An OT oscilloscope question

I been havin' fun with my TEK 465B 'scope. But now I want to do something serious. Check the output of a couple generators. I have a

1X/10X probe. Do I just set the 'scope to the right volts/div, the probe at 10x, and touch the probe to the hot wire? Should the ground clip from the probe be connected to the generator ground? I ordered the manual but it hasn't arrived yet. Thanks, ERS
Reply to
Eric R Snow
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Post this on Sci.Electronics Repair.

CAP

Reply to
MOP CAP

As long as the output is within what the scope can handle, I'd set to

1x, adjust the V/div as needed, and go. Yes, use the ground clip.

If the output from the genny is too high for the scope to handle straight, you're going to need to "dump" some of it - Since I assume you're wanting to do this to look at the waveform the genny is putting out, you'll want a "pure resistance" load so that inductance doesn't interact with/alter whatever ripple is present. A car headlight or three wired in series would likely do the job quite nicely, dropping the voltage without affecting the waveform.

Expect it to be a rather boring picture, though. You'll likely need to dial the scale way up to see the ripple on an otherwise flat line when looking at a generator output.

For an alternator, on the other hand, depending in spin speed/design intents, it could be anything from dreadfully boring to rather interesting to watch.

Reply to
Don Bruder

Agree with Don here. The output of the genny will be more meaningful (realistic) if driving some of it's rated load. Just running open won't tell you a lot. In any case use the 10x multiplier to range down into the vertical amplifier.

Reply to
Robert Swinney

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.

Reply to
DoN. Nichols

Eric -

I might have a manual on that for you.

What are you probing - one point referenced to ground ? if so ok.

However - be cautious - The scope ground - is the frame.

Most use a 2 to 3 prong adapter to isolate the ground lug from the power line. Then use caution.

The x10 probe has a metal spring wire that changes scaling.

Is the generator ground earth ground or floating - if you floated your scope then connect the scope lead to the ground lead as you say. Otherwise - what would happen is the earth ground in the scope is connected through the scope ground to the generator ground - and that might not be right.

send me an e-mail - I'll look in the shop to see what I have. Long time ago.

Martin

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:

Reply to
Martin H. Eastburn

If the signal you want to see is small to the DC voltage - use the AC coupled switch on the input and look at only the AC waveform.

Martin 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

D> >

Reply to
Martin H. Eastburn

Sure, if the resulting voltage is within the scope's capabilities. I have a operators and service manuals for your scope, free in electronic form.

i
Reply to
Ignoramus25009

What is the expected peak output voltage of these generators? Are they AC, DC, or whut?

Reply to
Don Foreman

Reply to
Eric R Snow

Don, AC. it's a small one. 850 watts. Good for little stuff but not quite enough for the fridge. Thanks, Eric

Reply to
Eric R Snow

Thanks. If I need your electronic ones I'll let you know. I am expecting a hard copy manual any day but it may be out of stock. Eric

Reply to
Eric R Snow

I wouldn't mind a copy as well. I have the same scope and pretty much know how to use it, but manuals are never a bad thing to have around.

Thanks

JW

Reply to
jw

Yes, but before you electrocute yourself be sure to go over to a sci.electronics group and post a lathe question.

Reply to
Dave

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Tek 475
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I will keep these files for a few days.

Here are some other manuals that I have, see filenames and try guessing if you need those. I would put them up

2005B_Magnetics_Ferrite_Catalog_uncut.pdf 3000TR-II.pdf 465b_opn.zip 465b_svc.zip ATT_954_Phone.pdf Boat-Trailer-Towing-Guide.pdf DV42_285Eng.pdf Deltaweld_450.pdf ESAB-1959-HeliArc-TIG-Welding-Manual.pdf Fluke-8050A.pdf Fuji_Finepix_602.pdf GIGATRONICS-900-OM-MM.pdf HP-333A-334A.pdf HP-5328A-HPIB.zip HP-8640B.zip Harris Hobart L_range_en.pdf MEP-002A MEP-017A Millermatic-251.pdf NEETS OtherGenerators PRC2000 RiggersPDF_200406.pdf Rigging-Handbook.fm5_125.pdf SMD_2000M_Manual.pdf TEK-1502-OM-SM.pdf TEK-2246-OM.pdf TEK-492-492P-OG.pdf Wavetek-148A.zip bodine-electric-motors.pdf casio-mtg-900-watch-ru.pdf cookies.txt crydom_H12D.pdf datamax lambda-lfs_fall92.pdf onan password.txt permissions.txt philips-dvp-632-02-rus.pdf pix tek475.zip tmp wayne-sprinkler-pump.pdf i
Reply to
Ignoramus11720

The safe way to do this is to make sure your generator is grounded because the ground lead on your scope will be grounded and you don't want current flowing in the ground lead or you will burn up something or shock yourself. Unless you REALLY know what you are doing you should not float the scope or alternator and obviously you would not be asking how to do it here if that was the case.

Next is to use a 10x or 100x probe and connect it to the alternator output. The probe choice will depend on the max input voltage of your scope. Read the manual to make sure that you don't overvoltage the input, lest you fry it. My guess is you will need a 100x probe. Even then, you need to be careful that you do not exceed the max rating of the probe. There are two little tiny resistors in there that are used as a voltage divider. If you exceed the power dissapation of the resistors, they burn out and your probe is now worthless.

This will allow you to check one leg. If you want to make leg to leg measurements, you will need a two channel scope and two identical probes. Put one probe on each leg and invert one channel and put the scope in ADD mode. Now you can safely look at the combined voltage.

chuck

Reply to
Chuck Sherwood

That's an excellent suggestion! I know that I could post the 'scope questions on sci.basics but the knowledge base here is pretty wide and I know from the poster's names that their info is trustworthy. Also, I answer questions here and am known here. This sometimes helps when I ask a question. ERS

Reply to
Eric R Snow

All the generators I have seen are floating. If that's what is meant by not being connected to ground. They only get grounded when something is plugged into them and that something is grounded. As far as the scope being grounded, it is grounded when it's plugged into the AC mains. So if I use it to check the AC generator output it will be grounded and the generator will not be. Unless it needs to be. If it should be grounded to the scope ground then that's what I'll do. If I can just touch the probe to one of the wires on the generator to measure the frequency then that's what will get done. ERS

Reply to
Eric R Snow

OK. Yes, ground your scope to genny ground. The safest way to operate might be to actually power the scope from the genny.

Set your probe on x10. Put it on channel 1. Set your trigger controls on AC and norm, trigger mode (white button) on auto. Set the little AC-gnd-DC switch under the channel 1 gain knob to gnd and center the trace vertically on the screen. Set your horizontal sweep at 2 mS/cm.

Now connect your probe to the hot wire. You should see about 1 cycle of your AC waveform. You can now play with the various gain, sweeprate and trigger settings to modify the display to see whatever you want to see. Oh, I'd pull out the trig view button (near the Ch

1 gain knob) to set the scope at 20 MHz bandwidth.
Reply to
Don Foreman

I would either ground the genny to the outlet box that powers the scope, or I'd just power the scope off the genny. If the genny is floating you could have a common mode voltage that could cause problems.

Another safe approach would be to drive a transformer with the genny and observe the secondary with the scope. That'll reduce the voltage and provide common-mode isolation. It'll also probably strip off any high frequency content present on the genny wave, but there probably isn't any there anyway.

Reply to
Don Foreman

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