# Oscilloscope question

Started by October 23, 2013
```I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
of the graticule. When using a 10x probe does this mean that trhe
'scope can measure a 400 volt signal? What if the signal is 500 volts?
will this damage the 'scope? What if the probe I'm using is 1x, 10x,
switchable probe and it is set to 1x? Will this damage the 'scope?
When measuring voltages higher than 24 volts I do take precautions,
such as making sure there is no path to ground through my body. But I
don't know what is safe for the oscilloscope. I am going to be trouble
shooting a power supply that has 200 volt input and several outputs
ranging from 5 to 24 volts. I will be using an isolation xmfr. The
'scope of course has a grounded plug. When scoping the power supply do
I ground the 'scope to the power supply? If I do then the power supply
will no longer be isolated, correct? Do I need to connect the 'scope
probe and ground to the power supply through an isolation xmfr too? If
I do won't this change the wave form on the 'scope display?
Thanks,
Eric
```
```On 10/23/2013 12:30 PM, etpm@whidbey.com wrote:
> I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
> of the graticule. When using a 10x probe does this mean that trhe
> 'scope can measure a 400 volt signal? What if the signal is 500 volts?
> will this damage the 'scope? What if the probe I'm using is 1x, 10x,
> switchable probe and it is set to 1x? Will this damage the 'scope?
> When measuring voltages higher than 24 volts I do take precautions,
> such as making sure there is no path to ground through my body. But I
> don't know what is safe for the oscilloscope. I am going to be trouble
> shooting a power supply that has 200 volt input and several outputs
> ranging from 5 to 24 volts. I will be using an isolation xmfr. The
> 'scope of course has a grounded plug. When scoping the power supply do
> I ground the 'scope to the power supply? If I do then the power supply
> will no longer be isolated, correct? Do I need to connect the 'scope
> probe and ground to the power supply through an isolation xmfr too? If
> I do won't this change the wave form on the 'scope display?
> Thanks,
> Eric
>
Hi,
Please don't take offense but it concerns me that someone about to
measure in the area with a couple hundred volts would ask theses questions.
The X10 means the voltage is 10 times higher than the display shows.
Over-voltage will cause the display to go off scale. Within the limits
of the vertical amplifier the scope will not be damaged. Anywhere you
clip the probe alligator clip will now be earth ground. If you are
isolating your device then clipping the probe will un-isolate it. I do
not recommend you bypass the scopes ground.
If anything I said confuses you then don't do it until you understand more.
Best,
Tom
```
```On Wed, 23 Oct 2013 12:43:44 -0400, Tom Biasi <tombiasi@optonline.net>
wrote:

>On 10/23/2013 12:30 PM, etpm@whidbey.com wrote:
>> I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
>> of the graticule. When using a 10x probe does this mean that trhe
>> 'scope can measure a 400 volt signal? What if the signal is 500 volts?
>> will this damage the 'scope? What if the probe I'm using is 1x, 10x,
>> switchable probe and it is set to 1x? Will this damage the 'scope?
>> When measuring voltages higher than 24 volts I do take precautions,
>> such as making sure there is no path to ground through my body. But I
>> don't know what is safe for the oscilloscope. I am going to be trouble
>> shooting a power supply that has 200 volt input and several outputs
>> ranging from 5 to 24 volts. I will be using an isolation xmfr. The
>> 'scope of course has a grounded plug. When scoping the power supply do
>> I ground the 'scope to the power supply? If I do then the power supply
>> will no longer be isolated, correct? Do I need to connect the 'scope
>> probe and ground to the power supply through an isolation xmfr too? If
>> I do won't this change the wave form on the 'scope display?
>> Thanks,
>> Eric
>>
>Hi,
>Please don't take offense but it concerns me that someone about to
>measure in the area with a couple hundred volts would ask theses questions.
>The X10 means the voltage is 10 times higher than the display shows.
>Over-voltage will cause the display to go off scale. Within the limits
>of the vertical amplifier the scope will not be damaged. Anywhere you
>clip the probe alligator clip will now be earth ground. If you are
>isolating your device then clipping the probe will un-isolate it. I do
>not recommend you bypass the scopes ground.
>If anything I said confuses you then don't do it until you understand more.
>Best,
>Tom
Greetings Tom,
I'm not offended. Basically what I want to know is what is safe for
the 'scope. Using the TEK 10x probe lights up the 10x numbers on the
selector dial on the 'scope so the numbers do indicate the proper
voltage. I know that using an isolation xmfr to power the power supply
means that the voltages present in the supply won't have a potential
to ground like the power from the mains will. I also understand that
connecting the 'scope ground makes the isolation xmfr useless because
then the voltages present in the power will have a potential to ground
through the 'scope ground. The reason I asked if the 'scope ground
should be connected to the power supply is because I don't know if the
'scope will show the proper voltages and wave forms if not grounded to
the power supply being tested. And if it does need to be connected to
the power supply ground and this is done through yet another isolation
xmfr will this change the display enough to make it meaningless?
Thanks,
Eric
```
```On Wed, 23 Oct 2013 09:30:31 -0700, etpm@whidbey.com wrote:

>I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
>of the graticule. When using a 10x probe does this mean that trhe
>'scope can measure a 400 volt signal? What if the signal is 500 volts?
>will this damage the 'scope? What if the probe I'm using is 1x, 10x,
>switchable probe and it is set to 1x? Will this damage the 'scope?
>When measuring voltages higher than 24 volts I do take precautions,
>such as making sure there is no path to ground through my body. But I
>don't know what is safe for the oscilloscope. I am going to be trouble
>shooting a power supply that has 200 volt input and several outputs
>ranging from 5 to 24 volts. I will be using an isolation xmfr. The
>'scope of course has a grounded plug. When scoping the power supply do
>I ground the 'scope to the power supply? If I do then the power supply
>will no longer be isolated, correct? Do I need to connect the 'scope
>probe and ground to the power supply through an isolation xmfr too? If
>I do won't this change the wave form on the 'scope display?
>Thanks,
>Eric

What does the scope manual say?
It is on the internet, if you don't have one.

A 10x probe will divide the voltage.
If I connect 400 volts, then the scope input sees 40 volts.
Measuring up to 1000 Volts should be no problem then.

If you erroneously switch to 1x, you buy a new input amplifier.
No problem.
Better use fixed 10x  probes.

Measurements on HV power supplies are done with two probes,
dual channel and switch to A minus B thus displaying the difference
between the two channels.

Scope ground should always be connected to protective ground.
I did in rare circumstances disconnect the scope ground wire
to get rid of line noise, but I do not recomment this to you.

w.
```
```<etpm@whidbey.com>
>
> I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
> of the graticule. When using a 10x probe does this mean that the
> 'scope can measure a 400 volt signal?

**  Means it can display a 400V peak -peak signal.

> What if the signal is 500 volts?

** Some of the signal will be off the display and you will need to use
vertical shift to see it.

> will this damage the 'scope?

** No.

> What if the probe I'm using is 1x, 10x,
> switchable probe and it is set to 1x?
> Will this damage the 'scope?

** No.

But any scope has a maximum ( no damage) continuous input voltage which
should be in the specifications.

Generally it is about +/-400V or 280VAC and applies to all vertical ranges.

Using a 10:1 probe extends this to the safe limit of the probe  -  which is
in the specs for the probe.

> When measuring voltages higher than 24 volts I do take precautions,
> such as making sure there is no path to ground through my body. But I
> don't know what is safe for the oscilloscope. I am going to be trouble
> shooting a power supply that has 200 volt input and several outputs
> ranging from 5 to 24 volts. I will be using an isolation xmfr. The
> 'scope of course has a grounded plug. When scoping the power supply do
> I ground the 'scope to the power supply? If I do then the power supply
> will no longer be isolated, correct?

** The WHOLE idea of using an isolation tranny is SO you can ground any part
of the circuit you like with a scope probe earth clip.

...  Phil

```
```On 10/23/2013 12:30 PM, etpm@whidbey.com wrote:
> I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
> of the graticule. When using a 10x probe does this mean that trhe
> 'scope can measure a 400 volt signal? What if the signal is 500 volts?
> will this damage the 'scope? What if the probe I'm using is 1x, 10x,
> switchable probe and it is set to 1x? Will this damage the 'scope?
> When measuring voltages higher than 24 volts I do take precautions,
> such as making sure there is no path to ground through my body. But I
> don't know what is safe for the oscilloscope. I am going to be trouble
> shooting a power supply that has 200 volt input and several outputs
> ranging from 5 to 24 volts. I will be using an isolation xmfr. The
> 'scope of course has a grounded plug. When scoping the power supply do
> I ground the 'scope to the power supply? If I do then the power supply
> will no longer be isolated, correct? Do I need to connect the 'scope
> probe and ground to the power supply through an isolation xmfr too? If
> I do won't this change the wave form on the 'scope display?
> Thanks,
> Eric
>

If you're going to be looking at the mains side of the PSU, it would be
safer to use a high voltage probe.  I have one of these
http://tinyurl.com/mupqz83 which works fine at low frequency.  There's
little reason to hang a scope on the HV side for troubleshooting, and
you'll live a lot longer if you don't.

You can get scopes with isolated probe pods, so you can hang the probe
ground pretty well anywhere, but you do still need to power down the
supply and verify that the primary caps are discharged before doing
anything around there.

Also most 10x probes are not rated for very high voltage.  Virtually
none, and certainly none of the switchable ones, is rated for high
voltage / high energy circuits.  That matters.  Once an arc gets
started, stopping it is _not_ easy in a high energy circuit.

I'd use a good quality, Cat III rated multimeter such as a Fluke 87V,
and keep my fingers out of the HV section.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
```
```"Phil Hobbs is a Wanker "
>
>> I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
>> of the graticule. When using a 10x probe does this mean that trhe
>> 'scope can measure a 400 volt signal? What if the signal is 500 volts?
>> will this damage the 'scope? What if the probe I'm using is 1x, 10x,
>> switchable probe and it is set to 1x? Will this damage the 'scope?
>> When measuring voltages higher than 24 volts I do take precautions,
>> such as making sure there is no path to ground through my body. But I
>> don't know what is safe for the oscilloscope. I am going to be trouble
>> shooting a power supply that has 200 volt input and several outputs
>> ranging from 5 to 24 volts. I will be using an isolation xmfr. The
>> 'scope of course has a grounded plug. When scoping the power supply do
>> I ground the 'scope to the power supply? If I do then the power supply
>> will no longer be isolated, correct? Do I need to connect the 'scope
>> probe and ground to the power supply through an isolation xmfr too? If
>> I do won't this change the wave form on the 'scope display?
>> Thanks,
>> Eric
>>
>
> If you're going to be looking at the mains side of the PSU, it would be
> safer to use a high voltage probe.  I have one of these
> http://tinyurl.com/mupqz83 which works fine at low frequency.

** Absolutely RIDICULOUS !!!

( snip more absurd shit)

> Also most 10x probes are not rated for very high voltage.

** FFS  -  the OP is  NOT  dealing with  KILOVOLTS  !!

> Virtually none, and certainly none of the switchable ones, is rated for
> high voltage / high energy circuits.  That matters.  Once an arc gets
> started, stopping it is _not_ easy in a high energy circuit.

** One this pompous fool starts down a side track he only goes further and
further.

> I'd use a good quality, Cat III rated multimeter such as a Fluke 87V, and
> keep my fingers out of the HV section.

** Not much good when used as a scope.

....  Phil

```
```On 10/23/2013 5:09 PM, Phil Allison wrote:
> "Phil Hobbs is a Wanker"
>>
>>> I have a TEK 465B 'scope. There are 8 divisions on the vertical axis
>>> of the graticule. When using a 10x probe does this mean that trhe
>>> 'scope can measure a 400 volt signal? What if the signal is 500 volts?
>>> will this damage the 'scope? What if the probe I'm using is 1x, 10x,
>>> switchable probe and it is set to 1x? Will this damage the 'scope?
>>> When measuring voltages higher than 24 volts I do take precautions,
>>> such as making sure there is no path to ground through my body. But I
>>> don't know what is safe for the oscilloscope. I am going to be trouble
>>> shooting a power supply that has 200 volt input and several outputs
>>> ranging from 5 to 24 volts. I will be using an isolation xmfr. The
>>> 'scope of course has a grounded plug. When scoping the power supply do
>>> I ground the 'scope to the power supply? If I do then the power supply
>>> will no longer be isolated, correct? Do I need to connect the 'scope
>>> probe and ground to the power supply through an isolation xmfr too? If
>>> I do won't this change the wave form on the 'scope display?
>>> Thanks,
>>> Eric
>>>
>>
>> If you're going to be looking at the mains side of the PSU, it would be
>> safer to use a high voltage probe.  I have one of these
>> http://tinyurl.com/mupqz83 which works fine at low frequency.
>
>
> ** Absolutely RIDICULOUS !!!
>
> ( snip more absurd shit)
>
(favour returned)

Read his answers.  He has no idea what he's dealing with, and I'm
interested in preserving his life long enough for him to figure it out.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net
```
``` "Phil Hobbs is a Fuckwit Wanker"
>
>>
>>> If you're going to be looking at the mains side of the PSU, it would be
>>> safer to use a high voltage probe.  I have one of these
>>> http://tinyurl.com/mupqz83 which works fine at low frequency.
>>
>>
>> ** Absolutely RIDICULOUS !!!
>>
>> ( snip more absurd shit)
>>
>

>  He has no idea what he's dealing with,

** You have no idea how to answer his questions.

The advice you gave was  COMPLETELY  USELESS  !!

Just like you.

Fuck off.

...  Phil

```
```On Thu, 24 Oct 2013 02:30:31 +1000, <etpm@whidbey.com> wrote:

>

Hello,

You have just meet two of the most famous people on sci.electronics.basics

Phill Hobbs is a PhD with many years experience who often works at the
very cutting edge of electronics. His answers are well thought out and

Phil Allison has autism, which has some surprising strengths when talking
about electronics and design. In the areas PA knows he is extremely
competent and he will give you the exact correct answer, but he may not