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
"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:
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
why?
the two methods you have rejected are the best that I know of.
perhaps you can make a capacitative divider work for you?
ent
se
"> ** Can a 2.65uF cap connected to a 240 volt AC supply pass enough current
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?
Say you've got a resistor and one end may be tied to the AC power line. How big a value does it have to be till you're willing to try touching the other end? (I'm a chicken... 10 meg and I might be willing to give it a quick brush with my finger.)
George H.
rrent
hese
Oh, I'll want to ask more questions than that!
In some cases, a capacitive load will contribute to arcing that can kill the circuit breaker. C loads take an inordinate amount of current in a fast transient pulse (it might burst the capacitor case and spew foil around the interior of your box, in millisecond #1, right before the circuit breaker responds in millisecond #2). Some safety-rated capacitors can be trusted connected to line voltage, and those are liberally decorated with safety approval stamps, right beside the heavy price tag.
If the measurement device isn't floating (like the old hot-chassis oscilloscope trick), and the source isn't isolated (every power system diagnostic bench should sport a good isolation transformer or two), 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 (minor irritation), so you have to work without GCFI. Then (and this is a MAJOR irritation) there is AC current, not to neutral with a grounded enclosure for protection, but to ground. If there's a break, even a brief one, in the ground wiring, your workbench's entire grounded-box ensemble becomes HOT. Normally, it takes TWO faults to fry the user: case 1: the hot-wire insulation fails result 1: wire hits grounded box, circuit breaker blows case 2: the grounded enclosure isn't grounded enough result 2: the enclosure is floating, currents up to a nanoamp can be expected into its stray capacitance case 3: hot-wire insulation fails and enclosure ground is not connected result 3: the nice gentleman at the pearly gates will review these events with you in due time
"George Herold" "Phil Allison" "George Herold"
" ** 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
"whit3rd is a witless turd "
In some cases, a capacitive load will contribute to arcing that can kill the circuit breaker.
** Totally irrelevant to a load of 26nF - f****it.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
in.
"The AC current is only a mA or two in any sane design."
OK I'd like a 0.1mA design.... Given the OP it makes you worry how many 'insane' designs are going to be out there.
Perhaps I'm overly sensitive though. I remeber this old HP RF power meter that wanted to 'live' at half the supply voltage. It was always biting me with 67VAC.
George H.
"George Herold"
"The AC current is only a mA or two in any sane design."
** Then apply ohms law - d*****ad.** The OP has never designed, made or sold anything.
Get real.
.... Phil
" ** The OP has never designed, made or sold anything."
Really, how do you know that?
George H.
"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 TROLLYou pathetic dope !!!
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
Think it through, though. If you want to look at a branch circuit, to see the power factor for individual appliances as well as of the branch as a whole, there might be AC monitors deployed in multiples. One or two mA means using three of the AC monitors will likely cause an abnormal shutdown. Depending on the connected devices, a single one can move the 'leakage' past trip point.
The test instrument (if that's the application; I was never clear on the details) ought not to introduce new uncertainties.
"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
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.