measure AC mains with oscilloscope

[1jam]

I've heard 'no never do that' and 'it'l blow your fuse / you will die'
etc... just trying to understand.

As long as you are careful to connect your probe ground to neutral and the
probe signal to hot, it should be ok right? Assuming the scope can handle
~350V peak.

No i'm not going to try it. I have a little AC walwart to use as isolation.

 

[krw@att.bizzzzzzzzzzzz]

On Sun, 25 Dec 2011 23:45:52 -0900, 1jam <com@example.net> wrote:

I've heard 'no never do that' and 'it'l blow your fuse / you will die'
etc... just trying to understand.

As long as you are careful to connect your probe ground to neutral and the
probe signal to hot, it should be ok right? Assuming the scope can handle
~350V peak.

There are ways of doing it but if you're asking this question, just *don't*.
The chances of smoking your scope are significant and the chances of injury or
death, nonzero.

No i'm not going to try it. I have a little AC walwart to use as isolation.

Most are isolated, but it's certainly worth checking.

 

[John Larkin]

On Sun, 25 Dec 2011 23:45:52 -0900, 1jam <com@example.net> wrote:

I've heard 'no never do that' and 'it'l blow your fuse / you will die'
etc... just trying to understand.

As long as you are careful to connect your probe ground to neutral and the
probe signal to hot, it should be ok right?

I wouldn't clip the probe ground to neutral. Neutral typically has
some voltage relative to ground, and that can cause complications.

Assuming the scope can handle

~350V peak.

No i'm not going to try it. I have a little AC walwart to use as isolation.

There's no problem with touching a 10:1 probe to the high side of the
AC line. I do that all the time. If you scope is grounded, and neutral
is close to ground, that should get you close to the actual waveform.

You can use two probes, and set your scope to A-B mode, and see the
actual line-neutral or line-line voltage. Just connect one probe to
line, the other to neutral or to the other line, ground the scope,
ignore the probe ground clips. If you do this, just don't crank up the
volts/div knob too much; if you overload the input of either channel,
the subtraction won't be right.

Try it!

John

 

[Phil Allison]

"1jam"

I've heard 'no never do that' and 'it'l blow your fuse / you will die'
etc... just trying to understand.

As long as you are careful to connect your probe ground to neutral and the
probe signal to hot, it should be ok right? Assuming the scope can handle
~350V peak.

** NO scope I have come across will accept 350 volts at the input without
severe internal overload. Usually scopes have protection against damage up
to some voltage like this, but don't count on it. Prolonged overvoltage at
the input will at least smoke a resistor an maybe kill a JFET or two.

Anyone with a need to view high voltages uses a suitable probe with either a
10:1 or 100:1 division ratio - the latter are often rated up to several
thousand volts.

No i'm not going to try it. I have a little AC walwart to use as
isolation.

** Transformer type AC wall warts are very safe - but be aware that the
output voltage will be higher than labelled under no load and the wave
becomes very distorted if loaded by a rectifier and filter cap. Even with
no load, the wave is often distorted by the effect of magnetising current in
the primary - typically the point in time where the AC voltage crosses
zero will be shifted.



..... Phil

 

[Tim Wescott]

On Sun, 25 Dec 2011 23:45:52 -0900, 1jam wrote:

I've heard 'no never do that' and 'it'l blow your fuse / you will die'
etc... just trying to understand.

As long as you are careful to connect your probe ground to neutral and
the probe signal to hot, it should be ok right? Assuming the scope can
handle ~350V peak.

No i'm not going to try it. I have a little AC walwart to use as
isolation.

Neutral is called "Neutral" instead of "the other ground" because it
isn't always right at ground. Sometimes the plug is wired backward and
it isn't close to ground at all.

Do like J.L. said -- use 10:1 probes and connect to hot. If you need the
accuracy and your scope supports it, connect the other to neutral and
subtract.

If it kills you right off the bat then I must not have been a very good
kid, because I've been dead for years now, and while it's nice here it
sure ain't heaven.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[Phil Allison]

"fungus"

"Phil Allison"

** NO scope I have come across will accept 350 volts at the input without
severe internal overload. Usually scopes have protection against damage up
to some voltage like this, but don't count on it. Prolonged overvoltage at
the input will at least smoke a resistor an maybe kill a JFET or two.

That doesn't add up to me.

** With a max setting for the vertical attenuator of 10V or 20V per division
and 8 divisions on the screen - what voltage limit does that suggest ?


In my ignorance I would expect 'scopes to
have a very input impedance so we can connect
them to tiny little circuits....

** The input protection circuit has to work on all vertical ranges, down to
5mV or less per division - cos a user might just probe say 240 VAC with the
scope set to max sensitivity.

This is a non trivial problem.

Have a look at some scope schematics to see how it is done.


.... Phil

 

[Phil Allison]

"fungus= cunt "
"Phil Allison"

** With a max setting for the vertical attenuator of 10V or 20V per
division
and 8 divisions on the screen - what voltage limit does that suggest ?

I don't expect to be able to measure it but
I don't see why it should destroy the 'scope.


** FFS - the scope is not destroyed.

But at some voltage resistors will smoke.

And stop OVER SNIPPING !!!!!!!!!!!!!!!!!!!!

You asinine pig.



...... Phil

 

[fungus]

On Dec 27, 12:24 am, "Phil Allison" <phi...@tpg.com.au> wrote:

** NO scope I have come across will accept 350 volts at the input without
severe internal overload. Usually scopes have protection against damage up
to some voltage like this, but don't count on it. Prolonged overvoltage at
the input will at least smoke a resistor an maybe kill a JFET or two.

That doesn't add up to me.

In my ignorance I would expect 'scopes to
have a very input impedance so we can connect
them to tiny little circuits....

 

[fungus]

On Dec 27, 10:43 am, "Phil Allison" <phi...@tpg.com.au> wrote:

** With a max setting for the vertical attenuator of 10V or 20V per division
and 8 divisions on the screen  -  what voltage limit does that suggest ?

I don't expect to be able to measure it but
I don't see why it should destroy the 'scope.

 

[fungus]

On Dec 27, 11:21 am, "Phil Allison" <phi...@tpg.com.au> wrote:

"fungus=  cunt "
 "Phil Allison"

Having a bad day?

** With a max setting for the vertical attenuator of 10V or 20V per
division
and 8 divisions on the screen - what voltage limit does that suggest ?

I don't expect to be able to measure it but
I don't see why it should destroy the 'scope.

Who wrote that? I think is was me ... but it
the single '>' seems to indicate it was you.

Maybe you ought to rethink your little girly
star-quote thing and start using the normal
quoting convention instead. Just saying...

** FFS  -  the scope is not destroyed.

So why are people saying, eg.:

"The chances of smoking your scope are significant..."

"** NO scope I have come across will accept 350
volts at the input without severe internal overload"

   But at some voltage resistors will smoke.

Of course... but at a voltage which is available
in every household and on every workbench?

 

[Jamie]

fungus wrote:

On Dec 27, 11:21 am, "Phil Allison" <phi...@tpg.com.au> wrote:

"fungus= cunt "
"Phil Allison"



Having a bad day?


** With a max setting for the vertical attenuator of 10V or 20V per
division
and 8 divisions on the screen - what voltage limit does that suggest ?

I don't expect to be able to measure it but
I don't see why it should destroy the 'scope.



Who wrote that? I think is was me ... but it
the single '>' seems to indicate it was you.

Maybe you ought to rethink your little girly
star-quote thing and start using the normal
quoting convention instead. Just saying...


** FFS - the scope is not destroyed.



So why are people saying, eg.:

"The chances of smoking your scope are significant..."

"** NO scope I have come across will accept 350
volts at the input without severe internal overload"



But at some voltage resistors will smoke.



Of course... but at a voltage which is available
in every household and on every workbench?

If you are using a scope Meter, most will handle up to 400V Cat II and

600 CAT III with a max peak of 1Kv...

If you are using a stand alone scope, like a bench style, you need to
check the model specs. Most Scope probes can only handle a 100 to 200 V.

Many scope meters, high end ones, will port the DMM probe signal over
to the scope screen along with the usual DMM stuff showing on the screen
however, you don't get the BW abilities that way and in your case you
don't need it. Those same scope meters do also use scope probes for the
high BW measurements but the probes do not support he voltage and in
most cases, the ones that use BNC for the full scope mode also won't
handle that.

If you want to do full bandwidth of the scope at HV, you need to get
a 100:1, 1000:1 probe. Otherwise, think only about 100Vs/ You can get
higher voltage probes with a 10:1 that can handle around 300v or more
but why waste money and not simply go for the big one?


I have a cheap german made 200Mhz 2Kv 100:1. Cost me $99 bucks, I am
sure you can find them for less.

Jamie

 

[Phil Allison]

"fungus = fuckead "

** Fuck off - you RETARDED puke.


<tooby@artlum.com> wrote in message
news:9f4d7cbc-bd18-4cef-b973-88e3e260b002@d10g2000vbh.googlegroups.com...
On Dec 27, 11:21 am, "Phil Allison" <phi...@tpg.com.au> wrote:

"fungus= cunt "
"Phil Allison"

Having a bad day?

** With a max setting for the vertical attenuator of 10V or 20V per
division
and 8 divisions on the screen - what voltage limit does that suggest ?

I don't expect to be able to measure it but
I don't see why it should destroy the 'scope.

Who wrote that? I think is was me ... but it
the single '>' seems to indicate it was you.

Maybe you ought to rethink your little girly
star-quote thing and start using the normal
quoting convention instead. Just saying...

** FFS - the scope is not destroyed.

So why are people saying, eg.:

"The chances of smoking your scope are significant..."

"** NO scope I have come across will accept 350
volts at the input without severe internal overload"

But at some voltage resistors will smoke.

Of course... but at a voltage which is available
in every household and on every workbench?

 

[Michael A. Terrell]

Jamie wrote:

If you are using a stand alone scope, like a bench style, you need to
check the model specs. Most Scope probes can only handle a 100 to 200 V.

Where do you buy such low grade crap?


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

 

[Phil Allison]

"Michael A. Terrell"

Jamie wrote:

If you are using a stand alone scope, like a bench style, you need to
check the model specs. Most Scope probes can only handle a 100 to 200 V.


Where do you buy such low grade crap?

** Even this bargain price probe is rated at 600V.

http://www.dealextreme.com/p/60mhz-oscilloscope-probe-with-x1-x10-switch-max-600v-34220



.... Phil

 

[fungus]

On Dec 27, 10:01 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

** Fuck off -  you RETARDED puke.

That thing with the two stars...is it because you're
writing footnotes? I don't get it.

 

[Phil Allison]

"fungus"
"Phil Allison"

** Fuck off - you RETARDED puke.

That thing with the two stars...is it because you're
writing footnotes? I don't get it.


** You don't get much - do you ?

 

[fungus]

On Dec 28, 8:46 am, "Phil Allison" <phi...@tpg.com.au> wrote:

That thing with the two stars...is it because you're
writing footnotes? I don't get it.

** You don't get much  - do you ?

The insults thing? You're right I don't get that at all.

Maybe it's normal in the less 'mainstream' newsgroups
but in sci.electronics.basics...? Maybe you should
seek professional help.



OTOH I *do* understand:

a) You don't know how to use your newsreader software
(you'd just filter out people you don't like...)

and

b) That you're incapable of understanding why people
inventing weird new quoting styles is a bad thing in
a public forum read by thousands of people.

 

[George Herold]

On Dec 28, 10:05 am, fungus <to...@artlum.com> wrote:

On Dec 28, 8:46 am, "Phil Allison" <phi...@tpg.com.au> wrote:



That thing with the two stars...is it because you're
writing footnotes? I don't get it.

** You don't get much  - do you ?

The insults thing? You're right I don't get that at all.

Maybe it's normal in the less 'mainstream' newsgroups
but in sci.electronics.basics...? Maybe you should
seek professional help.

OTOH I *do* understand:

a) You don't know how to use your newsreader software
(you'd just filter out people you don't like...)

and

b) That you're incapable of understanding why people
inventing weird new quoting styles is a bad thing in
a public forum read by thousands of people.

Phil's been pretty good in my opinion.
(What he's said has been 'spot on'. No?)
He's almost like a door guard here at SEB.

George H.

 

[fungus]

On Dec 29, 5:32 am, George Herold <gher...@teachspin.com> wrote:

Phil's been pretty good in my opinion.
(What he's said has been 'spot on'. No?)

I'm not questioning his electronics knowledge,
but this is 'basics' so people should be allowed
to ask questions, no?

And the insults part. fungus=XXXX

Was that 'spot on'?

He's almost like a door guard here at SEB.

You seem to know him. Maybe you can explain
where I went wrong... what causes doggy to bite.

 

[George Herold]

On Dec 29, 10:04 am, fungus <to...@artlum.com> wrote:

On Dec 29, 5:32 am, George Herold <gher...@teachspin.com> wrote:



Phil's been pretty good in my opinion.
(What he's said has been 'spot on'. No?)

I'm not questioning his electronics knowledge,
but this is 'basics' so people should be allowed
to ask questions, no?

And the insults part. fungus=XXXX

Was that 'spot on'?

He's almost like a door guard here at SEB.

You seem to know him. Maybe you can explain
where I went wrong... what causes doggy to bite.

Oh, Phil A. insults and bites everyone. You either get use to it, or
post questions somewhere else.

George H.