AC mains to scope input

[Michael A. Terrell]

George Herold wrote:

It'd at least blow out the 50 ohm termination.
(unless you'd used the x10 probe :^)
But personally I never liked 'scopes with switchable 50 ohm inputs.

Then you didn't work with a lot of RF.

It was just another setting I had to check.
What's wrong with a Tee and 50 ohm load...

Reflections at high frequencies.

or inline terminator?

One more thing to keep track of, on the bench.

--
You can't have a sense of humor, if you have no sense.

 

[Fred Abse]

On Tue, 03 Jan 2012 20:09:10 -0800, John Larkin wrote:

On Tue, 03 Jan 2012 09:37:09 -0800, Fred Abse
excretatauris@invalid.invalid> wrote:

On Mon, 02 Jan 2012 17:20:31 -0800, George Herold wrote:

(none of the x10 probes I use have a switch! I hate that thing.)

Me neither. How many times do you need a x1 probe?

For low-level signals. Or for using with a DVM!

Not that often, for me, then. 10, or even 50 mV per division is mostly
enough. I can always pinch a 1:1 probe off a DVM for the odd occasion I
don't mind the capacitive loading.

Switched probes, never.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

[John G]

fungus has brought this to us :

On Jan 4, 1:46 am, John G <greent...@ozemail.com.au> wrote:

The real answer is DONT DO IT until you have enough knowledge to
understnd all the ramifications, which the OP really does not. >:|



Theories about how many watts etc will only lead to lots of smoke and
maybe worse. :-?


Luckily for the world I mostly work with batteries
and stuff that comes out of small power supplies.

My A/C career so far has been limited to hooking
up the occasional light bulb.

That was my approach about 65 years ago and slowly as I learnt a bit
more (College and on the job) I was able to understand the risks and so
far have managed to only blow one Multimeter current fuse and never
damaged a scope.

--
John G.

 

[krw@att.bizzzzzzzzzzzz]

On Tue, 3 Jan 2012 19:31:21 -0800 (PST), George Herold <gherold@teachspin.com>
wrote:

On Jan 3, 7:00 pm, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz
wrote:
On Tue, 3 Jan 2012 01:11:11 -0800 (PST), fungus <to...@artlum.com> wrote:
On Jan 2, 9:43 pm, Bob Myers <bobmyer...@gmail.com> wrote:

That was good advice in any event; you should ALWAYS
be in the habit of spending a good deal more time setting
up the measurement than actually making it.  "Grab a
probe and stick it on" is a recipe for getting bad
measurements and/or frying lots of nice, expensive
equipment.

My reasoning was that a 'scope *has* to
have a very high impedance input. You don't
want it sucking current out of delicate little
circuits. Even at 10k ohms (quite low) you'll
only get 24mA from 240V A/C mains and
that's not enough to fry much.

Not all scopes have a high impedance.  Many have a 50 ohm input impedance. You
don't want to be hooking them to the 240V mains.  ;-)

It'd at least blow out the 50 ohm termination.
(unless you'd used the x10 probe :^)
But personally I never liked 'scopes with switchable 50 ohm inputs.
It was just another setting I had to check.
What's wrong with a Tee and 50 ohm load...
or inline terminator?

Speed. The highest speed amplifiers (this goes up with time) have 50 ohm
inputs. Active probes are the norm in some applications.

 

[John Larkin]

On Wed, 04 Jan 2012 08:28:11 -0800, Fred Abse
<excretatauris@invalid.invalid> wrote:

On Tue, 03 Jan 2012 20:09:10 -0800, John Larkin wrote:

On Tue, 03 Jan 2012 09:37:09 -0800, Fred Abse
excretatauris@invalid.invalid> wrote:

On Mon, 02 Jan 2012 17:20:31 -0800, George Herold wrote:

(none of the x10 probes I use have a switch! I hate that thing.)

Me neither. How many times do you need a x1 probe?

For low-level signals. Or for using with a DVM!


Not that often, for me, then. 10, or even 50 mV per division is mostly
enough. I can always pinch a 1:1 probe off a DVM for the odd occasion I
don't mind the capacitive loading.

Switched probes, never.

My Rigol came with some very nice switched probes. All the regular
(passive) Tek probes I have here are switchable 1x/10x.

John

 

[Fred Abse]

On Thu, 05 Jan 2012 15:25:32 -0800, John Larkin wrote:

My Rigol came with some very nice switched probes. All the regular
(passive) Tek probes I have here are switchable 1x/10x.

I've found that Tek probes have a habit of breaking at the tip. The PMK
ones I settled on have replaceable tips, choice of rigid or spring-loaded.
I don't like the spring-loaded ones much.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

[krw@att.bizzzzzzzzzzzz]

On Fri, 06 Jan 2012 08:30:55 -0800, Fred Abse <excretatauris@invalid.invalid>
wrote:

On Thu, 05 Jan 2012 15:25:32 -0800, John Larkin wrote:

My Rigol came with some very nice switched probes. All the regular
(passive) Tek probes I have here are switchable 1x/10x.

I've found that Tek probes have a habit of breaking at the tip. The PMK
ones I settled on have replaceable tips, choice of rigid or spring-loaded.
I don't like the spring-loaded ones much.

You're not supposed to use them as darts. I've broken a lot of probes but I
don't think I've ever broken a tip.

 

[Fred Abse]

On Fri, 06 Jan 2012 19:28:51 -0500, krw@att.bizzzzzzzzzzzz wrote:

On Fri, 06 Jan 2012 08:30:55 -0800, Fred Abse <excretatauris@invalid.invalid
wrote:

On Thu, 05 Jan 2012 15:25:32 -0800, John Larkin wrote:

My Rigol came with some very nice switched probes. All the regular
(passive) Tek probes I have here are switchable 1x/10x.

I've found that Tek probes have a habit of breaking at the tip. The PMK
ones I settled on have replaceable tips, choice of rigid or spring-loaded.
I don't like the spring-loaded ones much.

You're not supposed to use them as darts. I've broken a lot of probes but I
don't think I've ever broken a tip.

It's the teeny little molding that holds the tip in that cracks and falls
out, complete with tip.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)