On Sunday, 20 March 2022 23:59:14 EDT Thaddeus Waldner wrote: > Update on the laser probe. > > Thanks to some input from this group and a discussion with Peter at > Mesa tech, I now have a laser distance measuring device reading to > within 0.001”. The range of my instrument is about 2” and I need only > about 1/2”, so I can get the precision down to 1/4 of that. Not that I > need it. > > As I mentioned earlier, the laser instrument is a Keyence > iA-1000/iA-060. The output from this device is a scalable analog > 0.5-4V signal. > > I built a small board that powers the laser, converts the voltage to a > frequency, and feeds signal into an encoder configured for count mode. > 24v Power enters the board via a pair of screw terminals. This power > is filtered, regulated, then brought out to the laser. The analog > voltage signal is converted to a frequency signal, which then goes > through an isolator and is delivered to the mesa board via the P1 > expansion socket > > I used an Analog Devices AD7741 voltage to frequency converter. This > device needs to be clocked with either a clock input or a crystal. I > used a step generator output for this. > > The isolator I used is a NVE IL-712-2E. This is a 2-channel “digital > isolator” with channels running in opposite directions. This device is > remarkably fast; propagation delay is 15ns and max pulse width > distortion is 3ns. I have never before heard of digital isolators.
> Are > they a new thing? Any reason why not to use them over optical > isolators? Not particularly, TI has been making something like that for a couple decades. But at the time I considered using it, it wasn't functional at DC and I needed that more than the speed. If they'll do DC, the only reason not to use them would be cost. But theres a point of no return for that great speed, driving a stepper, which has inductance just like a 3 phase motor being driven by a 255 volt source, the inductance of the motor is limiting the field current to less than an amp at 200 hertz, so the torque vanishes about then unless your vfd is fed from a much higher line voltage. Because the electrolytic caps in the vfd can only take around 450 volts continuously, the line voltage limits are hit at about 380 volts, which still isn't enough to get you all the way to 400hz out of the vfd with any torque left, not to mention the possability of exploding the fan in the motor since a 4 pole, 3 phase motor is turning 12000 rpms at 400 hz. Most are made to run till the rapture at 1750. At my place, the rotor balance if iffy, and 6000 revs is beating the motor bearings pretty hard. > > If I had been smart, I would have just purchased a mesa THCAD card. I > would have accomplished more but learned less. > > Thaddeus Waldner > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > . Cheers, Gene Heskett. -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
