A very strange question about testing ignition timing

[Guest vvega]

Posted August 22, 2005 08:54 AM Hide Post

Rob: I wrote a paper for an electrical devices course that compared hall-effect vs VR sensors for automotive applications. I'll see if I can dig it up.

edit: looks like i'll have to go back into my *ugh* paper archives.

Anyways.. there are a few things to consider: resolution, mechanical setup, temperature rating, and cost.

VR sensors have trouble reading at low speeds and the voltage output of the sine wave decrease the slower you go. You can add more teeth to your wheel the alleviate this, but you may then have problems timing signals at high RPM.

Hall effect sensors will read as slow as you want (up to the overflow limit of your timing code), so you can run fewer teeth and still have a stable signal at low rpm.

because of the sine wave signal, VR sensors need additional circuitry. I've used the National LM1905? Variable Reluctance Sense Amplifier with good results. It filters the signal well and has hysteresis built in.

Hall effect sensors have the circuitry on the sensor itself. This is where the reliability and temperature problems come in. Granted, the honeywell GT101 is robust and can take the temps, but I don't know the long term reliability.

Mechanical setup: typically the VR sensors run pointed straight at a toothed steel wheel. Hall effect sensors can be arranged such that there is a magnet on one side, and the sensor on the other. A steel 'gate' wheel would then pass between them and interrupt the magnetic field. The honeywell GT101 is different, and works more like a VR sensor. (advantage GT101)

cost.. VR sensors are generally cheaper. but whats a few bucks on a prototype anyways?

I beleive VR sensors can also introduce a fair amount of EMI. a 30V unfiltered sine wave running all the way to the ecu is noisy compared to a 5V digital signal.

My conclusions: If your engine is already set up with VR sensors then use them, since they should be more reliable and configured properly. But if you need to add sensors, then go with the honeywell hall-effect.

Hall effect sensors put out a voltage that doesn't vary in amplitude vs. frequency (rpm).

Variable reluctance sensors put out a 20 mV signal at low rpm and up to 30 V signal at higher rpm. (Depends on air gap as well)

I think that one of the biggest issues you need to address is the temperature rating of the sensor. Make sure that it will stand up to hot oil immersion. VR sensors come stock on an F4i or similar bike engines, but you're running something different. VR sensors require a toothed wheel made of a magnetic material....i.e. steel, no stainless or aluminum. The air gap with VR sensors is fairly touchy, but reliable if you get it right.

[Unclejake]

Some good reading here too:

http://www.megamanual.com/ms2/pickups.htm

[Unclejake]

KKK-Kermit came and had a look last night. We all had fun but it was cold and Mongol wouldn't let us hook the MSD unit up to his new peircing

vvega had suggested spinning the dizzy the wrong way (clockwise) so I tried that and still good spark but instead of a problem with rising retard there was rising advance.

We took the reluctor off and turned it upside down and the problem persisted - but still good spark.

Then KKK-Kurdle noticed something I was thinking about the day before but forgot. The brown magnet under the steel pick-up posts didn't look quite lined up. KKK-Kustard flipped the magent upside down and it fitted better. We then re-assembled the unit, had to re-phase the rotor timing, span it up on the test rig and the thing is perfect!!!!!

The guy that put the dizzy together after locking it had replaced the pickup magent upside down.

KKK - You are my new hero. <3 <3 <3

[kyteler]

FUCKEN YES!

Stoked for you man, big ups to KKKKKKKKKKKKK

Now get the rest of that bitch sorted yo!

[Unclejake]

Yup yup yup. So happy too brew. This issue has been messing with my head for days. I hate things I can't understand.

Boat trailer comes back from the galvanisers tomorrow so the Cortina will need to wait for a few more days before she gets a lot more attention - but then I will be seriously into it (with a bit of time off to do a bit of house work)

[mikuni]

Mean, good shit fellas. Looks like such a bastard of a problem was a relatively simple fix in the end.

Now get the rest of that bitch sorted yo!

Agreed. OS Nats 09 please.

[KKtrips]

Its so hard to stay modest when you as awesome as me's... me lubs UJ 22222

maybe it just be he drink talking....