EdgarC
Member
- Location
- Fontana, CA
What is the voltmeter value readings???
Effective value
Pick value
Average value
Rms value
Max value
Effective value
Pick value
Average value
Rms value
Max value
VOLTMETER READINGS
- Thread starter EdgarC
- Start date
- Status
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Depends on the meter design and/or settings.
Most your average multimeters display RMS (which is the effective DC equivalent value) when measuring AC voltage.
MD84
Senior Member
- Location
- Stow, Ohio, USA
It would be volts.
Edit: Sorry, misunderstood question.
Edit: Sorry, misunderstood question.
Effective value is ... a somewhat vague term. Could mean "what you actually have" after all the distortion and harmonics have done their damage on the AC waveform. With DC it could mean what the effective DC value is after ripple has been factored in.
Pick value? Do you mean peak value? ...
Peak value is the maximum "peak" value of the crest of the waveform in AC and the maximum value of a DC signal. For example peak value of 120 VAC is 169.68 volts (120 x 1.414), which is the crest, or maximum value of the waveform. With DC it is the same as the max DC voltage.
Average value is the voltage or current with no regard for waveform distortion. Such a meter is only accurate on a pure sine wave or with DC. An averaging meter is usually cheaper than an RMS meter and "good enough" for most applications. Not so accurate on heavily loaded systems that have a lot of switching power supplies or electronic ballasts on the circuit.
RMS (aka true RMS) is the root mean square value that takes into consideration distortion. These meters are accurate with distorted waveforms like when you have harmonics from switching power supplies or electronic ballasts. They usually cost more than averaging meters. My first choice in meters types.
Max (and Min) value is usually a recorded value of the maximum (or minimum) value the meter records, AC or DC. The recording could be in amps or volts depending on the meter settings. For example if you record a terminal voltage and it varies from 117 VAC to 125VAC then 125 would be the max value and 117 would be the min value. For DC the max value would be whatever maximum DC voltage occurred at the terminal. Example, a 0 to 10 VDC VFD speed signal varies from 2 to 8 volts then 8 VDC would be the max value the meter recorded, 2 the minimum.
Pick value? Do you mean peak value? ...
Peak value is the maximum "peak" value of the crest of the waveform in AC and the maximum value of a DC signal. For example peak value of 120 VAC is 169.68 volts (120 x 1.414), which is the crest, or maximum value of the waveform. With DC it is the same as the max DC voltage.
Average value is the voltage or current with no regard for waveform distortion. Such a meter is only accurate on a pure sine wave or with DC. An averaging meter is usually cheaper than an RMS meter and "good enough" for most applications. Not so accurate on heavily loaded systems that have a lot of switching power supplies or electronic ballasts on the circuit.
RMS (aka true RMS) is the root mean square value that takes into consideration distortion. These meters are accurate with distorted waveforms like when you have harmonics from switching power supplies or electronic ballasts. They usually cost more than averaging meters. My first choice in meters types.
Max (and Min) value is usually a recorded value of the maximum (or minimum) value the meter records, AC or DC. The recording could be in amps or volts depending on the meter settings. For example if you record a terminal voltage and it varies from 117 VAC to 125VAC then 125 would be the max value and 117 would be the min value. For DC the max value would be whatever maximum DC voltage occurred at the terminal. Example, a 0 to 10 VDC VFD speed signal varies from 2 to 8 volts then 8 VDC would be the max value the meter recorded, 2 the minimum.
Last edited:
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The RMS "takes into consideration" the harmonics and other waveform issues in the sense that it tells you what the equivalent constant voltage DC or pure sine wave AC would be to produce the same amount of power into a linear unit power factor load.
For any other purpose (motors, electronics of all sorts, etc.) the RMS value may not in fact be the most useful.
For any other purpose (motors, electronics of all sorts, etc.) the RMS value may not in fact be the most useful.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
160107-2005 EST
The original post is not clear as to the question. I believe the question is:
Which of the following three choices is the same as the term "effective value"?
The answer is RMS.
One reference is "The heating effect of a current flowing in a resistor is given by i^2*R at any instant. If the current varies from instant to instant, the net heating effect is obtained by averaging the current-squared values, and multiplying by R. The result secured by taking the square root of the average of the instantaneous current-squared values is called the EFFECTIVE VALUE , or, frequently by the descriptive title, root-mean-square value (abbreviated rms).". From page 9 of "Analysis of A-C Circuits", Melville B. Stout, Professor of Electrical Engineering, University of Michigan, 1952. To access this book you would have had to have Stout as the teacher of the course or go to the University of Michigan Engineering Library.
https://books.google.com/books?id=L...ts&focus=searchwithinvolume&q=effective+value
If you have a resistor R with an irregular voltage applied, but repetitive, then the RMS or effective value of the voltage is of the same value as a steady DC voltage that produces the same average power dissipation in said resistor when the averaging is done over an integral number of periods of the repetition.
.
The original post is not clear as to the question. I believe the question is:
Which of the following three choices is the same as the term "effective value"?
The answer is RMS.
One reference is "The heating effect of a current flowing in a resistor is given by i^2*R at any instant. If the current varies from instant to instant, the net heating effect is obtained by averaging the current-squared values, and multiplying by R. The result secured by taking the square root of the average of the instantaneous current-squared values is called the EFFECTIVE VALUE , or, frequently by the descriptive title, root-mean-square value (abbreviated rms).". From page 9 of "Analysis of A-C Circuits", Melville B. Stout, Professor of Electrical Engineering, University of Michigan, 1952. To access this book you would have had to have Stout as the teacher of the course or go to the University of Michigan Engineering Library.
https://books.google.com/books?id=L...ts&focus=searchwithinvolume&q=effective+value
If you have a resistor R with an irregular voltage applied, but repetitive, then the RMS or effective value of the voltage is of the same value as a steady DC voltage that produces the same average power dissipation in said resistor when the averaging is done over an integral number of periods of the repetition.
.
Last edited:
Aleman
Senior Member
- Location
- Southern Ca, USA
Most meters read average volts. Some read true RMS which is a true average value of waveforms that are not true sine waves like VFD outputs etc. I have never owned a meter that would do peak
voltage or the other values. Nor have I ever needed one that would.
voltage or the other values. Nor have I ever needed one that would.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
160107-2051 EST
Aleman:
To add detail to your statement.
There are many types of AC volt or ammeters. Some of these are full wave rectified average reading calibrated in RMS values for a sine wave (a Simpson 260, Fluke 27), peak reading calibrated in RMS on a sine wave (I never saw one), peak reading calibrated for the peak value, an electrodynamometer (a true RMS electro-mechanical) (typical old large Weston meters), an electronic true RMS (Fluke 87), a hot-wire true RMS, and iron vane (some are somewhat good at RMS measurement), and electrostatic.
All ordinary meters, mechanical or electronic, do some sort of averaging. An oscilloscope does not average, other than by a bluring, unless some additional processing is done.
The nature of the signal being measured and your measurement goal will determine what is the best type meter to use, and/or how to use or interpret the reading.
Inexpensive UPSs tend to use a pulse type waveform. A scope is a good way to look at the peak value, and a true RMS meter to measure its effective value. Peak is important because that is what is needed by a full-wave rectified capacitor input filter (input to a computer). RMS is need for heating effect.
Wherever you are interested in resistive heating with a complex AC current or voltage waveform use a true RMS meter.
.
Aleman:
To add detail to your statement.
There are many types of AC volt or ammeters. Some of these are full wave rectified average reading calibrated in RMS values for a sine wave (a Simpson 260, Fluke 27), peak reading calibrated in RMS on a sine wave (I never saw one), peak reading calibrated for the peak value, an electrodynamometer (a true RMS electro-mechanical) (typical old large Weston meters), an electronic true RMS (Fluke 87), a hot-wire true RMS, and iron vane (some are somewhat good at RMS measurement), and electrostatic.
All ordinary meters, mechanical or electronic, do some sort of averaging. An oscilloscope does not average, other than by a bluring, unless some additional processing is done.
The nature of the signal being measured and your measurement goal will determine what is the best type meter to use, and/or how to use or interpret the reading.
Inexpensive UPSs tend to use a pulse type waveform. A scope is a good way to look at the peak value, and a true RMS meter to measure its effective value. Peak is important because that is what is needed by a full-wave rectified capacitor input filter (input to a computer). RMS is need for heating effect.
Wherever you are interested in resistive heating with a complex AC current or voltage waveform use a true RMS meter.
.
- Status