Floating the 'scope

the

That last link has a better picture.

Where are the scope inputs?

I see 4 multimeter-like inputs along the bottom, colored red, red, black, red from left to right. Are these also the inputs for the scope? I don't see any other inputs. Are they on the side?

That's what the vertical offset knob is for.

You only get one differential channel per 7A13. Each isolated channel on the TPS2024 is a differential input when the ground clip can be connected anywhere, so there are 4 differential channels.

Point taken.

Yep a scope with true isolated inputs is the best solution.

The last time I went looking for one they were all in the thousands or at least over a grand. That was a couple of years ago though.

There seems to be a lot more out there now for just a couple of hundred. Maybe its time to look around again.

the

yes, they are on the right bottom side. I don't know why they don't show the picture of them.

Power jack on the top left, along with the serial port/USB and back light switch on the left side.

I've seen a lot of IEC power cords with the ground pin cut off. Those were cut up for scrap.

hardware

WTF is a ground buster? Are you referring to a two to three wire ground adapter? If so, use the proper name.

I've been doing electrical measurements for nearly fifty years, and I've never had one.

Tek actually used to make one. Anything over about 15 - 20 volts float and it tripped the supply, I've only ever seen one, in the hands of someone else.

Some people are animals. Calibration? Wossat?

Some of the things I've seen done to instruments, you wouldn't believe.

Bandwidth / risetime isn't enough for what I need. The CT3686 might cut it.

How many screens will it window?

Does it have a calibrated comparison voltage? Useful for things like measuring staircase steps.

I've never needed 4 differential channels, but if I did, I'd use two mainframes and four 7a13s (Yes, I do have four)

I've used a 7a13 for vertical deflection on a couple of occasions. You can put amplifiers in timebase slots. Full differential X-Y.

I'll have to check that on Monday, but I've never needed more.

The value of the offset is displayed as a 3 digit number on screen. The deflection factor is also calibrated.

When using two mainframes, how do you see all four traces on the same screen?

Isn't vertical deflection the usual mode? Maybe you mean that you used a 7A13 for horizontal deflection. Isn't that what you'd have to do for X-Y mode?

Most modern scopes have an X-Y mode; so does the TPS2024. Since all the channels on the TPS2024 are effectively differential, its X-Y mode is a differential X-Y mode

The TPS2024 can do math functions on differential signals, too.

Sorry I'm not trying to be stupid. I certainly wouldn't float the scope if I was looking at high voltages or AC line signals. Most often I float the scope because I've got some interference that looks like it might be a ground loop. I want to see if it's through the scope. I have a single AC line cord with the third wire clipped. It's got green tape on both ends of the plug. It stays in my wire drawer. If it somehow makes it's way onto the production floor I can easily retrieve it (The green tape helps.)

George H.

es

Oh, connecting to line voltages is something I thankfully have to do rarely, and when I do it's with great care. (I do own a suicide plug that is a one piece AC to banana... scary...)

George H.

=3DEN

scopes,

=3DEN

Thanks Hammy, you're right we should buy an isolation transformer. Is it OK to power the 'scope with the isolation tranny? Or does this defeat the whole purpose again?

"> Its not really a good idea to float your scope."

What about floating it to get rid of ground loops?

George H.

=A0 =A0 =A0 =A0 =A0(Stephen Leacock)

Yup, that's what I should have done, But I'd have had to find the matching 'scope probe (They tend to wander around and become separated.) And the floating AC cable was lying there behind the equipment. (I'd just been using it.)

George H.

ce of

und

Yup, I'm just like most idiots! (But I put green tape on both ends of the cord.) The ground buster was before the universal AC input.

George H.

of

Good for you. That would get you fired any place I've ever worked. If you needed isolation, you plugged whatever you were working on into an isolation transformer. If OSHA found a cord like that, the company would be fined and it could run into thousands of dollars.

Lotsa luck selling the 'don't tamper' argument on this newsgroup. Better to point out the option of making a CLEARLY VISIBLE indication of the floating case, like a hulking isolation transformer next to the 'scope.

Floating the 'scope is one of the great useful techniques, it must be implemented somehow on a good test workbench.

That's at 1mV per division.

I guess you mean at greater input attenuator settings?

As can the 7A13

The 7A13 offset is actually a "real" DC voltage, indicated by a "real" DVM. Also available at a front panel socket for external measurement.

There aren't many instruments whose deflection factor isn't calibrated. They wouldn't be of much use without.

You don't. You use two screens.

You're right, I meant horizontal (X). I tend to think "X and Y". My mistake. Peccavi et mea freakin' culpa!

I don't think I've ever had a 'scope that wouldn't do X-Y. going back 40 years. Some had restricted X bandwidth.