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sampling 240VAC

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Thomas Magma

Jan 1, 1970
0
I'm looking for the best way to sample the 240VAC waveform from a powerline
well staying within my design constraints. I would like to go
transformerless because of size requirements and I would like to have a
fairly high bandwidth, so I am looking into other options other than a high
impedance resistive ladders. Does anyone have any suggestions on how to do
this in a modern fashion? What about using a hall effect IC and a load
resistor to convert the current back to a low enough sampling voltage?

Thanks,
Thomas
 
R

Rich Grise

Jan 1, 1970
0
I'm looking for the best way to sample the 240VAC waveform from a
powerline well staying within my design constraints. I would like to go
transformerless because of size requirements and I would like to have a
fairly high bandwidth, so I am looking into other options other than a
high impedance resistive ladders. Does anyone have any suggestions on how
to do this in a modern fashion? What about using a hall effect IC and a
load resistor to convert the current back to a low enough sampling
voltage?
Hack a 'scope and use its attenuator?

Good Luck!
Rich
 
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Thomas Magma

Jan 1, 1970
0
Rich Grise said:
Hack a 'scope and use its attenuator?

Good Luck!
Rich

I looked into a few schematics of scopes and looked at their attenuators.
The circuity looked a little tweeky with the use of communication capacitors
to overcome the RC input capacitance. I'm kinda looking for an 'outside of
the box' modern approach (if it exsists).

Thomas
 
T

Thomas Magma

Jan 1, 1970
0
Thanks John,

I hadn't really thought of capacitors as voltage dividers and you got me
thinking, which lead me to determine that the reactance and frequencies
would make it difficult to design anything that would be stable. First off
you would be AC coupled which would prevent you from seeing any low
frequency or DC offsets. Secondly, the large capacitor values needed to
divide the low frequencies would be subject to inductive reactance at the
higher frequencies and also subject to thermal tolerances.

It would probably be wise to steer clear of any reactive components, when
trying to design a higher bandwidth analyzer.

Thomas
 
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Rich Grise

Jan 1, 1970
0
I looked into a few schematics of scopes and looked at their attenuators.
The circuity looked a little tweeky with the use of communication
capacitors to overcome the RC input capacitance. I'm kinda looking for an
'outside of the box' modern approach (if it exsists).

I once bypassed a large resistive divider to stop an HVPS "hunting". It
didn't get approved, because every arc on the HV wrecked the input
circuit, but if you can protect your input from LARGE glitches, and/or
don't expect arcs, you might be able to get away with it.

Good Luck!
Rich
 
P

Phil Allison

Jan 1, 1970
0
"Thomas Magma is a Pisshead "
I hadn't really thought of capacitors as voltage dividers and you got me
thinking, which lead me to determine that the reactance and frequencies
would make it difficult to design anything that would be stable. First off
you would be AC coupled which would prevent you from seeing any low
frequency or DC offsets.


** Don't expect to see frequencies below 50Hz on the AC supply and there are
no " DC offsets " as such - but the average value may sometimes become non
zero due to uneven negative and positive peak values.

There is nothing wrong with using a resistive divider to monitor the mains
active relative to ground.

Secondly, the large capacitor values needed to divide the low frequencies
would be subject to inductive reactance
at the higher frequencies


** ROTFL !!

You are talking straight out your arse - fool.

and also subject to thermal tolerances.


** The caps would be at the same temp - fool.

It would probably be wise to steer clear of any reactive components, when
trying to design a higher bandwidth analyzer.

** You have no idea how to design anything.

There is STILL nothing wrong with using a resistive divider to monitor the
mains active relative to ground.


...... Phil
 
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Phil Allison

Jan 1, 1970
0
"John Fields"

240VAC>---+
|
[26.8nF] Xc = 99000R
|
+----->2.4V
|
[2.65µF] Xc = 1000R
|
240VAC>---+----->COM


** The OP is a trolling fool with no clue about anything - consequently he
has not considered the safety angle at all.

But YOU should have !!!

What you have drawn is potentially lethal.



..... Phil
 
A

amdx

Jan 1, 1970
0
Phil Allison said:
"John Fields"

240VAC>---+
|
[26.8nF] Xc = 99000R
|
+----->2.4V
|
[2.65µF] Xc = 1000R
|
240VAC>---+----->COM


** The OP is a trolling fool with no clue about anything - consequently
he has not considered the safety angle at all.

But YOU should have !!!

What you have drawn is potentially lethal.



.... Phil
I take it the risk is with the 26.8nF shorting and putting line voltage on
the output?
How about replacing the 26.8nF with 4 series 107.2nF 1000 Volt caps, with a
5.1V
zener on the output and a suitable fuse? If one 107.2nF shorts the output
voltage
goes high causing the zener to conduct and opening the "suitable fuse".
Heck, let's put a crowbar on it.
Running for cover :)
Mike
 
P

Phil Allison

Jan 1, 1970
0
"amdx"
"Phil Allison"
"John Fields"

240VAC>---+
|
[26.8nF] Xc = 99000R
|
+----->2.4V
|
[2.65µF] Xc = 1000R
|
240VAC>---+----->COM


** The OP is a trolling fool with no clue about anything - consequently
he has not considered the safety angle at all.

But YOU should have !!!

What you have drawn is potentially lethal.
I take it the risk is with the 26.8nF shorting and putting line voltage
on the output?

** NO !


..... Phil
 
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Thomas Magma

Jan 1, 1970
0
What's wrong with resistors? 10M scope probes work into the hundreds
of MHz. At MHz sorts of frequencies, a purely resistive front-end will
work fine.

John

I'm starting to lean towards resistors. I guess the only problem with high Z
resistors is that it will form a RC with the input capacitance of the ADC.
In oscilloscopes they put coupling capacitors in parallel with the resistors
to compensate for this effect. I haven't done the math to see were the
roll-off is though for my design and bandwidth.

Transformers are too big for the design and don't have the required
bandwidth. Also I haven't found one with a <10mm profile for that frequency.

I'm really just fishing to see if there was any alternative designs.

I'm not sure what is 'deadly' about using capacitors. Phil must be worried
that I'm designing him a new ass dildo.

Thomas
 
T

Thomas Magma

Jan 1, 1970
0
Use an opamp. In fact didn't John L. suggest a differential opamp for
the front end? (And after all it's only the second resistor in the
divider that you care about... you can design that to be almost any
value you need.)
I think it's a mistake to pick on Phil. I find he's right at least
99% of the time.
George H.

The use of an opamp is definitely a good idea. A good way to set gain and
frequency response.



I never said Phil was wrong...perhaps a little vague. I do apologize for my
moment of weakness. I do expect an earful.

Thomas
 
P

Phil Allison

Jan 1, 1970
0
"George Herold"


Phil, If I ask nicely will you tell us what is the problem with the
series capacitors?


** Can a 2.65uF cap connected to a 240 volt AC supply pass enough current
to kill ??

Whenever you see some circuit powered directly by the AC supply - ask these
two what ifs:

1. What if the phase and neutral connections are reversed ?

2. What if the neutral is not connected but the phase is ?

Consider if the circuit breaks safety standards in either of the above
scenarios.

Is it still safe to use, handle and connect to other devices ?



..... Phil
 
J

Jasen Betts

Jan 1, 1970
0
I'm looking for the best way to sample the 240VAC waveform from a powerline
well staying within my design constraints. I would like to go
transformerless because of size requirements and I would like to have a
fairly high bandwidth, so I am looking into other options other than a high
impedance resistive ladders.
why?

Does anyone have any suggestions on how to do this in a modern fashion?

the two methods you have rejected are the best that I know of.


perhaps you can make a capacitative divider work for you?
 
P

Phil Allison

Jan 1, 1970
0
"George Herold"
"Phil Allison"
"George Herold"
Phil, If I ask nicely will you tell us what is the problem with the
series capacitors?

** Can a 2.65uF cap connected to a 240 volt AC supply pass enough current
to kill ??

Whenever you see some circuit powered directly by the AC supply - ask
these
two what ifs:

1. What if the phase and neutral connections are reversed ?

2. What if the neutral is not connected but the phase is ?

Consider if the circuit breaks safety standards in either of the above
scenarios.

Is it still safe to use, handle and connect to other devices ?

" ** Can a 2.65uF cap connected to a 240 volt AC supply pass enough
current to kill ??"

Call it an impedance of a few k ohms. (at 50/60 Hz) that'll be 100mA
or so.... sure enough to kill me!

Thanks for the pointers.

Isn't this still going to be a problem even with resistors?


** Not if the resistance in series with phase and neutral is 100kohms or
more.

The resistors need to be adequately voltage rated too.


....... Phil
 
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Phil Allison

Jan 1, 1970
0
"whit3rd is a witless turd "
Oh, I'll want to ask more questions than that!


3. The circuit breaker protects this circuit, right?

** Not relevant to the electrocution hazard of an appliance that plugs in.


4. In case of (for instance) lightning, it isn't going to become a
bomb, is it?

** Wot insane crap.


In some cases, a capacitive load will contribute to arcing that can
kill the circuit breaker.

** Totally irrelevant to a load of 26nF - fuckwit.


the capacitor
divider (and the resistor input circuit, too) will take current from
the AC and divert it to GND. That will trip GCFI protection ..


** Bullshit.

The AC current is only a mA or two in any sane design.

Piss off - you RABID NUTTER !!!



..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"George Herold"


"The AC current is only a mA or two in any sane design."
OK I'd like a 0.1mA design....

** Then apply ohms law - dickhead.

Given the OP it makes you worry how
many 'insane' designs are going to be out there.


** The OP has never designed, made or sold anything.

Get real.


..... Phil
 
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Phil Allison

Jan 1, 1970
0
"George Hair Oil"

" ** The OP has never designed, made or sold anything."

Really, how do you know that?



** Cos he is VERY obviously a totally clueless TROLL

You pathetic dope !!!
 
T

Thomas Magma

Jan 1, 1970
0
The Phantom said:
Just how high bandwidth do you require?

Bandwidth limits are not really specified by IEC 61000-4-30 or IEEE C37.118.
DC to 10kHz for sure, but we would like to design in the ability to go up to
several hundred kHz for the "who knows" factor.

(Yes very active in R&D Phil...r u)

Thomas
 
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Phil Allison

Jan 1, 1970
0
"whit3rd is a witless TURD "


the capacitor
divider (and the resistor input circuit, too) will take current from
the AC and divert it to GND. That will trip GCFI protection .


** Bullshit.

The AC current is only a mA or two in any sane design.

Piss off - you RABID NUTTER !!!



..... Phil
 
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