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Forum Index : Electronics : PTO RPM meter
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| Buchan Newbie  Joined: 25/09/2011 Location: AustraliaPosts: 12 |
Hi Folks, I need to measure (on the run so to speak) the RPM of my tractor's PTO shaft. The reason is to ensure that clutch connected equipment (such as a slasher) is working at the optimal RPM and the tractor PTO clutch is not slipping. Slippage in the tractor PTO clutch will necessitate a rebuild of the tractor which will cost several thousand $. I am not able to place a sensor directly on the shaft due to balance (it spins at 540 rpm for most applications or about 1100 for a few applications). As you can appreciate, this is an environment that is dirty, dusty and vibrates a lot. As implements are connected using a universal joint, I was thinking of trying to sense magnetically each part of the joint as it turns, but I can't find anything to do this. Maybe someone can help me with this. I am able to build the display and use a PIC to do the calculations, but the sensor is the part I am not able to figure out yet. Regards, Doug. The Farmer |
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muddy0409 Senior Member  Joined: 15/06/2011 Location: AustraliaPosts: 125 |
What comes to mind first is a proximity sensor. These can be obtained from electrical wholesalers, or even Ebay. I am not certain of just what speed they can operate at so a bit more investigation would be needed. Sensing distances also vary with models, so you should be able to find one that you could mount on a bracket to detect the uni joint spinning? www.oceancontrols.com.au has quite a lot listed. Don't poo poo conspiracy theories. Remember that everything ever discovered started somewhere as a theory. |
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Bryan1 Guru  Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
G'day Doug, As the PTO will have a bit of space where it leaves the rear of the tractor one could mount a neo magnet and use a 1101 hall effect sensor to monitor pulses. If you like I do have some 3x3mm cube neo's and some of hall effect sensors which I send you if you like. By using a slow revving drill one should be able to drill a hole for the neo and as far as the hall sensor goes, make a bracket to hold close to the magnet then pot it to keep the dirt,mud and any other crap out. Now as you have said you can use a pic Timer0 can be used as an external count but only being 8 bit one will have to count less than a second them multiply the result to get the correct rpm. Too easy..... Let me know if you want the magnet and hall effect sensor and PM me with your address and I'll send them over to you, no problems. The only thing I will ask is that you make it open source and if it does work out Glenn can always make a page on his website to cater for it. Regards Bryan |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Yes Doug, you can place magnets on a rotating shaft without affecting the balance. Just place 2 identical magnets at opposite sides of the shaft. This is how the cruise control that I retro fitted to an old troopie got its speed info. The drive shaft of a big 4WD is a bit like your PTO when it comes to running in an harsh environment. For really *securely* attaching the magnets, just sticking them in place with some epoxy is not good enough. The magnets I used came potted in little holders that were epoxied and wired to the shaft. I used ss wire. It was still working reliably many years later when I sold the troopie. Using the small but powerful neo magnets lets you to mount the sensor a little further away with less dirt clogging problems. Keep in mind that these hall type sensors are directional and the magnet has to be oriented correctly for maximum sensing distance. Klaus |
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| Janne Senior Member Joined: 20/06/2008 Location: FinlandPosts: 121 |
I would also go with the proximity sensor, or inductive pickup sensor as they're otherwise known. No need to fiddle around placing magnets on the U-joint, they will not probably stay there for long anyway. 540RPM is only about 20 pulses / second from the U-joint, so it would be suitable for most of the inductive sensors. Something like this: Ebay link If at first you don't succeed, try again. My projects |
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| Buchan Newbie Joined: 25/09/2011 Location: AustraliaPosts: 12 |
Thank's for your help. I have decided to try an IBP-003 proximity sensor from Ocean Controls. This allows enough room from the shaft and shield to mount and run a cable back to the cabin. I am not sure what PIC to use yet, but as was written, this is a simple job - only to sense, calculate the RPM then drive a display screen. Doug. The Farmer |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Doug, The 16F628A would be suitable. Altronics sell them for $6.50. This PIC has 3 hardware timers/counters. So you could use one to count the time period & another to count the proximity sensor pulses. Len |
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