phase

[kurt stocklmeir]

I am trying to understand how connecting a resistor or capacitor
to a ground can change the phase of an electric circuit - I guess
connecting a resistor or capacitor to a ground can act like a
filter

thank you for any answers

Kurt
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[Ralph Mowery]

"kurt stocklmeir" <kurtcursed@yahoo.com> wrote in message
news:md5br7$10la$1@adenine.netfront.net...

I am trying to understand how connecting a resistor or capacitor
to a ground can change the phase of an electric circuit - I guess
connecting a resistor or capacitor to a ground can act like a
filter

thank you for any answers

Kurt
--

A resistor will not change the phase. An inductor or capacitor will.

They do that by either the current or voltage will lead or lag the other.
That is if you can put a very fast voltmeter and ampmeter in the circuit,
the voltage will rise faster than the current or the current will rise
faster than the current flows. It depends on if it is an inductor or
capacitor as to which one reaches the maximum value first.

If I remember correctly, say you have a capacitor and put a voltage to it,
the current will start to flow at a very high rate as the capacitor is like
a short circuit to start with. It will take the voltage a short time to
charge the capacitor.
The inductor is the opposite of this.

 

[Bill Bowden]

"kurt stocklmeir" <kurtcursed@yahoo.com> wrote in message
news:md5br7$10la$1@adenine.netfront.net...

I am trying to understand how connecting a resistor or capacitor
to a ground can change the phase of an electric circuit - I guess
connecting a resistor or capacitor to a ground can act like a
filter

thank you for any answers

Kurt

Imagine a sinewave applied to a series resistor and capacitor. As the
sinewave reaches a peak, the capacitor is not fully charged and has a
voltage somewhat less than the applied sinewave. Now as the sinewave reaches
a peak and starts falling, the capacitor continues to charge because the
sinewave voltage is still greater than the capacitor voltage even though the
sinewave is falling to a lower value. At some point, the sinewave will fall
to the same voltage as the capacitor and the capacitor will stop charging
and begin discharging. So, you can see the peak voltage of the applied
sinewave occurs before the peak voltage on the capacitor. The amount of time
shift between peaks depends on the resistor and capacitor values, and the
frequency of the sinewave. Also note the amplitude of the sinewave across
the capacitor decreases as the phase shift increases. By the time you get to
90 degree shift, there is no amplitude at all. The capacitor voltage at that
point is just DC.

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If you don't have them yet, you should get a cheap dual trace scope, like a Tenma for $25 or so, and an audio sine wave generator.

Put the scope in dual trace chop mode, put the generator to one channel and adjust it to sync in, and then the generator output also goes to a resistor and capacitor. Put the second scope probe to the juncion of the resistor and capacitor. Of course the loose end of the R C network" goes to the common gorund.

Which comes first ? The resistor or capacitor ? It doesn't matter but once you play with it one way, reverse them and see the opposite effect.

If you can measure the phase shift you can calculate the amplitude as a fraction or percentage of the total applied signal. If you can measure the drop in the aplitude of the signal you can calculate the phase shift. It's either the sin of the phase lead or lag, or the arcsine of the measued amplitudes' ratio. Of course you have to know which way to flip the formula, and I think the reality of seeing it on the scope screen helps to understand alot of this type of stuff.

Audio generators are not expensive, so find a cap that has about the same Xc as the resistor's value to start. Figure 1 kHz, that's a good middle of the road frequency. Figure 1,000 Ohms. Now to find a capacitor with 1,000 ohms Xc (capacitive reactance) at 1 kHz. the formula is :

Xc = 1/(2pi F C)

where:

Xc is the capacitive reactance (kinda resistance) of thre capacitor in question
pi is of course 3.14159265 give or take
F is the frequency in Hertz
C is the cpacitance in Farads

Now you are going to have a value in microfarads so you have to adjust the math accordingly. For nanofarads or picofarads, it is a matter of the decimal place in a different position.

Actually, there should be no harm in telling you that the value (I think) for the cap will be about 0.018 uF. you'll want to figure that out for yourself though I think. Also, I think 0.015 is a standard value and alot easier to come by. you just adjust. Refigure the Xc and make your resistor so, or vary the frequency to where Xc = R. It's all up to you.

When the Xc equals the resistance, the phase shift is 45 degrees. the voltage at the junction of the R and C will be 0.70711 times the total - which is the sine of a 45 greee angle. If you put in a frequency at which the ratio of Xc to R is 0.86603 and 0,5, the phase is going to lead or lag by 30 or 60 degrees, depending on which way you look at it.

Those numbers are straight out of the trig tables. And that is what you use when you do the vector algebra to figute amplitude to phase.

Lately, I have this math tutor on once in a while. Informal, when we get in the mood. He got me to read a book that started explaining just ow the trig tables are generated. I find it fascinating, and do NOT understand it yet.. But that is just someting I thought to mention because if I read your post right, you are not afraid of math. The more i earn the more I find I don't know. (well that pretty much applies to everything eh ?)

But this is getting good, sines and cosines (which you will use to calculat phase shift) are all generated based on parts of a circle. Bottom line, there is geometry in electronics.

In his book, George F. Simmons says the waste time in the schools telling sutents to go out and figure out the height of a flagpole base on its shadow.. He says that it a waste of time right in the preface. He says nobody has to do that. Nobody dios that, even architects. He said the most impotant uses of math like geometry have very little do to wiht actual shapes of things. electronics is a perfect example.

 

Oh, and after you get used to sine waves, try square waves. Theoretically they ahve all odd order harminics to infinity in a certain phase relationship. Actually, they are pretty square if you cna reproduce like the 21st harmonic.

Take and sens that thropugh your R C network. In fact, if you really want to have a blast, send a 1 kHz square wave through a ten band graphic equaliizer. If you happen to smoke the funny stuff, hook it up first, and then play wiht it and see what happens to the waveform. It is alot harder to view that and get more understanding, but you will notice certtain things. you'll notice with the R C network as well.

It's all part of the cool stuf you can do on a dime. On eBay I am sure you can get an adequtae scope and generator for under a hundred bucks, and you know if you like electronics it woul not be like the famous oxycetylene torches. They were a syn=mbol of suburbia and grandeur almost. Had to have them. YOU CAN WELD ! So you get them, maybe fix one thing, loan them out to your brother in law once, get them back two years later and never missed them, he retirned them because he is moving. And then they sit there for five years. Like, I have a lathe and milling machine, though I don't want to get rid of them they have not been turned on in months.

A scope won't be like this. for the want of a few other components like maybe some coils etc., you can do all inds of cool experiments, and you can actualy measure and see if the math you did is correct. yup, solve it first and THEN observe. Good way to learn because when you make a mistake you have to find out why and how.

 

[default]

On Tue, 3 Mar 2015 18:06:54 -0500, "Ralph Mowery"
<rmowery28146@earthlink.net> wrote:

>That is if you can put a very fast voltmeter and ampmeter in the circuit,

Readily apparent on an oscilloscope too.

 

[whit3rd]

On Tuesday, March 3, 2015 at 2:16:15 PM UTC-8, kurt stocklmeir wrote:

I am trying to understand how connecting a resistor or capacitor
to a ground can change the phase of an electric circuit ...

First, a little background. Any circuit with connected resistors, DC voltage sources,
current sources etc. can be characterized by a set of equations (derived
by Kirchoff's rules). You may designate any node as ground, and any
node (other node than ground, if you want anything interesting) as output.
Then the output is (after solving the set of equations) always a voltage source
with a series resistance (Thevenin's theorem). It is also a current source
with a shunt resistance (Norton's theorem); these two circuits BOTH are
complete descriptions of the current/voltage curve of the output.

Now imagine that instead of DC sources, you allow exp(j * (phase +2*pi*F *T)) factor times
an amplitude, and agree that only the REAL component of this complex function
of time is measurable (voltage, or current). Then, the exact same solution of
equations gives rise to a different solution for each value of frequency, F.
For F = 0, this repeats the resistors-only case. For nonzero F values, however,
there are impedances that are frequency-dependent, like capacitance (impedance
of a capacitor is constant/(j*2*pi*F)), and inductance (impedance of an inductor
is constant * j*2*pi*F).

Now, the Thevenin equivalent has voltage amplitude, phase (if the frequency is nonzero) and
a complex output impedance, and these three things are all frequency dependent.
But, you can sum multiple single-frequency solutions and get a solution for composite
input signals (containing multiple single-frequency components, or even
a continuum of frequencies). That linearity property is lost if you have
any spark gaps, zener diodes, rectifiers... anything other than R, L, C.

'connecting a resistor or capacitor to ground' means changing an infinite impedance
connection from a node to ground, to a resistor or capacitor finite impedance, and that
changes the equations that have to be simultaneously solved.
The circuit doesn't have a phase associated with it, though, only a single frequency
component of an (output or input) signal can be assigned a phase. The 'input'
phase comes from the signal source, not the network of components. The 'output'
phase comes from the source(s) of some particular frequency of interest, and the
network of components, not excluding any test instrument you connect to do
a measurement.

 

[Tim Wescott]

On Tue, 03 Mar 2015 18:06:54 -0500, Ralph Mowery wrote:

"kurt stocklmeir" <kurtcursed@yahoo.com> wrote in message
news:md5br7$10la$1@adenine.netfront.net...
I am trying to understand how connecting a resistor or capacitor
to a ground can change the phase of an electric circuit - I guess
connecting a resistor or capacitor to a ground can act like a filter

thank you for any answers

Kurt --

A resistor will not change the phase. An inductor or capacitor will.

The whole problem is so ill defined it's hard to say anything -- but if
the circuit node in question is being fed a sinusoid through an inductor
or a capacitor, putting a resistor from that node to ground will, indeed,
change the phase of the voltage on that node.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Tim Wescott]

On Tue, 03 Mar 2015 22:16:08 +0000, kurt stocklmeir wrote:

I am trying to understand how connecting a resistor or capacitor to a
ground can change the phase of an electric circuit - I guess connecting
a resistor or capacitor to a ground can act like a filter

thank you for any answers

Your question is very ill-posed.

ASSUMING that the circuit in question has some sinusoidal voltages or
currents running around.

And ASSUMING that the node in question is fed through some reactive
component.

THEN adding a resistor to ground could change the phase of the voltage at
that node.

A better question will get you better answers. One way to make your
question better is to give a concrete example of the circuit you're asking
the question about. If you're looking at some discussion on a web page, a
URL is always a quick way to give us the necessary background.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

>"Your question is very ill-posed. "

I seem to have understood him just fine. It wasn't all that badly put for a newbie. This is sci.electronics.basics. BASICS. If this post was in sci.electronics.design, tear into it.

 

"First, a little background. Any circuit with connected resistors, DC voltage >sources,
current sources etc. can be characterized by a set of equations (derived
by Kirchoff's rules). "

This is the LAST kind of shit to throw at a newgie. Nodes and all that. And you know something, I did a hell of alot of shit before ever hearing of Kirschoff and his circulat reasoning equatipons that maker much otodo about nothing. The concept is simple. The thesis is useless to somneone who wants to learn.

All the voltages in a circuit add up to zero if you take them al in series and subtract them, whatever. Well DUH. Of course. Currsent is the same in all points of a series (DC) circuit. Well DUH. Now the exception is a buck convertor. Puts out more current than it takes in. And the only other thing is has it a short to ground !

So instead of a functional explanaition we need five years of calculus to understand what I did as a teenager,l right ?

hey, I am not saying this shit is useless, but this is BASICS. Soem fuckers in hewre miught be straight out of Ohm's law and going into Xc and X, and impredance formulae. We do not need a quadratic equation here, something with 2pi and F, and then either C or L. Simnple. Let them figure otu all the promulgations, I DID . And I am a dropout. And I can do longhand square roots.


Anyone else up to that ?

Keep It Simple Stupid. That is the theory. Some of these high fallpouing egghead types (you know who you are lol) should try their shit on someone thar does not share a language of any kind. On a desert island. For a long time. And no sex until the other understands Kirschoff's theorum.

 

Do what I said, you'll br glasd you did. Cheap scope and audio generator. you'll learn the concept first and the math later.

 

And make sure it has XY operation, that you cna switch the B channel to the horizontal amp to view those Lisajouis patterns, those are neat as well.