Hello Kirk, I don't see why you should not be able to measure your mains phases with an ordinary oscilloscope, set up as usual. At least in this country, the three phases of mains current are ground referenced, 230 V effective voltage to neutral. Between the phases, as can be figured with a triangle formula or by trigonometry, there are 400 V eff. (not ground referenced, of course). Connect each phase with a high resistance probe or, if exact magnitude is not important, with a small capacitor. It's just measuring a ground referenced voltage, a little higher than usual, but still. No floating oscar, as long as you don't want to measure differentially between phases.
E.g., right now, I am working on an induction heater which outputs 28 kHz at 800 V maximum, 500 V eff. No problem with my 40 year old oscar. Since this voltage is ground referenced, I can hook it up to the oscar input with the ordinary 10 MOhm probe, 1:10. I leave the probe's ground crocodile off to avoid cross ground currents through the oscar. I only have to watch the way the plug is connected to the wall outlet to make sure the leg I am measuring at isn't the grounded one :-) Since you have only a 2-channel oscar, connect one phase permanently to one input for triggering and switch the other beam between the two other phases. This will show you their phase difference. Best spring greetings Peter Blodow Kirk Wallace schrieb: > In order to investigate three phase issues more, it would be nice to > measure at least two waves at a time. I have a two channel scope, but > the channels are ground referenced. I can float the scope, but I think > this will only allow me to measure one signal, or two if they happen to > have the same reference point. Plus I don't think floating the scope is > the safest practice for me or the scope. What might be good is to have a > box that floats like a DVM but can feed a scope channel. What sort of > keywords should I use to find such a thing, or is there a better way? > ------------------------------------------------------------------------------ Colocation vs. Managed Hosting A question and answer guide to determining the best fit for your organization - today and in the future. http://p.sf.net/sfu/internap-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
