# Questions tagged [rms]

Root Mean Square. Mathematical method to calculate effective value from an AC signal.

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### Flyback output capacitors and extremely high RMS current

I'm designing a DCM flyback converter for the first time and I've encountered a problem where the RMS current through the output capacitors reaches 5.6A. I started looking for suitable capacitors, and ...
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### How does a digital multimeter measure?

I have a pulsating signal (always positive) with a frequency of 50 Hz and a true RMS multimeter. Should I measure the voltage with the multimeter on DC or AC? What´s the multimeter doing in each case?...
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### Why does 9.7Vrms == 27 Vpp? I thought it was 9.7/0.707 == 13.72!

At first, I thought this calculator was wrong, because I have always used an RMS to peak-to-peak conversion as $V_{RMS} = \frac{V_{pp}\sqrt{2}}{2}$: https://benchmarkmedia.com/blogs/calculators/...
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### Two formulas for defining RMS and average of a waveform through a diode [duplicate]

A textbook problem where we have this given current waveform through a diode. We are required to determine the maximum and RMS values of it [ Irms and Ip ] giving the average current= something ...
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### RMS of sine wave curve defined between two points

Could someone explain for the following attachment (waveform image) how were exactly the values of "RMS" and "average" determined this way (for that curve of sine)? Given the duty ...
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### Is there a DC voltage on a transmitter power amplifier's output?

When studying the answers to Are my power calculations on this MOSFET Power Amplifier accurate? , I noticed this contradiction: If you integrate V * A, you get ...
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### Issue with formula for Total Harmonic Distortion of a pure rectangular switching function

The known value of THD for a pure rectangular switching function, for which the duty ratio D = 0.5, is 0.483 or 48.3%. I have tried to back-calculate this using formulae for THD in order to work out ...
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### Proof of ripple voltage of capacitor filter?

From Electronic Devices and Circuit Theory by Robert L. Boylestad: To get an equation for ripple voltage, the book wrote, $$\frac{V_{r(p-p)}}{T_1}=\frac{V_m}{\frac{T}{4}}$$ How did they come up with ...
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### Power output of a full bridge diode rectifier

Assume a simple circuit with a 12 V (RMS) AC supply and a 100 ohms load resistor. The power dissipated is P = V^2/R = 1.44 W. Now assume that a full bridge diode rectifier (without filtering) is ...
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### Resistor power rating in an AC circuit

Looking at this question and answer: Source: Practical Electronics for Inventors, Page 91, Example 5 Shouldn't we use the peak voltage instead of the RMS voltage to calculate the minimum power rating?...
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### How can I calculate an average value of specific inductor current? [closed]

There is a inductance current signal in below. I want to calculate the average value of the current. Possitive peak value is 33.4 A Negative peak value is -20 A Peak to peak time is 36 µs. But I do ...
1 vote
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### Is my average power logic correct?

Original question I am trying to solve: This question is from "Fundamentals of Electric Circuits", 7th Edition from Sadiku and Alexander For this question, capacitors don't have average ...
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### RCA RMS voltage

Searching the RCA phono input spec online does not garner any official documentation, probably due to the large number of voltage levels and power levels being used in commercial products. Looking at ...
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### Do industry true RMS volt meters use a transformer?

I'm trying to build a true RMS volt meter that plugs into my 120 RMS outlet. Since I want to do it safely, I'm using a very handy transformer (ZMPT101B AC voltage transformer module) that takes the ...
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### Does RMS value of AC signal depend on frequency?

The formula for voltage RMS is usually given as the peak value divided by the square root of 2. I feel like maybe I am missing something: how can two AC signals with same amplitude but different ...
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### Pulsed current measurement and power factor calculation

I want to measure pulsed current in a 3-phase power meter application. I understand that the waveform will be random, as the current in question is the overall current consumed by different types of ...
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### DC Load Current Vs RMS Load Current in single phase half wave rectifier

While solving a problem of a single wave half wave rectifier. using an "Ideal Diode" Given Details: Load Resistance - 1020 Ohms Supply - 230V 50Hz AC (Connected in series) To find : DC ...
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### Create an expression for impedance on the form Z = R + jX

I'm supposed to create an expression for impedance on the form: $$Z = R + jX$$ I didn't know how to that so I looked at my teacher solution, but I don't really understand that either. The question ...
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### Why does an AC Voltage reading on a DMM decrease as the frequency is increased?

I'm doing an assignment for a lab and I've found that frequency doesn't affect the voltage reading of an oscilloscope while it does for a DMM. Online, it says this is because an oscilloscope displays ...
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### What assumptions are made by UL when they equate 30Vrms to 60Vdc for LVLE circuits?

UL defines Low Voltage Low Energy circuits as "A circuit involving an alternating current voltage of not more than 30 volts, rms (42.4 volts peak) or a direct current voltage of not more than 60 ...
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### How to calculate the average voltage and VRMS of a non sinusoidal waveform [duplicate]

I need to calculate the average voltage and VRMS of this. It's given that Vp=41V, Vn=-6V and T=13ms. I know the answer for the average voltage is 12.8V, but I can't find the formula that gets this ...
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### A fully clamped sinusoidal wave has its RMS multiplied by the square root of 3. Is my textbook mistaken?

A fully clamped sinusoidal wave has its RMS multiplied by the square root of 3: Vo = 1.73Vi My textbook says that clamper circuits don't affect the Vpp and Vrms of an AC signal. Obviously, Vpp didn't ...
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### Mistake in calculation of RMS current flyback primary switch node

I'm trying to calculate the RMS current of a flyback converters primary switch node. The Waveform is shown below: I'm okay with assuming it is a triangle wave with a duty cycle of 50%. The peak value ...
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### Y-connected 3-phase voltage source RMS voltage

If I have a three-phase Y-connected voltage source, and the voltages are $V_{a} = V_{m}cos(\omega t)$ $V_{b} = V_{m}cos(\omega t-120^{\circ})$ $V_{c} = V_{m}cos(\omega t-240^{\circ})$ At a ...
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### What does the RMS value of a DC current waveform represent?

I understand (or at least think I understand) the math and calculation of RMS values and that it generally is used for representing equivalent power of non-DC circuits, like typical sinusoidal AC ...
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### Averaged first-order difference of Vout in QUCS

I am looking at a very simple LM317 voltage regulator circuit to drive a motor (represented by R3 in the diagram). I want to be able to sweep capacitor C2's capacitance and plot the mean 1st-order ...
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### Peak detector circuit for AC RMS value

The peak detector circuit based on a precision rectifier with buffer allows to obtain the peak value. The RMS value in an AC circuit is obtained from: RMS = V peak / sqrt (2) = V peak * 0.7071 AC ...
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### How do you calculate the average current of a square wave?

I'm working through the exercises of Art of Electronics and exercise 1.21 asks to calculate how big a fuse a circuit (full-wave rectifier using a center-tapped transformer) needs to be. The current is ...
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### Finding Vrms over time

The plot of voltage over time is given in below plot. As you can see, $V_{max}=2v \text{ and } V_{min}=0v$ $t1=2ms, t2=8ms, t3=5ms, \text{ and period, } T = 15ms$ Question is to find $V_{rms}$ ...
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### Summing RMS values proof [duplicate]

I have a simple circuit with two sources of different frequencies. I was tasked to get a voltage output across a component. I know for a fact that adding the derived voltage of both sources acting ...
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### Intuitive explanation for RMS voltage of discontinous sinewave

A sinewave with a peak voltage of 325.3V. The RMS voltage would be 230V Assumption1: If I were to run this AC sinewave through a resistor it would be the same power dissipated as running 230V DC ...
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### Phasor format vs time domain format question

I have a quick question regarding phasor format vs time domain format. Whenever we write in the phasor format, the magnitude that we use must be the RMS value for voltage/current, correct? Then we ...
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### Why is this ideal diode bridge rectifier simulation in LTSpice not working as expected?

I'm trying to simulate a full wave bridge rectifier circuit with the capacitor filter. The alternating voltage supply is 30 V at 50 Hz. The peak value for the voltage across the load is 28.5 V. ...
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### AC voltmeter circuit

I was searching a way to get the VRMS of an AC voltage. The main transformer drops down the 230 VAC to 15 VAC and with a potentiometer I'd like to display it on a DC digital voltmeter (the AC ...
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### Trying to design a circuit where it transforms its input voltage to a RMS output voltage

I'm trying to implement the RMS block in analog, i think doing only a peak detector would be way easier but perhaps the RMS would be more interesting. Other sources online suggest this: A squaring ...
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### Usage of peak-to-peak voltage and RMS voltage

Why are RMS values and peak-to-peak voltages common in use? For example RMS voltages in the context of noise. I see especially for peak-to-peak voltage no practical usage. Why should I need more ...
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### Is the reference voltage for voltage control the RMS between the three phase voltages?

Suppose to provide voltage control with an AVR connected to a synchronous generator. A voltage reference is compared with the output terminal voltage of the generator, and the error between them is ...
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### Measuring AC current with a current transformer and ADC

I'm looking at using a current transformer (CT) to measure 50hz sinusoidal AC current with a microcontroller's ADC. Is there a way to measure the RMS or average of an AC signal with good response ...
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### Boost PFC power loss calcaulation

I am studying boost PFC topologies. I run into a question, how to calculate the CCM / CRM /DCM boost PFC power loss. I read the On semi document. I would like to derive the Diodes RMS current, but I ...
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### Measure power with multiple measurements

I want to measure the mean power draw of a Jetson Nano. I did this by using a digital multimeter and running the measurement 60 times with a fixed integration time of 0.3s. The result of each ...
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### Nominal or real AC/DC power supply values

I have three older AC/DC power supplies with these nominal values: Input 120 Vac, 0.3 A, 60 Hz Output 16 Vdc, 900 mA Input 120 Vac, ?, 60 Hz Output 16 Vdc, 1 A Input 120 Vac, 60 Hz, 4 W Output 9 Vdc, ...
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### Best way to decompose addition of waveforms?

I am searching for a way to decompose the exact components of additions of known waveforms. For example, lets say there is a waveform that is sum of multiple sinc functions. The sinc function's ...
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### Calculate power output of 3 phase generator - uneven sine wave

I am using this BLDC motor [https://uav-en.tmotor.com/html/2018/navigato_0402/52.html] as a generator. The device providing the mechanical drive turns the motor about half a turn and not at a linear ...
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### Connecting peak voltage, RMS, line-to-line and line-to-neutral

In EU the line-to-neutral voltage from a power outlet which is single phase (if I understand correctly) is 230V RMS and 50Hz. Then the line-to-line voltage (for the three-phase connection coming to ...
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### How does the RMS voltage capture the time varying part in the conversion ratio of the half wave rectifier?

I am studying conversion ratio of a halfwave rectifier from here. It says that Conversion ratio (also called "rectification ratio", and confusingly, "efficiency") η is defined as ...
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### Understanding stepper motor as generator Vs DC motor (RMS to equivalent DC)

I am using a stepper motor as a generator in a proof of concept experiment for something. The motor came from an old printer so do not have specs for it, but I believe it's unipolar. It has 5 wires, ...
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### How to get RMS voltage and frequency from datapoints read from an ADC?

I have an ADC that samples 4000 times per second or 0.25 ms interval per sample. I would like to extract the RMS and frequency value of the signal being read. How do oscilloscopes and multimeters do ...
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### Which theory do oscilloscopes or multimeters follow to measure RMS value?

For calculating RMS value , what I have found so far is that samples of a full cycle are taken then the ADC values are used to calculate RMS. Thus the RMS value stays independent of signal frequency. ...