# Questions tagged [rms]

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

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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 ...
1answer
81 views

### 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 ...
0answers
54 views

### 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 ...
4answers
58 views

### 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 ...
1answer
45 views

### 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 ...
4answers
91 views

### 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 ...
3answers
148 views

### 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 ...
0answers
34 views

### 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 ...
0answers
34 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 * ...
2answers
61 views

### 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 ...
3answers
95 views

### 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....
0answers
37 views

### RMS error of a phase shifter

I am trying to develop a Matlab code that calculate the RMS error of a digital phase shifter. After writing the code I have used the s2p data provided by different manufacturers and tried to produce ...
2answers
91 views

### 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).
2answers
104 views

### 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 ...
3answers
997 views

### 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?
0answers
29 views

### 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. ...
0answers
25 views

### Double buffer & ADC Data processing

I'm using HT (Half Transfer) and TC (Transfer Complete) interrupts in STM32 to do a ping pong buffer. I would like to find the RMS value of the array captured. Sampling frequency is 6 kHz and buffer ...
3answers
390 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 ...
1answer
66 views

### 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 ...
2answers
355 views

### 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 ...
1answer
257 views

### 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 ...
0answers
24 views

### Do same current formulas apply if a capacitor is added, and vice versa for inductor

Ok so the title question is a bit misleading but its hard to explain in that small space. My questions concern themselves with the analyzing of the circuit observed below, however fundamentally ...
1answer
188 views

### CMSIS DSP Library and RMS

I'm using a STM32 Cortex M0+ controller which does not have FPU. I'm reading 50/60Hz sine wave and I would like to calculate the RMS using the DSP library: keil.com/pack/doc/CMSIS/DSP/html/group__RMS....
1answer
116 views

### RMS and average value of a DC signal - Which is the correct way to eliminate the inaccuracies due to incorrect measurement setup?

I have a 5V DC signal and there are some ripples on top of the DC signal in the range of 50-100mV (maybe due my measurement inaccuracies or the switching noise coupling from other sources.) In that ...
0answers
61 views

### Why do we use RMS current as the input current for calculating efficiency of half-wave rectifier?

Vi = Vmsin(ωt) Im = Vm⁄R = maximum amplitude of dc current Irms = Im⁄2 Iavg = Im⁄π η = Pdc⁄Pi = efficiency Pi = (Iavg)2R Pdc = (Irms)2R Since the negative portion of the wave is not involved : Why ...
1answer
37 views

### Finding the RMS value

Here, I can't understand the third step. Why they ignored other three terms $(40000\sin\omega t\sin 3\omega t, 10000\sin 3\omega t\sin 5\omega t, 20000\sin 5\omega t\sin\omega t)?$ Please help.
2answers
142 views

### 50/60 Hz signals and ADC sampling frequency

As some of my previous posts, I'm trying to find the RMS of sine wave during the first cycle, but I still have some questions as for the sampling frequency. Let's say I choose a sampling frequency of ...
2answers
153 views

### When to consider Peak current/voltage vs. RMS current/voltage and vice versa

When manufacturers create power labels for AC electrical devices, what value to they use for the current and voltage? Do they use the RMS of the sine wave? Or do they use the peak of the sine wave? ...
2answers
159 views

### RMS of an inverted sine wave

I'm building a circuit similar as below. The input signal is a current which will be converted to voltage using a burden resistor. The inverted output sine wave will go into an ADC to calculate the ...
1answer
58 views

### How to measure only the true RMS AC component of the waveform in an ADC?

I need to read an AC signal on an ADC. I have already conditioned the signal with an offset of 2.5V, which will vary from 0 to 5V. How to calculate the Vac true RMD voltage of any signal (sinusoidal, ...
2answers
193 views

### How do I calculate the root mean square voltage of a square wave (with drawing)?

I need to find the root mean square voltage based on this drawing, knowing that the period (T) is equal to 6 seconds, and the voltage (V) is equal to 14 Volt. I know that the rms can be calculated ...
0answers
82 views

### RMS calculation in cheap microcontroller

I normally see that RMS calculation is done using some kind of DSP or more high end microcontroller. I'm using this microcontroller and I would like to know if it could do RMS. I need to read 60 Hz ...
1answer
57 views

### Understanding voltage sampling rate of induction motors

Why it is required to have a sampling rate of at least 4kHz when sampling the voltage waveform of a three phase induction motor? I find most research papers use 4kHz but they don't state why. I want ...
1answer
444 views

### Strange measurements for Vrms in LTspice

For my experimental methods class (basically an intro to electronics) in university we had to simulate a circuit, which was nothing out of the ordinary, it just produces different sine waves of 2 ...
2answers
515 views

### Why is the output DC voltage of full wave rectifier not equal to the RMS of the original AC input?

https://www.electronics-tutorials.ws/accircuits/average-voltage.html https://www.electronics-tutorials.ws/accircuits/rms-voltage.html I understand that the RMS of an AC voltage is the magnitude of ...
1answer
44 views

### Formula seems to be wrong into a PFC application note

Here is the formula that I found into the following application note: https://www.infineon.com/dgdl/an-1166.pdf?fileId=5546d462533600a40153559aabdf1128 The formula seems to be fault? Am I wrong? ...
1answer
109 views

### Why isn't RMS called SMR, when it's (linguistically) a square mean root? [closed]

This question falls into the funfact category, but I'm anticipating this question from my next course students and I'd like to have the answer, if there is any. In the spirit of English language, RMS ...
2answers
80 views

### Calculating RMS of Simple Waveform

A problem in my textbook gives this task: A solution is given as: I tried to work this problem using a different method. I simply calculated the areas of the triangles as if the height of the ...
2answers
159 views

### How do you differentiate between rms and peak voltage?

In the circuit above I've been asked to calculate the average power absorbed by the 10 Ω resistor. I managed to calculate a value for $V_0=40\sqrt2\,\angle{-25}$. But I'm not sure if this is peak ...
2answers
172 views

### Why are inductive loads an issue for the power grid?

I understand from Power = V_rms * I_rms * cos(phi) Being phi the phase difference between current and voltage. The power consumed by the a circuit is reduced in the case of having inductive or ...
1answer
79 views

### AC-AC Converter 3 phase, Line to line voltage calculation

I’m working one some assignment like this circuit (AC-AC converter 3 phase, 89 degree firing period). I've done this on PSIM software with 110 Volts 3 phase voltage source. I've been told to analyze ...
1answer
678 views

### What is the difference between RMS and DC?

The "RMS" value of an alternating voltage is equivalent to a DC voltage that would generate the same amount of heat in a resistor as the AC voltage would. And RMS = 0.707 * Peak value [N.B. Sine ...
0answers
2k views

### How to calculate RMS current from the rated current? Are they the same in a stepper motor?

I want to use the TMC2130 driver with the stepper motor I show below. This driver has these main features amongst others: Integrated power MOSFETs handle motor currents up to 1.2A RMS (QFN package) / ...
2answers
217 views

### Capacitor Vrms vs Vpeak Rating in Transformerless Supply

Why is it that when calculating for voltage across the capacitor in transformerless power supply we need to use peak voltage not RMS voltage value. To be clear I am referring to the rating of C1 in ...
3answers
414 views

### What's the use of the average voltage in rectifiers?

I've noticed that there is much talking about $V_{dc}$ in rectifiers (specifically, the half-wave rectifier) and less focus is given to $V_{rms}$. Why is that? I thought the RMS value was the much ...
2answers
106 views

### What is the RMS value of this waveform

I would like to know what is the RMS value of this waveform. I would like to see the mathematics. I ve done the mathematics but it seems that the result has a lot of terms ... If some approximations ...
1answer
92 views

### Load RMS voltage of a bridge rectifier

I was given a homework assignment shown below and I have a few quick questions that I appear to be stuck on. Any help would be appreciated. I can get Part i) and the answer is 168.64 degrees. Part ...
2answers
160 views

### What is the required VA rating of the transformer in this LTSpice power supply?

I have this circuit that I'm going to build, including the transformer. It is a simple power supply, with RC filters and one choke, I know all the voltages and currents. Because I will design, wind ...
4answers
1k views

### How to calculate RMS power of an offsetted sine wave

I know when it is centered at 0, Vpeak/sqrt(2) gives the RMS. When I do FFT on LTspice, it gives a peak at -17dB which is equal to 0.141254 On the FFT page, program says that it shows RMS values. ...
1answer
44 views

### Factor of 1/2 in RMS Voltage

Given the following circuit, I would like to calculate the Thevenin equivalent of the voltage in RMS. I know that R = 400 [Ω]; e(t) = 40 cos(10^4 t) [V]. However, I can't understand why there is a ...