# Help in electronics

#### Syed Naqvi 7

Joined Oct 14, 2015
14
Salam Friends.I have just started electronics,So I have a lot of questions.
If I connect one diode and a resistor in series and supply AC voltage,then resistor will get DC voltage as diode would have rectified the AC signal,So where should I set the knob of multimeter to find voltage of resistor i.e DC or AC.If your answer is DC,then which value of voltage will multimeter tell me means peak value,average or rms value.
A big thanks to all in advance.

#### GopherT

Joined Nov 23, 2012
8,009
Salam Friends.I have just started electronics,So I have a lot of questions.
If I connect one diode and a resistor in series and supply AC voltage,then resistor will get DC voltage as diode would have rectified the AC signal,So where should I set the knob of multimeter to find voltage of resistor i.e DC or AC.If your answer is DC,then which value of voltage will multimeter tell me means peak value,average or rms value.
A big thanks to all in advance.
You have to look in the manual. Some assume AC is a sign wave and others give true rms of any wave form.

Some give a DC component plus an AC component. (Ripple on a DC signal).

Post a picture of your schematic and we can work from there for your diode plus resistor question.

#### Syed Naqvi 7

Joined Oct 14, 2015
14
You have to look in the manual. Some assume AC is a sign wave and others give true rms of any wave form.

Some give a DC component plus an AC component. (Ripple on a DC signal).

Post a picture of your schematic and we can work from there for your diode plus resistor question.
My multimeter tells me peak value of AC signal,but my question is which value will i get when signal is half wave rectified voltage.

#### GopherT

Joined Nov 23, 2012
8,009
My multimeter tells me peak value of AC signal,but my question is which value will i get when signal is half wave rectified voltage.
Try it in AC and again in DC mode and report back. You won't break anything in voltage mode.

#### AnalogKid

Joined Aug 1, 2013
10,575
My multimeter tells me peak value of AC signal...
Do you know that for a fact, or is that an assumption? Most meters in AC mode average the input and then adjust the displayed value to equal the equivalent RMS value. BUT (this is important) that adjustment assumes that the input is a sinewave. For anything else, the "conversion" from average to RMS will be inaccurate, something we all have to live with. And it varies a lot from one meter manufacturer to another; there is no "standard".

The same is true for the DC input - if the signal isn't pure DC, then the meter might not display what you want. Your signal sometimes is called pulsating DC, and again there is no industry standard for how a meter is supposed to interpret this because different people want different things. Some want the average value, some want the RMS value, and some want the peak value. OBTW, which do you want? What is it about the signal you are trying to measure?

ak

#### Syed Naqvi 7

Joined Oct 14, 2015
14
Do you know that for a fact, or is that an assumption? Most meters in AC mode average the input and then adjust the displayed value to equal the equivalent RMS value. BUT (this is important) that adjustment assumes that the input is a sinewave. For anything else, the "conversion" from average to RMS will be inaccurate, something we all have to live with. And it varies a lot from one meter manufacturer to another; there is no "standard".

The same is true for the DC input - if the signal isn't pure DC, then the meter might not display what you want. Your signal sometimes is called pulsating DC, and again there is no industry standard for how a meter is supposed to interpret this because different people want different things. Some want the average value, some want the RMS value, and some want the peak value. OBTW, which do you want? What is it about the signal you are trying to measure?

ak
I thought that it was peak value that multimeter displayed and now I will look into user manual for info.You have explained it broadly.Thanks a lot for your time.

#### recklessrog

Joined May 23, 2013
985
That's also why having access to an oscilloscope is invaluable as then you will be able to measure all the parameters and by visualising the signal, It will give you a better understanding of what is actually going on.

#### Syed Naqvi 7

Joined Oct 14, 2015
14
That's also why having access to an oscilloscope is invaluable as then you will be able to measure all the parameters and by visualising the signal, It will give you a better understanding of what is actually going on.
Yeah.Oscilloscope is must.

#### wayneh

Joined Sep 9, 2010
17,405
I thought that it was peak value that multimeter displayed ...
I think that's unlikely unless it's specifically marked that way. By far more common is a reading that is the RMS value of an assumed sine wave. Stick the leads in the wall socket and it will read 120V (here in the US), not 170V.

#### dl324

Joined Mar 30, 2015
15,827

#### Syed Naqvi 7

Joined Oct 14, 2015
14
I think that's unlikely unless it's specifically marked that way. By far more common is a reading that is the RMS value of an assumed sine wave. Stick the leads in the wall socket and it will read 120V (here in the US), not 170V.
So,you mean 120V is rms value of electricity supplied to homes in USA and its peak value is 170V.

#### dl324

Joined Mar 30, 2015
15,827
So,you mean 120V is rms value of electricity supplied to homes in USA and its peak value is 170V.
Yup. Vpeak=1.414*Vrms