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  • Writer's pictureSunil Rawat

Which AC Value does Voltmeter and Ammeter measure ?

There are different types of values which are associated with the alternating current as follows:

  • Instantaneous Value

  • Peak Value

  • Peak to Peak Value

  • Average Value

  • RMS Value

The Voltmeter and Ammeters measure the RMS Value of an AC waveform.

Let us look at all the values in details for a sine wave.

Different Values of AC sine Wave

Instantaneous Value:

The value attained by an alternating quantity at any instant is known as instantaneous value. It is denoted by “i” and e.

In other words, the value of an alternating current or voltage at any particular moment is called as instantaneous value

Peak Value/Maximum Value/Crest Value/Amplitude:

The maximum Value a sine wave can take (positive or negative) is called as Peak Value. It is denotes by Em (Emax) or VP.

Peak to Peak Value:

The sum of positive and negative peak values is known as peak to peak value. Its expressed as IP-P or VP-P.

VP-P = 2 x VP

Average Value/Mean Value:

If we convert the alternating current (AC) sine wave into direct current (DC) sine wave through rectifiers, then the converted value to the DC is known as the average value of that alternating current sine wave.

In other words, the Average Value (also known as Mean Value) of an Alternating Current (AC) is expressed by that Direct Current (DC) which transfers across any circuit the same amount of charge as is transferred by that Alternating Current (AC) during the same time.

Vavg = (2/π) VP = 0.637 VP

Keep in mind that the average or mean value of a full sinusoidal wave is “Zero” the value of current in first half (Positive) is equal to the the next half cycle (Negative) in the opposite direction.

Rms Value/Effective Value/Virtual Value:

The value of an AC which will produce the same amount of heat while passing through in a heating element (such as resistor) as DC produces through the element is called R.M.S Value.

In other words, the RMS Value of an Alternating Current is that when it compare to the Direct Current, then both AC and DC current produce the same amount of heat when flowing through the same circuit for a specific time period.

VRMS = VP /√2 = 0.707 VP = √0.5 VP

Additional Formula:

For Peak Value

VP = 0.5 x VP-P

VP = √2 x VRMS = 1.414 x VRMS

VP = π/2 x Vavg = 1.571 x Vavg

For Peak to Peak Value

VP-P = 2 x VP

VP-P = 2√2 x VRMS = 2.828 x VRMS

VP-P = π x Vavg = 3.141 x Vavg

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