Measuring Mains Waveforms with Oscilloscope

[Paul Howard]

Hiya,

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?

Paul

 

[Mitchell]

"Paul Howard" <paulh@adelaide.on.net> wrote in message
news:c4d12689.0407082236.4d5fe095@posting.google.com...

Hiya,

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?

Paul

From what I can remember.

using an isolation transfor is good or
two of the same transformers back to back.


Regards,
Mitchell


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[Phil Allison]

"Paul Howard"

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?

** Use a 10:1 probe and **FORGET** the ground clip !!!




............. Phil

 

[Bodgey]

If you hook the ground clip up you'll get a real nice bang as the fuse in
your fuse box goes bang as well.

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:2l70f2F9712uU1@uni-berlin.de...

"Paul Howard"

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?



** Use a 10:1 probe and **FORGET** the ground clip !!!




............ Phil

 

[Trevor Wilson]

"Bodgey" <ihate@spam.com> wrote in message
news:6GvHc.85691$sj4.23863@news-server.bigpond.net.au...

If you hook the ground clip up you'll get a real nice bang as the fuse in
your fuse box goes bang as well.

**Not necessarily.


--
Trevor Wilson
www.rageaudio.com.au

 

[Mark Little]

"Bodgey" <ihate@spam.com> wrote in message
news:6GvHc.85691$sj4.23863@news-server.bigpond.net.au...

If you hook the ground clip up you'll get a real nice bang as the fuse in
your fuse box goes bang as well.

Not if everything is wired correctly. You can find out the relative voltage
levels between the earth, neutral and active and then decide if it is all
wired up correctly.

If the person has a dual channel CRO, the safest way to get an accurate
picture is to make a differential measurement between the active and
neutral. The ground leads of each probe can be safely connected to the earth
connection. Otherwise, take Phil's suggestion. The x10 probes are a good
sugestion in any case.

Mark

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:2l70f2F9712uU1@uni-berlin.de...

"Paul Howard"

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?



** Use a 10:1 probe and **FORGET** the ground clip !!!




............ Phil

 

[Mike Harding]

On Sat, 10 Jul 2004 10:16:51 +0930, "Mark Little" <mark@au.id.little>
wrote:

"Bodgey" <ihate@spam.com> wrote in message
news:6GvHc.85691$sj4.23863@news-server.bigpond.net.au...
If you hook the ground clip up you'll get a real nice bang as the fuse in
your fuse box goes bang as well.

Not if everything is wired correctly. You can find out the relative voltage
levels between the earth, neutral and active and then decide if it is all
wired up correctly.

If the person has a dual channel CRO, the safest way to get an accurate
picture is to make a differential measurement between the active and
neutral. The ground leads of each probe can be safely connected to the earth
connection. Otherwise, take Phil's suggestion. The x10 probes are a good
sugestion in any case.

Many scopes are not rated for 240V mains direct to their input
so a X10 probe is a requirement.

Do you _really need_ to measure the mains? Can you look
at the low voltage side of a transformer instead? What is
your application?

Mike Harding

 

[David L. Jones]

paulh@adelaide.on.net (Paul Howard) wrote in message news:<c4d12689.0407082236.4d5fe095@posting.google.com>...

Hiya,

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?

Paul

A high voltage differential probe is the proper and safest way to do
it. They come with real big and safe ez-hook probes too.

Dave

 

[Brian Goldsmith]

"David L. Jones"wrote

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?

Paul

A high voltage differential probe is the proper and safest way to do
it. They come with real big and safe ez-hook probes too.

Dave


****** Differential probe???????????????????????????

Brian Goldsmith.

 

[Mark Little]

"Brian Goldsmith" <brian.goldsmith@nospam.echo1.com.au> wrote in message
news:5NNHc.87406$sj4.7539@news-server.bigpond.net.au...

"David L. Jones"wrote

I remember from my apprenticeship that measuring mains waveforms with
an oscilloscope was dangerous. But I don't remember why, or how to do
it safely.

Can anyone enlighten me (with regards to this question)?

Paul

A high voltage differential probe is the proper and safest way to do
it. They come with real big and safe ez-hook probes too.

Dave


****** Differential probe???????????????????????????

See http://www.tek.com/site/ps/0,,51-11195-INTRO_EN,00.html

Brian Goldsmith.

 

[Brian Goldsmith]

"Mark Little" <mark@au.id.little> wrote > Dave

****** Differential probe???

See http://www.tek.com/site/ps/0,,51-11195-INTRO_EN,00.html

Brian Goldsmith.

**** Thanks Mark,appreciated.

Brian Goldsmith.

 

[Paul Howard]

Okay, but what exactly was/is so dangerous. Is it something to do with ground loops?

Paul

 

[Phil Allison]

"Paul Howard"

Okay, but what exactly was/is so dangerous. Is it something to do with
ground loops?

** The 240 volt AC mains is lethal, didn't anyone tell you - dickhead.

Using a BNC cable with clip lead on the end is *asking* for trouble -
*even* if the CRO input attenuator will accept the voltage.




.......... Phil

 

[Mike Harding]

On Sun, 11 Jul 2004 00:25:26 +1000, "Phil Allison"
<philallison@tpg.com.au> wrote:

"Paul Howard"

Okay, but what exactly was/is so dangerous. Is it something to do with
ground loops?


** The 240 volt AC mains is lethal, didn't anyone tell you - dickhead.

240V mains _may_ be lethal. I've had more shocks from it
than I can remember - but I would not recommend the
experience - it was shocking

Of course it also quite common to work on live 240V and
a _lot_ higher - but you _really_ do need to know what
you're doing then.

btw. Did you really need to call him a dickhead, Phil?

Using a BNC cable with clip lead on the end is *asking* for trouble -
*even* if the CRO input attenuator will accept the voltage.

I tend to agree.

All connections to the mains circuit should be made with
240V power removed.

Mike Harding

 

[Phil Allison]

"Mike Harding"
"Phil Allison"

"Paul Howard"

Okay, but what exactly was/is so dangerous. Is it something to do with
ground loops?


** The 240 volt AC mains is lethal, didn't anyone tell you -
dickhead.

btw. Did you really need to call him a dickhead, Phil?

** What else do you call someone who imagines 240 volts AC is harmless and
ground loops are dangerous ?




............. Phil

 

[Phil Allison]

"Mike Harding"
"Phil Allison"

** The 240 volt AC mains is lethal, didn't anyone tell you -
dickhead.

240V mains _may_ be lethal. I've had more shocks from it
than I can remember -

** Can you organise yourself a really decent one ?





............ Phil

 

[Mike Harding]

On Sun, 11 Jul 2004 12:17:56 +1000, "Phil Allison"
<philallison@tpg.com.au> wrote:

"Mike Harding"
"Phil Allison"


** The 240 volt AC mains is lethal, didn't anyone tell you -
dickhead.

240V mains _may_ be lethal. I've had more shocks from it
than I can remember -

** Can you organise yourself a really decent one ?

Every time I read one of your posts Phil.

Mike Harding

 

[Mikegw]

"Paul Howard" <paulh@adelaide.on.net> wrote in message
news:c4d12689.0407100511.2c5d76d5@posting.google.com...

Okay, but what exactly was/is so dangerous. Is it something to do with
ground loops?

Paul

Other than all the usual bad that goes with mains stuff, it is bad because
the gnd connection on the probe is joined to the Earth pin on the CRO.
Other problems include insufficient ratings on the probe wire. Where things
get really fun/bad is on autotransformers where the output is not isolated
and the both terminals are high realtive to earth.

Mike

 

[Paul Howard]

Thank you Mike,

I knew in amongst the usual BS, there would be a good, well written
answer there somewhere.

Paul

"Mikegw" <mikegw20@spam.com.spam.hotmail> wrote in message news:<ccremg$gi6$1@tomahawk.unsw.edu.au>...

"Paul Howard" <paulh@adelaide.on.net> wrote in message
news:c4d12689.0407100511.2c5d76d5@posting.google.com...
Okay, but what exactly was/is so dangerous. Is it something to do with
ground loops?

Paul

Other than all the usual bad that goes with mains stuff, it is bad because
the gnd connection on the probe is joined to the Earth pin on the CRO.
Other problems include insufficient ratings on the probe wire. Where things
get really fun/bad is on autotransformers where the output is not isolated
and the both terminals are high realtive to earth.

Mike

 

[Mikegw]

"Paul Howard" <paulh@adelaide.on.net> wrote in message
news:c4d12689.0407120551.75932062@posting.google.com...

Thank you Mike,

I knew in amongst the usual BS, there would be a good, well written
answer there somewhere.

Paul

No worries. It is sad that A.E seems to get more than its fair share.

Mike