An OT oscilloscope question

Does it bother you that I posted an electronics question on the metalworking newsgroup? Don't you think that oscilloscopes could be useful in a machine shop? And that others might also find the answers to my question useful? I have used mine, with guidance from RCM, to decipher encoder signals for digital readout of machine travel. And to properly adjust, once again with directions, servo amps for a home made cnc machine. Both of these examples are of interest to others on this group. And the responses to my OT oscilloscope question leads me to believe that other people on this newsgroup are interested in this post also. ERS

I found the manual in the shop - it is a tech full parts/design inside. In the leather type covers tek used. If you get a xerox kind of junk - let me know - and it is yours. Doesn't do me any good, my scope I bought new from Tek and have the manual set. Phew!

Wish I had the B though - it was a good scope when I had it at work. They dumped it - I kept the manual.

Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

Eric R Snow wrote:

According to Eric R Snow :

[ ... ]

No bets. It depends on other interconnections. If it is running from gasoline, and it is not connected to the house wiring at all, then it is *probably* floating, at least until you touch some part of the metal.

You would probably be safer to use the differential measurement setup which I described last night in another branch of this thread. That way, you don't have to worry whether there is an accidental path to ground from any part of it.

Good Luck, DoN.

Not all readers of RCM are one-trick ponies. Spehro is one professional very competent in elex that contributes to this ng from time to time.

Yes, but... as a reasonable newsgroup user... you will also find Sperho over in the electronics groups. To ask an oscilloscope question in RCM you should at least pretend it is connected to your Bridgeport's VFD.

It seems as though the OP is trying to use an oscilloscope to test a electrical generator, which is close to the topic of this NG.

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Yes, if you were discussing what the oscilloscope could show you about your generator I would not have an issue, but for oscilloscopes 101 or a discussion of the Tektronix 465B calibration procedure I don't think RCM is the best place. I own a 647A and a TDS 210 but I do not own a

465B. Until you are talking about both the generator and the scope I think you would be simply be better off talking to another 465B owner in an electronics newsgroup. Once the 465B is no longer the central topic then please return to RCM and discuss what it has told you about your generator.

Ohhhh Kkkkk. ERS

A 10X probe will be fine for that 'scope.

Pete Stanaitis

P.S. Talk about Old scopes: I still have a 422 that works.

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Chuck Sherwood wrote:

Yes, AFTER you set your vertical sensitivity to something sane.

If the generator itself is floating, then yes. I wouldn't recommend using the scope's ground clip for anything like line voltage - it's 60 (or 50) Hz, so the inductance of the ground loop will be swamped out by whatever you're measuring, and the scope's ground should provide a "good enough" ground return to the mains to get a reasonable view of what your mains looks like.

Or, as has been suggested, but isn't recommended, is to "float" the scope, by using one of those 3-to-2 prong cheaters, and leave the ground lead open - but then the whole scope case and everything sits at the potential of whatever you clipped your ground clip to.

Now that I think about it, it'd be best to put your scope in differential mode, and use two probes without ground clips - the scope will show you whatever it sees between the probe tips, and neither one needs to be grounded, in fact, _shouldn't_.

Hope This Helps! Rich

And/or crosspost it. :-)

Cheers! Rich

Actually, your name sounds familiar to me, and I'm more of a regular on sci.electronics.design/.basics, but also lurk rec.puzzles and sci.engr.mech from time to time. :-)

Cheers! Rich

Greetings Rich, I do post on the basics group also. So I recognize your name and advice. RCM has such a varied group of folks that there are lots of good answers available. And since the knowledge base is so wide the interests are also. Even though the name is METALWORKING many other posts of interest to a large number of readers get posted here too. I don't mind the off topic posts. If I don't wanna read 'em then I don't. I do try to make sure any off topic posts I make are marked as such so others can avoid reading them. ERS

According to Don Bruder :

In particular, if the voltage is less than perhaps 30V, for a scope with 3 divisions above the center line and 3 below (with the grounded line adjusted to zero), then a 1X setting on the probe, and 10 V/Div setting on the scope input should be fine.

If you adjust the grounded line to the bottom of the display, or if your scope has a 20 V/Div range, then you can stay with the 1X setting up to 60V. (If it is a bit higher, it won't hurt anything, you will simply not be able to get the entire trace within the vertical dimensions of the screen.

There are also 100X probes, for dealing with higher voltages, and Tektronix once made a Freon filled one with a 1000X capability, for

*serious* high voltage.

As for the ground clip -- if the other side of the generator is grounded, then you connect the ground clip to the generator ground. If, however, the voltage is floating significantly above ground, you may want to operate the scope in differential mode.

1) Use two probes on two inputs. 2) Both probes should be the same setting (1X or 10X) 3) Both probes should be the same speed, or differences in reaction times between the two could distort the trace. 4) Both inputs should be the same (e.g. 20V/Div). 5) You need to switch the "invert" switch on for one of the two channels only. 6) You need to switch the scope to "Add" mode (instead of "Alt" or "Chop". 7) *Don't* connect the ground clips to anything. Remove them from the probes so they don't hit anything above ground. (The ground clips connect through to the ground pin on the power plug, so you would be grounding the device through the scope, probably burning up the wires on the probe.

At this point, you will be displaying the *difference* between the two probes, so you can measure the voltage across something that is well above ground. You will want the voltage capability of the probes to be high enough to handle the voltage difference from ground. (I think that 600V is typical for the 1X/10X switchable probes.)

I can't tell you exactly which switches to use, because I don't have a 465 to see what they are labeled. My description was mostly based on the 454 scopes, which I have used for many years, and generically other Tek scopes use something somewhat similar.

Of course, there is the question of what he means by "generator" in this case. It could be the DC power source from older cars used to recharge the battery (as you are assuming). It could be an alternator (as you have also suggested). It could be some form of audio or RF signal generator (in which case typically the 1X range of the scope probes is probably reasonable.

Or -- it could be some form of high voltage generator, in which case none of the probe settings mentioned would be reasonable at all.

Enjoy, DoN.

I'd very much appreciate these two manuals.

Ned Simmons

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Thanks much.

Ned Simmons

Ig, do you have a manual for a Wavetek 144?

nope... the only wavetek that I have a manual for is 148A... sorry...

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