Questions tagged [rms]

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

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3answers
93 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 ...
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0answers
39 views

RMS value of a combine waveform

I can find the rms value of that waveform any help will be welcomed
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1answer
48 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 ...
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2answers
49 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 ...
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4answers
107 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. ...
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1answer
38 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 ...
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1answer
31 views

change in ac reading relative to the frequency

I'm working on a school project, just measuring the Vrms of two different waveforms at different frequencies. The function generators output is connected directly into an oscilloscope therefore the ...
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2answers
67 views

How to calculate rms current from impedance and voltage?

If a circuit has these values Vac = 20Sin 130πt, L = 32.6 mH. Do I have to get Xl first and V/Xl gives the rms current value?
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117 views

Why is RMS used for P=VI (where there are no squares)?

I understand why RMS values are used for $$P = {\bar{v^2} \over R}$$ because \$\bar{v^2}\$ would be the "MS" so to speak, and then by square rooting we get the "RMS" (\$\sqrt{\bar{v^2}}\$), which ...
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1answer
201 views

RMS value of fundamental harmonic vs RMS of third harmonic

If we have a periodic signal (square wave) with amplitude of 100V. Then what would the RMS value of the fundamental harmonic be compared to the RMS value of the third harmonic? After some suggestion ...
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105 views

Why are different rms noise sources added in this way?

I'm wondering why noise sources are added such a way their rms values are added in square root of sum of squares fashion. For instance if the rms noise values from three sources are X,Y and Z, then ...
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1answer
43 views

Question about calculating the rms noise from sampled DC measurement

If I want to estimate the rms noise of a DC signal, like a DC offset reading of an analog transducer sampled at a certain frequency. So imagine I used the anti-aliasing filter correctly and and fed ...
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1answer
86 views

Is A4988 and DRV8825 Current Limit Setting RMS or Peak?

I'm trying to aggregate information on config settings and current limit calculations for all the popular "StepStick" style motor drivers. However, I've noticed that while the older type (A4988 & ...
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1answer
60 views

bidirectional (biphasic) RMS value

I have searched online and can find RMS calculations for many waveform shapes. What I cannot find however, is a calculation for a typical neuro stimulation wave as shown in the attached image. What ...
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59 views

How to find the RMS value of a sine wave with DC offset and retain the negative sign

I'm trying to build a Quadrature setup where an input signal is mixed with a reference signal that is in-phase and another one out-of-phase by 90deg. The idea is to extract the real and imaginary ...
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2answers
63 views

Lead-acid battery charging fixed current stage specification

This post doesn't question the charging process or its theory. I seek to understand how to read the battery manufacturer's requirement of fixed current stage. They prescribe a current to be held at ...
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3answers
153 views

Clamp multimeter RMS current measurement, AC versus DC confusion

This question doesn't relate to a specific meter, I am using AMPROBE AMP-220 manufactured by Beha-Amprobe. I believe am an experienced engineer but only in the digital world, not really in power and ...
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1answer
67 views

RMS value of a line to neutral voltage on a three phase inverter

Basically, I feel like this is an incredibly simple thing, but my brain is stuck on it for hours now, and I can't find the answer anywhere. How do I find the RMS value of the signal shown, assuming ...
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2answers
41 views

Low DC power consumption: RMS or mean?

I've been measuring low DC-powered devices consumption, by measuring the current at the needed frequency (able to detect the fastest consumption changes). I can then have the mean, max, min. To get ...
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1answer
36 views

Oscilloscope V_rms vs V_avg for effective voltage across an LED?

I'm using a PWM signal to vary the effective voltage seen by the high side of an LED. When probing this signal on an oscilloscope, I can read the RMS voltage or the average voltage, which vary ...
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3answers
121 views

RMS power and phase angle control

We have a piece of industrial equipment using a phase angle controller (PAC), and are having some issues calculating the RMS power used by the load. Personally I am of the opinion that you measure ...
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1answer
52 views

Tripping a circuit breaker when using a half wave rectifier

How does a half wave rectifier or phase control dimmer affect the triggering of a circuit breaker? For example, if a 20A resistive load was on a 15A breaker with a half wave rectifier. Now average RMS ...
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2answers
60 views

Confused on when to use RMS current or voltage in calculations (regarding rectifiers)

For question a, why is the power absorbed by the DC source : P=Vo*Io However, for the same exact question, the power absorbed in the resistor is P = (Irms)^2 * R Hence when do we use RMS current/...
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2answers
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Is the input voltage on power adapters RMS voltage or peak AC voltage?

For example, would a laptop power adaptor with a voltage input of 100-240V ~ be safe to use in a country with 230V RMS wall voltage? Thanks in advance!
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316 views

What is the typical RMS noise of a lithium battery?

Take a typical CR2032 battery, if it is not discharging, what is the typical variation in voltage over a short period of time (eg a few seconds or minutes)?
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1answer
86 views

Random Noise Voltage

I have a signal I am interested in obtaining power from. The best way to describe the signal is that it is random. In the graph, the voltage fluctuates from negative to positive with an RMS of 0.5 ...
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1answer
246 views

PCM5102A: analog output level not what I expected?

I cannot achieve a 2.1 Vrms mentioned in their datasheet (pages 4 and 9). I can only output 1.04Vrms from the 1kHz source. Do I measure it wrong or this is what I should expect? Or maybe I get such ...
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1answer
316 views

Peak Current vs RMS Current when calculating Reactance

I am having a hard time getting a grip on AC circuit analysis. I have been taking my peak voltage/current and converting it to RMS current and RMS voltage so I can use ohms law and things like that to ...
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3answers
515 views

Calculate Angle for Triac Phase Control

Triac-based phase control of the mains power into resistive load. According to this post, https://www.physicsforums.com/threads/how-to-calculate-rms-voltage-from-triac-phase-angle.572668/#post-...
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2answers
161 views

How to Find R.M.S value [closed]

how can I find the R.M.S value of this question?
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2answers
2k views

BLDC Motor Constants: Why is my Kt and Ke different?

I'm new to working with motors. Reading up on BLDC theory, it is repeatedly said that in SI units, the Ke and Kt will be numerically equal. I downloaded the motor spec excel sheet of the T1101 motor ...
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2answers
1k views

Multimeter true RMS [closed]

I'm just getting started with electronics (arduinos and friends) and I would like to get a multimeter. As far as I can tell arduinos and any other logic chips and circuits I'm gonna be using are using ...
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2answers
328 views

AC Circuits: Determine the RMS current in the Inductor in the circuit diagram attached below. (Voltage is 40V, RMS)

Here is the image of the circuit diagram. I wanted to know the method to evaluate the RMS current in the inductor branch. I would prefer to use complex analysis!
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1answer
111 views

LTC1966 Sallen-Key post-filtering application question

Just a quick question about an application circuit in the LTC1966 datasheet. Figure 13 on page 18 shows a third order (when considering output resistance of the LTC1966) Sallen-Key filter, with a ...
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1answer
354 views

What matters, the rms or peak value of the Analog signal to choose appropriate ADC for digitization?

i have an 23 bit ADC with voltage reference of 1.4 V. If my input Analog signal is AC with frequency 50 HZ and its rms ranges from 0.2 Vrms to 1.3 Vrms. Then its peak voltages will vary from 0.28 V to ...
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1answer
359 views

How can I reduce the RMS value for a bridge rectifier?

I need to reduce the rectified DC voltage. Is it possible to reduce the RMS value after the bridge rectifier i.e before the capacitor? Practical value (at the capacitor) is 34 DC voltage. I need to ...
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1answer
233 views

Why use RMS instead of the average voltage of half the cycle for power

In a AC sine wave, the RMS voltage value is \$\frac{V_{p}}{\sqrt{2}}\$ where \$V_{p}\$ is the peak voltage whereas the average voltage value over half the cycle is \$V_{p}\cdot \frac{2}{\pi}\$ If we ...
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1answer
106 views

What current should be used to calculated the drop across the diode? RMS current or average current?

I was designing a power supply, following is the output bridge diode current waveform from LTSpice simulation . My intention is to calculate the power drop across the diode. What value of current (...
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3answers
577 views

Convert Power to a Peak Voltage, when to multiply by sqrt(2) - Not so simple?

I have a dBW value and dBW I understand to normally be given as representing a RMS Power (however this is not specificically ever stated and I am told its just assumed?) from dBW to Watts = \$10^{\...
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2answers
577 views

Measure RMS voltage from AC Grid

Circuit design I need design a circuit for read rms AC grid, its function is obtain the RMS value and generate a PWM signal, this PWM signal feeds my AC/DC LED driver (PWM/1-10V input pin), the ...
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108 views

Can I measure the voltage noise with True RMS function

I have a measurement setup with which I want to measure high voltages. Now I want to evaluate the noise this setup produces (preferably in V/sqrt(Hz)). I short circuited the input and I am now ...
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2answers
54 views

Finding phase angle of AC

After solving for a system of complex equations, I got the following currents: $$I1= -.80669-.35675j$$ $$I2= -1.8546+1.30730j$$ Firstly, I found the current magnitude: $$|I_1|=.88205A$$ $$|I_2|=2....
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120 views

Finding the average and RMS value of this signal

How can I find the RMS and the average voltage of the following diagram?: My work: The RMS: $$\sqrt{\left(\sqrt{\frac{1}{3\times10^{-3}}\int_0^{3\times10^{-3}}\left(\frac{5000}{3}\cdot t\right)^2\...
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2answers
45 views

Which one is correct for this power consumption estimation?

If a MOSFET gate driver is supplied by a 12V DC power supply and if it is drawing a current I(t) from the power supply, what can we say about the power consumption in terms of voltage and current? I ...
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4answers
192 views

AC Effect Value

"The effective value of an alternating current is that current which will produce the same heating effect as an equivalent direct current. The effective value is called root mean square (r.m.s.) value ...
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1answer
110 views

Mistake in reading a rms voltage

I got a really strange result. I've build a full-bridge rectifier with a capacitor filter. And I used the following values \$\text{C}=500\cdot10^{-6}\$ and as a load \$\text{R}=1000\$. The maximum ...
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1answer
450 views

Do I have a true rms meter

I bought an Excel XL 830L multimeter with the understanding that it was a RMS voltmeter. I also have UEI ElectroMate DM 200. When I checked the output of my APC unit with both meters, the readings ...
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1answer
530 views

Is the Diode RMS Reverse Voltage spec important in a DC circuit?

Consider a 12Vdc automotive power supply design where +12V power connects first to a Vc=49.9V bidirectional TVS diode (e.g., TPSMB36CA) and subsequently connects to an SB370 Schottky diode. The SB370 ...
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1answer
127 views

Question about the RMS value of the real input power

I've the following circuit: simulate this circuit – Schematic created using CircuitLab I know that the relation between the input voltage and the input current is given by: $$\begin{cases} \...
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0answers
104 views

Calculating dissipation of a CCR powered via a full bridge rectifier

I'm putting together a string of UV/purple LEDs for photoetching purposes. The idea is the following: simulate this circuit – Schematic created using CircuitLab The 80 LEDs are in series, ...