Author Topic: Need somebody to talk to about AC concept  (Read 6770 times)

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Offline C

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Re: Need somebody to talk to about AC concept
« Reply #50 on: June 29, 2018, 02:13:22 am »
How about the wheel it self has a mass which is significantly greater than the mass of the flowing water (the parasitic inductance) ?

The effect of Inductance changes with a change in current.

The water wheel mass does not change in the same way.

The mass of water is a closer match to what happens with inductance.
This also includes effects that happen in water systems.  With water you can have a water hammer and this can look like an inductive kick.

The area where this fails is in the magnetic coupling  that you get from an inductor.
Trying to use water in place of electricity is a comparison of different physical properties. The different physical properties leads to errors in the comparison.

You can find many physical things that match a part of what happens, but only a part.

In a previous post, I used example of supper long wire to show some effects that become more hidden as wire gets shorter.

That supper long wire would also show time delays that also have an effect.

By thinking about what happens as some value in a circuit changes can also show things to think about.

Today you see a lot of thinking about voltage. But there is three parts to  V = I * R
Today you often see a temperature sensor that has a voltage output. This would not work at the end of a 1000 feet or meters of wire where a temperature sensor that has a current output would. In this case a temperature sensor that has a output of voltage or resistance would be a failure due to resistance of connecting wire.

When you add AC then you can have a temperature sensor with an output of frequency, inductance or capacitance change.

When you think in voltage you see some things.
When you think in current or resistance you can see different things.
If you do not look at the different ways, what are you missing?

And when looking at the individual parts, you still need to think of total system and how this is effected.


 

Offline tester43Topic starter

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Re: Need somebody to talk to about AC concept
« Reply #51 on: June 29, 2018, 09:56:41 am »
Practically speaking in actual implementation. Is using a Rectifier Bridge good or bad choice to get my solid platform as a reference to measure all other potentials? How is it typically achieved?
 

Offline Zero999

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Re: Need somebody to talk to about AC concept
« Reply #52 on: June 29, 2018, 10:47:05 am »
Be careful with taking analogies too far, as it can cause confusion.

Practically speaking in actual implementation. Is using a Rectifier Bridge good or bad choice to get my solid platform as a reference to measure all other potentials? How is it typically achieved?
I'm not sure what you're asking.

As far as 0V or ground is concerned, it has nothing to do with AC, DC, capacitors, inductors and bridge rectifiers. It's just a reference point, in the circuit, from where all voltages are measured from and is arbitrary. In a circuit, running from a battery, the reference point is usually the negative terminal, which makes things easy, since most of the voltages in the circuit will be positive numbers, but it could just as easily be the positive terminal, which would result in negative voltages, akin to putting the common probe of a multimeter on the battery's anode and the other probe on the cathode, which would give a negative reading.

In a circuit, running from a bridge rectifier and smoothing capacitor, the 0V is typically the negative side of the bridge rectifier, but this isn't always the case.
 

Offline Brumby

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Re: Need somebody to talk to about AC concept
« Reply #53 on: June 29, 2018, 12:16:42 pm »
I agree with the above.

Also, you seem to be transfixed with the idea of a single, special reference point to measure everything against.  You need to lose that idea.

Voltage measurements are dependent on the circuit you are measuring and the reason you are making a measurement and one measurement on a circuit may not have a reference point that makes sense for another.

For example, you may wish to check the secondary voltage of the transformer.  For this, you select AC volts, put one probe on one of the secondary wires you want to measure between and the other probe on the other secondary wire you want to measure.  Your result is AC volts.  If you want to test the secondary voltage when the circuit has different loads, then you just do this same measurement for each load.

If, however, you wish to test the voltage on the power rail of the circuit, then the points used in the AC measurement above aren't going to be of any use - especially if you use a bridge rectifier.  For that measurement, you will select DC volts, put one meter probe on one rail and the other meter probe on the other rail ... and you get your measurement.

You can do this without ever having a GND.  As has been said before, the use of GND is more often used to indicate a reference point, rather than a true Ground.
 
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