The 7i92 plugs into a dedicated Ethernet port and is $89 and http://store.mesanet.com/index.php?route=product/product&product_id=306&sear ch=7i92 for standard step/dir requires 7i76 for $119. Total $218. http://store.mesanet.com/index.php?route=product/product&product_id=119&sear ch=7i76 Or just into a Breakout board of your own choosing so the lowest cost option.
As I see it the 7i90is $59 but needs a parallel port or some other interface card or in fact you'd plug the 7i92 into the 7i90 to be able to add the multiple expansion cards if you didn't have a parallel port on the PC. Probably the most expensive approach. http://store.mesanet.com/index.php?route=product/search&search=7i90 Then there's the 7i96 at $119 http://store.mesanet.com/index.php?route=product/product&product_id=311&sear ch=7i96 which is Ethernet controlled and has the screw terminals for connections for a step/dir interface. Saves the cost of a breakout board. John Dammeyer > -----Original Message----- > From: Chris Albertson [mailto:[email protected]] > Sent: April-22-18 10:30 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Mesa choices > > Back to the title subject. I'm going to need to buy a Mesa card soon. > Is there any reason to prefer the 7i90 over the 7i92 or other ethernet > cards. It seems to me that even if I still owned a PC with a parallel > port the computer would also have an Ethernet port which is 10X faster and > uses cheaper cables. Possibly there is something about the 7i90 I'm over > looking? > > On Sun, Apr 22, 2018 at 10:19 AM, John Dammeyer > <[email protected]> > wrote: > > > Well said Chris. > > > > I worked on a system once where the 24V system bus shared a common > ground > > with a 12V instrument bus. The system bus could have as much as 20A > > flowing > > through it as a Servo motor moved one section. There was also other > > equipment that sporadically drew more and less current. They used one > > common ground from the battery/charger systm to all the devices tapping > > onto > > this ground wire where needed. > > > > On a small panel that approach had worked for them. When the > > batteries/chargers and 12V power supply along with one instrument were > 30m > > away from the rest of the instrumentation they had all sorts of induced > > noise issues. They argued that they had measured the noise on the 24V > > system in the control box with a scope and it was minimal. > > > > I demonstrated that if they ran the scope ground 30m back to the battery > > and > > measured the ground at the control box they would see lots of noise. > > Splitting the 12V and 24V grounds made the problem go away. The 30 > meter > > distance was still an issue since it wasn't physically possible to run a > > star ground for ever device back 30m to the battery. Add that some of the > > 24V devices had a non-isolated CAN bus and shared their CAN bus ground > with > > the 24V system the potential for the 24V return path to take the 12V return > > path. > > > > But the major 24V ground separation from the 12V was a big step in the > > right > > direction. > > > > John > > > > > > > Gene is right. Many people don't understand grounds. The star ground is > > > not magic. It is based on two basic laws of physics. Just two things > > to > > > remember > > > > > > 1) It is a fundamental law of electricity the current ONLY flows if there > > > is a loop. Take a straight piece of wire and connect one end to a > > battery > > > and leave the other end free and absolutely zero current flows and the > > > wires has EXACTLY the same voltage all along it's length. THIS is why > > > you use a star ground. No current will flow in the ground wire if ONLY > > one > > > end of each wire is connected to your ground reference. Make a loop > and > > > you have current. > > > > > > 2) Mr. Ohm has a law that says if there is current you have voltage. In > > > fact the volts are proportional to the current. So if you make a loop > > > with your ground wires there will be current and hence different parts of > > > the loop will have different voltages on them. It will not be zero > > > everywhere as you might think. > > > > > > Basically the combination of Kichoff's and Ohm's laws. People try can > > > get around this by using real heavy and thick ground wires. But they > > > forget (or never knew) that impedance has an imaginary component and > the > > > thick wire only effects the real component. This noise that is > > > transmitted is high frequency AC not DC. you have to make the path > "low > > > impedance" if you want to get around Ohm's law. This noise is basically > > > in the radio spectrum, big wires don't help much there. > > > > > > Just make sure ALL you grounds are "dead ends" There are places where > > > where loops sneak in. One of then is shielded cables where the ground > > > shield is connected to each end of the cable. > > > > > > There are more sophisticated systems where they shunt the AC to > ground > > > using capacitive coupling but don't even try unless you are a specialist > > > engineer. You do see this in some equipment. They use a capacitor in > > > parallel with a high value resister and they connect signal and > > protective > > > grounds this way. What they are doing is making a low impedance path > > for > > > AC to ground. > > > > > > The other thing you can and should do is try to stop this electrical > > noise > > > at the course. The best way to is again remember Kichoff. Current > > flows > > > in a loop. So any time to have a wire with current, say going to a > > motor, > > > some place there is another wire with that same current flowing in the > > > opposite direction. Always route those to wires as close as possible > > > Best way to do that is to twist them together. The opposing directs > > will > > > cancel any electric field. At about 8 wire diameters, from a twisted > > pair > > > the field will be nearly zero. So if you d this the noise will only > > > radiate for less then about an inch. Wire routing and layout matters. > > > > > > > But this brings up a second recommendation, which is to establish a > > > > single bolt as a common ground point, with the commons of everything > > > > else connected ONLY to this bolt. This is known as a star ground > > system. > > > > Stuff connected to the nearest ground often results in having more > than > > > > one ground and that constitutes a ground loop, which acts as an > > antenna, > > > > picking up noise from anything radiating it, and this noise can easily > > > > blow gates in the fpga on the 7i90. That bolt should also be the only > > > > place the 3rd rounded in the US pin in the power cord is connected, cut > > > > them off till you've only one left to get rid of ground loops, just > > > > don't cut the last one! > > > > > > > > > > ------------------------------------------------------------ > > ------------------ > > 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 > > [email protected] > > 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 > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
