Questions tagged [rms]
Root Mean Square. Mathematical method to calculate effective value from an AC signal.
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1answer
65 views
Series RC circuit phase difference [on hold]
I have a series RC circuit . AC sine wave source peak to peak voltage is 4Volts.In I=V/Z formula I don’t know what should I write the Voltage.Should I write Voltage RMS value or Peak voltage value? ...
4
votes
1answer
115 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
56 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 ...
1
vote
1answer
77 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 ...
0
votes
1answer
49 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
147 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
115 views
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2answers
316 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 ...
4
votes
2answers
829 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
48 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!
0
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1answer
52 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 ...
0
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1answer
115 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
142 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 (...
0
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1answer
101 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 ...
0
votes
1answer
48 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
111 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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votes
2answers
365 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
60 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 ...
0
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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:
$$|I_1|=.88205A$$
$$|I_2|=2....
0
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0answers
29 views
Finding root mean square of a periodic function with transient phenomenon
I've a electronic signal that is periodic after some time. Let's say in the first \$n\$ seconds the (transient phenomenon) can be described my the function \$f(t)\$ (for \$0\le t<n\$) and after ...
1
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0answers
78 views
Noise Power Spectral Density
So, I'm a physics student who threw himself into an electronics class with very little experience with circuits, amplifiers, and the like. So, please forgive me if my question is trivial or is totally ...
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3answers
107 views
Finding the average and RMS value of this signal
How can I find the RMS and the average voltage of the following diagram?:
My work:
The RMS:
$$\sqrt{\left(\sqrt{\frac{1}{3\times10^{-3}}\int_0^{3\times10^{-3}}\left(\frac{5000}{3}\cdot t\right)^2\...
0
votes
2answers
36 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 ...
0
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4answers
99 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
78 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 ...
0
votes
1answer
307 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 ...
0
votes
1answer
298 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 ...
1
vote
1answer
72 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
78 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, ...
1
vote
1answer
351 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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votes
2answers
98 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 ...
0
votes
1answer
465 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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vote
2answers
517 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 ...
0
votes
1answer
61 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 ...
1
vote
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 ...
0
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0answers
176 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 (...
0
votes
1answer
958 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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votes
1answer
2k 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\$^{\...
0
votes
2answers
49 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 ...
0
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1answer
903 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
748 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 ...
3
votes
3answers
520 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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vote
2answers
605 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
957 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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0answers
109 views
What is the RMS voltage value of the transformer powering a six stage Greinacher circuit?
A six stage Greinacher circuit is powered by a 60Hz transformer. The voltage is measured through a 1 Giga-ohm resistive divider. The output voltage is 300kV.
My question is about which formula I can ...
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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 ...
0
votes
1answer
113 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 ...
...
0
votes
1answer
46 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 ...
0
votes
2answers
141 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 ...
