WhatIs.com

peak-to-peak (pk-pk)

By Gavin Wright

What is peak-to-peak (pk-pk)?

Peak-to-peak (pk-pk) is the difference between the highest and the lowest values in a waveform. In alternating current (AC) the peak-to-peak value is twice the peak value or 2.828 times the root-mean-square (RMS) value. Peak-to-peak voltage is indicated by V_PP.

The difference between peak-to-peak, peak, amplitude and RMS

In alternating current (AC) power, the voltage goes up and down in a smooth sine wave. The voltage goes up to the maximum positive voltage, back down to zero, then to the maximum negative value, and back to zero to start over again. Because the voltage changes over time, there are various ways to express it depending on what aspect you are trying to emphasize.

Peak voltage, shown as V_P, is the highest voltage value compared to zero volts. The amplitude is similar to the peak value as it expresses the highest value of the waveform. The peak and amplitude values are more used in waveform analysis, and less often with AC electrical work.

Peak-to-peak voltage, shown as V_PP, is the difference between the highest and the lowest voltage values in AC. In AC applications, the peak-to-peak value will be two times the peak value. The peak-to-peak value is more used in waveform analysis or amplifier design, and less often with AC electrical work.

Root mean square (RMS) voltage, expressed as V_RMS, is the direct current (DC) equivalent voltage of AC power. Because AC voltage goes up and down over time, it does not provide the peak maximum power all the time. The RMS value gives the effective voltage of AC power for wattage and other calculations.

For example, RMS is used when calculating Ohm's law for AC. Peak-to-peak value is equal to two times the square root of two times V_RMS, or roughly 2.8284 times V_RMS. RMS is most used in AC electrical work.

To illustrate the difference between peak, peak-to-peak and RMS voltage we can use standard North American residential power. Most people only know that it is 120 volts but might not know what type. It is 120 volts RMS (V_RMS). This is handy for calculating power wattages of appliances.

120 V_RMS is equal to 170 volts peak (V_P), so up to 170 volts can come out of the wall. 170 V_P is equal to 340 volts peak-to-peak (V_PP), which is the difference between +170V and -170V.

Mathematically this can be expressed as:

V_PP = 2 x V_P = 2 √ 2 x V_RMS

See also: resistance, ampere, impedance, reactance, oscilloscope