the average voltage of a sine wave is zero volts!!!!????so how come?... 10 points to one who answer them all?

Question

its said that the average value of a sin wave is zero volts so
1) the voltage we measure by voltmetre in ac is 110 or whatever its not zero?
2)how to measure the measure value of a sine wave by the help of a multimeter??
3)how to measure pulsating dc by a voltmeter yeah but on AC setting or DC setting?
4)if the average valuse of pulsating dc is measured will it be zero?
thanks plz do categerize ur answer by question numbers

Answer 1

1) Most analog voltmeters (and all digital voltmeters) with an "AC" setting have rectifiers and filters inside, that convert the AC to DC. They measure the root-mean-square (RMS) value of the AC, assuming it is a sine wave, and is within a certain frequency range (i.e. 1 Hz to 1000 Hz)

2) In order to measure peak-to-peak values very accurately you should have an oscilloscope, but if you don't have one an AC voltmeter will give you a good answer. Again, assuming the input wave is a sine wave (no square waves, or triangle ranps, etc.), and it is in the frequency range of the meter (no RF, no high frequency stuff, just 60 Hz or less than ~1 kHz) the reading should be the RMS value. To get the peak value multiply by 1.414. To get the peak-to-peak value multiply the peak value by 2.

3) Pulsating DC should be measured with the DC setting.

4) The average value of the pulsating DC (measured with the DC volt setting) will be smaller than the peak value, and will depend entirely on the waveshape of the DC pulses. for example, if there is one 5 volt pulse that lasts 1 millisecond, but only occurs every 1 second, the average DC value is 5 millivolts. If the meter has a fast time constant filter, you won't see the 5 millivolts -- the meter will read zero (or much less than 5 mV). An oscilloscope is needed, then, to see this.

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Answer 2

I go along with most of the answers already given. However, voltmeters are supposed to read the RMS voltage of the ac waveform. The RMS is that value of dc voltage, which would give the same heating effect as an ac waveform. Thus, the only TRUE RMS measure is a meter involving a thermocouple. However, there is a relationship if sine waves are involved, which links the peak value to the RMS value. In your average voltmeter, a bridge rectifier inverts the negative half cycles so that a series of positive half cycles are produced. The average of these is NOT zero of course, and so gives an indication on the meter. On the assumption that sine waves are involved, the meter can then be calibrated to show the RMS value, even though the average of the rectified wave is what is actually measured.

Answer 3

1. Assuming no DC offset, a sine wave will have equal magnitude in both the positive and negative directions across the 0 axis. So its average is zero.

2. 110V is not the average but the rms value of the voltage, that value is what is measured. In a sinewave, the rms value is the peak value of the voltage waveform divided by the square root of 2.

So a sine wave with a peak value of 156Vpk will have an rms value of 110Vrms. The rms value is all that matters when calculating power.

3. A multimeter set to measure an DC voltage should give you a fairly close approximation of the average value of the waveform.

4. If the pulsed waveform is not truly DC but a square wave waveform that crosses the zero axis with no offsets, then the average would be zero. If it is truly DC then we can assume all the pulses are in positive territory. Then the average voltage will be dependant on duty cycle (how long the pulse stays on vs. how long it is off)

So a 50% duty cycle will mean the average voltage is 50% of the peak. 30% duty cycle means the average voltage is 30% of the peak.

For measuring DC pulses an Oscilloscope (set on DC coupling) is a far better means to measure what is truly happening.

Answer 4

1. the average voltage of a sine wave is zero because a sine wave is both positive and negative. When you read the voltage you only read the positive voltage but there is always a period of negative voltage (current moving the other way) to counter it.

2. Just like above you measure the positive voltage with a multimeter.

3.If you're measuring DC voltage then put the setting on DC voltage, it shouldn't matter if it's pulsing or not.

4. The average of a pulsing DC current will not be zero unless the current is reversing which is unlikely. In almost all cases DC moves in only one direction so the average can't be zero unless there is no current.

Answer 5

An ac voltmeter contains a rectifier to measure the average voltage of the positive or negative half of the sine wave.
You can measure the average of a pulsating DC voltage on the DC setting. If the average is zero it isn't DC.