Maker Pro
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New Project -- Isolated Scope Probe

J

James Meyer

Jan 1, 1970
0
That's an interesting start. How about continuing this thread and
making the isolated probe linear and accurate?

...Jim Thompson


Using only 4 or fewer 2N3904's in a class A configuration.

Jim
 
J

John Larkin

Jan 1, 1970
0
That's an interesting start. How about continuing this thread and
making the isolated probe linear and accurate?

...Jim Thompson

And fast.

John
 
J

Jim Thompson

Jan 1, 1970
0
And fast.

John

"fast" and "linear" may be mutually exclusive, or at least
out-of-capability for most lurkers here.

(That statement ought to be good enough to qualify as a troll :)

John, What's your definition of "fast"?

...Jim Thompson
 
J

Jim Thompson

Jan 1, 1970
0
Why do I get the feeling this is some 'inside' joke????

Refer to the "fsm*.jpg" and "Field Strength Meter" threads ;-)

...Jim Thompson
 
L

Luhan Monat

Jan 1, 1970
0
Jim said:
That's an interesting start. How about continuing this thread and
making the isolated probe linear and accurate?

...Jim Thompson

Great, any ideas are welcome, but even as-is, I have found this device
extrodinarilly useful.

If I want to know the exact signal voltage (rather than just its shape
and timeing), I note the reading on the scope and then move the probe to
my bench supply and duplicate the amplitude in DC. Then the power
supply shows me the actual voltage level.
 
J

John Larkin

Jan 1, 1970
0
"fast" and "linear" may be mutually exclusive, or at least
out-of-capability for most lurkers here.

(That statement ought to be good enough to qualify as a troll :)

John, What's your definition of "fast"?

...Jim Thompson

Well, there aren't a lot of really fast floating signals around, like
in the picosecond range. I'd think that something around 1 MHz would
be handy for power supplies, power stages, stuff floating on the AC
line, most switchers... things like that. Maybe 100 MHz would be about
as far as it would be sensible to go for logic and more exotic stuff.

There are integrated linear optoisolators good for 25 MHz or something
like that. I don't think that extreme linearity or accuracy would be
all that important, so a simple thingie should be possible. I guess
highside power would be needed to make things work well... batteries
or a (quiet) inverter.

Group project?

John
 
J

John Fields

Jan 1, 1970
0
Hi,

Check this out if you need to make scope measurements on 'phone line' or
other floating circuits.....

---
Junk.

1. There is no real repeatable so-called X1 or X10 capability for the
thing unless each circuit it's connected to has exactly the same
Zout.

2. There is no X1, X10 correspondence between the output voltage and
the position of the X1 - X10 switch with the same input voltage to
the probe. For the PS2505 the CTR changes by about 2:1 for a 10:1
variation in input current below 5mA, with the absolute CTR varying
over about a 4:1 range from unit to unit.

3. It's a _bad_ idea to force forward current into a watch battery and,
I would suspect, a _very_ bad idea to subject it to the 100V reverse
polarity half-sine it'll get across it from the ringing signal.

4. There must be _something_ else... ;-)
 
J

James Meyer

Jan 1, 1970
0
Jim Thompson wrote:


Why do I get the feeling this is some 'inside' joke????

Inside? By now it's the "Joke Heard 'Round the World". See almost any
post by Paul Burridge. I can say that because Paul's a good natured guy. At
least so far.

Jim
 
R

Robert Monsen

Jan 1, 1970
0
John Fields said:
---
Junk.

1. There is no real repeatable so-called X1 or X10 capability for the
thing unless each circuit it's connected to has exactly the same
Zout.

2. There is no X1, X10 correspondence between the output voltage and
the position of the X1 - X10 switch with the same input voltage to
the probe. For the PS2505 the CTR changes by about 2:1 for a 10:1
variation in input current below 5mA, with the absolute CTR varying
over about a 4:1 range from unit to unit.

3. It's a _bad_ idea to force forward current into a watch battery and,
I would suspect, a _very_ bad idea to subject it to the 100V reverse
polarity half-sine it'll get across it from the ringing signal.

4. There must be _something_ else... ;-)

How about two oscilloscope probes and subtraction mode? How far apart can
ground and probe head get before it gets bad? How linear is the result of
subtraction on, say, a Tek 475?

What about tying the grounds together and letting them float?

Regards,
Bob Monsen
 
J

James Meyer

Jan 1, 1970
0
There are integrated linear optoisolators good for 25 MHz or something
like that. I don't think that extreme linearity or accuracy would be
all that important, so a simple thingie should be possible. I guess
highside power would be needed to make things work well... batteries
or a (quiet) inverter.

Group project?

John
I can make a slow (100~200 Hz BW), DC accurate (1% or better), isolated
to 500 Volts, probe with only three parts.

Jim
 
M

mike

Jan 1, 1970
0
Luhan said:
Hi,

Check this out if you need to make scope measurements on 'phone line' or
other floating circuits.....

http://members.cox.net/berniekm/isoprobe.html

I've got a TEK A6902 I don't use.
Make an offer.
mike

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
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