Hey there,

A question I was hoping in a couple you guys can help me out with. This mainly dealing with a handheld digital 2 channel 100mhz oscilloscope. "MicSig"

So I've got this to use on my Tesla coil, I first designed one using one of those $80 handheld Chinese ones. Not bad for car use but that's about it. so now that I have this one I can actually see what needs to be seen.

So my actual scope question is what do I do when I get in these situations where I can't ground in two different places but need to? For example say on a full H Bridge you want to check the gate signal on the corresponding IGBT, if just checking one, your ground to the Collector and probing to the gate pin. If wanting to do both of these at the same time (same switch time opposite polarity) you can't ground one Probe on one collector leg and the other probe also ground on the other collector, when that Tesla turns on you would short those to IGBTs through your internal ground plane and probes.

Also please keep in mind that this is a portable handheld scope, so I don't have to worry about the Earth grounding issue, I can practically connect to my ground Gator Clips to whatever I want, obviously as long as the other is not on the opposite polarity. Lol but that's kind of my issue here with the Tesla coil and many other issues.

So my real question is this is happened to come up in a few different situations and difficulty how to surpass this, I have heard you can leave the ground open, and do a math function, but that never shows the same signal as if the ground was connected. But this issue has now come up at least 20 times in my electrical Hobby, if anyone has any tricks to help get around this issue I would love to hear any ideas, Thanks

 

Both the shells on the vertical inputs of your scope are common to each other. The scope does not have differential input channels. About the only option you have is to buy some differential input probes for your scope. Since you mention MicSig as to the scope here is an example of a differential input scope probe. The problem being you need differential floating inputs and only have single ended inputs. The link is merely an example, dozens of manufacturers make differential input probes for scopes in a wide range of flavors.

Using both channels as you mention and applying a math function will result in what amounts to one channel.

Ron

 

Does you scope allow differential measurements, probe grounds un connected ?

Google "differential measurement oscilloscope", several videos on doing this.

https://electronics.stackexchange.c...signals-like-rs-485-or-dmx-on-an-oscilloscope


Regards, Dana.

 

RE:""Lol but that's kind of my issue here with the Tesla coil""
Then Your situation is some hundred time more bad as mine where I am playing all beyound the 10kV. The only solutions are 1) two separate oscillos floating on the separate batteries 2) HFBR23xx to HFBR13xx series (to and from) glass-fiber converters, and rely that Your million Volts may not flow through via meters and meters long glass piece.

 

P.S. For the H-bridge gate probes may be used the inductively coupled one-turn coils along the wire. Dont make then common mistake, coil over the wire has orthogonal field thus no effect at all, it must be along the wire.
Second - most of H bridges never are going over the 535 or 600 Volts. Thus the robust sensitivity may be set and ray shift button may be used.
Third, for many cases there You are not bother of absolute voltage levels, but only relative. Then may use the capacitative divider circuit to insulate from DC component. So, for the H-bridge most situations the more sophisticated systems are unneded.