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Wheel speed / Hall Sensor sheilding

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals


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Should Hall Effect sensors used for wheel speed sensors (or any other non engine trigger use) use shielded cable the same as if the sensor was being used for a engine pickup or is it only the sensitivity / impact to engine when used as a crank sensor that requires shielding?

It is probably good practice, but I have never bothered and never seen any issues in any installs I have done. I would possibly consider it if I had to run my speed sensor wires parallel to HV ignition wires or a CDI box etc otherwise I would say don bother.

I have seen issues with in-car 2-way radios. Generally we solve that by re-routing antenna wiring, but using proper shielding should also work.

Often when you're shielding digital signals, its about limiting the noise those wires radiate out, as opposed to noise injected into them. I've not struck a problem with digital wheel speed sensors using standard wiring, but It's certainly something to be aware of.

Often when you're shielding digital signals, it's about limiting the noise those wires radiate out, as opposed to noise injected into them.

Zac, Im curious about this comment as I cant apply my logic to it (Im a mechanical engineer, only basic electronics). A hall effect speed signal would normally only be 5V square wave, maybe 1KHz and very low current ~1mA depending on pullup value (Im not even sure if current influences emi?). If we were worried about emi from that, wouldnt the E-throttle, ISC or VVT solenoid be like infinitely worse (higher voltage, current and sometimes frequency)? I dont think I have ever seen any of those shielded...

I have seen issues with in-car 2-way radios. Generally, we solve that by re-routing antenna wiring, but using proper shielding should also work.

Again, Im asking a question due to my curiosity rather than trying to make a statement here, my RFI & antenna theory is even less than my EMI knowledge... The radio antenna would already be shielded (coax) right? So you would think induction would already be minimised. Im wondering if the problem in this case might be something to do with the antenna ground (same as the coax/shield ground) usually gets grounded to the chassis via the antenna mounting bolt and in some situations (carbon skin bonded with urethane for instance) the mounting point gets insulated so the coax shield/gnd never gets grounded?

I don't know what to tell you. But when the radio is transmitting, noise is induced into the hall-effect sensor, and we are suddenly going 300 mph. Stops when the radio stops transmitting -- only effects the sensor with the wiring that is close to the antenna wiring.

You're right Adam, it's more of a thing for stronger digital signals, like RS232 which is +12 to -12V, so can have a bit of oomph behind it. Its the 'speed of the edges' that account for a lot of the noise, as in how fast the signal changes. It's possible I'm just paranoid from PCB design days though ;-). Often there, if a comms signal didn't need to have particularly fast edges I'd actually slow them down with a bit of capacitance to help reduce their emissions.