On Wed, Jan 24, 2018 at 4:06 PM, Dave Cole <linuxcncro...@gmail.com> wrote:
> That is likely an unshielded prox switch. That means that the sensing > pattern is a blob that sits right at the base of the plastic tip, not > above it. > That means that they can also sense to the side of that plastic tip as > well. You need to be careful that you don't have any metal next to the > plastic tip. > > The prox switches which do not have a plasic tip, but where the plastic > tip is within the sides of the metal sensor tube are considered shielded > prox switches. They only sense above the tip and not to the side. Their > sense pattern looks like a short flame that comes out of the tube. > > I tend not to use unshielded proxes as they can trigger sometimes when you > don't expect it due to brackets nearby etc. > > Its amazing that they can sell those for just over $2 bucks.. Crazy cheap! > When these show up I will test there pattern my intentionally misaligning them. But if used for a machine end-stop the target can be pretty well controlled. That is $2 with FREE shipping from China. It is pretty much the standard price, not a special deal. Factory workers in China make about $3.50 per hour so $2 retail allows for maybe 5 minutes of labor per unit. Reasonable if the factory is automated. I was watching a video id Apple MacBook cases being milled from billet. The Mac has just one structural part, the unibody case itself. These are made literally by a millions from one foot diameter aluminum "logs" that are the size of utilty poles. VERY little human labor is required, the "logs" are pressed into plates, cut and milled by a special purpose machine. So even with labor at $3.50/hour they don't use much labor. I > > Dave > > On 1/24/2018 3:18 PM, Chris Albertson wrote: > >> An interesting you tube video by "Tom's 3D". He talks about 3D printers >> but much of the technology applies to machine tools. After all they both >> run G-code. >> >> In this video he measures the accuracy of end-stop or "home" sensors and >> compare microswitches, with and without levers and also varies kinds of >> non-contact sensors. He runs each kind into a stop at both high and low >> speed and after 100 tries has data for standard deviations. >> >> Result is that removing the lever from the microswitch reduces standard >> deviation by about 3X. I assume because the per has about a 3X >> mechanical >> advantage. But it's surprising is that a $2 inductive sensor beats even >> the non-lever switch. >> >> It might be moot as all the measurements are in microns (micro meters) >> >> But on the other hand if these dirt-cheap inductive sensors are this good >> and importantly they are water and oil tight with no moving parts we >> should >> be using them. >> >> Here is the winner at 0.27 microns standard deviation >> ebay.com/itm/LJ12A3-4-Z-BX-Inductive-Proximity-Sensor.... >> <https://www.ebay.com/itm/LJ12A3-4-Z-BX-Inductive-Proximity- >> Sensor-Switch-NPN-DC6-36V-Great/272907213327?hash= >> item3f8a899a0f:g:6fwAAOSw~gRVyHZ-> >> >> The blue end looks like a button switch but it isn't. This is a >> non-contact sensor. It triggers when it senses a metal part at 4mm >> distance (with a surprising 0.27 micron standard deviation) >> >> Here is the video, The application is different but look at his test >> setup. It pretty much mimics what you would do on a milling machine. >> https://youtu.be/il9bNWn66BY >> >> How to use them: There are three wires two are power, you apply between 6 >> and 36 volts, typically 12 volts. The third wire is either normally 12V >> or zero and then switches state when the sensor is tripped. Of course 12 >> volts would fry your computer so people use a voltage divider of optical >> isolator or even a switching diode. >> >> The typical use for these is industrial automation, food processing, >> manufacturing or whatever. >> >> I have ordered a few and will experiment. >> > > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
