Instrument grounding leads

[Battson]

Hello Dynon support,

I have been installing the D120 harness and I have a couple of questions about the three instrument grounding leads.

With a Ray Allen Comany servo for trim, I see the three position display wires go to the a GP input wire, 5V excitation, and ground. Does this ground need to be an instrument ground or would airframe ground be acceptable?

With those sensors which are highly sensitive to the earth voltage, should I ground them where they are mounted or should I isolate their mount and connect them to instrument ground?

 

[Dynon]

Airframe ground is acceptable for the Ray Allen.

 

[Dynon]

So the one that is most sensitive to ground is the oil temperature on lycoming/continental setups, and you can't easily isolate it. So, then, the ground path between the engine and the negative side of the electrical system (battery, as well as other avionics and electrical loads) is what really matters. In metal aircraft, it's usually not an issue, but it can be if the motor or avionics is isolated from the rest of the aircraft in any aircraft construction type.

 

[Battson]

Ok thanks - that's good to know. Would connecting and instrument ground to the oil temperature sensor help improve that situation, or will the other ground-path prevail (through the engine case)?

So, I have a Bearhawk (tube fuselage) and I will be remote mounting the pressure sensors to avoid vibrations, as directed. This will have to be done with rubber hose and adle clamps, there is also paint on the tube which is another dielectric.
Should I be running those 3 instrument ground wires into the engine bay for connecting to the instrument cases to improve the grounding?
I guess I'm not clear what those instrument grounding wires should be used with on my 6 cyl Lycoming install with the full Dynon instrument set. 

So the one that is most sensitive to ground is the oil temperature on lycoming/continental setups, and you can't easily isolate it. So, then, the ground path between the engine and the negative side of the electrical system (battery, as well as other avionics and electrical loads) is what really matters. In metal aircraft, it's usually not an issue, but it can be if the motor or avionics is isolated from the rest of the aircraft in any aircraft construction type.

 

[Dynon]

Adding an additional small wire between the oil temp sensor and the instrument won't make a difference (and can actually have detrimental effects if your other ground paths go bad, which would cause the wire to carry more current than it should. Essentially, the main ground path prevails (and matters), and there needs to not be potential (voltage difference) between the engine, the battery, avionics, etc.

On the pressure sensors: If you have the newer Kavlico style (active sensors), use the ground wires from EMS harness. If you're using the older style, ground the case (its ground) of the sensor locally.

 

[Battson]

Thanks for the clarification, I have the new pressure sensors and will ground then using the wires on the harness as directed.

Should I insulate those pressure sensors from the airframe ground so the EMS ground is the dominant path?

 

[Dynon]

The sensor case isn't ground on the Kavlico sensors, so the ground wire is all that matters there.

 

[Battson]

Thanks for clarifying that.