# RPM sensor



## TTmartin (Feb 7, 2012)

I've started connecting up my soliton 1 controller.
Just finished making the rpm sensor pick up.

The two 8mm bolts are screwed into the collar and drill dimpled into motor shaft, also loctited with stud lock. the two bolts create a 120mm diameter.
The switch I have used is a siemens 10-30v dc pnp 6mm field, Bero 3rg 4612-0ag01. my question is, will this switch be ok with the soliton 1 or would a 2mm field be better, also for a (non electronics) mere mortal like me could someone explain what the pulldown or pullup (depending on pnp or npn) resistor does? is this resistor built into some switch types, as I work with these switch types alot in the industry I'm in, but no extra resistors are involved.
If I'm asking a stupid question then sorry in advance, I would prefer to understand what I am actually doing


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## ruckus (Apr 15, 2009)

My understanding of 'pull down' vs 'pull up' is that it is really the same as saying normally open or normally closed. A pull down is taking a steady signal and cutting it for a split second as the bolt goes by. A pull up is normally dead but sends out a pulse signal as the bolt goes by. I could be wrong.

I don't think 1mm vs. 2mm matters, as long as you get a consistent signal. Obviously, the 2mm gives you a bit more room for error. Does your inductive proximity sensor have a little light on the back? I like that kind because you can see that it is working and it helps with adjustment.

I tried a bolt sensor (with much shorter bolts!) with the Zilla but it was really picky and needed a full 50% duty cycle (half metal, half air) so I had to buy a special reluctor ring from rechargecar. It works great.

Good luck.


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## skooler (Mar 26, 2011)

Loads of good informaton in this thread

http://www.diyelectriccar.com/forums/showthread.php?t=71903

Theres also a nice picture of my pullup resistor on the soliton.

My understanding is that a pullup resister increases the voltage - which increases the voltage of each pulse making it easier for the controller to recognise.

Hope this helps.

Cheers,

Mike


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## TTmartin (Feb 7, 2012)

:


skooler said:


> Loads of good informaton in this thread
> 
> http://www.diyelectriccar.com/forums/showthread.php?t=71903
> 
> ...


Thanks Mike, 
But all that maths is a bit beyond me 
so is my 120 diameter rpm pickup with 13mm wide sensing bolt heads x 2 going to do the job?My plan was to see what it does compared to a rpm tester that I can borrow from work.

I've just spent 30 minutes on the big wide web, looking for explanations for pull up and pulldown resistors used with proximity switches, just so I might understand a small fraction of the magical world of (electricery). I should be on the patio drinking beer, we have some sun for a change

It seems to go like this,
if using a PNP proximity switch for a task like an rpm
sensor you don't want any stray voltage/interference/noise, to upset the signals, so you wire a resistor from the signal connection to ground (pulldown) this ensures any unwanted (noise?) Goes to ground giving crisp clean on off switching to give accurate rpm sensing.
If using a NPN proximity switch it's the opposite you wire a resistor from the signal connection to +V (pull-up).
I think I've got it? Now wheres that beer?
If that explanation is wrong, some one please let me know


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## TigerNut (Dec 18, 2009)

@TTMartin: Correct. A pull-up or pull-down resistor provides a conductive path when the switch that it's tied to is open-circuit. Otherwise the input line will float to whatever voltage it wants... not what you want.

@ruckus, skooler: Not correct. You need a pullup or pulldown resistor with both NO and NC switches; the only case that's not true is if you have a double-throw switch, with one side wired to (say) 12V, the other side to ground, the common to your signal input, and the switch is guaranteed to be break-before-make. In that case, though, it may exhibit 'bounce' in the brief interval that nothing is connected to the (common) input.

For maximum interference suppression, you want the pullup or pulldown resistor to be as low as possible bearing in mind that when the switch is closed, you'll draw a corresponding amount of current, and if the switch is a PNP or NPN transistor, it has a maximum current limit. The power rating of the resistor is also worth considering, if the duty cycle of the switch is at all significant.


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## MalcolmB (Jun 10, 2008)

Hi TT

There's no need to use such long bolts. The aim is just to produce two pulses for each rotation. You could make the bolts much shorter and move the sensor closer to the shaft to reduce the risk of unbalancing your motor. If the heads of the bolts are closer to the shaft it will also increase the duration of the pulse, which will make it easier for the controller to 'see' the pulses.

Here's a pic of my setup.


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## TTmartin (Feb 7, 2012)

MalcolmB said:


> Hi TT
> 
> There's no need to use such long bolts. The aim is just to produce two pulses for each rotation. You could make the bolts much shorter and move the sensor closer to the shaft to reduce the risk of unbalancing your motor. If the heads of the bolts are closer to the shaft it will also increase the duration of the pulse, which will make it easier for the controller to 'see' the pulses.
> 
> Here's a pic of my setup.


Thanks for the input,
The two bolts are accurately drilled & tapped into collar aposing each other and are of equal length so I think balance of motor should be fine.
The reason I made the set up with bolts of this length was to create a big enough diameter so the soliton 1 controller can actually count the pulses at high rpm to give an accurate reading. As I understand it, the smaller the diameter the faster the controller has to read the switching and I think there is limit.
I happened to read this description from another thread about rpm sensors, See-below,



> Finally, the Soliton controllers need the pulses from the tach sensor to be at least 200us wide (whether starting from ~12V and dropping to 0V when the target approaches or vice versa) or the hardware filter/squaring circuit will ignore them. In other words, the sensor targets need to be a certain minimum width relative to the circumference of the circle they scribe as they rotate. For example, let's say you want to read up to 7200 rpm so you can effectively limit the motor to 6000 rpm (the controller needs to be able to read a higher rpm than the desired limit). If you make a disc out of aluminum and cut two notches in it for an inductive prox to sense, the notches need to be at least 1cm wide if the disc is 12cm in diameter.
> 
> The math behind this is straightforward: the linear velocity on the surface of the disc is pi*d then multiply by RPM, divide by 60 to get the surface speed in cm (or inches) per second. Divide the width of the sensing target in cm (or inches) by the surface speed and the distance component cancels out, leaving you with the pulse width in seconds. Multiply that number by 10^3 to convert to milliseconds, or by 10^6 to convert to microseconds. The resulting pulse width must be comfortably larger than 200us at the highest RPM to be read.
> 
> ...


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## MalcolmB (Jun 10, 2008)

TTmartin said:


> Have I got it wrong?


No, you haven't got it wrong, you've just met the minimum requirement. As you move the bolt head closer to the shaft you increase the time it takes for the head of the bolt to pass the sensor. It might be easier to picture if you think of slices of pie, drawn from the centre of the shaft to the outer edges of a bolt head. The slices get fatter as you move the bolt head closer to the shaft. The fatter the slice, the easier it is to 'see'.


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## TTmartin (Feb 7, 2012)

MalcolmB said:


> No, you haven't got it wrong, you've just met the minimum requirement. As you move the bolt head closer to the shaft you increase the time it takes for the head of the bolt to pass the sensor. It might be easier to picture if you think of slices of pie, drawn from the centre of the shaft to the outer edges of a bolt head. The slices get fatter as you move the bolt head closer to the shaft. The fatter the slice, the easier it is to 'see'.


I think I'm missing something here,
As I see it the larger the diameter, the longer between switch signals making it more possible for the controller to be able to count the switch pulses at high rpm.
If you make the diameter two small it would eventually become one continuous signal to a controller at high rpm, at some point before that state you will receive inaccurate data, at low rpm its not an issue.
At the end of the day I suppose the best way to monitor whether an rpm sensor set up is working accurately is to use a hand held tacho-meter, 
Luckily I am able get my hands on a rpm tester.


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## ruckus (Apr 15, 2009)

TTmartin said:


> I think I'm missing something here,
> As I see it the larger the diameter, the longer between switch signals making it more possible for the controller to be able to count the switch pulses at high rpm.


Here is long-bolt rpm sensor result:
----------^----------^----------^----------^----------^
Here is short-bolt rpm sensor result:
-----^-----^-----^-----^-----^-----^-----^-----^-----^

Which has better resolution and accuracy? At low rpm your tach needle will go THump Thump Thump. It won't be smooth.

We are talking about electronics here. They can handle very high frequencies with no problem. Creating a low-frequency tach output is not necessary or desirable. 

I would shorten the bolts as much as possible.

Either way should work though... It is merely a matter of aesthetic and accuracy. 

Here is the Tach sensor on the 37 Jaguar:








This is fresh install before the wire was secured...


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## MalcolmB (Jun 10, 2008)

OK, I think I see the source of the confusion. I'm assuming that the bolt head is the target, and you're assuming it's the gap between them? I agree, the quote you posted from Tesseract can be read both ways, but even so if the notch or bolt head has to be a minimum of 1 cm wide at a diameter of 12 cm, it only needs to be 5 mm wide at a diameter of 6 cm.


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## ruckus (Apr 15, 2009)

MalcolmB said:


> OK, I think I see the source of the confusion. I'm assuming that the bolt head is the target, and you're assuming it's the gap between them? I agree, the quote you posted from Tesseract can be read both ways, but even so if the notch or bolt head has to be a minimum of 1 cm wide at a diameter of 12 cm, it only needs to be 5 mm wide at a diameter of 6 cm.


Not exactly, the RATIO of no-signal to signal is what we are trying to get at. 

Please read my post carfully:



ruckus said:


> Here is long-bolt rpm sensor result:
> ----------^----------^----------^----------^----------^
> Here is short-bolt rpm sensor result:
> -----^-----^-----^-----^-----^-----^-----^-----^-----^
> ...


Like I said, your tach WILL work (maybe). It is just not optimum. Please note the 50% duty cycle inductor ring I had to use to make the Zilla happy. Even this is a bit jumpy at low rpm. You are not merely trying to give the controller a signal, but also the analogue tachometer. A severe up-pulse followed by a very long pause leaves it to fall quite a bit between pulses. Again, not optimal. An 8-pulse tach would be smoother than a 4-pulse tach. 2-pulse is rather coarse. 2-pulse with looong bolts is ULTRA coarse. ---------------------------------------^-------------------------------------------------^------------------------------------------------^


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## MalcolmB (Jun 10, 2008)

Hi Ruckus

Thanks, but I was replying to TTMartin.


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## ruckus (Apr 15, 2009)

MalcolmB said:


> Hi Ruckus
> 
> Thanks, but I was replying to TTMartin.


Yeah, me too. I agree exactly with your statements. You are very correct. I was just quoting you to get at the pulse ratio thing. 

Short bolts will produce a better tach signal than long bolts. More bolts will be better than less bolts.

Cheers


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## TTmartin (Feb 7, 2012)

ruckus said:


> Yeah, me too. I agree exactly with your statements. You are very correct. I was just quoting you to get at the pulse ratio thing.
> 
> Short bolts will produce a better tach signal than long bolts. More bolts will be better than less bolts.
> 
> Cheers


Ok guys, thanks for your patience MalcolmB / Ruckus.
I am trying to gain knowledge of stuff I know little about and some times it helps me to push a bit, 
I could take this a bit further  but I think better not to: 
I've looked at Tesseracts explanation again (twice)


> Finally, the Soliton controllers need the pulses from the tach sensor to be at least 200us wide (whether starting from ~12V and dropping to 0V when the target approaches or vice versa) or the hardware filter/squaring circuit will ignore them. In other words, the sensor targets need to be a certain minimum width relative to the circumference of the circle they scribe as they rotate. For example, let's say you want to read up to 7200 rpm so you can effectively limit the motor to 6000 rpm (the controller needs to be able to read a higher rpm than the desired limit). If you make a disc out of aluminum and cut two notches in it for an inductive prox to sense, the notches need to be at least 1cm wide if the disc is 12cm in diameter.
> 
> The math behind this is straightforward: the linear velocity on the surface of the disc is pi*d then multiply by RPM, divide by 60 to get the surface speed in cm (or inches) per second. Divide the width of the sensing target in cm (or inches) by the surface speed and the distance component cancels out, leaving you with the pulse width in seconds. Multiply that number by 10^3 to convert to milliseconds, or by 10^6 to convert to microseconds. The resulting pulse width must be comfortably larger than 200us at the highest RPM to be read.
> 
> ...


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## ruckus (Apr 15, 2009)

TTmartin said:


> Ok guys, thanks ... In other words, the sensor targets need to be a certain minimum width relative to the circumference of the circle they scribe as they rotate...


Exactly right on. Longer bolts mean a shorter % is 'on'. Likely not meeting the requirement you laid out using fancy formulas...



TTmartin said:


> ... If you make a disc out of aluminum and cut two notches in it for an inductive prox to sense, the notches need to be at least 1cm wide if the disc is 12cm in diameter.


WOAA!! Inductive means 'can be attracted by magnets'. AKA 'ferrous'. code name: Steel. Stainless and aluminum do not apply.

In your example, imagine if you cut the 'iron' disk to 50% (please see my picture showing the inductor ring). You don't want to be anywhere near the threshold. Imagine an rpm sensor working fine at low rpm, but being right near the sensing threshold at max rpm. Inability to read means catastrophic failure. Much better to error on the side of a wider pulse. 

Cheers


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## MalcolmB (Jun 10, 2008)

I agree with your other points Ruckus, but an inductive material doesn't have to be attracted by magnets. It's any material that you can induce an electric current in – so any metal. It doesn't have to be ferrous.


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## ruckus (Apr 15, 2009)

MalcolmB said:


> I agree with your other points Ruckus, but an inductive material doesn't have to be attracted by magnets. It's any material that you can induce an electric current in – so any metal. It doesn't have to be ferrous.


Holy Smokes! Do I ever have egg on my face! 

Thanks for the correction. I looked it up and it sounds like aluminum works even BETTER than steel. I don't know why I made the jump from 'inductive' to 'ferrous' in my mind.

I did find that some sensors are designed for ferrous materials only. So I guess it comes down to the individual sensor construction.

Thanks


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## Tesseract (Sep 27, 2008)

TTmartin said:


> ...
> I've looked at Tesseracts explanation again (twice)
> ...
> 
> ...


Setting the math(s) aside for a second, the gist of what I was trying to say is that the width of the sensing target must be proportional to the diameter of circle it scribes as it rotates. If you use a larger diameter pulley then you must use a bigger sensing target. Simple as that. I gave an example of the MINIMUM required target (1cm) for a 12cm diameter pulley. You would be well-advised to use a larger target because this is not a guaranteed specification.


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## TTmartin (Feb 7, 2012)

Tesseract said:


> Setting the math(s) aside for a second, the gist of what I was trying to say is that the width of the sensing target must be proportional to the diameter of circle it scribes as it rotates. If you use a larger diameter pulley then you must use a bigger sensing target. Simple as that. I gave an example of the MINIMUM required target (1cm) for a 12cm diameter pulley. You would be well-advised to use a larger target because this is not a guaranteed specification.


Now that, I understand, thank you.
whoops I think I got the wrong end of the stick
Slight modification required by me
if I annoyed anyone, really sorry, 
not trying to, just want to understand stuff.


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## Tesseract (Sep 27, 2008)

No worries. I wasn't annoyed, just a little surprised at your interpretation of my earlier advice on RPM sensors and targets. Now back to your initial questions:

A PNP proximity sensor (just called a 'prox' for short) requires a resistor from TACH to SGND to operate correctly. This resistor is often called a pulldown because it pulls the output down to ground whenever the transistor is off. A pullup resistor, which is used with NPN output sensors, pulls the output up to the positive supply voltage (ie - S12V on the Soliton controllers) whenever the transistor is off. Whether you use a pullup or pulldown resistor, then, depends only on the polarity of the output transistor. 

I'm not familiar with the Siemens prox you selected, but if it has 1-2mm sensing distance, is an "inductive" type (that is, it detects any change in metal, and not just ferrous or magnetized metals), runs on 10-30VDC and has a PNP open collector output then it should work fine.

Finally, I concur with the suggestion that you use shorter bolts as a sensing target, not only because it will increase the output pulse width from the sensor, but also because you really want the bolt head to be tightened up against a surface (preferably with a toothed lockwasher underneath it) so that it won't loosen up from vibration over time.


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## TTmartin (Feb 7, 2012)

Tesseract said:


> No worries. I wasn't annoyed, just a little surprised at your interpretation of my earlier advice on RPM sensors and targets. Now back to your initial questions:
> 
> A PNP proximity sensor (just called a 'prox' for short) requires a resistor from TACH to SGND to operate correctly. This resistor is often called a pulldown because it pulls the output down to ground whenever the transistor is off. A pullup resistor, which is used with NPN output sensors, pulls the output up to the positive supply voltage (ie - S12V on the Soliton controllers) whenever the transistor is off. Whether you use a pullup or pulldown resistor, then, depends only on the polarity of the output transistor.
> 
> ...


Thank you for suffering a fool gladly
I think I must of latched on to the pulse width thing, meaning longer between pulses, not longer pulses.
The reason I used long bolts was to create a larger diameter with out increasing the collar size, so as to give a longer time between pulses, (stupid me)
But as regards the security of the bolts, they are actually screwed into drill dimples in the motor shaft locking the collar and the bolts , they were going to be locked with stud, Loctite fluid.
Anyway, slight modification required (SHORTER BOLTS WITH LARGER DIAMETER HEADS)
Really appreciate your advice/guidance 
Thank you.
Oh, if Ruckus and Malcomb are around sorry for sounding like I new what I was talking about, I clearly didn't. I got it wrong big time, thank you for your input also.
On a positive note, I'm learning


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## MalcolmB (Jun 10, 2008)

No problem Martin. Glad you got it straightened out. Most of us are still learning here, and that definitely includes me


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## PStechPaul (May 1, 2012)

You could make a speed sensor from a shaft collar, machining two sides so that the on/off periods will be about equal. Like this:


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## TTmartin (Feb 7, 2012)

PStechPaul said:


> You could make a speed sensor from a shaft collar, machining two sides so that the on/off periods will be about equal. Like this:


That's nice and simple, looks good.
I've nearly finished modifying the one I already have but if it gives any problems, I think your suggestion will my be plan B

Thanks

Martin.


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## teoami (Jun 8, 2012)

Not to go too far off topic, or beat a dead horse, but I just wanted to clear something up. (Being a math nerd and all)

The diameter of a circle (in this case, created by the bolts) does not affect the frequency of said circle. 

Two long bolts vs two short bolts placed at equal intervals will yield the same number of pulses. The only thing that would increase the number of pulses is to add more bolts or increase the RPM.

Two circles of different diameters spinning at the same RPM will give you the exact same speed (or number of pulses).

However, I do agree that the bolts need to be locked in somehow and the shorter bolts with lock washers suit that need better. 
Also, the width of the bolt head will affect the pulse so you do need to follow the formula from Tesseract.


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## skooler (Mar 26, 2011)

teoami said:


> Not to go too far off topic, or beat a dead horse, but I just wanted to clear something up. (Being a math nerd and all)
> 
> The diameter of a circle (in this case, created by the bolts) does not affect the frequency of said circle.
> 
> ...


Yes you are correct.

The point that was being made was not about frequency. It was about the width of the pulse generated. 

By reducing the rotating circumference of the target (by shortening the bolts), the pulse width is increased (the bolt head is the same size but travel less per rotation). Therefore, the bolt head spends longer in an area where it can be picked up by the proximity sensor to generate the pulse.

Make sense?

Cheers,

Mike


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## Hyatt (Dec 3, 2012)

Hello Ruckus,

I am about to buy my sensor and thought I would just buy one I know is working with a Soliton controller. Can you give me the part number of your sensor? I can see the "E2E" in the picture, but that's all.

Thanks,

Hyatt


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## Tesseract (Sep 27, 2008)

Hyatt said:


> Hello Ruckus,
> 
> I am about to buy my sensor and thought I would just buy one I know is working with a Soliton controller. Can you give me the part number of your sensor? I can see the "E2E" in the picture, but that's all.
> ...


Ruckus doesn't have a Soliton controller and this question is very Frequently Asked, hence there is a FAQ entry about it on our website:

http://www.evnetics.com/support/faq/

Lots of good info in this thread as well.


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## Hyatt (Dec 3, 2012)

Thanks Tesseract! I had already been planning on buying from Automation Direct, it was a pleasant surprise to see that this is your recommendation.

Hyatt


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## ruckus (Apr 15, 2009)

Tesseract said:


> Ruckus doesn't have a Soliton controller...



Well, not yet, anyway...

Yes, the rpm sensor was for the Zilla in the 37 Jaguar. Soliton was not available then. Hopefully the Soliton is not so picky about the pulse length as the Zilla.

No complaints once I got the reluctor ring from RechargeCar. Tach works great.

Cheers


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## Hyatt (Dec 3, 2012)

Hello Tesseract,
I just ordered my PNP inductive sensor P/N AM1-AP-1A from Automation Direct and I’m trying to calculate the diameter of my sensing targets using your formula. Apparently my math skills aren’t up to date as my answers do not come out the same as yours. Can you tell me how long my sensing targets should be for 1” diameter shaft shaved down on either side as PStechPaul’s shaft collar is above? By way of explanation; I have an Advanced Motors FB1-4001A motor without a tail shaft. The shaft is slightly recessed into the housing and has a ¼” 20 NC thread bolt hole in it. I plan on turning a soft steel 1” cylinder and machine the sides down like PStechPauls shaft collar diagram. I want to keep the mass down (therefore the small diameter) of the target cylinder because it will only be attached by a 1/4” bolt to the end of the shaft. If I have to make the top of the cylinder larger, I can, but it will be more stress on that ¼” bolt turning at 6000 rpm (I’m not sure if this is the best idea). Any other ideas would be greatly appreciated. Hyatt


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## Tesseract (Sep 27, 2008)

Hyatt said:


> ...Can you tell me how long my sensing targets should be for 1” diameter shaft shaved down on either side as PStechPaul’s shaft collar is above?...


A picture is worth a thousand words, so below is a picture showing two examples of how to mill RPM sensing targets into a 1" stub shaft. The first example shows a channel cut with a 3/8" diameter end mill. This is the preferred method because cutting depth is not critical and sharp transitions in shaft radius will make it easy for the prox to detect them. The second example shows cutting flats (or "chords", as they are called in geometry) into the shaft. This will result in less sharply defined transitions but may be easier to do with a small manual mini-mill or with a file. It is important that the depth of flat (ie - the chord length) be the same on each side and that they are parallel to each other otherwise the controller might reject the pulses as noise.


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## Hyatt (Dec 3, 2012)

Thanks Tesseract,

I will use the "channel" meathod: One last question: Your drawing shows the channel depth going 3/8" from the center of the shaft (i.e. 5/8" deep), but your description says the depth is not critical. Would a 3/8" deep channel be deep enough?

Thanks again. I really appreciate the help.


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## Tesseract (Sep 27, 2008)

Hyatt said:


> ...Your drawing shows the channel depth going 3/8" from the center of the shaft (i.e. 5/8" deep), but your description says the depth is not critical....


Depth is not critical as long as it is outside of the sensing distance of the particular inductive prox that is used. If the prox says its sensing distance is 3mm and the spacing between the prox and the shaft is 2mm then the depth of the channel needs to be more than 1mm. It ain't rocket science, folks... 

Edit: shaft diameter is 1" so if the distance from the center to the bottom of the channel is 3/8" then the depth of the channel is 1/8", not 5/8". Radius is 1/2"...


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## Hyatt (Dec 3, 2012)

Thank you Tesseract,

I was covertly planning on machining a disc on the end of the shaft that was 2" in diameter and I forgot your diagram was for 1". Thanks for the help....I'd rather ask a few dumb questions and have it work the first time!

Hyatt


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## TTmartin (Feb 7, 2012)

Just like to share the Problem I had with my rpm sensor in case it could help anyone.
I've been testing my TT with some cheap lead to gain confidence in the conversion before taking the plunge with the big bucks lithium!
I have a soliton 1 with a kostov 11" 192v..
The rpm information in my case is so the controller can provide over speed protection for the motor.
I'm using a PNP proximity switch with a 1k pull down resistor
The rpm sensor is mounted on the motor tail shaft and sends the controller 2 pulses per revalolution, when I ran the logger program the rpm would only read correctly when coasting in gear, as soon as throttle was applied rpm reading would go to zero. I tried different pull down resistor values with no change.
I assumed the problem was interference from the H/V cables so I ordered an equivelent prox- switch but with a shielded cable, fitted switch/cable and grounded the shield to controller signal ground. 
The rpm signal is now spot on correct, I have set the motor maximum rpm in the controller settings to various speeds to test, and the controller cuts power where ever I have it set, I now feel confident there is reliable motor over speed protection.
So just trying to say go with a shielded cable if you want stable readings.
I know, most on this forum already know this but if there is anyone out there like me, hope this helps.


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## mk4gti (May 6, 2011)

^^ I've had a similar problem, the sensor needed to be closer to the ferrous material (in my case, set screws threadlocked).

Question:
I'm using a PNP Normally open LJ18A3-5-Z/BY, wired to a soliton jr (and also to the car's tach, in series). To my surprise, It's working quite well without a pull up resitor. Is this resistor really required?


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## Tesseract (Sep 27, 2008)

mk4gti said:


> ...
> Question:
> I'm using a PNP Normally open LJ18A3-5-Z/BY, wired to a soliton jr (and also to the car's tach, in series). To my surprise, It's working quite well without a pull up resitor. Is this resistor really required?


Yes this resistor is required. I get at least one tech support email per week concerning problems with erratic tach readings and the three most common causes are: 1) weak/missing pullup resistor (or pulldown, for PNP output sensors like yours); 2) running the tach cable alongside high power cables; 3) wrong sensing target distance.

NB - your sensor, specifically, has a maximum frequency capability of 100Hz, which means it will max out at 6000 RPM with 1 target; 3000 RPM with 2 targets, etc...


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