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Author Topic: Accurate Measurements on pulsed system's harder than you think.  (Read 83338 times)

tinman

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #30 on: December 10, 2015, 03:27:47 PM »
TK
Try an inductor with a core.
I think the results will be better and more evident.

P.S--forgot to ask--no power measurements mentioned on the video?.

Brad

seychelles

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #31 on: December 10, 2015, 04:14:45 PM »
IT SEEMS THAT WE ARE LOOKING AT REFLECTIVE POWER..

picowatt

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #32 on: December 10, 2015, 05:06:48 PM »
Tinman,

Surely you are not serious...


Incandescent bulbs have a very large positive temperature coefficient.  As such, they present very non-linear I versus V behavior. 

Incandescent bulbs tend to regulate the current flowing thru them.  As more voltage is applied to the bulb and it attempts to draw more current, the temperature of the filament increases, which increases the filaments resistance, which reduces the current flowing thru it.  This inherent behavior has been used for many years in unique applications such as current limiters and sine wave oscillator AGC circuits.

Incandescent bulb filaments have thermal mass and, therefore, thermal inertia.  Because of this thermal inertia, the temperature of the filament, and therefore its resistance, will be different for applied voltages having different frequency, duty cycle, and peak voltage values, even if the average value of those applied voltages are identical.

Incandescent bulbs are very inefficient emitters of visible light.  The bulk of their emissions is in the far infrared and their emission bandwidth (spectrum) is highly dependent on the temperature of the filament.  The limited spectral response of a typical solar cell is not going to respond to the long wavelength IR which represents the bulk of the bulb's emissions. 


Lesson to be learned, always use a low temperature coefficient, non-inductive resistor for your CVR...

PW

tinman

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #33 on: December 11, 2015, 12:08:32 AM »
Tinman,

Surely you are not serious...


Incandescent bulbs have a very large positive temperature coefficient.  As such, they present very non-linear I versus V behavior. 

  This inherent behavior has been used for many years in unique applications such as current limiters and sine wave oscillator AGC circuits.

Incandescent bulb filaments have thermal mass and, therefore, thermal inertia.  Because of this thermal inertia, the temperature of the filament, and therefore its resistance, will be different for applied voltages having different frequency, duty cycle, and peak voltage values, even if the average value of those applied voltages are identical.

 


Lesson to be learned, always use a low temperature coefficient, non-inductive resistor for your CVR...

PW

I am very serious PW,and i think you missed the boat here some where.
Did you watch the first two video's ? ,do you know what this thread is all about.

Quote
Incandescent bulbs tend to regulate the current flowing thru them.  As more voltage is applied to the bulb and it attempts to draw more current, the temperature of the filament increases, which increases the filaments resistance, which reduces the current flowing thru it.

Please post a short video here showing us how you can raise the voltage across an incandescent bulb without the current also rising. Yes,the resistances rises as the element rises in temperature,but in order to gain a temperature rise,the current flowing through that bulb must increase,and as the temperature rises,so will the visible light output.

Quote
Incandescent bulbs are very inefficient emitters of visible light.  The bulk of their emissions is in the far infrared and their emission bandwidth (spectrum) is highly dependent on the temperature of the filament.  The limited spectral response of a typical solar cell is not going to respond to the long wavelength IR which represents the bulk of the bulb's emissions.


This is telling me that you have not watched the first video,where there was no solar cell being used,and the rise and fall of visible light was very apparent. Once again,the only way to increase the visible light output of an incandescent bulb is to increase the current flowing through it-->which will increase the voltage across that bulb.

And then there is the CVR-what of that-->and please do not go on about how those wire wound resistors are no good because they have inductance,as no inductance at all can be seen on the scope from that CVR at these low frequencies. How is it that in the last video,the voltage across the CVR remained the same,indicating that the current flowing through the system was the same,and yet my very reliable amp meter says the current increased by 70mA when the cap was conected.

In this thread,only those that can ! show ! what they say to be true will be taken notice of. So your first task is to show Quote: Incandescent bulbs tend to regulate the current flowing thru them.  As more voltage is applied to the bulb and it attempts to draw more current, the temperature of the filament increases, which increases the filaments resistance, which reduces the current flowing thru it.
So i would like you to show us how you can increase the voltage across an incandescent bulb,while maintaining or decreasing the current flowing through it. Show us how you can dissipate more power from an incandescent bulb with less current flowing through it,and dissipate less power with more current flowing through it-->as i have shown.

I have shown the effect in the form of experiment's,and presented those experiments and results by way of video. In this thread,those that choose to argue the point will do so with actual experiments-->(! not text book physics !),and will present there experiment right here on this thread. No credibility will be given here to words without experimental  data to back up there claims.
Words are no longer good enough.

P.S
I would like to add this quote from ION
Quote:  Even the lowly incandescent bulb can be viewed as a measuring device.


Brad

EMJunkie

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #34 on: December 11, 2015, 12:18:17 AM »
I am very serious PW,and i think you missed the boat here some where.
Did you watch the first two video's ? ,do you know what this thread is all about.

Please post a short video here showing us how you can raise the voltage across an incandescent bulb without the current also rising. Yes,the resistances rises as the element rises in temperature,but in order to gain a temperature rise,the current flowing through that bulb must increase,and as the temperature rises,so will the visible light output.
 

This is telling me that you have not watched the first video,where there was no solar cell being used,and the rise and fall of visible light was very apparent. Once again,the only way to increase the visible light output of an incandescent bulb is to increase the current flowing through it-->which will increase the voltage across that bulb.

And then there is the CVR-what of that-->and please do not go on about how those wire wound resistors are no good because they have inductance,as no inductance at all can be seen on the scope from that CVR at these low frequencies. How is it that in the last video,the voltage across the CVR remained the same,indicating that the current flowing through the system was the same,and yet my very reliable amp meter says the current increased by 70mA when the cap was conected.

In this thread,only those that can ! show ! what they say to be true will be taken notice of. So your first task is to show Quote: Incandescent bulbs tend to regulate the current flowing thru them.  As more voltage is applied to the bulb and it attempts to draw more current, the temperature of the filament increases, which increases the filaments resistance, which reduces the current flowing thru it.
So i would like you to show us how you can increase the voltage across an incandescent bulb,while maintaining or decreasing the current flowing through it. Show us how you can dissipate more power from an incandescent bulb with less current flowing through it,and dissipate less power with more current flowing through it-->as i have shown.

I have shown the effect in the form of experiment's,and presented those experiments and results by way of video. In this thread,those that choose to argue the point will do so with actual experiments-->(! not text book physics !),and will present there experiment right here on this thread. No credibility will be given here to words without experimental  data to back up there claims.
Words are no longer good enough.

P.S
I would like to add this quote from ION
Quote:  Even the lowly incandescent bulb can be viewed as a measuring device.


Brad



@Tinman, you do great work, always!!!

in an Incandescent Bulb, Resistance changes with heat - See: Nonlinear Conduction

Any Resistor that changes in Temperature will suffer changes in resistance.

An Incandescent Bulb is not Linear...

   Chris Sykes
       hyiq.org

tinman

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #35 on: December 11, 2015, 12:32:08 AM »


@Tinman, you do great work, always!!!

in an Incandescent Bulb, Resistance changes with heat - See: Nonlinear Conduction

Any Resistor that changes in Temperature will suffer changes in resistance.

An Incandescent Bulb is not Linear...

   Chris Sykes
       hyiq.org

Yes,the current/voltage curve is non linear,but the only way to dissipate more power from an incandescent bulb is to increase the amount of current flowing through it,and this increase of current will increase the voltage across that globe.

I show the exact opposite,where i decrease the amount of current flowing through the bulb,decrease the voltage across that bulb,but increase the dissipated power across  that bulb.
We are using our CVR to watch this happen,so either the CVR is not telling us the true current flowing through it,or our light bulb has everything back to front--it has to be one of the two,as the current flowing into the system ! MUST! flow through the CVR and bulb first.

Take that inductor away,and what do you think will happen?


Brad


picowatt

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #36 on: December 11, 2015, 12:43:36 AM »
Tinman,

I watched video two, could not find video one, scanned thru video three.  Some of what I heard in the videos and read in this thread just made me shake my head.

Perhaps it is you that is missing the boat.  Please reread my post and tell me which of the points I raised you disagree with.  I can't believe there is anything I stated in my post that you could possibly disagree with.

Read up on positive and negative temperature coefficient resistors.  Look at the data sheets for various resistors, the temperature coefficient is almost always given (usually stated as ppm/C).   

Measure the cold resistance of a 100 watt incandescent and calculate its power draw based on that resistance.


PW

 

picowatt

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #37 on: December 11, 2015, 12:50:16 AM »
Tinman,

Perhaps you should consider building a very simple Wien bridge sine wave oscillator using an incandescent bulb as the gain control element. 

Marvel at how, without even glowing, the varying resistance of the lamp regulates the positive feedback.

Very old school...

PW

EMJunkie

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #38 on: December 11, 2015, 12:54:38 AM »
Yes,the current/voltage curve is non linear,but the only way to dissipate more power from an incandescent bulb is to increase the amount of current flowing through it,and this increase of current will increase the voltage across that globe.

I show the exact opposite,where i decrease the amount of current flowing through the bulb,decrease the voltage across that bulb,but increase the dissipated power across  that bulb.
We are using our CVR to watch this happen,so either the CVR is not telling us the true current flowing through it,or our light bulb has everything back to front--it has to be one of the two,as the current flowing into the system ! MUST! flow through the CVR and bulb first.

Take that inductor away,and what do you think will happen?


Brad

The Current/Voltage Curve is the Change in the Resistance of the Globe. Because: I = V/R and V = R x I - If R changes, then I and or V must also change because: R = V / I.

Even the CVR will have an amount of Non Linearity to the result.

Current flowing through a Circuit Element is normally proportional to the Applied Voltage across a Circuit Element, not taking into account the Time Domain and the instantaneous measurement in a Non Linear Situation. A Voltage drop Across a Circuit Element, is associated with Heat dissipated from that Circuit Element. Electrical Energy Transformed to Heat. So I am sorry, I don't fully agree.

It is however another good experiment and I may have totally missed something...

   Chris Sykes
       hyiq.org


P.S: The only reason I know this is because I thought I was onto something and this was what it turned out to be.

picowatt

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #39 on: December 11, 2015, 01:10:46 AM »
From Wiki:

https://en.wikipedia.org/wiki/Incandescent_light_bulb

Quote
Current and resistance

The actual resistance of the filament is temperature dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold resistance is much lower (about 9.5 ohms).[50][93]

PW

poynt99

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #40 on: December 11, 2015, 02:02:12 AM »
PW/TK,

These familiar "Gotchas" raise their ugly heads from time to time. Last time I involved myself with this one in particular was with Luc on his Recirculating BEMF circuit.

This was back in 2009, and I did up an analysis which explained his observations and showed, as often seems the case, that erroneous assumptions were being made.

Here is that analysis: Luc_flyback01.pdf

A lot of time and effort went into this document (as did all my documents uploaded here), and aside from a few too many references to "RMS", it is still relevant, and should I believe shed some light on this scenario as well.

A couple of excerpts in summary:

Quote
The Rbulb intensity (or heat) can not be used reliably to indicate the total amount of power used by the entire circuit!

Quote
When there are other components in the circuit (such as resistors and coils) and the bulb is in series with them and the power supply, the bulb's intensity is only indicative of the power being dissipated in the bulb itself. It does not indicate how much total power is being taken from the power supply and being used in the whole circuit.

Peace Out.

EMJunkie

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #41 on: December 11, 2015, 02:41:56 AM »
Perhaps this is a good opportunity to ask one of the most important questions of all: "How is it that a change in Temperature changes the resistance so much? What is going on to make this happen?"

We know this is Nonlinear Conduction - From this we can see that the "Conductivity" of the Filament has changed. Temperature is the cause. Why?

What else can change the Conductivity of an Element?

   Chris Sykes
       hyiq.org

verpies

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #42 on: December 11, 2015, 03:03:35 AM »
Incandescent bulbs have a very large positive temperature coefficient.  As such, they present very non-linear I versus V behavior. 
Yes, incandescent bulbs are not linear but that does not mean that they are not monotonic.
Light bulb's brightness depends on the current flowing through it and Tinman is correct that more current always means more brightness....and in his experiment this is all that matters.

I am more concerned how his scopes calculates the average of these pulses, e.g. from the screen data, from memory or from the waveform period...

TinselKoala

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #43 on: December 11, 2015, 03:19:39 AM »
Hmmm.... I think some people are still missing some points and being distracted by Red Herrings.

1. The current measured by monitoring the voltage drop across the CVR is also the current flowing through the bulb. The elements are in strict series so the same current is flowing through them both. Right?

2. The brightness of the bulb is an indication of the power being dissipated in the bulb. A dimmer bulb means less power dissipated in the bulb, a brighter bulb means more power dissipated in the bulb. This is true regardless of factors like the temperature coefficient of resistance of the bulb, and the duty cycle of pulsation.  Right?

3. The instantaneous power being dissipated in the bulb is Watts=I2R, where I is the current at the instant of measurement and R is the bulb's resistance at that instant. Right? And this is also equivalent to Watts=V2/R, so solving for R we have R=V/I by Ohm's Law. Right?


4. When the capacitor is connected, the current through the bulb is (relatively) constant, so there is no difficulty with the "mean" value of the current. So the power dissipated in the bulb is also constant. The resistance of the bulb can be calculated by R=V/I. We know I from the CVR measurement, but what is V?
Question: Does the voltage drop across the bulb as measured by the scope give us the "V" value for this equation when the voltage is constant, duty cycle 100 percent?

5. When the capacitor is _not_ connected, the current through the bulb is pulsed. So the power being supplied to the bulb is no longer constant. Depending on the thermal lag of the filament, this power is "smeared out" or averaged over some time interval, so the bulb is actually dissipating some power even when the filament is not receiving any current. Hence it can appear to be glowing steadily even though its current supply is pulsed. During the current peaks, as measured by the scope, the power dissipated is related to the _square_ of the current, adjusted somehow for the thermal lag and the temperature coefficient of resistance of the filament. Right?
Question: Is it legitimate to use the simple "mean" value of the current to calculate the average power dissipated by the bulb in this case, since the power supplied during the peaks is related to the square of the current?



Are the Red Herrings starting to jump out of the bucket yet?

TinselKoala

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Re: Accurate Measurements on pulsed system's harder than you think.
« Reply #44 on: December 11, 2015, 03:29:04 AM »
Yes, incandescent bulbs are not linear but that does not mean that they are not monotonic.
Light bulb's brightness depends on the current flowing through it and Tinman is correct that more current always means more brightness....and in his experiment this is all that matters.

I am more concerned how his scopes calculates the average of these pulses, e.g. from the screen data, from memory or from the waveform period...

I believe the scope calculates the measurements from the data displayed on the screen, or, in the case of my Rigol, it can also calculate between cursors. Yesterday I did a rough visual analysis of TinMan's scope traces and I think it is calculating the "mean" value correctly. A better question might be, as I've tried to clarify above, "Is the mean value of the current (and/or voltage drop) the appropriate measurement to use here when estimating the power dissipated in the bulb?"
Looking at the screenshot below, is the "A" area the same as the "B" area? I think it is, pretty close anyway, which tells me that the scope is calculating the mean value correctly. I think.