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Thank you. Very good and practical info. I have noticed the need for closely coupled bypass capacitor even with HAL-switched, some need a little capacitor from output to ground too, even though it seems counter intuitive on OC-output.

I am surprised that you got away without degausing the toroid.

Did you got a whole lot of noise from the output even without the toroid? Did it had chopper or auto-zero artefacts?

CNC / Re: DDCSV1.1 4 Axis controller
« Last post by blades on Today at 02:10:39 PM »
It took awhile, but I finally got my parts from China. It lives!!  :ddb:
Yes, there were some problems.

At first the sensitivity of that sensor was not good enough in order to be used without concentrator.

I tried several variants of these and had a few problems:

First it was really hard to create a gap on a glass hard ferrite. Finally bought a diamond blade for my dremel and did the cutting under water. Ferrite reacts with diamond (the iron in it) and cripples the blade in no time. Underwater cutting had several advantages. Lubrication, cooling and dust control. When I finally got the toroid gapped and placed the sensor there the result was far from amazing. Seemed like the toroid had some sort of a hysteresis which made it so that it remembered previous current and suddenly fell back to new value when the difference was big enough. Might be a material issue. The toroid also picked up all possible disturbances around.

A much better candidate was the iron powder toroid. It was easy to cut and it did not have as much of hysteresis. Nevertheless it was even more sensitive for disturbances. The sensor output was far from stable.

The best solution was also the cheapes and easiest to do. Ordinary iron plumbing pipe (very mild steel). It was easy to cut into suitably long toroids and the gap was also really easy to make. I actually used my angle grinder for this. Further more the material dampends high frequency noise and the output was really stable. It is also possible to ground the toroid as the material is conductive. Also mild steel had some magnetic memory but it was way better that the other two.

The output of the Allegro device is rail-to-rail 5V. The output is in the middle when there is no magnetic field. The output goes towards ground or 5 volts depending on magnetic field strength and direction.

The sensor needs a good quality ceramic capacitor on supply wires to avoid internal oscillations. The capacitor should be as close as possible of the sensor.

As you know well, it's the journey that I enjoy rather than the end result   :clap:

I just love taking some neglected unloved bit of machinery and putting it right, if only some young slip of a gal  would do the same with me  and put  a smile on my face :lol:
So Andrew....

Nice find! But, are you gearing up to run a production line?

Project Logs / Re: Induction heater project
« Last post by Pete W. on Today at 12:22:54 PM »

.... and the experiences I have from hall sensors are not that encouraging.

I made a hall sensor thing for one of my friends to measure the windmill output current and that sensor was far from accurate. The result depended on the orientation with earth magnetic field - this had to be compensated and in addition those ferrites have some sortr of a hysteresis so that after a decent current spike there was remaining magnetism which affected the result as well.

Do you mind opening up a new (short) thread for it? I'm interested how did you do it and how it went wrong. To my understanding shunt resistor/kelvin connection is most accurate (and problematic too), then current transfomer is prefered on mains frequency and HAL is used when those don't fit.

I have semidecent, pretty cheap Hal probe for oscillsocope and I suspect it uses the universal priciple of using detect "zero" flux, ie. there is a compensation winding to generate opposite flux to flux generated by measured current:

This is something I haven't eperimented first hand..might be all BS.


There is another way that doesn't need the magnetic field sensor.  You detect the second harmonic of the input signal generated by the magnetic non-linearity of the core material.  Then you use that signal to servo the compensation current to drive the second harmonic to zero amplitude.  Very similar to how a flux-gate magnetometer works. 
Do you believe in co-incidences ?

Turns out that the probe I've found is coming from Gosport - now the lathe was originally at Portsmouth University 13 miles away by road, but by Gosport ferry across  Portsmouth Harbour probably less than a mile  :bugeye:

Now from my research Beaver were making about 45 TC-20 per year from 1987 to 1992 - or approximately 225 as a total world population - surely there has to be a very high chance that this is the original probe.

. . . how cool would that be . . . suitable question fired off to probe seller regarding his affinity to the Engineering Dept at Portsmouth University  :ddb: :ddb:
New from Old / Re: New Cylinder and Piston for TS350 Petrol Saw
« Last post by awemawson on Today at 09:31:32 AM »
I took the opportunity of the enforced hiatus to clean up the carburettor. Only externally, though it's passages got a liberal dose of carburettor cleaner.

I won't pull it apart unless I still get starting difficulties - this isn't supposed to be a full rebuild !
Well today is officially a GOOD DAY  :thumbup:

The touch probe seller has been in touch (no pun intended!) and confirmed that it was off a TC-20 lathe, and not only that he still has manuals for the Sinumerik controller - so how good is that  :clap:

. . . . negotiations are in progress . . . .  :ddb:
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