Optical tach recommendations? - Page 1
Forum section: electronics / testgear

author: IDEngineer
author_rank: Super Contributor
timestamp: October 27, 2020, 05:48:18 am
content: I tried going cheap but get wild readings all over the place. A search here didn't reveal any recent recommendations. Any decent optical tachs out there at reasonable prices? Thanks!

author: tautech
author_rank: Super Contributor
timestamp: October 27, 2020, 07:59:31 am
content: The reflective pad used can make an absolute world of difference !Recently I had to use my old one to get an accurate shaft RPM and the few reflective pads that I have left that came with the thing weren't up to the task. I suspected as much so took some other tricks like white fly tying head paint and Twink type correction paints. None gave repeatable results.White electrical tape....forgetaboutit !However at the location was some plastic road cones with their highly reflective sticky tape wrap so a small sliver was taken with a craft knife and repurposed for optical tach needs.The result was like night and day !The RPM certainly wasn't demanding, only some 1500-2500 RPM however it was on a shaft of a monster vibrationary plate mounted on and hydraulically driven by a 35 tonne digger so there was a shaft vibration factor that right royally stuffed RPM readings of what should have been a piss simple job. We ended up able to see rock stable single digit RPM changes close to what had been calculated rather than all over the place and even double of what they should've been.As I type that unit is now some 300km away installing seven hundred 300mm SED timber poles 21m into the ground.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 27, 2020, 12:07:33 pm
content: That's an inspiring story, thanks! I'm on the road but will specifically try different reflectors when I return. I have been using metal foil tape which certainly seems reflective enough, but who knows. Thanks again!

author: wizard69
author_rank: Super Contributor
timestamp: October 28, 2020, 03:12:06 pm
content: Quote from: IDEngineer on October 27, 2020, 12:07:33 pmYou didn't mention if you needed a handheld or mounted solution however one brand that has worked great for use at work is Shimpo. We have used older variants of the DT-207 series at work for years:http://shimpoinstruments.com/tachometers/dt-205lr_-_dt-207lr.These are built like tanks and the only failures we have had are leaking batteries creating grief. They have a whole series of tachs so you have choices beyond that.At work we make use of permanently installed tachs that use a laser head combined with a DIN rail module. Unfortunately I'm not at work and can't remember the brand name.As Tautech pointed out there is a massive difference in the quality of retro reflective tape which causes us problems with not only tach readings but in the use of various optical sensors. As such you may have to experiment with the various reflective tapes on the market. Sometimes you are better off with a retro reflector but those seldom are usable on rotating shafts.As for brands of reflective tapes, we have many around the shop so I can't tell you off the top of my head which have proven to work well. Sadly some tapes are not much better than black flocking, seriously!!!! I can also confirm that what is supplied with a meter isn't always the best retro reflective material out there.The other issue you might run into is lack of contrast between the reflection off the target and the shaft itself. We have had this issue with stainless steel and have made use of black tape to mask off everything on the shaft but the retro reflective target. Fortunately this is on a low speed, small diameter shafts so we don't have balance issues. On high speed devices you may have to take precautions with respect to balance.One other trick that I've had work for me is the no reflective tape method that makes use of a setscrew hole or other hole that might be on the shaft or component on the shaft. Instead of a reflection you rely upon the lack of a reflection. In terms of electronics it would be like looking at the portion of a square wave that goes to zero. You would likely need a laser baser tach for this and one that would understand what amounts to an upside down wave form. The no tape method can save you some grief. Other no tape approaches include Sharpy markers, flat black paints, and even white out "ink".By the way White Out Ink should be in every bodies tool box. There are all sorts of uses for the material that have nothing to do with typing. That would be a thread all on its own.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 28, 2020, 03:46:51 pm
content: Quote from: wizard69 on October 28, 2020, 03:12:06 pmput reflective tape on both side of rotating disc/shaft, make sure glue is strong to avoid tape flying away. you'll get double the rpm, simply divide it by 2. combination of both black background tape with white or reflective tape may improve result. for much higher speed that tacho cant measure reliably, increase white:black tape ratio. if that still cant work, try to test indoor. outdoor light maybe overwhelming. the only limitation so far with my cheap china laser tacho is when rotating mechanism that need measuring is too small to put any adequate reflective tape for the tacho to measure or differentiate. sometime the trick can be done is if we can stick a bigger/dummy disc to the mechanism just for reflective area and successful measurement, ymmv.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 29, 2020, 02:29:21 am
content: Sorry I didn't provide speed info. Max RPM is ~6000, so not that fast. Most measurements will be ~3500 or lower.Handheld with batteries. This application is automotive so AC power is unavailable and I really dislike 12V adapters and inverters and the like when battery solutions are available.

author: wizard69
author_rank: Super Contributor
timestamp: October 29, 2020, 10:06:06 am
content: Quote from: IDEngineer on October 29, 2020, 02:29:21 amWhen doing anything automotive there is always the automotive specific solutions. SnapOn for instance has a couple of units.In any event a laser based unit is possibly safer due to being able to put some distance between the shaft and the tach. You might also want to consider tachs, usually integrated into other instruments, that use inductive (spark) pickups. Of course inductive pickups assume internal combustion engines using spark ignition.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 29, 2020, 06:20:21 pm
content: Recently I had a little job of checking the lineairity of the PWM signal of a CNC machine to a 1.5kW inverter and 24000rpm spindle, but I do not have a RPM meter.I improvised with a small magnet, Hall sensor, Breadboard and oscilloscope.It worked nicely, but luckily I had some more magnets, as the first one flew away when the spindle reached 18000rpm. Next magnet was fixaded with a few layers of tape.

author: mjkuwp
author_rank: Unknown
timestamp: October 29, 2020, 07:45:11 pm
content: https://www.amazon.com/Neiko-20713A-Digital-Tachometer-Contact/dp/B000I5LDVC/ref=sr_1_3?dchild=1&keywords=neiko+optical+tachometer&qid=1604000549&sr=8-3less than $25 USD and I am reasonably sure that it will come with a length of the reflective tape that you need.Neiko or other brands that look like this work well. I've purchased at least 3 of these and measure things up to at least 3000 rpm. I also bought a more expensive one from UNI-T that worked less reliably even though it seemed to have nicer-looking optics.You do need to use the special reflective tape. Sometimes it can work better to be a little bit off-angle. If the background is shiny metal then you need to paint it black or put masking tape on it to mute the reflection.that said, I have had this tachometer work with the sticker on shiny plated metal just by having the tachometer off-angle as already mentioned.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 29, 2020, 09:22:54 pm
content: almost similar to mine but since the OP hinted that he didnt want the cheap option so i didnt make the suggestion. i still keep some reflective tape that came with it in the carrying bag since normal white tape (or paper) bought from local shop can do the job as well, so i prefer to keep the original.. my record said i bought it 6 years ago and i havent change the battery iirc (seldomly used) here is $8 in ali...https://www.aliexpress.com/item/32891590838.html?spm=a2g0o.productlist.0.0.6f524babwdkbhC&algo_pvid=f83e972d-d8cf-44ca-be04-12898c8b014d&algo_expid=f83e972d-d8cf-44ca-be04-12898c8b014d-0&btsid=0bb0623316040062801462093eb99a&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

author: Circlotron
author_rank: Super Contributor
timestamp: October 29, 2020, 09:51:39 pm
content: I’ve got one of these I’m happy with. Calibration is reasonable, with a function generator pulsing an LED aimed into the lens 90,000 rpm reads as 89,999. Has a USB output for data logging. As others have said, sometimes you need to aim off angle, and contrast between reflective and non reflective can be an issue.