Testing; Choosing the right sensor for RPM
Testing; Choosing the right sensor for RPM
(OP)
I have no previous experience collecting RPM data so would like advice from those with previous experience. I need to collect RPM data from my machine and record it's behavior as I apply and remove power. I'll be engaging and disengaging a load. So I'm trying to find out how long it takes for it to come to a rest when I remove power. There are a few pulleys and spindles I could have a sensor observe to collect the data from.
My question, what is the optimal sensor for this job? I've come across information to suggest a hall effect sensor or an optical lazer sensor could fit the bill. There will be a fair amount of vibration so I'm not sure if that creates a big disadvantage for either sensor.
-Max RPM is under 4,000
-time for the output to come to a rest should be about 2~10 seconds.
-sample rate only needs to be about 100 Hz. (would like to reliably know within at least 0.1 s of output stopping)
Anyone familiar with this type of test have some recommendations??
Thanks
My question, what is the optimal sensor for this job? I've come across information to suggest a hall effect sensor or an optical lazer sensor could fit the bill. There will be a fair amount of vibration so I'm not sure if that creates a big disadvantage for either sensor.
-Max RPM is under 4,000
-time for the output to come to a rest should be about 2~10 seconds.
-sample rate only needs to be about 100 Hz. (would like to reliably know within at least 0.1 s of output stopping)
Anyone familiar with this type of test have some recommendations??
Thanks





RE: Testing; Choosing the right sensor for RPM
What is the expected max speed?
How long do you expect it will take to "come to a rest"? Minutes? Seconds? Micro-seconds?
How accurate do you need to be for the overall time?
How accurately do you need to know what happens while it is coming to rest?
Many of those question also affect the choice of data logger.
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
I assume your vibration is not specifically the shaft against its mount.
There are lots of possibilities:
> Hall effect
> Absolute encoder
> Back EMF measurement at motor windings
> gyro
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
For the vibration, my first test is gonna be a lawn mower, so the whole chassis of the mower deck should be vibrating a fair amount, but I'm not sure how much movement there will be from the shaft relative to the deck.
@MintJulep, When I remove the power it should be the start of the timer, since it will need power to remain engaged.
RE: Testing; Choosing the right sensor for RPM
The shaft had better not be translating relative to its bearings, otherwise, you have bigger problems than starting and stopping times.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Testing; Choosing the right sensor for RPM
Well, maybe you can; I haven't worked with an Arduino, so maybe they are fast enough, but time-based sampling, as noted, is not going to give you what I think you want. You need something that produces a fair number of pulses per revolution, and measures the time between successive pulses, then computes RPM from the pulse rate.
Mike Halloran
Pembroke Pines, FL, USA
RE: Testing; Choosing the right sensor for RPM
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
I'll possibly save you some time here; plastic gears exist, of course.
If you wish to use one with an optical sensor, face it with metal foil or brass.
Even 'black' plastics are translucent at the infrared wavelengths used by optical sensors.
Worst case; you start with a low-gain sensor that can't see through plastic, and
later you get a batch of sensors with higher gain, same part number, and
they can see through your gear or interrupter flag or whatever, and
you get to retrofit truly opaque parts because you can't get a sensor
that's reliably bad enough to work. Happened to me a long time ago..
Mike Halloran
Pembroke Pines, FL, USA
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
with ttl output.
https://monarchinstrument.com/collections/tachomet...
RE: Testing; Choosing the right sensor for RPM
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
@GregLocock, dead posh? I'm not familiar, could describe?
@CWB1, Since I'm trying to be cost effective, that sounds in-line with my preferred approach. I'll probably utilize this on multiple machines, so if it is easier to setup, that will be a bonus too. Do their tend to be calibration issues with the reflective tape option?
Thanks
RE: Testing; Choosing the right sensor for RPM
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
There is still an infinitely large solution space. One could use a tachogenerator or a magnetoinductance tachometer or just two pickup wires that are shorted by a paperclip taped to something that moves attached to a timer or a centrifugal switch via slip ring or ................
What still impresses me is that your stated goal is measuring coast down time, which is a matter of losing kinetic energy stored in the machine (can be calculated) to various friction losses (some can be measured, others estimated) eliminating the need for testing.
Alternatively, the whole thing can be estimated by running the machine at various RPMs and measuring the power required to drive it at those speeds and then integrating to get an energy-loss curve. The area under the curve to any point represents the kinetic energy that will be absorbed when the power is cut off. This can be integrated over RPM to create a direct reading chart. Since the mechanical energy storage can be calculated for any RPM it's just a matter of looking at the chart.
Or you could just use a camera and record a video. Depending on the camera you can easily get the time to within 1/50th or 1/60th of a second or less. Or a sound recorder and run the result through Audacity or something similar.
RE: Testing; Choosing the right sensor for RPM
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
Walt
RE: Testing; Choosing the right sensor for RPM
RE: Testing; Choosing the right sensor for RPM
This is a good idea. Having measured many machine startups and coast-downs, I can say that transient measurememnts of speed, vibrations, sound, ultrasound, motor current, torque, and torsional vibrations presents greater challenges than steady-state measurements.
Walt
RE: Testing; Choosing the right sensor for RPM
Monarch could probably give you some idea as well. I would trust them to shoot straight.
RE: Testing; Choosing the right sensor for RPM
If you truly need to detect when Zero speed (at rest) occurs, then you should look at encoders and not 1xSS sensors, of any type. There are some hollow shaft encoders, but most mount on the end of a shaft. If you can do your test down to some defined "minimum speed", for example 5-rpm, then you could probably use a 1xSS or multi-pulse tachometer. I suggest additional study on what you want/need and what can be done with various speed measurement methods and sensors. Consider getting a free demonstration or renting before purchasing stuff that does not work to your expectations.
Walt