flickroll
Well Known Member
I have a Dynon EMS D120, and everything seems to work well during inital check out. The only issue I have is the fuel pressure reads 0.4 psi with no pressure on the fuel system. Dynon sent me a replacement sender, and it reads the same, so it's not a sender issue. I reread the installation manual, and it has the following regarding grounds:
"Because of the current drawn by the EMS-D120, even very small resistances between battery ground and instrument ground can cause voltage differences which adversely affect engine sensor readings. An easy way to test the quality of the instrument?s ground is to measure voltage between the ground pin at the EMS-D120 and the ground lead at your aircraft?s battery. With the EMS-D120 powered on, connect one lead of your voltmeter to a free ground lead coming from the EMS-D120. Connect the other lead of your voltmeter to the ground terminal of your battery. The voltage between these two points should measure very close to 0 mV (within 5 mV). If it does not, you must improve the ground connection between the ground of your battery and that of your avionics bus."
If I check the voltage between my battery ground and the avionics ground I get 3 mv. However, if I check voltage between a Dynon free ground lead (the one used for fuel pressure or the one used for carb temp yields the same result) and the battery ground I get about 45 mv. My ground system is like this:
All of my instrument grounds go to electrically isolated ground blocks in the instrument panel area. The ground blocks are tied back to the battery ground via a #8 cable. And again, the voltage between the ground blocks and the battery ground is 3 mv. It's the return to the Dynon that has the higher reading.
Any ideas? Is this OK? Or could it be the cause of my high fuel pressure reading?
Thanks
"Because of the current drawn by the EMS-D120, even very small resistances between battery ground and instrument ground can cause voltage differences which adversely affect engine sensor readings. An easy way to test the quality of the instrument?s ground is to measure voltage between the ground pin at the EMS-D120 and the ground lead at your aircraft?s battery. With the EMS-D120 powered on, connect one lead of your voltmeter to a free ground lead coming from the EMS-D120. Connect the other lead of your voltmeter to the ground terminal of your battery. The voltage between these two points should measure very close to 0 mV (within 5 mV). If it does not, you must improve the ground connection between the ground of your battery and that of your avionics bus."
If I check the voltage between my battery ground and the avionics ground I get 3 mv. However, if I check voltage between a Dynon free ground lead (the one used for fuel pressure or the one used for carb temp yields the same result) and the battery ground I get about 45 mv. My ground system is like this:
All of my instrument grounds go to electrically isolated ground blocks in the instrument panel area. The ground blocks are tied back to the battery ground via a #8 cable. And again, the voltage between the ground blocks and the battery ground is 3 mv. It's the return to the Dynon that has the higher reading.
Any ideas? Is this OK? Or could it be the cause of my high fuel pressure reading?
Thanks