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 Post subject: Ferrite and Hall Sensors
PostPosted: Thu Aug 16, 2018 4:05 am 
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Can adding a Ferrite ring to the signal out wire of a hall sensor reduce the Electrical noise that It might pick up?


I have had alot of trouble with my trigger wheel and Hall sensor over the years possibly because the diameter was too small and it was too close to the balance, but I wonder about the Ferrite Rings that can easily be pirated from old electronic cables. Could they be used in this application?


Greg

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PostPosted: Thu Aug 16, 2018 7:48 am 
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It is definitely worth a try. Probably try it first near where the wires for the sensor enter the ECU.

Lou

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PostPosted: Thu Aug 16, 2018 9:37 am 
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Isn't the sensor cable shielded and grounded at the ECU?

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PostPosted: Thu Aug 16, 2018 10:04 am 
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Joshie225 wrote:
Isn't the sensor cable shielded and grounded at the ECU?



Yes but still was having problems.

Greg

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PostPosted: Thu Aug 16, 2018 11:50 am 
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With the cable being shielded it shouldn't be picking up interference. I acknowledge the difference between should and in reality so give the ferrite a try. It would be interesting to see the difference on an oscilloscope.

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PostPosted: Thu Aug 16, 2018 3:47 pm 
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FWIW, the shield is supposed to be grounded at one end only. It's what's done on all of our equipment where I work, and is the recommended method for shielded cables. I won't speculate how effective it might be at lower voltages, but it might make a difference in your case.
And yes, give the ferrite coils a try. I see them a lot in our electrical cabinets.

Roger


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PostPosted: Thu Aug 16, 2018 4:05 pm 
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Greg
I went through a huge issue this past January with EMI interference and the MS3 Pro.
The Mega Squirt would see the cranking RPM's as 30,000 +, send the injector pulse signal
to the stratosphere and flood the motor....instantly.

The fix was to improve the initial battery ground, moved the battery ground from the engine block to the
engine starter and to add additional shielding to the crank position sensor wiring.
I am using a Lean Burn Distributor,
The crank position sensor wiring was already shielded, foil shield internal to the insulation and
grounded at one end. I added a braided wire shield, also grounded at one end over the existing
foil shielded wire.
The results were mind-blowing, all the EMI issues resolved, ignition-engin performance hugely
improved.
I did two things, improved ground and improved shielding. I think I got the biggest bang out of the
improved shielding, although the improved ground was directionally the right thing to do.


this post has links that go to internet articles that do a god job of explaining EMI and RF interference

and how to resolve them.

viewtopic.php?f=28&t=62171&p=464762&hilit=EMI#p464762


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PostPosted: Thu Aug 16, 2018 6:50 pm 
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Great, thanks john for the ideas.

2 questions....

1. I have shielded 3 conductor wire for my hall sensor.
Wires are 5v power, sensor gnd to mega squirt, and sensor output signal.

Should the shield of the wire be tied into the sensor ground wire? Now it is just an AL foil shield.. not connected to anything.

2. For the braided/woven wire sheathing that you mention from ebay @ $8.00.. is it made of fabric or copper?


Thanks! Greg

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PostPosted: Thu Aug 16, 2018 7:00 pm 
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For the foil to function as an electronic shield, it must be grounded, at one end only.
The braided shield that I used was stainless.
If you use that you will need to build in a ground wire. At one end I loosened the braids and
wove in strands from a copper wire, i soldered them and covered that with heat shrink tubing.
Then connected the copper wire to a good ground, engine block or battery, not sheet metal.
copper shield is probably available, but it would be more expensive.
Fabric would not be effective as a RFI / EI shield.


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PostPosted: Thu Aug 16, 2018 7:29 pm 
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Cool.

Will foil shield wire on one end be grounded to ecu or chassis?

Greg

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PostPosted: Thu Aug 16, 2018 7:49 pm 
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I got out a piece of the woven shielding that I had left over, it is tin plated copper, not stainless,

The MS3 Pro that I have, has the foil shielding grounded back through the ECU.
When my RFI issue started one of the first things I did was to verify continuity
from the furthest tip of the foil back to the connector that plugs into the ECU. Then
I also verified continuity of the foil pin connector to the ECU ground wire.
No issue found there. So the foil was grounded, however apparently the foil was not
enough of a RFI / EI shield for my install. Adding a grounded woven wire shield over the grounded foil shield
resolved the issue.

here is 10 feet of 1/4 inch diameter copper-tin wire sheathing for $12.00
https://www.ebay.com/itm/Tubular-Braide ... 6220!US!-1


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PostPosted: Sat Aug 25, 2018 10:39 am 
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Its always been my understanding foil shielding is a better shield, but braid is better should cable see a lot of flexing over time regarding durability. Online there is the thinking braid is better at lower frequencies, I suspect because even with less coverage (foil is 100%), braid is thicker and better at lower frequencies. How one knows what the problem frequencies are before starting, is over my pay grade.


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PostPosted: Sun Aug 26, 2018 2:07 am 
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Note that "low frequencies" probably means up to 100 kHz or so (100,000 Hz or 6,000,000 cycles per minute). I suspect some of the noise spikes we see from our engines could be at ignition frequencies or alt rotation frequencies, which are below about 12,000 cycles per minute or 200 Hz. If the noise power is high enough, the foil may not be able to shield it effectively and you need the braid.

Lou

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PostPosted: Sun Aug 26, 2018 12:59 pm 
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Am I wrong however to assume that say a 200hz square wave noise spike, has many, much higher included frequencies in its makeup, that exceed say the arbitrary, for this discussion, 100,000hz mark?
It would seem, if indeed braided is the holy grail in aftermarket automotive applications here, it should be a widely promoted solution and almost mandatory to reduce these issues, by the designers. And I am not hearing that, yet. :D


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PostPosted: Sun Aug 26, 2018 6:21 pm 
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Yes, there is plenty of higher frequency noise on those signals too. If you have ever observed the signal across the coil leads, it looks mighty scary across a wide range of frequencies. But, it is possible to cancel out any noise you want, with the right gear and strategy. It's a question of how big the spikes are. Also lower frequencies take more effective capacitance to bring them down if the shield acts like a filter (which at some points of frequency and power, I think it must do).

I am not saying I am necessarily right about all of this, but it makes sense based on my electronics knowledge and it would explain why DadTruck saw the results he did.

Lou

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