According to Don Bruder :
In article ,
Eric R Snow wrote:
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.
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.
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.
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.
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.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. |
http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---