MSD polarity tech question

[Dragsinger]

In recent years the MSD trigger polarity has received some attention. In the "olden days," it was never considered.

For this question, we are talking about an analog MSD 6AL control.

I do understand that for the analog controller, the most retarded timing is the correct polarity. Since the subject began getting attention I have checked a number of 6AL and 7AL analog controllers and so far, each had the correct polarity when the wires connected "color to color" [green to green, purple to purple]

When the colors are swapped, [green to purple] the timing advances about 5 degrees.

Now the question;

Why does the wrong polarity advance the timing? It is as if the controller is predicting the future

Does the control box, when polarity is correct, have that much signal delay? [about 5 degrees]

Anyone know the truth?

[Roundybout]

I think it has to do with how the signal is processed. If it's set to rise and fall as it approaches the tooth compared to as it passes the tooth on the reluctor. If the pickup wiring is opposite then the signal is happening either sooner or later. Having it advance would mean it's seeing the signal sooner than designed.

I remember seeing a few topics here on this issue. Try a search for a wealth of info.

[Ks Fats]

Lately on the circle track stuff I've seen more incorrect than correct. I have gotten to the point that I check every dist. for polarity (most retarded) on installation. To that end I'll post a question: IF the permanent magnet in the pick up coil was installed incorrectly (north/south flipped) in relationship to the coil color code wouldn't that reverse the signal polarity out of the pick-coil? Given the time pressures of assembly lines it seems that could be easily done.

[Schurkey]

IF the permanent magnet in the pick up coil was installed incorrectly (north/south flipped) in relationship to the coil color code wouldn't that reverse the signal polarity out of the pick-coil? Given the time pressures of assembly lines it seems that could be easily done.

Wild Guess: The magnet on the pickup coil isn't magnetic until AFTER the assembly is built.

Sort of like speaker driver magnets. The driver is built up--frame, cone, spider, voice coil, magnet, pole piece--before the thing is crammed into a magnetizing machine.

https://youtu.be/izQHjVWfzDQ

[Ks Fats]

"The magnet on the pickup coil isn't magnetic until AFTER the assembly is built." Hadn't considered that possibility; it would eliminate the polarity variable completely.

[user-23911]

The pickup coil puts out 2 pulses, one positive, one negative, one as the magnet approaches, the other as the magnet departs.
The electronics will only pick up one of them, the one it was designed to detect.
Reverse the magnet, you'll detect the wrong pulse....at the wrong time.

[user-23911]

I doubt it's a magnet anyway, normally a reluctor but the same theory applies......2 signals of opposite polarity.


So first of all you need to know what sort of sensor is used, that's if you're interested in knowing how it works.

Otherwise just do as most others do....random swapping of parts.

[emsvitil]

Read this:

http://www.useasydocs.com/theory/pickups.htm

[Dragsinger]

Thanks to all, I now understand.

In the case of my original question, the signal in either triggered at the leading edge of the wheel magnet [incorrect polarity] or the trailing edge of the wheel magnet, [correct polarity] thus, the difference in timing.

The analog controller is designed to process the trailing edge signal.