Hall Effect

[J-G]

Continuing my research into variable speed motors - and the control thereof - about which I received excellent support a little while ago, I'm now looking for detailed knowledge about how best to position both the magnet and the sensor.

I have a 'device' which has a 12mm dia. body, 57mm long and comes with a 10mm dia. magnet, 2.7mm thick.

Now, I could make room for the body to sit vertical (which I assume is the 'ideal' arrangement) but it would mean adding nearly 50mm to the height of the case. Refer to the first image below

Can anyone confirm that the arrangement in the second image would also work?

I'm not yet in a position to carry out empirical tests

 

[joncooper27]

What are you trying to do with the sensor?
Sorry I did not read your last post

 

[J-G]

It's used to show the pully rpm.

 

[Woody Alan]

The second image is how I have one set up on my metal machining lathe. Edit: sorry just seen the magnet in th image I think you will struggle with the north south poles of the magnet so my thoughts are no. However if you swap the small round magnet for a short bar magnet (flat oblong) it might work.

 

[John Brown]

I wonder why the Hall effect device is so big? Is it maybe an industrial device?
The actual semiconductor sensors are quite small..

 

[J-G]

The second image is how I have one set up on my metal machining lathe. Edit: sorry just seen the magnet in th image I think you will struggle with the north south poles of the magnet so my thoughts are no. However if you swap the small round magnet for a short bar magnet (flat oblong) it might work.

Is 'North' / 'South' relevant ? - does the sensor simply recognise a magnetic field?

 

[J-G]

I wonder why the Hall effect device is so big? Is it maybe an industrial device?
The actual semiconductor sensors are quite small..

I bought it as a 'package' so I assume that there is some circuitry in there to calculate the rpm and passing that to the display via the three wires coming from the base.

 

[Sideways]

I doubt north south matters for the sensor's purpose, but field strength will matter for getting a clear reading, and maybe more so as speed increases. Arrange it anyway you like but have the N or the S pole of the magnet pointing directly at the sensing face and keep the distance between them as small as practical, 1 or 2mm say.
If you look at the hall sensors on the end of powertool armatures, the clearance is 1mm or less and the magnets must be small based on overall dimensions.

The "display" in your module is doing all the work, timing and display driver. The sensor has a common -ve, a live feed in and an output wire which will be carrying pulses as the magnet turns the hall sensor on and off.

 

[Sideways]

I wonder why the Hall effect device is so big? Is it maybe an industrial device?
The actual semiconductor sensors are quite small..

The hall effect sensor is a small device in the end of what is basically a threaded tube. Stick the tube through a hole and secure with nuts either side and you have a robust, easy way to hold and position the sensor close to the passing magnet. Small is nice in the right place but in machinery, a certain size and robustness makes things easier to use and harder to break.

Like this maybe ?

 

[Phill05]

Think the one in the image above is more for using on a cnc for limit switch.
Have a look at the attached far more compact for your application you can get it from https://uk.rs-online.com/web/p/hall...18DiDxKjaEcb0aDOkFxoCKMYQAvD_BwE&gclsrc=aw.ds

 

[joncooper27]

This is a good description of how Hall effect sensors function
https://uk.rs-online.com/web/c/auto...effect-sensors/?applied-dimensions=4294967071

 

[ChaiLatte]

Could you mount the magnet in the boss on the pulley? Then you can have the receiver horizontal and save some width.

For the same width, add a pineapple ring to the pulley boss, and lower the horizontal sensor in your diagram by the diameter of the magnet.

Depending on the environment it is in, an alternative might be an optical sensor (like on the reflective rpm meters you can buy).

Unless you like goats, be sure it was not a Monty Hall effect sensor you bought.

 

[Sideways]

Think the one in the image above is more for using on a cnc for limit switch.
Have a look at the attached far more compact for your application you can get it from https://uk.rs-online.com/web/p/hall...18DiDxKjaEcb0aDOkFxoCKMYQAvD_BwE&gclsrc=aw.ds

The one in my photo is what's supplied with these £7 Chinese rpm display modules. Quite practical if you want to read, say, the rpm of a lathe spindle but not if you want closed loop control of a universal motor doing 20,000 rpm.

@J-G
One thought for a compact installation. If the pulley is bigger than the diameter of your motor, could you place the sensor body alongside the motor body, close to it, facing the same way and parallel with the spindle ? If the pulley is large enough diameter the outer edge could extend to where the end of the sensor is. Drill right through the pulley and glue a little round magnet into the hole.
And, you may not need to measure the motor rpm specifically. Any part of the drive train could be measured. All that matters is you know what rpm number represents full speed.
With machine tools, it's spindle speed after the gearbox or belt tdrive that is really of interest, not the speed of the motor.

 

[Woody Alan]

Yes the magnetic polarity matters if you get it reversed it won't work

 

[ChaiLatte]

With machine tools, it's spindle speed after the gearbox or belt drive that is really of interest, not the speed of the motor.

...until the day the belt slips or, worse, breaks or the gearbox finds a false neutral.

That will, at best, compute the confuser. Hence, if taking that path, investigate and mitigate the system behaviour if such a fault does occur rather than panic when it does happen for the first time.

 

[Spectric]

This all depends upon the accuracy of your speed requirements, for complete control and precision the sensor would need to be part of a feedback loop in the control system. If you want reasonable precision then you can use the control signal itself, ie if 67 Hz = 1200 RPM then just use this signal into a display to allow you to set the speed. Another way to get speed and position is to use a quadrature encoder .

 

[John Brown]

This all depends upon the accuracy of your speed requirements, for complete control and precision the sensor would need to be part of a feedback loop in the control system. If you want reasonable precision then you can use the control signal itself, ie if 67 Hz = 1200 RPM then just use this signal into a display to allow you to set the speed. Another way to get speed and position is to use a quadrature encoder .

Does a quadrature encoder give you position? Speed and direction, but not position, surely. Enlighten me.

 

[J-G]

Well - - - you've been a busy lot whilest I've been out - I have been back a while but had other things to attend to as well!

Some very good suggestions that hadn't occured to me and I suspect that when I get to look at the issue in the morning I'll find a better alternative from my initial ideas.

Fitting the magnet to the pully boss does look to have a high possibility at the moment.

 

[flying haggis]

Are these basically what's in any housing?
https://www.ebay.co.uk/itm/11227674...lp:4429486&itmmeta=01HT1ZSJ8SM1DXGKBHM5S6CQ97
such that it might be easier to fix something smaller?

 

[HamsterJam]

Is 'North' / 'South' relevant ? - does the sensor simply recognise a magnetic field?

North/South won’t matter.
However, the field density will be greatest closer to the poles.
In addition, in the first image the field is in line with the sensor and in the second, perpendicular.
It difficult to say whether the second option will work without understanding how sensitive the sensor is to field strength and field orientation.
As Woody suggested, a bar magnet might work better for you in the second set up.

Another option is a photocell. You can get sensors that detect to a white (reflective) target on the pulley. I have seen a system that used white paint to detect the position of church bells to trigger a simulated chime but a small piece of white plastic would do the job.