02-08-2006 09:08 AM
02-09-2006 10:53 AM
02-10-2006 09:30 AM
Thanks Thaison, That was very helpful. Now I have a followup question. I also plan to use the digital I/O on the same 622X board, and I wonder if I'll have the same problem with that. My gauge readout has some digital output lines that indicate which scale its on. They use the same ground as the analog signals. How do you recommend I handle those?
Thanks,
Tim
02-13-2006 06:22 PM
02-24-2006 09:52 AM
Thanks Thaison,
Now I have a followup question related back to my original analog input situation, this time having to do with signal cable shielding.
I have several gauge readout units and for each one I will have an individual twisted pair going to its analog output signal and ground (the other end will be connected to differential inputs of a PCI-6225). The shells on the DB9 output connector of the gauges don't seem to be connected to either the signal ground or the case ground. Actually, neither the shell nor the signal ground nor the instrument case seem to be connected electrically. So I'm suspecting I could connect these shells together, unlike the analog signal grounds. When a cable is connected to an output jack like this, usually the shell of the jack would get electrically connected to the shielding of the cable. I plan to have a multi-conductor cable bundle, from which one twisted pair from the bundle will go to each unit. I can either have one overall shield for the whole cable bundle and connect it to the DB9 shell of each gauge unit (thereby connecting all the shells together), or I can use a cable bundle that has individual shields for each pair of wires, and then connect each individual shield separately to each shell of every gauge readout, thereby avoiding connecting any shells together. So my question is, is it necessary to avoid connecting the shells together, requiring me to use individual shields, or can I just use an overall shield and connect the shells together to the shield? Since the shells seem to be floating, that would mean any shield connected to it would also be floating, and that isn't good according to the article you referenced. That would also mean there wouldn't be any advantage to using individual shields. Perhaps I should avoid using the shells altogether and just use an overall shield and connect it to the case of each gauge. If there is another recommended way to do this, I'd also like to know that.
Thanks,
Tim
02-27-2006 12:11 PM
02-27-2006 01:23 PM
Thaison,
I anticipate using a cable bundle that splits at the end into 9 twisted pairs, each pair being soldered to a male DB9 connector that mates with the DB9 female connector on a gauge readout unit. The shell of the DB9 output connecter on each gauge readout unit would become connected to the shell of the connector for the twisted pair when it gets plugged in. I guess the shells don't need to be connected - I could make sure the cable is constructed so that if I use individual shields, none of them gets tied to any of the connector shells. I could then connect a short lead from the shield to the gauge's chassis. But if the gauge's shell is really floating, then it wouldn't matter if it is connected to the shield, as long as the shield gets connected to the chassis to ground it (or them). Now, since all the gauge readouts are all mounted to the same strip of steel, if I do connect the shield to the gauge's chassis, it shouldn't matter if I use one overall shield or if I use individual shields. I think I should go with a single overall shield and then connected that shield to one of the gauge readout's chassis and not worry about the shells on either the cable or the gauge readouts. Does that sound reasonable to you?
Thanks,
Tim
02-28-2006 07:15 PM