gauges at the helm, but according manual (http://www.actisense.com/products/nmea-2000/emu-1/download-emu-1), if you're going to use the gauges, you should attach the wires from the EMU-1 to the gauges instead of at the engine sensors. It's highly problematic to do that. If you're just monitoring via the EMU-1, you can connect directly at the sensors.

I'm trying to figure out what the difference is as it would be much easier for me to monitor directly at the sensors. Any help understanding this would be greatly appreciated.

-- Geoff

 

[joker460]

I used http://nolandeng.com/rs11.php which can read off existing gauges.

 

[Gunni]

I had the MBW Tech engine monitor installed on my 4JH3E. EM2000. Couldn't have been easier, it just plugs up to your engine harness and pulls the sensor signals off to your digital system. Gauges and alarms all still work. What you may find is that some of your sensors are yes/no alarm and do not give gradient data (temp, pressure). Pricey but a nice upgrade. I get lots of system voltage data to my helm.

 

[LeslieTroyer]

+1 on the noland RS11 - If you want to read the sensor directly without a gauge you need to flip a software switch so the RS11 provides the current. I have one on my (early) Universal M25, I really like it. I kept my water temp gauge, added a dual-oil pressure sensor/switch - The switch goes in the old analog circuit, pressure sensor drives the RS11 directly.

Les

 

[geoffschultz]

While the MBW sounds nice, I don't want to spend another $200 for the luxury of just hooking into the harness. I'm just trying to understand what the difference is between measuring the sender output (oil pressure & coolant temp) at the sender or the gauge.

-- Geoff

 

[LeslieTroyer]

It might have to do with their automatic detection of gauge existence.

The EMU-1 can be connected in parallel to existing gauges or as a replacement for some or all of the gauges. The EMU-1 automatically detects whether a gauge is present or not and configures itself to provide a current feed to the sender where required.​

 

[geoffschultz]

It might have to do with their automatic detection of gauge existence.

The EMU-1 can be connected in parallel to existing gauges or as a replacement for some or all of the gauges. The EMU-1 automatically detects whether a gauge is present or not and configures itself to provide a current feed to the sender where required.​

Thanks, but I know this. I'm simply trying to figure out why I have to attach the EMU-1 within 2 meters of the gauges vs connecting it at the sender units. For physical placement and wire routing, it would be much better for me to grab the data right from the senders rather than at the engine panel.

 

[dlochner]

Thanks, but I know this. I'm simply trying to figure out why I have to attach the EMU-1 within 2 meters of the gauges vs connecting it at the sender units.

I am treading at the very edge of my knowledge of electronics here, so don't take this as gospel.

When electrical signals are sent through wires a bunch of stuff happens besides the electrons zipping along. First there is wire resistance, the signal will decay over the length of the wire. Another is impedance, which is sort of like resistance, but has to do with the magnetic fields generated by the signals passing through the wire. This is why phone cables are twisted pairs, to reduce the impedance. Wires may also act like antennas picking up additional electrical noise that would distort the signal. On an engine, the alternator and regulator would be at the top of the list, followed by an electric fuel pump.

Any of these could degrade the signal from the sending unit and affect the readings on the gauges and for the NMEA coupling. Some electrical engineer with more knowledge than I, figured out that 2 meters is the sweet spot, shorter is OK, longer affects the signal quality.