- #1
alchemist
- 50
- 0
When a voltmeter measures the AC voltage in a circuit, does it measures the root-mean-square value of the voltage? Is the same true for ammeters and AC current too?
Cheap ones measure the peak voltage assume it is a sign wave and multiply by sqrt(2) to give the RMS.
f95toli said:Just out of curiosity: Where did you find a meter that displays the peak value?
I most have used seveal dozen different models of multimeters by now (I thknk I have about ten models in my lab) and I have never come across a multimeter that shows the peak value; not even my bench multimeters have that as an option.
Cheap multimeters just assume that it is a sine-wave and divides the peak value by sqrt(2); the only time you need to actually convert anything is if you are using a cheap multimeter and KNOW what kind of waveform you are measuring; then you can sometimes get the true RMS (or the amplitude) by multiplying by a numerical factor.
Anyway, the point is that ALL multimeters display the RMS value; but cheap (i.e. non "true RMS") will simply show the wrong value if you try to measure anything but a sine-wave.
Just out of curiosity: Where did you find a meter that displays the peak value?
f95toli said:Cheap multimeters just assume that it is a sine-wave and divides the peak value by sqrt(2);
mgb_phys said:Cheap ones measure the peak voltage assume it is a sign wave and multiply by sqrt(2) to give the RMS.
stewartcs said:No, the cheap ones generally measure peak voltage. So, take that reading and multiply by 1/sqrt(2) to obtain the RMS voltage.
stewartcs said:Cheap multimeters do not measure true RMS. They measure the average positive voltage of a waveform and scale this value using the square root of two to produce a display value. They may call this value RMS, but it is not a true RMS.
rbj said:actually the cheap voltmeters measure the DC component of the full-wave rectified waveform (the average of the absolute value), assume it's a sine, and multiply by [itex] \frac{\pi}{2 \sqrt{2}} [/itex] to get a pseudo-RMS reading.
mgb_phys said:"After winning the Galactic Institute's prize for extreme cleverness, he was later lynched by a mob of respectable physicists, who finally worked out that what they really could not stand was a smartass."
Alternating current (AC) is a type of electrical current that constantly changes direction. This is in contrast to direct current (DC), which flows in only one direction. AC is the type of current that is used in most household appliances and electric power systems.
Alternating current is measured using an instrument called an ammeter. This device measures the amount of electrical current flowing through a circuit. The unit of measurement for AC is the ampere (A).
The main difference between AC and DC is the direction of flow. AC switches direction continuously, while DC flows in only one direction. Additionally, AC can be easily transformed to different voltages, which is necessary for long-distance transmission, while DC cannot be easily transformed.
Alternating voltage is measured using a device called a voltmeter. This instrument measures the difference in electrical potential between two points in a circuit. The unit of measurement for AC voltage is the volt (V).
Measuring alternating current and voltage is important for several reasons. It allows us to monitor the amount of electricity being used, which is important for managing energy consumption. It also helps ensure the safety and efficiency of electrical systems, as well as troubleshooting any issues that may arise.