Questions tagged [rms]
Root Mean Square. Mathematical method to calculate effective value from an AC signal.
188
questions
0
votes
8answers
217 views
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 ...
-2
votes
3answers
87 views
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.
3
votes
2answers
240 views
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 \$ ...
0
votes
3answers
83 views
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/...
0
votes
2answers
55 views
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
$$ \...
0
votes
0answers
18 views
How to remove the noise current values during CT disconnected?
i am doing a energy monitoring system.
i have done High pass filter in the values of ADC current and getting correct. but when CT disconnected some current(noise) getting how to fix it.
device - ...
0
votes
2answers
73 views
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
...
0
votes
1answer
160 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 ...
2
votes
0answers
110 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 ...
1
vote
4answers
96 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 ...
0
votes
1answer
209 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 ...
0
votes
4answers
102 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 ...
0
votes
3answers
450 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 ...
0
votes
0answers
51 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 ...
0
votes
0answers
40 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 * ...
0
votes
2answers
112 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 ...
0
votes
3answers
119 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....
0
votes
2answers
180 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).
0
votes
2answers
238 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 ...
0
votes
3answers
1k 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?
0
votes
0answers
37 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. ...
2
votes
3answers
410 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 ...
2
votes
1answer
71 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 ...
2
votes
2answers
688 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 ...
0
votes
1answer
433 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 ...
0
votes
0answers
25 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 ...
2
votes
1answer
307 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....
0
votes
1answer
210 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 ...
0
votes
0answers
62 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 ...
0
votes
1answer
38 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.
0
votes
2answers
238 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 ...
2
votes
2answers
237 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? ...
0
votes
2answers
192 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 ...
0
votes
1answer
122 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, ...
0
votes
2answers
317 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 ...
0
votes
0answers
103 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 ...
0
votes
1answer
67 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 ...
6
votes
1answer
549 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 ...
0
votes
2answers
1k 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 ...
2
votes
1answer
46 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?
...
0
votes
1answer
130 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 ...
0
votes
2answers
91 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 ...
4
votes
2answers
196 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 ...
1
vote
2answers
263 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 ...
1
vote
1answer
90 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 ...
0
votes
1answer
1k 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 ...
0
votes
0answers
3k 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) / ...
2
votes
2answers
278 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 ...
0
votes
3answers
572 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 ...
-1
votes
2answers
110 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 ...