Shielding Question

Hi HPA team! Let me take the opportunity to say thanx for the course! I guess a lot of people were involved to make it that level, - so thanx a lot to all of you.

My question is re Shielded cable section, particularly at 00:30: ".. Its critical that it is shielded at one end, if the shielded braid is grounded at both ends you will certainly violate or stop the earting rules.."

So could you plsease be more specific about that. Lets take the particular case, - imagine we have a GM E67 ECU (it has no dedicated shielding pin) that recieves its groung from the engine block (thats clear and not discussable). Crank position sensor is wired using a 3 wire shielded cable. Shielded cable has a shield that has 2 ends :) one at the ECU side, that is definitely connected to the ECU ground (which respectively goes to the engine block), another one at the connector side. So all the game it happening at the connector side. There are several options:

1) Leave it unconnected

2) Ground shield at connector side to Engine block

3) Run a separate wire connected to shield at the connector side back to ECU and connect it to ground there (both ends would be grounded at ECU side)

Option 1 - is what Zak is saying. Options 2 and 3 are the two side termination and i would greately appreciate if you could comment what's wrong with these.

The question is mostly due to my curiosity, but it was also triggered by this article:

http://pdb-media.leinelinde.se/media/file/9700/Shielding_connection_eng.pdf

Hope the question is not that much stupid..

Tks in advance

Rgds

R

The reason you only want to ground your shield at one end is that if you ground it at both ends, to different ground points, it will give a path for current to flow between these two ground points that might not be considered in the design. Large transient current events can cause spurious current to flow along the shield, which can actually induce noise in the wires below, if large enough. Grounding the shield at either end is likely to be fine, but still steer away from grounding it at both.

Has anyone used ferrite core magnet sleeve to reduce interference and di they work?

yes, the ferrite will tend to reduce the transmission of noise from a high-frequency signal. Often used with video signals. I've never found it necessary outside of video or radio systems on a race car.

This is definitely something I’m curious about. I have recently started making a harness for my 4G63 powered Eclipse, and the knock sensor is shielded. The lead from the sensor is long enough to make it to the firewall. So my impression is, while it’s a single wire sensor, it has a two pin connector that I could depin, pin both wires (the signal and shield ground) with the Deutsche pins, and run through bulkhead, shorten the ECU side of the shield and still have the shield ground side terminate inside the car (it doesn’t go to the ECU). Is this a logical solution? I’m kind of at a stopping point due to this issue and I need to continue progress if I’m to be ready for next season. Thanks!

I like to keep the OEM connector for sensors, so you can just buy a replacement and install. But do what you want. I often pass signals and shields through an Autosport connector with shielded cable on each side.

Gotcha. The issue I just realized is the knock sensor is potted, so the connector needs to spin with the sensor which makes things a little more interesting.