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Shaft rotation sensor?

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nigelmercier

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I've building a device that needs to sense when a shaft has turned 360°. My current prototype uses a Hall-Effect sensor, with a magnet on the shaft. However, it is quite critical as to the distance from the shaft, and I really don't want them to touch. I've also tried a light sensor, but this was worse.

I can't mount a sensor wheel on the end, or the perimeter of the shaft, it has to be something like a magnet or a dark stripe (the shaft is aluminum, 100mm diameter, about 250RPM). No need to detect direction or speed, just full rotations.

Any suggestions as to a sensor with more than a few mm of range?
 

Normally hall effect sensors are quite enough, anyhow. You may use proximity sensors (Inductive for metalic sense and Capacitive for Other senses) These proximities are coming in wide ranges, and are high speed. but these sensors are expansive than hall effect sensors.

Other idea is to use encoder or simple DC motor coupled with the main shaft of your disc. Encoder gives digital pulses and DC motor gives you an analog voltages for certain voltages.
 

I hope this gives you an idea....

Prox&Ax.jpg
 
At industrial systems is ussual apply Encoders ( magnectic or optic ). The advantage is the possibility to determine exact angular position.
On other hand, Tachometers just provides information about multiple turns, usual at high rotation rate applications.

+++
 

Tachometer and encoder is really a expansive thing to use as an amateur but are very very accurate in results. however making your own with less accuracy using proximity or light sensor is quite inexpensive
 

nigelmercier said:
Any suggestions as to a sensor with more than a few mm of range?
Click to expand...

Sorry, perhaps I didn't make it clear: I'm asking if anyone knows of a particular (Hall effect or optical) sensor with more than a few mm of range, say 10mm or so. To reiterate: an disc encoder is not possible, or necessary.
 

For a distance of 10mm a hall sensor or bridge is not sensitive enough. With a MR-sensor bridge followed by an interpolator with integrated sensor signal conditioner you could make it if the magnet is strong enough. In general it is also a question of resolution and accuracy needed. With a 6-bit interpolator, like the iC-NV, you will get 64 pulses per rotation. Application example you find on page 19 of the DS (**broken link removed** ). It works with optical and magnetic sensors. For higher resolution you could look at the iC-NQC or others here: iC-Haus Homepage - keyword: Interpolators .
 

masterleous said:
Your RPM is too fast, you may use a magnetic reed switch for your disc, as hall sensor has small sensing range
Click to expand...

250RPM (about 4Hz) is too fast? The sensor I've been using goes up to 10kHz!

I've now found another sensor (AH180) that has twice the sensitivity, so it will probably be OK.
 

Thanks for the suggestions, but I'm considering a problem with stray magnetic fields from the motor that turns the drum, so have decided to investigate the possibility of using a reflective optical switch.

Revised info:

The drum itself is about 100mm diameter, and revolves at speeds of up to 180RPM, or 3Hz. There is a 25mm hole in the circumference, about 40mm deep; ideally the sensor would be able to detect this hole due to lack of reflection in this area. See this very short video clip on **broken link removed**.

The sensor distance from the surface would ideally be about 5mm, more being better. The sensor output needs to be a positive or zero going pulse, from a 5V rail. The output drives a PIC microcontroller, configured as a digital input.
 

For eliminating outer magnetic fields , use embeddable type
and install it inside steel tube or block.

or there is magnetic field resistant types
of inductive prox. switches too

for example....
Inductive sensor NBB5-18GM50-E2-C
Constant magnetic field 150 mT
Alternating magnetic field 150 mT

Inductive sensor*NBB5-18GM50-E2-C
 

Just a thought. But it would seem to me that it would be a whole lot eayser to take that pulse and flip flop it so it would have two output lines one + and one - line
each line would output 1 puls per rotation so whitch ever puls you wanted, a + puls or a - puls and it would only take very little components. You Might be able to do it with 2 transisrors

---------- Post added at 15:09 ---------- Previous post was at 15:04 ----------

Or one output line with a diode

---------- Post added at 15:16 ---------- Previous post was at 15:09 ----------

Or a counter IC with the reset line huched to Q2 with Q2 being the puls line as well
 

If you are able to mark one position on the 100mm diameter aluminum shaft with black color it would allow to go reflective with a position sensitive sensor (like the iC-OD/ODL: iC-Haus Homepage - product: iC-OD, iC-ODL ) and use a LED as a light sourse. Another option would be just a photo switch like the iC-LQNP (iC-Haus Homepage - product: iC-LQNP ). This is the system often used on a electronic water tap. If you dont want to bild your own sensor with component you can look at commercial optical sensor if they fit the size requirements (example **broken link removed** ).
 
HTA said:
...Another option would be just a photo switch like the iC-LQNP ...
Click to expand...

Thanks, this doesn't have the range that I need, but I've emailed their technical department.

To RobotManMike, I don't see the purpose in your suggestions.
 

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