Re: Re: Re: Re: Question for O-scope people out there…

Here is the excellent o-scope grounding video I mentioned below:

http://www.youtube.com/watch?v=xaELqAo4kkQ

… Altan

On Sep 15, 2012, at 12:14 PM, Altan Stalker <pinball@aaarfamily.com> wrote:

> Mark,
>
> I appreciate the comment and agree with the safety points.
>
> I was only asking about 110/120v as an example... It seemed simple
> conceptually and the answer would apply to other situations.
>
> I found a superb video on oscope grounding. I'll post it when back at
> my real computer.
>
> ... Altan
> (from smartphone)
>
> On Sep 15, 2012, at 11:29 AM, Mark Shostak <shostakmark@gmail.com> wrote:
>
>> Altan,
>>
>> Not to be a fire hose (possibly literally), and it's great to learn
>> through experimentation, but not as much when there are knives in the
>> sandbox. With all due respect, you're playing in an area where best
>> case, you may destroy your scope, and worst case you could get hurt.
>>
>> If you really want to hook your scope to the "line" (when you find
>> it), I suggest you buy a device specifically designed to make that
>> happen. I've used one made by Oneac, and you can probably find them on
>> ebay (I was using them in the '80s, so they're probably cheap). It has
>> an IEC connector on one end and BNCs on the other, doing exactly what
>> you're asking about.
>>
>> You'll also need a scope with a lot of storage, possibly more than
>> exists. A lot of waves go by at 60Hz while waiting for an event. An
>> alternative would be to see if you can find a recording line monitor,
>> which will capture these events. I suspect this is more of what you're
>> looking for (as opposed to what you're asking for). Again, in the '80s
>> they just printed on register tape, and now probably usb stick or
>> something. Look and you can probably find one cheap. This will take a
>> lot of the time and effort out of the adventure, and provide
>> information more useful to what you are trying to accomplish. Granted,
>> it may not be as entertaining as connecting your scope ground lead to
>> "the line". :-)
>>
>> My 2 credits*
>>
>> Thanks,
>> -Mark
>>
>> * - w/ credit to whomever came up with that line
>>
>>
>> On 9/13/12, Altan (GAPAS) <pinball@aaarfamily.com> wrote:
>>>
>>> Great info, William. Thanks for replying.
>>>
>>> Could you clarify a couple of things for me?
>>>
>>>>>> "… you have to be careful that you never connect the scope probe ground
>>>>>> lead to the Line because that's a short circuit."
>>>
>>> What is the "Line"? Does this mean the home's ground or neutral line?
>>>
>>> What is a reasonable place to connect the probe's ground when checking an AC
>>> signal?
>>>
>>>>>> "The ground of the two sources gets connected by the scope probe ground
>>>>>> leads to the Earth ground of the mains AC system but as long as the
>>>>>> supply of the DC system is isolated from the AC mains then there's no
>>>>>> problem"
>>>
>>> If the power board uses the typical 4 diode approach (bridge rectifier) to
>>> convert from AC to DC, does this count as isolated? I believe every pin/vid
>>> I've seen uses this approach. Although there is a transformer more
>>> upstream. Is the transformer performing the isolation?
>>>
>>>>>> "A solution is to plug the scope into its own isolation transformer.
>>>>>> This is what I always do"
>>>
>>> Could you provide me a link to a reasonable isolation transfer, just so I'm
>>> sure I'm looking at the right thing?
>>>
>>> Thanks again!
>>>
>>> … Altan
>>>
>>>
>>> On Sep 11, 2012, at 9:06 PM, William Boucher <wboucher6@cogeco.ca> wrote:
>>>
>>>> Typical scopes can certainly handle the voltage of 110/220 VAC (aka mains
>>>> power), but as always when dealing with AC power you have to bear in mind
>>>> that the standard scope probes are not "isolated" meaning that the probe
>>>> ground leads are common to the scope chassis and so are also common to the
>>>> AC mains Earth ground (which ultimately is tied to Neutral at some point
>>>> in the system).
>>>>
>>>> So to answer your question, you can certainly measure 110VAC with a scope
>>>> but you have to be careful that you never connect the scope probe ground
>>>> lead to the Line because that's a short circuit. Also, the short path is
>>>> through the scope probe lead so it might in fact "light up" quite
>>>> literally unless something else inside the scope blows out first.
>>>>
>>>> You can measure DC voltage on one channel and AC voltage on the other
>>>> channel, but again, keep in mind that the ground (or 0V point) of each
>>>> channel must already be common or you will short them together as soon as
>>>> you connect the scope probe ground leads to the 0V point of each circuit
>>>> that you are trying to measure.
>>>>
>>>> This is the same situation as using two probes to measure two different DC
>>>> voltages. The two voltage sources must have a common ground. The ground
>>>> of the two sources gets connected by the scope probe ground leads to the
>>>> Earth ground of the mains AC system but as long as the supply of the DC
>>>> system is isolated from the AC mains then there's no problem. This said,
>>>> some DC systems must remain isolated from the AC mains. For instance,
>>>> most, if not all, raster monitors have internal circuitry that must remain
>>>> isolated from AC mains. Connecting a scope (that's plugged directly into
>>>> the wall) probe ground to the video input connector ground will likely
>>>> blow the monitor (for example the HOT horizontal output transistor may
>>>> instantly die). A solution is to plug the scope into its own isolation
>>>> transformer. This is what I always do.
>>>>
>>>> Whenever you want to measure the voltage across something like a "current
>>>> sensing resistor", you should use two probes connected one on each side of
>>>> the resistor and both of the probe grounds to the circuit ground. The
>>>> difference between the two signals provides the desired waveform. If you
>>>> feel that you must connect a single probe directly across the sense
>>>> resistor, you can under certain conditions. For instance, if one side of
>>>> the sense resistor is already connected at the 0V point (common ground)
>>>> then you can use the 2'nd probe to measure something elsewhere. Bear in
>>>> mind that id neither side of the sense resistor is at 0V (ground) then
>>>> when you connect a probe directly across it, you cannot use the other
>>>> probe for anything because it's ground lead would short one side of the
>>>> sense resistor to whatever point to which you connect the 2'nd probe
>>>> ground lead.
>>>>
>>>> The best solutions:
>>>> 1/ Think carefully about what you are doing before connecting anything.
>>>> 2/ Use isolated probes (cost more and must be purchased separately)
>>>> 3/ Use an isolation transformer where appropriate
>>>> 4/ Use a battery powered scope so that it remains isolated from Earth
>>>> ground.
>>>>
>>>> DO NOT cut the ground lead off of the scope power cord. Doing this will
>>>> not isolate it. Remember that the output ground terminal is connected to
>>>> the Neutral terminal back at the breaker box. Keep in mind that the
>>>> Ground return is a redundancy/backup path for the Neutral path.
>>>>
>>>>
>>>> William Boucher
>>>> http://www.biltronix.com
>>>>
>>>>
>>>> ----- Original Message ----- From: "Altan (GAPAS)"
>>>> <pinball@aaarfamily.com>
>>>> To: <vectorlist@vectorlist.org>
>>>> Sent: Tuesday, September 11, 2012 8:34 PM
>>>> Subject: VECTOR: Question for O-scope people out there…
>>>>
>>>>
>>>>
>>>> Is it safe to use an entry level o-scope (like the Rigol DS1102E or Owon
>>>> xxxx) with AC voltage? I suspect the answer is an obvious "Yes", but
>>>> wanted to verify. It doesn't seem to be specifically stated (again,
>>>> probably because it's obvious).
>>>>
>>>> Being able to look at AC as well as DC would be helpful when trying to
>>>> trigger on AC voltage drops and viewing results on regulated DC.
>>>>
>>>> The follow up: is one able to have an AC source on CH1 and a DC source on
>>>> CH2?
>>>>
>>>> Thanks!
>>>>
>>>> … Altan
>>>> www.aaarpinball.com---------------------------------------------------------------------------
>>>> ** Unsubscribe, subscribe, or view the archives at
>>>> http://www.vectorlist.org
>>>> ** Please direct other questions, comments, or problems to
>>>> chris@westnet.com
>>>> ---------------------------------------------------------------------------
>>>> ** Unsubscribe, subscribe, or view the archives at
>>>> http://www.vectorlist.org
>>>> ** Please direct other questions, comments, or problems to
>>>> chris@westnet.com
>>>
>>> ---------------------------------------------------------------------------
>>> ** Unsubscribe, subscribe, or view the archives at
>>> http://www.vectorlist.org
>>> ** Please direct other questions, comments, or problems to
>>> chris@westnet.com
>>>
>> ---------------------------------------------------------------------------
>> ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
>> ** Please direct other questions, comments, or problems to chris@westnet.com
> ---------------------------------------------------------------------------
> ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
> ** Please direct other questions, comments, or problems to chris@westnet.com

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Sun Sep 16 15:34:45 2012