# Questions tagged [rms]

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

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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 ...
295 views

### 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 ...
157 views

### 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. ...
675 views

### 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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How to calculate the power (dBm) of this signal which is fed into a receiver with an input impedance of 50 ohms? The power in dBm formula is 10log(Vrms^2/R)/1mW and R equals 50 ohms. In this case how ...
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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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1 vote
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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 ...
203 views

### 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. ...
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### Circuit that converts sine wave to RMS voltage

How do I design a simple circuit that converts a sine wave to an RMS voltage? The input will be a sine wave and the output an RMS voltage. I know I will need an ADC, but not sure which one. I also ...
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### Using 110 Vac incandescent light bulb at 220 Vac with a series diode

I have a 110 Vac incandescent light bulb but I need to use it in 220 Vac. If I add a diode in series with the bulb, the RMS power is the same as before but the peak value of voltage and current is ...
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### How do I calculate an incomplete sinusoidal signal's average value and RMS value?

I couldn't be sure because there are parts with size 0 in the signal.
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### How do you convert dBm to Vrms?

I'm trying to convert dBm to Vrms. The formula for dBm is $dBm = 10 * log(P1 / P0)$ where P0 = 1mW so $+13dBm = 20mW$ If I convert this to a voltage using the formula $P = Vrms^2/R$ ...
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### Calculating peak period jitter from datasheet that lists phase noise

The oscillator I plan on using list phase noise for a 20MHZ signal as: (100Hz) -124 dBc/Hz (1kHz) -140 dBc/Hz (10kHz) -148 dBc/Hz 100kHz -155 dBc/Hz (1MHz) -157 dBc/...
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### Why is average power: the average of the voltage squared/resistance rather than the ((voltage average)^2)/resistance?

Regarding pulse waves specifically. So this should be especially simple. I see it written that $$\text{average power} = \text{average current} \times \text{average voltage}$$ which also equals  \...
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### RMS Current calculation from MCP3008

How to find RMS value of current from ADC value gets from CT??? . I have done like below Made a burden resistor and voltage divider circuit for CT MCP3008 connected with Jetson through SPI 5V to VDD ...
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### Average power when a periodic, non-sinusoidal waveform is applied across a resistor with a given voltage across it [closed]

If I have a resistor across which some voltage is provided and a periodic ( non-sinusoidal and non-zero) wave of current is given to the same resistor, then what would be the average power? Do I need ...
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### Average power dissipated by a diode

EDIT: Added a picture with values and a better explanation. I need a little help over this calculation. I have to calculate the average power dissipated by a bootstrap diode (actually a MOSFET ...
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### How to measure power consumption of pulsed DC motor correctly?

I built a permanent magnet pulsed DC motor, and am trying to accurately measure power input, which proves to be harder than expected. The motor is pulsed with a 25% duty cycle square wave and powered ...
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### Finding RMS current of BLDC motor

I have a BLDC motor rated at 72V 1500W. I am working on an application that requires me to perform certain computations using the RMS current but I understand that I can only get the rated current ...
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### What's the RMS voltage of this asymmetric rectangle function?

I recorded this asymmetric rectangle function: I calculated the RMS voltage to be equal to the amplitude (4,10 V in this case) However when I measured this exact signal with a TrueRMS multimeter, it ...
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### Trapezoidal wave RMS value

I am calculating RMS value of trapezoidal wave. I found its formula like below: and at last the RMS value formula: u = 30degree or pi/6 --> especially pi/6 A = 12 When I calculate RMS value by ...
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### the best way to calculate rms voltage from 10Hz to 20KHz

We need to calculate the RMS voltage of a signal that can work from 10Hz to 20 KHz with a duty of 5% to 95%. I decided to use a dsPic33CK256EP202 with the ADC sampling at 500Ksps at 12 bits of ...
80 views

### How do I control the speed of a universal AC motor and measure the voltage and current flowing through it?

It is desired to be able to control the speed of my rotary drill as well as measure the average torque (or is RMS torque a thing?) of the universal AC motor. I am using this torque equation: τ = (I * ...
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### Why is induced EMF of an inductor considered as average voltage and not RMS or maximum?

So my professor discussed to us about induced EMF of an inductor and mentioned that it is an average value and not maximum or RMS if you were to consider which type of voltage it is from the different ...
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### How can I calculate total RMS value from one pulse?

I tried to solve this myself, but I'm forced to beg for help. I have a very short waveform, too short to resolve accurately on my scope. When I expand the waveform, the RMS of one complete pulse is 6....
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### RMS Value of a voltage waveform consisting of a superimposition of 2V DC and a 4 V peak to peak square wave is?

RMS value should be sqrt(2^2 + (4/sqrt(2))^2) which is equal to sqrt(12), but the answer is sqrt(2^2 + (4/sqrt(2))^2) which is equal to sqrt(8).
1 vote
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### Multisim RMS value

I am trying to measure RMS value of full wave rectifier but I don't know why, I see two different RMS value. See the image below According to voltage prob, RMS value is 3.25V and according to ...
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### How can I find the RMS value of a wave in irregular form?

As a sine wave passes through a circuit, it clips and the waveform in the figure is formed. How can I find the RMS value of a full wave?
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### Calculating RMS current from AC712 chip (AC system)

I have read several articles with code examples on how to calculate the actual current with a ACS712 chip with AC involved. I understand what RMS is and I feel like I am able to implement it myself. ...
580 views

### Voltage and current rating of electrical systems

Why voltage and current ratings of almost all electrical systems are RMS value of voltage and current not peak value of voltage and current? First I thought maybe because mostly ac input is sinusoidal ...
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### RMS values and Phasors

I need to solve these two exercises but I really have no idea where to start. How should I proceed to solve this kind of problems? I tried to find something on my teacher's files but haven't ...
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### Measuring RMS power output from audio amplifier channel

I am looking for a simple way for getting the RMS power output of an amplifier channel set to some arbitrary gain. I want this in order to find the maximum level I can safely set the amplifier at for ...
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### Estimate the speed of BLDC motor using back-EMF constant

I want to mesure the speed of BLDC motor using back-EMF constant, $Ke=Vrms/rpm$, so the speed is $rpm=Vrms/ke$. What I want to know is how to get the Vrms? Suppose I have DC supply=40 V and the ...
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