Increment/Decrement Control Loops

Anyone know the history of Increment/Decrement Control loops?

There's a paragraph on page 56 of the October "Microwaves and RF" magazine about AGCing a VCO using an up/down counter and D-A in an increment/decrement control... touting it as if it's the next best thing to sliced bread.

But I hardly think it's novel... I was setting the timing of automobile ignition systems in 1968, but used a squirt of charge into/out-of a capacitor to increment/decrement.

The paragraph references an IEEE article in October's "IEEE Transactions on Instrumentation and Measurement", which I can't access since I object to $35/month for the privilege (as I noted today as I renewed my memberships).

Maybe someone who subscribes to that service can look it up?

Thanks!

...Jim Thompson

That's what I thought, too.

...Jim Thompson

Try looking for "single-speed floating control". I think it's a really old and not-so-great control strategy.

Best regards, Spehro Pefhany

Sounds pretty much like the old 'huff-and-puff' VFO stabiliser the radio hams used. regards john

I thought it worked rather well. My scheme looked at dwell, decided if it was early or late and moved a threshold accordingly... this happened _after_ firing so was not subject to noise from the spark.

Just like having an elf sitting there turning a knob just a small amount after each firing ;-)

...Jim Thompson

If you choose a fixed increment that is small enough it closes at "left-right-left-right-left......" ;-)

Driving a big-assed T-bird (400+CID) in 1968, up and down 101 (near Sunnyvale) at over 100MPH, I was never able to cause the ignition to stumble... scared the hell out of my boss, though ;-)

...Jim Thompson

I think it generally works better if the elf moves the knob more for large differences and less for small differences.

Best regards, Spehro Pefhany

Perhaps I should elaborate. Waveform form (simplified, it's more rounded) from magnetic pickup in distributor:

_ _ _ / | / | / | | / | / | / | /

----------------------- THRESHOLD | / | / |_/ |_/

Downstroke is firing. When ramp crosses threshold power device (driving coil) turns on. So this crossing determines "dwell".

Device control is simple-minded (my preference :)...

Device has three states:

Off... Fired Saturated, coil charging Current mode, regulated at 5.5Amp

So I only look at two conditions... when firing occurred was I in saturation or in current regulation.

If device was in saturation, dwell didn't start soon enough so I decrement the threshold. If device was in current regulation dwell started too soon so I increment the threshold.

Worked like a champ.

...Jim Thompson

I will send you a copy if that is your real email address.

I have already been sent a copy, Thanks! (The header E-mail address is false... read the SIG to obtain a valid E-mail address.)

...Jim Thompson