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Questions tagged [rms]

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

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1answer
43 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
51 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
30 views

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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1answer
123 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
63 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
113 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
119 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
223 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
125 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
582 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
934 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
104 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
62 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
163 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
170 views

how to reduce the rms value for a bridge rectifier?

hello!! can any one help me with this circuit.i need to reduce the rectified dc voltage.is it possible to reduce the R.M.S value after the bridge rectifier i.e before the capacitor? practical value (...
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1answer
127 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
52 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
186 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
426 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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0answers
70 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
50 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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3answers
107 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
38 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
108 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
93 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
350 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
347 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
85 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
83 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, ...
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1answer
378 views

Measuring True-RMS voltage of different waveforms - error?

I'm trying to measure True-RMS voltage for these three types of AC waves: (freq, amplitude - waveform): 1) \$ 200Hz\$, \$2V\$ - sine wave 2) \$ 150Hz\$, \$3V\$ - triangle wave 3) \$ 250Hz\$, \$2V\$ - ...
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2answers
106 views

True RMS for circuit breaker

Electronic Circuit breaker On page 9 of the breaker above, they take a sample of the full cycle and calculate the true rms. That would mean for a 50 Hz wave, a time of at least 20 ms before it trips. ...
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2answers
2k views

AC RMS and DC average voltage

Imagine we're trying to get 120V output. For AC, we must have a source with a peak voltage of 169.7V to achieve an RMS voltage of 120Vac. (169.7V * 0.707). For pulsating DC, whether rectified by a ...
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1answer
535 views

AC RMS current measurements with oscilloscope

I am going to measure the AC current(three phases), with a current probe, of a large machine, with an oscilloscope. The scope I am using has the following two options: RMS: RMS (Root Mean Square) ...
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2answers
586 views

Confusion between average and rms calculation for power

I have a DC source where DC Voltage = Vdd and the current supplied by this source is rectified sine wave to a circuit. Now I would like to find the average power delivered by DC source. There are ...
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1answer
69 views

Accurate RMS voltage measurement of DC with RF ripple

As the title says, I have a signal which is mostly DC but has some RF ripple on-top of it. The signal comes from a pickup coil that receives a 13.56Mhz signal (RFID). That signal gets rectified by a ...
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2answers
2k views

Calculating max power of bicycle dynamo

So I have some old dynamo, and I want it to power my GPS navigator. But first of all I want to calculate its maximum power it can deliver. Setup: two wires are soldered to dynamo on one end, on ...
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0answers
196 views

How to mathematically calculate of RMS of a Sine Wave filtered out PWM

I'm generating a Sine Wave without DC offset from a Square wave with 1Khz 1.5V offset by filtering it first with a High Pass firs (to remove the DC) and then with a 3rd Order Low Pass Active filter (...
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1answer
1k views

how to calculate rms voltage value of PWM motor [closed]

My motor is of brushless type controlled by a PWM signal, it is three-phase synchronous. I measured the three voltages of each phase and now I need to calculate the RMS value on all 3 phases.
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1answer
3k views

Full-wave controlled bridge rectifier and the RMS voltage derivation?

I have a question that reads: A full-wave controlled bridge rectifier is considered, shown below. Vs = 230V. Load is represented by \$i_o = 10\$ A. Frequency is 50 Hz and the delay angle is 45\$^{\...
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2answers
52 views

Amplifier output wattage and speaker wattage [closed]

I have a Creative Inspire M2600. The Satellite speakers have broken and I have to use another 2 speakers. A note here says the RMS Value of Satellites is 6 W each. It is bit difficult to get speakers ...
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1answer
984 views

Why RMS value used in transformer equivalent model?

The equivalent model of a real transformer is given: Why do we use RMS values of input and output voltage when analyzing the model? The main confusion comes from the fact that real transformers only ...
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3answers
827 views

What does “AC frequency response : (60-1000)Hz” mean for multimeters?

I'm considering to buy a multimeter. The following is its specs as listed at Amazon: Size:KT6666 Featuring a wealth of functions, it is intended for troubleshooting various electrical issues arising ...
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3answers
531 views

Reverse engineering a power supply characteristics

I have this schematics and the following information: connect the + of the multimeter to test point A and the ...
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2answers
658 views

Can I measure the relative output gain of a power amplifier with a multimeter?

If I wanted to measure the gain that a power amplifier provides to a signal with a multimeter, do I simply do the following: Measure the input signal's voltage e.g. 1 Vrms Turn the amplifier up to ...
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1answer
1k views

RMS of a complex waveform

For a complex waveform as follows: One can find the squared rms of the complete waveform by finding rms of individual components and then square multiplying it with the corresponding duty cycle. $$...
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3answers
7k views

How to a derive average and effective values of half wave rectified sine wave and full wave rectified sine wave?

I know the basics of how to find these values from a graph, but not sure how to prove that average voltage of half-wave rectifier is peak/pi and rms is peak/2. Same for full-wave rectifier where ...
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1answer
126 views

Average power across a resistor [closed]

I am solving a problem here that asks for average power across a resistor.... the resistor is 3k and V(s) = 1.897sin(500t - 71.6)... I found 0.8 mW ....but the answer book says that it is 0.6mW ... ...
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1answer
51 views

AD736 input amplitude for 32kHZ

I want to convert a sine voltage with frequency around 32kHz , what should i keep the amplitude of this signal to get the best conversion. I looked up the datasheet , but the input range given is ...
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2answers
146 views

Output the DC average value of a waveform

I have the task of designing a circuit that will, given a sine or square wave as input, output the RMS value of that input. I believe this task essentially has three parts Squaring circuit Averaging ...
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0answers
529 views

Vrms, Vpk-pk, Vpk, Vavg for AC signal with DC offset

This might be a dumb question, but what values change when applying a DC offset to an AC signal? Does Vpk represent the maximum voltage of the signal, in which case it increases directly with the ...