Ammeter shunt -- protection enclosure (isolation)

[lolachampcar]

I copied the shunt sensor deffinition and renamed it to myplaneshunt or something like that then changed the cal until it read correctly. It was a nice simple solution using the already existing wiring (which provided more signal for a given current). I'm sure the temperature stability is not as good as the shunt provided by Dynon but that is such a small error that it really will not matter (especially given that the display rounds to the nearest amp).

sensor={
id=AMMETER SHUNT (100412-000)
function=AMPS
pins=C37_P24/25
name=BATT
name=ALT
name=LOAD
min_val=-100
max_val=100
resolution=0
round=1
is_piecewise=0
low_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=1000
c_x0=0
}
low_resistance=PULL_UP_200
low2high_cross=0
high_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=0
c_x0=0
}
high_resistance=NONE
high2low_cross=0
shift=5
}

 

[ggerhardt]

I copied the shunt sensor deffinition and renamed it to myplaneshunt or something like that then changed the cal until it read correctly.  It was a nice simple solution using the already existing wiring (which provided more signal for a given current).  I'm sure the temperature stability is not as good as the shunt provided by Dynon but that is such a small error that it really will not matter (especially given that the display rounds to the nearest amp).

sensor={
id=AMMETER SHUNT (100412-000)
function=AMPS
pins=C37_P24/25
name=BATT
name=ALT
name=LOAD
min_val=-100
max_val=100
resolution=0
round=1
is_piecewise=0
low_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=1000
c_x0=0
}
low_resistance=PULL_UP_200
low2high_cross=0
high_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=0
c_x0=0
}
high_resistance=NONE
high2low_cross=0
shift=5
}

Where in that sensor definition do you put the scalar?  I don't see it anywhere.

Thanks.

Geoff

 

[dynonsupport]

The "c_x1=1000" line is the scalar. This means 1V = 1000A, which is 1mA = 1A. The sensors use 4th order polynomials, not simple gain and offset, so that's why there is a x0, x1, x2, x3, x4.

You should read the post on how to make your own sensors, it would be helpful:
http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1268164287

 

[kastein]

A few things -
- yeah I know this is a pretty old thread.  It answered the question I had (how to set up custom ammeter shunt mV/A scaling) but raised a few very important points in my mind.
- first of all - make sure the shunt is mounted on a vertical surface, with the terminals in a horizontal plane, so that natural convection cools the flat manganin alloy resistive elements.  If you don't, you have to derate the current rating quite significantly in some cases.
- second - it shouldn't be covered!  if it is, make sure the cover doesn't affect cooling air flow.
- third - using the alternator feed wire as the sensing element is a clever solution, but please check (I can't remember) if the thermal coefficient is better or worse than a typical manganin current shunt.  If it's worse, you will have less accurate readings at elevated/lowered temperatures than you would with an actual current shunt installed.  If it's better, congratulations!  You win both ways. edit: I missed that the third point was covered by lolachampcar on my first reading, sorry!

I can't post a direct link since I haven't made many posts on this forum yet, but if you google search for "murata dms accessories 3020-01097-0" the first result is an excellent datasheet from MuRata on their current shunts.  Page 2 covers thermal derating.

I am not sure what brand/part number the Dynon shunt is, or whether a derating for aircraft use has already been applied, but I would strongly recommend not preventing convection cooling air from reaching the shunt.  It'll cause inaccurate readings and can damage the shunt.

 

[MWDG3]

Old post but it might be useful to someone.  MS18029 terminal covers come in a variety of lengths and widths.  Pricing varies wildly so research which length you need to modify for the shunt's mounting screw hole dimension.  Running a 10-32 or 8-32 bolt through the bottom with MS21042 steel lock nut would make a very secure installation.  No idea if a #8 0r #10 nut would inside the mount recess.

randbelectronics dot com/Catalog/CATALOG.pdf