Understanding Electronics Basics #1

[cowboybob]

Like this?:

If [latex]y=4[/latex], and [latex]x=\sqrt{y}[/latex]. What is the value of x ?

[latex]\sqrt{y}[/latex] is the "square root" symbol. The answer to the above is x=2.

OR, in a reverse fashion using the derived value of x: if [latex]y=x^{2}[/latex] then x is squared or, "raised to the power of 2", or 2X2) so y=4.

Taking it another step:

If [latex]y=9[/latex], and [latex]x=\sqrt{y}[/latex], then x=3, just as if [latex]y=x^{2}[/latex] or, "raised to the power of 2",or 3X3, so y=9.

0r, further:

If [latex]y=8[/latex], and [latex]x=\sqrt[3]{y}[/latex]. What is the value of x ?

[latex]\sqrt[3]{y}[/latex] is the "cube root" symbol. The answer to the above is also x=2.

OR, in a reverse fashion using the derived value of x: [latex]y=x^{3}[/latex] (x is cubed, or "raised to the power of 3", or 2x2x2, so y=8.

 

[Muttley600]

You do realise you've just shot my meaning squared clean between the eyes don't you.lol
So my working out of 12.6mV could now be wrong again
Your X with exponent of 2 means I've misunderstood, I thought you took the original number them & added number of exponent then times them, never mind I'll get it in the end.
Yes, it was the square root symbol or maybe not if it means different things.lol but that was the symbol I was on about

 

[Muttley600]

View attachment 61888 View attachment 61889

Can you do me a favour CBB

Can you translate 12.6mV so I can see how we get PP of 3.84VAC

Back on computer now, it's quite difficult getting your head around math while cleaning windows in the cold **broken link removed** I can see where I was messing up exponent

Ok, why can I only get the 12.6mV in DC on the multimeter & not AC **broken link removed** sorry, still working on your sim from post #85

That link you put in doesnt work on computer either?

 

[cowboybob]

Right off the bat, I don't know what point is "VP_5" or "VP_9".

12.6mV is 0.0126V.

 

[Muttley600]

Right off the bat, I don't know what point is "VP_5" or "VP_9".

left of C2, both VP5/9 are same point on sim, just different numbers on different meters

All this is relating to my struggle in post #194

 

[cowboybob]

OK.

The scope is displaying the AC component of the signal. The multimeter is displaying the DC component (12.6mV).

The zero reading on the multimeter in the AC selection is a mystery. I'm not at all certain that multimeter is reliable in all cases. And, frankly, it has never given us a reliable frequency readout.

 

[Muttley600]

So I'm not going mad not being able to understand this then & 12.6mV does not convert into 3.84V......phew, thought I'd lost the plot.lol

If you put probe to gnd shouldn't it be a flat line? on sillyscope, it is still showing same signal it just stops quivering, ignore me, I just needed to change the gnd to VP_5

Don't you love playing **broken link removed** the VP_5 signal if you change it to 1V instead of 500mV is identical to VF1 if you bring VF1 down to position 0 or export curves then view & click show hide curves, delete VF2 then press putting VF1 on/off is it the same signal

 

[KeepItSimpleStupid]

BTW:

[latex]x^{\frac{1}{2}}=x^{0.5}=\sqrt{x}[/latex]

and

[latex]\sqrt{x}\sqrt{x}= x^{0.5}x^{0.5}=x^{(0.5+0.5)}= x[/latex]

The simple p-p to to RMS conversions only work for sine waves.

I cheat when I make the formulas above. If you do a reply with quote you will see the code and tags. I use the windows program lyx. I create a document and insert an inline formula. I them do a copy and enclose the pasted stuff within the [latex][/latex] tags. I check the result with preview.

 

[Muttley600]

So without giving me the answer so I can & work this out, I get Vrms = means the answer, the Vpeak must be the 3.84 so what value goes where ? mark is

 

[KeepItSimpleStupid]

The "?" should be a 2. Vpeak is the 0 to peak value. A lot of times you will be converting the p-p (peak to peak) value of a sine wave to RMS. Be careful which formula you use. I have to remember a relationship of the AC line voltage. I know that in the US the 0-peak is about 155V and the RMS is 120 V, so I always go back to that to check my formula.

 

[Muttley600]

BTW:

[latex]x^{\frac{1}{2}}=x^{0.5}=\sqrt{x}[/latex]

and

[latex]\sqrt{x}\sqrt{x}= x^{0.5}x^{0.5}=x^{(0.5+0.5)}= x[/latex]

You've been off so long you missed the new rule, every time you put something like this up you have to explain it to me **broken link removed**

The simple p-p to to RMS conversions only work for sine waves.

That means you cannot convert a DCV to ACV?

I cheat when I make the formulas above

**broken link removed**

So where you been hiding, are you still playing drains **broken link removed**

 

[Muttley600]

The "?" should be a 2. Vpeak is the 0 to peak value. A lot of times you will be converting the p-p (peak to peak) value of a sine wave to RMS. Be careful which formula you use. I have to remember a relationship of the AC line voltage. I know that in the US the 0-peak is about 155V and the RMS is 120 V, so I always go back to that to check my formula.

So If I learn to find the rms on 3.84VAC, I need 1.94 which is the 0-peak, is that right?

So does that mean as follows:
1.94x1.94 = 3.76 then divide 3.84 by 3.76 = 1.021 = Vrms

Made slightly confusing by the fact the -Vpeak was lower than the +Vpeak

Of course I'm yabbering total tosh again aren't I **broken link removed**

 

[KeepItSimpleStupid]

You've been off so long you missed the new rule, every time you put something like this up you have to explain it to me

It's simple actually. When you multiply like terms like x to any power, you add the exponents or the superscripted value. When you divide similar terms like (x^3)/(x^2) would equal X^(3-2) or X^1 or X, you subtract the exponents.

That means you cannot convert a DCV to ACV?

This gets complicated. We can convert a DC value to a TRMS value. It is the same value.

We can convert an AC signal on top of a DC signal to a TRMS value. Usually we are interested in the DC and the AC component separately, but not always.

Meters exist that can measure TRMS as the AC portion and TRMS as the AC+DC portion. They are harder to find.

 

[KeepItSimpleStupid]

So If I learn to find the RMS on 3.84VAC

makes no sense.

You have to have a 0 to peak value to use that formula and the peak to peak value must be 1/2 the 0 to peak value.

 

[Muttley600]

Ok, I surrender, I'm not ready for these symbols yet, I'll keep plodding away with learning algebra etc & hopefully then I will understand at some point

So is there anything else we can over on basics while I'm learning or are we at a crossroads with needing to know to go forward or turning back (which is never going to be an option) or turning off & carrying on making that thingy/reader/measuring thing for project
Easy on either way

 

[KeepItSimpleStupid]

Vp = 3.84/2

Now use the formula.


If the RMS = DC value is applied to a fixed resistor the dissapated power will be identical.

1 V RMS is equlivent to1 V DC in this case.

 

[Muttley600]

So are you saying that any rms value is simply 0-P

The annoying part is, I'm sure CBB & I covered this a while back & I'd forgotten, I have actually made a file on computer now so I can double check

I could make sense of that formula but can't see why the square root symbol is there?
Unless 0-P = V peak / 2 x PP

As you can see, I simply can't relate the symbols to the numbers, more math video learning until I understand this side of things

 

[cowboybob]

Keep in mind, Graham, that for the most part, this is all an exercise to explain the difference between the peak AC level(s) you see on a scope and what a multimeter will display as an AC voltage level.

With a Sine Wave ONLY:

If the Peak to Peak value (from the scope) is 3.84VAC, then the 0 to Peak is 1/2 that, or 1.92.

Multiply 1.92VAC times 0.70711 and you'll get the 1.357VAC RMS value.

Multiplying ANY 0 to peak AC voltage level by 0.707 will give you the RMS value that you will see on most multimeters, sim or real.

I got the sim multimeter to behave in the three sims below.

Note the VG1's SETUP: Frequency (10KHz), AND the Amplitude (1VAC 0 to Peak):

Sims are Setup first, then Multimeter RMS Volts second, then Multimeter Frequency.

View attachment 61902 View attachment 61900 View attachment 61901

Does this help?

I should add that I generally limit my use of a multimeter in circuits of this type to DC and resistive values. For all AC work I use a scope.

 

[Muttley600]

Thanks CBB, that how shown me how to do it, I'll try & translate that to symbols now

Just when I thought I'd lost the will for today

 

[Muttley600]

Need to be on computer to do this & my brain is calling time for today, will try in morning

I was simply trying to relate some numbers to symbols so I could actually see how the symbols work

Night both