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Default voltage of dimmer output not reading same on two different DVM's

I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM's show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM's and how to remedy?
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Default voltage of dimmer output not reading same on two different DVM's

major wrote:

================
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM's show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM's and how to remedy?


** Both are correct, but only one of them is "true RMS " ?

OR the controller use high frequency PWM and one meter cannot read it.

Next time, leave out all the facts just to make it harder.


..... Phil
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Default voltage of dimmer output not reading same on two different DVM's

On 11/5/20 1:10 AM, Phil Allison wrote:
major wrote:

================
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM's show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM's and how to remedy?


** Both are correct, but only one of them is "true RMS " ?

OR the controller use high frequency PWM and one meter cannot read it.

Next time, leave out all the facts just to make it harder.


.... Phil


Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V. The dimmer is one from
Amazon (sorry, 30 amps not 20 as I said originally):

https://www.amazon.com/Lighting-Cont.../dp/B076MVT1CR

Not sure about dimmer frequency, but I can hear a faint whine as it runs.


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Default voltage of dimmer output not reading same on two different DVM's

On 5/11/2020 2:00 pm, major wrote:
I am using a 12 V 20 amp lamp dimmer to control some LED lighting. While
my two DVM's show nearly equal input voltage to the dimmer, they both
read separate voltages on the output side.¬* One is reading 9 V and the
other 4 V.¬* I am trying to determine wattage output at various dimmer
settings.¬* Why the different in voltage readings on two different DVM's
and how to remedy?


**Measure the output of the dimmer with a CRO and it may make a lot more
sense.

--
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www.rageaudio.com.au

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Default voltage of dimmer output not reading same on two different DVM's

major wrote:

===============


Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V.

Not sure about dimmer frequency, but I can hear a faint whine as it runs.


** What range are you using ???

AC volts or DC volts?

PWM voltage waves can be read as an average value on any DC meter - but true power will require something much fancier.

Why not just measure the DC battery current and multiply by the voltage?

Then subtract a watt or so for losses in the controller.


..... Phil





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On 11/5/20 6:48 AM, Phil Allison wrote:
major wrote:

===============


Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V.

Not sure about dimmer frequency, but I can hear a faint whine as it runs.


** What range are you using ???

AC volts or DC volts?


DC on both meters on lowest range, 20 V.


PWM voltage waves can be read as an average value on any DC meter - but true power will require something much fancier.

Why not just measure the DC battery current and multiply by the voltage?



If you mean input from the battery into the dimmer, yes, tried that.
Both meters show the same 12 VDC @ 7 A when the dimmer is set at
maximum. Will have to check and see what happens as dimmer is adjusted.


Then subtract a watt or so for losses in the controller.


Would I only lose a watt or two through the dimmer? If so, I guess I
could take all my readings from the input side and go with those.



.... Phil




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Default voltage of dimmer output not reading same on two different DVM's

On 11/5/20 3:48 AM, Trevor Wilson wrote:
On 5/11/2020 2:00 pm, major wrote:
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM's show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side.¬* One is reading 9 V
and the other 4 V.¬* I am trying to determine wattage output at various
dimmer settings.¬* Why the different in voltage readings on two
different DVM's and how to remedy?


**Measure the output of the dimmer with a CRO and it may make a lot more
sense.

You talking a scope here or something else? If a scope,
unfortunately, I don't own one.

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Default voltage of dimmer output not reading same on two different DVM's

major wrote:

I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM's show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V and
the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two different
DVM's and how to remedy?

These dimmers MUST be pulse width modulated, othwerwise the heat production
would be huge. You can't expect a DVM to give accurate reading of a
pulsating source. Possibly some true-RMS meters may do a decent job of
averaging the result, but I would not trust such a reading without verifying
it with another instrument, like an oscilliscope.

Jon
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Default voltage of dimmer output not reading same on two different DVM's

On 11/5/20 10:05 AM, major wrote:
On 11/5/20 6:48 AM, Phil Allison wrote:
major wrote:

===============


Sorry, the meters are a GE2524 Digital Multimeter that reads the 9V and
the other meter is a Etek 10709 that reads 4 V.

Not sure about dimmer frequency, but I can hear a faint whine as it
runs.


** What range are you using ???

¬* AC volts or DC volts?


DC on both meters on lowest range, 20 V.


PWM voltage waves can be read as an average value on any DC meter -
but true power will require something much fancier.

Why not just measure the DC battery current and multiply by the voltage?



If you mean input from the battery into the dimmer, yes, tried that.
Both meters show the same 12 VDC @ 7 A when the dimmer is set at
maximum.¬* Will have to check and see what happens as dimmer is adjusted.


Then subtract a watt or so for losses in the controller.


Would I only lose a watt or two through the dimmer?¬* If so, I guess I
could take all my readings from the input side and go with those.



....¬* Phil





Ok, just as a follow up, I did keep both meters on the input side of the
dimmer. Voltage remained constant and nearly the same on both meters,
11.97 and 12.01 VDC, respectively, with dimmer off. At dimmer maximum
setting, voltage remained nearly constant (drop of -0.3 V) but current
changed from nearly nothing to the 7 A maximum with dimmer at max
setting. I swapped out the meters to read current just to be sure and
each showed the 7 A maximum. Then, I just adjusted the dimmer to
different positions, made some tick marks with current values indicated.
I think I'll just go with this. As you mentioned, losses through the
dimmer are probably slight and not an issue, at least in this
application. Thanks for your suggestions.

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Default voltage of dimmer output not reading same on two different DVM's

On 6/11/2020 2:06 am, major wrote:
On 11/5/20 3:48 AM, Trevor Wilson wrote:
On 5/11/2020 2:00 pm, major wrote:
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM's show nearly equal input voltage to the dimmer,
they both read separate voltages on the output side.¬* One is reading
9 V and the other 4 V.¬* I am trying to determine wattage output at
various dimmer settings.¬* Why the different in voltage readings on
two different DVM's and how to remedy?


**Measure the output of the dimmer with a CRO and it may make a lot
more sense.

¬*You talking¬* a scope here or something else? If a scope,
unfortunately, I don't own one.


**Well don't waste your time until you acquire one. In this application,
most meters are almost useless.

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Default voltage of dimmer output not reading same on two different DVM's

Trevor Wilson wrote:

==================


**Measure the output of the dimmer with a CRO and it may make a lot
more sense.

¬*You talking¬* a scope here or something else? If a scope,
unfortunately, I don't own one.


**Well don't waste your time until you acquire one. In this application,
most meters are almost useless.


** So you are unaware even the simplest DC meter can read the power drain from a battery ?

I average x V ?


..... Phil
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Default voltage of dimmer output not reading same on two different DVM's

Jon Elson wrote:

================


These dimmers MUST be pulse width modulated, othwerwise the heat
production would be huge.
You can't expect a DVM to give accurate reading of a
pulsating source.


** Still can certainly show the average DC voltage.

The usual input RC network doe the job nicely.


Possibly some true-RMS meters may do a decent job of
averaging the result,


** Only if the have response down to DC and up to the high harmonics of the PWM.

..... Phil




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On 6/11/2020 8:02 am, Phil Allison wrote:
Trevor Wilson wrote:

==================


**Measure the output of the dimmer with a CRO and it may make a lot
more sense.

¬*You talking¬* a scope here or something else? If a scope,
unfortunately, I don't own one.


**Well don't waste your time until you acquire one. In this application,
most meters are almost useless.


** So you are unaware even the simplest DC meter can read the power drain from a battery ?

I average x V ?


**Or you could do that.


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www.rageaudio.com.au

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Trevor Wilson wrote:

===================


** So you are unaware even the simplest DC meter can read
the power drain from a battery ?

I average x V ?


**Or you could do that.


** ;-))


...... Phil
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Default voltage of dimmer output not reading same on two different DVM's

major Wrote in message:r
I am using a 12 V 20 amp lamp dimmer to control some LED lighting. While my two DVM's show nearly equal input voltage to the dimmer, they both read separate voltages on the output side. One is reading 9 V and the other 4 V. I am trying to determine wattage output at various dimmer settings. Why the different in voltage readings on two different DVM's and how to remedy?


i'd guess because they are non-sinusoidal outputs and one of the meters is not true rms
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Default voltage of dimmer output not reading same on two different DVM's

brucek wrote:

i'd guess because they are non-sinusoidal outputs and one of the meters is not true rms


I'd say neither of them are true RMS.
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Default voltage of dimmer output not reading same on two different DVM's

On Sunday, November 8, 2020 at 12:46:33 AM UTC-8, Andy Burns wrote:
brucek wrote:

i'd guess because they are non-sinusoidal outputs and one of the meters is not true rms

I'd say neither of them are true RMS.


Good point--measuring DC current average is the appropriate setting, and there's
no DC-scale on any of my meters that does RMS measure.

Voltage, averaged or RMS averaged, is going to deliver at-or-near nonsense numbers
for the purposes of evaluating an LED illuminator.
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Default voltage of dimmer output not reading same on two different DVM's

On Thursday, November 5, 2020 at 10:06:43 AM UTC-5, major wrote:
On 11/5/20 3:48 AM, Trevor Wilson wrote:
On 5/11/2020 2:00 pm, major wrote:
I am using a 12 V 20 amp lamp dimmer to control some LED lighting.
While my two DVM's show nearly equal input voltage to the dimmer, they
both read separate voltages on the output side. One is reading 9 V
and the other 4 V. I am trying to determine wattage output at various
dimmer settings. Why the different in voltage readings on two
different DVM's and how to remedy?


**Measure the output of the dimmer with a CRO and it may make a lot more
sense.

You talking a scope here or something else? If a scope,
unfortunately, I don't own one.


Its probably a great idea if these questions were actually posed to the DMM or oscilloscope mfg'erers, too.
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Default voltage of dimmer output not reading same on two different DVM's

DC on both meters on lowest range, 20 V.

AHA, the keystone part of the puzzle. This blows Phil's statement out the water which is rare, there is no TRMS in DC.

Now you are down to the meters being plain old wrong, after all one just be, right ?

First of all realize that 100% LED compatible dimmers, which could be used on multiple lights must be the raw PWM. ON OFF ON OFF. If you smooth it off the a DC voltage, LEDS in parallel might fire at slightly different voltages and screw ya all up. So PWM is fine with LEDs as long as you never exceed the Imax (current rating) As such your meters on DC are actually measuring AC in the wrong mode.

It will help to know how the digital voltmeter works. Now when a voltage is applied to a DVM it is of course divided by the range control and whatever.. After that it goes to a comparator. The other input to the comparator is a sawtooth wave, generated quite accurately. When your input voltage and the voltage from the sawtooth cross, the comparator changes states and puts out an output. The exact time that happens is used to stop or read a counter to know just how much the internal voltage has risen.

It is easy to see that each DVM can have its own timing, or speed. higher speeds read faster and they are more expensive if they are accurate.

Now if you want a DC measurement, which could be useful, then you must feed the meter DC, not AC. As you can see frigs it all up. So, an extremely simple way would be to get like a 5K resistor and like a maybe what guys, 68uF ? Take the resistor from the output, connect it and the probe there, and the cap and the other end of the cap to ground. yyou just made an R/C filter.. This should make the meters read the same.

That is because they are measuring DC on the DC range.

I can't remember when the last time it was I had to make an R/C filter like that but I know I did a couple of times.
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wrote:
====================

AHA, the keystone part of the puzzle. This blows Phil's statement out the water which is rare, there is no TRMS in DC.


** FYI:

" true RMS " = DC equivalent value for the *heating* effect on a resistance.

Repeating waveforms may have a DC offset = average DC value.

The "true RMS" value of such wave is:

sqrt ( DC ^2 + ACrms ^2 )



...... Phil







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Default voltage of dimmer output not reading same on two different DVM's

" true RMS " = DC equivalent value for the *heating* effect on a resistance.

Known. but a DC meter might not be set up for that.To be, it would have to have some sort of filter and they don't really do that because they don't want the load. I think I told the guy to get a resistor and a cap, damn such uncritical values really, cana be 10K and a 47uF, or a 470 and a 10uF. It just doesn't matter if that meter has an input of 10 megs.

Of course TRMS might come in handy for an incandescent or some sort of heating element, but for LED it is out of the game.

I would think most LED dimmers say rated 400 watts (?) would be ready for multiple LEDs in parallel. This absolutely requires the max voltage delivered with PWM or they will not come on or dim at the same rate.

So he was trying to measure PWM on a DC scale, might work on an old style meter with a real meter, but not on this.

The first time TRMS did me any good was on TVs. Of all things, the filament winding of the power transformer opened up. I decided rather than change it, run the filament off the flyback. So I did and I wound the wire around the core and the meter read about 6.3 or so on TRMS and I connected it. ZAM it worked.

I found out that with that half sine, 70KHz wave repeating at 15.7Khz came to the right voltage at 22 volts peak to peak off the fly.

I had adventures in that. Shorted H-K ? We I got a winding for that. Panasonics seemed to be really affected by the capacitance though I tried to keep it low. So I EQed the video output circuit for it, just a cap in the emitter of one of the transistors. Short intermittent ? Fine, I just put like a 4.7 K in there to make it shorted all the time.

I did all kinds of **** for that company that nobody else would do.

Now this devout, religious person who is partner wants me to lie, to put in a good review on their local whatever they got. I would in exchange for a really glowing review of me but I am not looking for work. I even stopped advertising my business. I got enough now.

I doubt the guy in Florida has my number, I might leave it that way. After all this starting a business to **** off the goniffs etc in this business and put them out of business with truth and nice reasonable repairs, I am going to lie ?

Geez.
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wrote:
============================

This blows Phil's statement out the water which is rare, there is no TRMS in DC.


" true RMS " = DC equivalent value for the *heating* effect on a resistance.

Known. but a DC meter might not be set up for that.


** You are not paying proper attention.

DC voltage and true RMS voltage are equivalent.
DC meters read the average, DC value of a wave.



...... Phil




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Default voltage of dimmer output not reading same on two different DVM's

DC voltage and true RMS voltage are equivalent.
DC meters read the average, DC value of a wave.


No dispute on that, just why a DVM might not read it right.

Anyway, of the TRMS, I have noticed my average responding meter comes fairly close.

The TRMS one is a Fluke 8050A which I keep on the top shelf, it has more than enough accuracy and the LED display (which is in perfect shape HAHA) is not as easy to read as the 8000A I use as a daily driver. The 8000A has one less digit and is fast, I like it. When I need accurate then well... But then sometimes I read DC voltages with a scope. Put it on DC in most things you get like maybe 25 volts tops ? Five volts per division. Most **** you just need to know if it is there. I don't care from 4.96 or 5.03.

"Hack", say it.
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wrote:

=====================

DC voltage and true RMS voltage are equivalent.
DC meters read the average, DC value of a wave.


No dispute on that, just why a DVM might not read it right.


** Cannot possibly help but do so.

Analog ones do so by virtue of meter needle inertia.

DVMs do so by virtue of a simple LP filter at the input.




...... Phil




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Ralph Mowery wrote:
===================

DC voltage and true RMS voltage are equivalent.
DC meters read the average, DC value of a wave.



That really should be qualified.


** No need exists.

The way I understnd it is that the RMS voltage produces the same ammount
of heat in a resistor as a DC voltage will.

However RMS voltage could be a high peak value that will damage solid
state devices. The meter could show 5 volts, peaks could be 50 volts.

Again DC meters could read many different values depending on the meter
and wave form.


** What I wrote was accurate.

Strange how so many are baffled by such simple stuff.




....... Phil

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Default voltage of dimmer output not reading same on two different DVM's

let's say the following:

TRMS meters generally have AC and AC+DC modes, but usually your interested in the AC portion.
The TRMS voltage of a waveform will have the same heating value of a DC voltage set to the TRMS value.

AC meters have a frequency response. They also might be limited by the crest factor of the waveform.
There were thermal AC TRMS meters at one time.

Non TRMS meters are what you might call. Average reading, TRMS responding.
What does that mean? Take line voltage of 120 V 60 Hz sine wave. It flips the voltages below zero (i.e. precision full-wave rectify and it averages. Throws it into a capacitance filter. The result is the average value.
The meter then multiplies that average value by a constant so it reads the RMS value of the hypothetical sine wave.

The meter basically assumes it's being fed a sine wave, averages whatever it gets and multiplies by some k.
if you feed it a 60 Hz sine wave, you will get out the RMS value of the sine wave.

We talk about average, but the average of a typical sine wave is zero. it's really the average of the absolute value.of the waveform.
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Ron D. wrote:
=============
let's say the following:

TRMS meters generally have AC and AC+DC modes, but usually your interested in the AC portion.


** Not true.

The reason for needing a true RMS value is to predict heating in a resistance or maybe a fuse .
So you cannot omit the DC component.


AC meters have a frequency response.


** But DC ones do not and so are all the same.


We talk about average, but the average of a typical sine wave is zero.


** Correct.

Standard AC meters show the "average *rectified* value " scaled up by 11% to the RMS for a sine wave.


...... Phil



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On Friday, April 9, 2021 at 12:19:10 AM UTC-7, wrote:
wrote:
============================

This blows Phil's statement out the water which is rare, there is no TRMS in DC.


" true RMS " = DC equivalent value for the *heating* effect on a resistance.

Known. but a DC meter might not be set up for that.

** You are not paying proper attention.

DC voltage and true RMS voltage are equivalent.
DC meters read the average, DC value of a wave.


The voltage, though, for an LED lighting system is NOT
proportional to current; it's the current average that makes
the light output bright or dim. Neither average DC nor RMS
are suitable measures unless it's on a CURRENT scale rather than voltage.
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whit3rd wrote:
================


DC voltage and true RMS voltage are equivalent.
DC meters read the average, DC value of a wave.


The voltage, though, for an LED lighting system is NOT
proportional to current; it's the current average that makes
the light output bright or dim. Neither average DC nor RMS
are suitable measures unless it's on a CURRENT scale rather than voltage.


** As previously posted *here* by me - the *power* delivered by a DC source is:
I average x DC voltage.

A moving coil DC meter or regular DMM will show you both.

Do the math any way you like.




....... Phil








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TRMS meters generally have AC and AC+DC modes, but usually your interested in the AC portion.

** Not true.

The reason for needing a true RMS value is to predict heating in a resistance or maybe a fuse .
So you cannot omit the DC component.

====

I'll bite. 99% of what I did using an AC meter was measuring power supply ripple and abcense/presence of house AC or 24 VAC systems.

When I designed an I-V converter so we could measure the outut of a UV arc lamp source, that had to be TRMS.

We had lots of phase angle fired AC controllers (before I was hired) operating into variacs to drive 40V tantalum heaters (200-300W). They either worked, had a short inside the vacuum system or blew the semiconductor fuse. I then made sure they SCR;s were 25A, added the current limit option and an extra 3AG fuse. Life got better.

New or upgraded systems went with 1200W DC power supplies. 30V 40A or so. We would have liked a power meter and a programmable temperature controller. The other controllers were obsolete. They had no temperature display and had a proprietary dual SCR unit. Newer replacements would use standard process signals like 4-20 mA 0-5, or 0-10V
That allowed us to reduce panel size and not have a "stupid panel" that read ersatz AC voltage and ersatz AC current and had a temperature display. At one point in the earlier system, Power was important. A three-phase power meter was adapted to do the power of two low voltage single phase heaters at the cost of about $1000.00 USD. There were 7 heaters in a typical system. Sometimes wired wierdly.

In a custom system (prior to the IBM PC) that I was involved in, we did it the right way. The heaters could be controlled by voltage, current, temperature or power. The uncontrolled variable became a limit. I implemented an energy calculator and stability creiteria and recipies. The energy calculator could detect a shorted thermocouple onheat up or a misplaced on, The spreadsheet programs were not invented yet.
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Ron D. wrote:
===========
TRMS meters generally have AC and AC+DC modes, but usually your interested in the AC portion.


** Not true.

The reason for needing a true RMS value is to predict heating in a resistance or maybe a fuse .
So you cannot omit the DC component.
====

I'll bite.


** Don't bite off more than you can chew.

99% of what I did ..


** Totally irrelevant to the issue.

using an AC meter was measuring power supply ripple and abcense/presence of house AC or 24 VAC systems.


** Got SFA to do with needing true RMS values.

IF you need the true RMS value, the DC component must not be omitted.



...... Phil

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