Floating Sact with Hall Effect Sensor

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Floating Sact with Hall Effect Sensor

Postby Zadig » Sun Dec 30, 2018 1:00 pm

I’ve installed a Hall effect sensor on my mill spindle. The signal is getting through to the software but the Sact DRO is all over the place. The mean of the readings looks like it is around the right place but ultimately they are unusable. Is there anything I can do to dampen the readings to a mean of some sort? The BOB is PLC4X-G2 from Purelogic which has served well over the years and looks well put together and would imagine the optocouplers are of reasonable quality. The max mill speed is around 5000+. The sensor is a cheap import but appears to function correctly. Im stuck with single index channel working so any help would be gratefully received.
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Re: Floating Sact with Hall Effect Sensor

Postby Battwell » Mon Dec 31, 2018 11:01 am

does it settle and read correctly at lower rpms? ie 1000 rpm?
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Re: Floating Sact with Hall Effect Sensor

Postby Robertspark » Mon Dec 31, 2018 11:20 am

What is the hall effect sensor? (Model reference)

Some of them don't give a clean output.... A hall effect sensor by its nature is not a square wave. Hence it normally has some signal conditioning to create a square wave output and amplify the signal


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Re: Floating Sact with Hall Effect Sensor

Postby Zadig » Mon Dec 31, 2018 5:24 pm

Cheers Guys for the response.

No, it doesn’t seem to settle at lower rpm, which I find odd. Maybe the swing in the DRO is not quite as significant at lower rpm, but it is still unworkable.

I’ll get back with the make and model of the sensor. I can say it is a cheap Chinese one, but I don’t want to knock it for that just now. It is supposed to have a Schmitt trigger as part of its internals and it does work inasmuch as the right thing is happening at the right time, when measured with a multimeter. I’ll stick a scope on it after new year and see what the output is like. I’ll let you know what I find.

Do they need a pull down resistor when connecting to an optocoupler? I was wondering if maybe the cut off is floating?

Under normal operation do these sensors work as they should and provide stable output 6000rpm and below?

Thanks again and all the best for the New Year.

Mike
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Re: Floating Sact with Hall Effect Sensor

Postby Robertspark » Mon Dec 31, 2018 5:33 pm

My router uses a hall effect sensor (it is not optical) from the manufacturer..... But I don't know which one as it's all sealed in a speed controller package (it's a Makita) .... I don't know what the Triton uses.

The first time I came across hall effect sensors where on a rover V8 electronic distributor, 30 yr old design now ... And they are good for ~ 6000 engine rpm, so ~ 3000 distributor rpm, with 8 sensor points.... So 24,000 pulses per min..... All depends on the amplifier
Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
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Re: Floating Sact with Hall Effect Sensor

Postby Robertspark » Mon Dec 31, 2018 5:36 pm

A scope will clear everything up regarding signal quality... If you have one then you may as well use it

I would allow for a load resistor.... But it depends on your bob
Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
UC400eth, UC300eth, UCCNC v1.2109, Neuron Lite
UCCNC v1.2108 Macro Manual
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Re: Floating Sact with Hall Effect Sensor

Postby Robertspark » Mon Dec 31, 2018 5:52 pm

Looking at your Bob manual it states it has a 1k load resistor built in. Also have a look at the RHS image at figure 4.

I don't know what voltage the hall effect sensor is being fed, but if it's 12v, then across a 1kohm load that is 12mA.... In reality it will be less than this because of the forward volt drop across the optocoupler... You may need an additional parallel resistance across the two pins of the optocouplor and the resistor ..... Depends on the spec of the hall effect sensor what load it is expecting to see...

https://www.google.com/url?sa=t&source= ... J5825jgd4R

Again..... A scope will clear everything up.
Measure the output out of the sensor and also the lpt port pin from the Bob to the UC motion controller too.... So you can see exactly what the Bob is getting.

Try to run it at a low medium and high rpm with some stability (not sure how you are controlling it but you just want it running at a fixed speed (no uccnc pwm input)
Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
UC400eth, UC300eth, UCCNC v1.2109, Neuron Lite
UCCNC v1.2108 Macro Manual
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Re: Floating Sact with Hall Effect Sensor

Postby Zadig » Mon Dec 31, 2018 6:08 pm

Cheers Rob I’ll do that. It’ll be after tomorrow now for obvious reasons but I’ll get back with what I find.

Have a good night and see you later.

Mike
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Re: Floating Sact with Hall Effect Sensor

Postby Zadig » Sat Jan 05, 2019 9:08 pm

I managed to get an hour on the mill today and scoped out the output from the Sensor. When it is disconnected from the BOB it seems to be generating a good, reasonably clean signal, but probed from the BOB it is very noisey and I can see how this would cause some of the spurious readouts.

When I came to the machine cold, the Sact was reading pretty well with just the odd couple of RPM fluctuation, perfectly workable for my needs. As the day wore on the DRO figures started to go increasingly wild, to the point where the output was intermittent. I’ll change out the sensor tomorrow and see what that does. My time was cut short and I need to do some more work to get a better idea of what questions to ask.

Cheers,

Mike
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Re: Floating Sact with Hall Effect Sensor

Postby Zadig » Mon Jan 07, 2019 11:54 am

I’ve had some success, I swapped out the sensor only to find that the magnet polarity was different to the one purposely set into the mill head. I’ve glued another one opposite with some decent epoxy so fingers crossed. The sensor is now working and providing a stable output to the BoB. I’ve had to up the voltage from 12v to 24v to drown out a bit of noise on the line which I have no idea where it’s being generated. The Sact is stable within 1rpm and it concurs with a tachometer. I am getting some intermittent interference which need further investigation, but so far so good.
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