Floating the 'scope

[Paul E. Schoen]

"George Herold" <ggherold@gmail.com> wrote in message
news:bc9be5af-425a-4e7e-9fe4-4c3593ca438c@o30g2000yqb.googlegroups.com...
On Mar 8, 11:46 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:

George Herold wrote:

Michael A. Terrell wrote:

Good for you. That would get you fired any place I've ever worked.
If you needed isolation, you plugged whatever you were working on into
an isolation transformer. If OSHA found a cord like that, the company
would be fined and it could run into thousands of dollars.

Thanks Michael, The isolation transformer is on order.

Good deal! Just don't get careless when using it.

--
Greed is the root of all eBay.

"Yeah well Phil A. hasn't answered, but it seems that even with the
scope plugged into an isolation transformer, you can still get
'whacked' if you attach the probe 'ground' to the wrong spot."

You can get whacked if you don't follow the one-hand-in-pocket rule, but
otherwise you're fairly safe. However, some isolation trannies have fairly
large capacitance across the isolation barrier, and you could get a nasty
tingle that might startle you and cause you to self-inflict injury. A
medical grade tranny is the best, but you're looking at big bucks unless you
get a good surplus deal.

It may also be prudent to use a GFCI circuit. It is cheaper and smaller than
a transformer and will protect against an inadvertant conduction of line
voltage to ground through the user's body. But if you use both hands and
make a normal mode connection across the line voltage through your body, you
might be toast. Or more likely get a case of V-fib. 60 Hurts Per Second is
just about the most dangerous frequency.

Paul

 

[Paul E. Schoen]

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:ng9ap5p9o12bl6eekp5a1lujmiubsab8i3@4ax.com...

On Mon, 8 Mar 2010 07:53:52 -0800 (PST), George Herold
ggherold@gmail.com> wrote:


Digital scopes use to have terrible user interfaces. But they are so
much better now. The colored knobs are associated with the trace
color. It's so easy to know which knob to grab... try it you may
like it.

George H.

Yeah, some of the early digital scopes, especially the HPs, were
nightmares to drive. It turns out that the classic arrangement of
knobs is best, so most digital scopes now resemble old analog scopes.

Way back in 1989 I decided to buy a DSO, and I had been working at a company
that was a distributor for Tektronix, so I was able to evaluate one of their
scopes and I could have gotten it at cost. But I found the interface very
confusing and frustrating. In general, I liked HP's panel layout better than
Tek's. But I think the HP DSOs were too pricey for my budget. I ended up
purchasing a Hitachi VC-6025, for something like $2000, and it is still
working perfectly. It meets all my needs and I find the user interface
simple and comprehensive.

At that time I also had used a LeCroy digital scope, which was nice, but
hugely expensive. And I also used a Data Precision waveform analyzer, which
was also very expensive, but we needed the high accuracy and the math
functions such as true RMS of portions of the waveform between cursors.

We didn't need high frequency response, as we were measuring mains AC
voltages and currents at 60 Hz. But we were developing instrumentation rated
at 1% accuracy, so we needed 0.25% or better for our standard.

Prior to the DSOs and waveform analyzers, back in 1975-1979 when I was first
working on this class of instrumentation, we bought a Visicorder from
Government Surplus to observe the waveforms of the current pulses we needed
to analyze. That was fun, loading up rolls of photosensitive paper, and
timing the start of the recorder with the test set, and then going through
the pile of paper and trying to make accurate guesstimates of RMS value and
time. Ah, the good old days...

Paul

 

[Paul E. Schoen]

"Fred Abse" <excretatauris@invalid.invalid> wrote in message
newsan.2010.03.08.19.42.06.287699@invalid.invalid...

I'd still be happier with 12 bits, but then I just don't like digital. I
always feel like I wanna see between the samples ;-)

Cubic (or polynomial) spline curve fitting.
http://en.wikipedia.org/wiki/Spline_(mathematics)

Of course, you can never be sure that the waveform didn't go bonkers between
two samples!

Paul

 

[George Herold]

On Mar 8, 5:18 pm, "Paul E. Schoen" <p...@pstech-inc.com> wrote:

"George Herold" <ggher...@gmail.com> wrote in message

news:bc9be5af-425a-4e7e-9fe4-4c3593ca438c@o30g2000yqb.googlegroups.com...
On Mar 8, 11:46 am, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:

George Herold wrote:

Michael A. Terrell wrote:

Good for you. That would get you fired any place I've ever worked.
If you needed isolation, you plugged whatever you were working on into
an isolation transformer. If OSHA found a cord like that, the company
would be fined and it could run into thousands of dollars.

Thanks Michael, The isolation transformer is on order.

Good deal! Just don't get careless when using it.

--
Greed is the root of all eBay.

  "Yeah well Phil A. hasn't answered, but it seems that even with the
  scope plugged into an isolation transformer, you can still get
  'whacked' if you attach the probe 'ground' to the wrong spot."

You can get whacked if you don't follow the one-hand-in-pocket rule, but
otherwise you're fairly safe. However, some isolation trannies have fairly
large capacitance across the isolation barrier, and you could get a nasty
tingle that might startle you and cause you to self-inflict injury. A
medical grade tranny is the best, but you're looking at big bucks unless you
get a good surplus deal.

It may also be prudent to use a GFCI circuit. It is cheaper and smaller than
a transformer and will protect against an inadvertant conduction of line
voltage to ground through the user's body. But if you use both hands and
make a normal mode connection across the line voltage through your body, you
might be toast. Or more likely get a case of V-fib. 60 Hurts Per Second is
just about the most dangerous frequency.

Paul

Thanks Paul, mostly I don't deal with line voltages. And when I do I
like to hook things up cold, stand back, switch it on, and be ready to
switch it off if it goes pop and starts to sizzle.

Hmm, I should look into a GFI. I assume I can get one that I can plug
into the outlet and then plug my distribution strip into that.


George H.

 

[The Phantom]

On Mon, 8 Mar 2010 17:18:21 -0500, "Paul E. Schoen" <paul@pstech-inc.com> wrote:

"George Herold" <ggherold@gmail.com> wrote in message
news:bc9be5af-425a-4e7e-9fe4-4c3593ca438c@o30g2000yqb.googlegroups.com...
On Mar 8, 11:46 am, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:
George Herold wrote:

Michael A. Terrell wrote:

Good for you. That would get you fired any place I've ever worked.
If you needed isolation, you plugged whatever you were working on into
an isolation transformer. If OSHA found a cord like that, the company
would be fined and it could run into thousands of dollars.

Thanks Michael, The isolation transformer is on order.

Good deal! Just don't get careless when using it.

--
Greed is the root of all eBay.

"Yeah well Phil A. hasn't answered, but it seems that even with the
scope plugged into an isolation transformer, you can still get
'whacked' if you attach the probe 'ground' to the wrong spot."

You can get whacked if you don't follow the one-hand-in-pocket rule, but
otherwise you're fairly safe. However, some isolation trannies have fairly
large capacitance across the isolation barrier,

This one uses split bobbin construction with large creepage distance. It's
rated for 4000 VAC isolation. I got one a while ago, and I've measured the
capacitance, primary to secondary, and it's 33 pF. The price from Mouser is
about $27 for one.

and you could get a nasty
tingle that might startle you and cause you to self-inflict injury. A
medical grade tranny is the best, but you're looking at big bucks unless you
get a good surplus deal.

It may also be prudent to use a GFCI circuit. It is cheaper and smaller than
a transformer and will protect against an inadvertant conduction of line
voltage to ground through the user's body. But if you use both hands and
make a normal mode connection across the line voltage through your body, you
might be toast. Or more likely get a case of V-fib. 60 Hurts Per Second is
just about the most dangerous frequency.

Paul

 

[Michael A. Terrell]

George Herold wrote:

Thanks Paul, mostly I don't deal with line voltages. And when I do I
like to hook things up cold, stand back, switch it on, and be ready to
switch it off if it goes pop and starts to sizzle.

Hmm, I should look into a GFI. I assume I can get one that I can plug
into the outlet and then plug my distribution strip into that.

You can mount a standard GCFI in a plastic or metal outlet box, along
with a power cord. That way you can move it around the workbench or
shop to where you need it.


--
Greed is the root of all eBay.