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

I was on You-tube tonight and found this interesting video regarding the use
of scopes around mains power lines. Enjoy,
http://www.youtube.com/watch?v=xaELqAo4kkQ&feature=relmfu

William Boucher
http://www.biltronix.com

----- Original Message -----
From: "William Boucher" <wboucher6@cogeco.ca>
To: <vectorlist@vectorlist.org>
Sent: Saturday, September 15, 2012 3:03 PM
Subject: Re: VECTOR: Re: VECTOR: Question for O-scope people out there…

> >What is the "Line"? Does this mean the home's ground or neutral line?
>
> "Line" is another way of saying "Live". This is the polar opposite of
> 'Ground' and 'Neutral'.
>
>>What is a reasonable place to connect the probe's ground when checking an
>>AC signal?
>
> 'Ground' would be the safest. In theory, the 'Neutral' should be safe but
> someone might have wired the outlet incorrectly so you are better off
> checking it using a 3-light plug-in outlet checker first to make sure.
>
>>If the power board uses the typical 4 diode approach (bridge rectifier) to
>>convert from AC to DC, does this count as isolated?
>
> Absolutely not. The rectifiers definitely do not provide any isolation.
> Connecting a scope ground to the 0VDC side of a bridge or rectifier will
> make a short across the rectifier. Never do that.
>
>>I believe every pin/vid I've seen uses this approach.
>
> No they don't. You have to be misinterpreting something because it would
> for sure damage something.
>
>
>>Although there is a transformer more upstream. Is the transformer
>>performing the isolation?
>
> Transformers themselves do provide isolation from the main AC line,
> however that doesn't mean that there are no windings tied to AC or Earth
> ground so you have to be sure that there are not. Most arcade games have
> an isolation transformer specifically for safety and because most monitors
> require one. If you take a scope that is plugged into the wall and connect
> its probe ground to the 0VDC point within a monitor that is required to
> operate with an isolation transformer, YOU WILL BLOW the monitor and
> possible damage your scope. To use the scope safely, you MUST use either
> isolated probes or plug the scope into its own isolation transformer.
>
> An important word about using an isolation transformer with a scope.
> While the L and N wires will be isolated, the Earth/Chassis ground
> typically is a direct path. This is important to note because this is the
> path that needs the isolation! To break this path, you must remove the
> ground prong from the scope power cord. Some isolation transformers come
> without an enclosure so you would install it inside a project box and wire
> through only the 2 primary coil wires from the AC supply side (through a
> fuse and power switch is recommended) and wire only the 2 secondary coil
> wires out to an outlet that you then plug the scope into. You do not want
> to connect the ground wire of the output side outlet to anything. Some
> isolation transformers come with their own 3-prong outlet on them. The
> ones that I have had the ground prong on the output side connected to
> their chassis/Earth ground. I thought about disconnecting that wire but
> instead I use a power cord with the ground prong removed. The trick is to
> remember that removing the ground prong from the scope power cord only
> isolates the scope if you have it plugged into an isolation transformer,
> not the wall !
>
>
>>Could you provide me a link to a reasonable isolation transfer, just so
>>I'm sure I'm looking at the right thing?
>
> I'm sure that you can Google this as easily as I can. An isolation
> transformer is a 1:1 with single coil primary and single coil secondary.
> Most arcade supply online stores sell them. I believe Happ Controls also
> sells them. I did a quick search on eBay and tons of different ones came
> up. All you have to do is consider the number of amps that it must
> handle.
>
>
> Also, I read Mark's suggestions and agree 100% with everything that he
> said. There's some excellent advice there. While standard oscilloscopes
> can measure AC line power and certain DC stuff at the same time, it's
> really not something that I'd recommend anyone doing. There is
> specialized equipment available that works safely with AC line power. All
> it takes is one little mistake and bang, you or your equipment can be
> fried toast.
>
>
> William Boucher
> http://www.biltronix.com
>
>
>
> ----- Original Message -----
> From: "Altan (GAPAS)" <pinball@aaarfamily.com>
> To: <vectorlist@vectorlist.org>
> Sent: Thursday, September 13, 2012 9:07 PM
> Subject: VECTOR: Re: VECTOR: Question for O-scope people out there…
>
>
>
> 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---------------------------------------------------------------------------
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Received on Wed Oct 3 22:56:02 2012