Gearslutz.com - View Single Post - what is the difference between rms and peak

mgarrett · 17th February 2008

In the 'classical' (engineering) sense, the RMS value is the DC value that creates the same amount of work (or heat in a resistor) in a load as the AC..

So when said that the RMS is the 'equivelent DC' of the AC signal, its the DC voltage that generates the same thermal energy as the AC signal when placed accross the same load resistor. (the DC (Non Changing) signal that does the same amount of work as the AC signal)

There are RMS converters (linear Technologies) that have two resistors, the signal is applid to one, and an internal circuit servo loops the DC trough the other one, to make them the same temperature. This DC value is the RMS value of the AC...

It happens that If I have a sine wave accross a resistor, is generates the same energy as a DC signal (PKPK/2)*0.707, the 'RMS Value'.

Crest Factor is an expression for the deviation from a sinusoid... If I have a very narrow pulse (low duty cycle, lots of off time) that has a peak to peak of 2 Volts, it will not generate as much heat as a sinusoid, but if we correct it utilizing the 'crest factor' we can get the RMS answer, based on knowledge of the wave shape (crest factor).

The RMS value, can have an averaging time associated with it, which is really the amount of time that we are going to use to determine the signal ENERGY (not power!!) (energy heats), (power applied for some amount of time). So to know the amount of heat that would generated (energy consumed) we would need to apply the signal for some amount of time, in order to determine the DC voltage that would generate the same heat, DC in the sense of the non changing voltage over the averaging time chosen.

50 mSec is usually chosen as the integration (or averging time) because it is one cycle of 20 hZ. One cycle is required to determine the RMS value for 20 hZ..... a 50 mSec averaging time would give incorrect results for a 5 hZ sine wave..

So... The RMS value is indicative of the amount of energy, energy transfered from the radiator into the absorber... Voltage into Current into magnetic field into air movment into ear drum vibration... all energy transfer... the amount of work done.

The RMS value give you a quick way of determining how much work you can get out of a 'waveform' or signal.

17th February 2008	#31
mgarrett Gear Head Joined: Oct 2007 Posts: 32	In the 'classical' (engineering) sense, the RMS value is the DC value that creates the same amount of work (or heat in a resistor) in a load as the AC.. So when said that the RMS is the 'equivelent DC' of the AC signal, its the DC voltage that generates the same thermal energy as the AC signal when placed accross the same load resistor. (the DC (Non Changing) signal that does the same amount of work as the AC signal) There are RMS converters (linear Technologies) that have two resistors, the signal is applid to one, and an internal circuit servo loops the DC trough the other one, to make them the same temperature. This DC value is the RMS value of the AC... It happens that If I have a sine wave accross a resistor, is generates the same energy as a DC signal (PKPK/2)*0.707, the 'RMS Value'. Crest Factor is an expression for the deviation from a sinusoid... If I have a very narrow pulse (low duty cycle, lots of off time) that has a peak to peak of 2 Volts, it will not generate as much heat as a sinusoid, but if we correct it utilizing the 'crest factor' we can get the RMS answer, based on knowledge of the wave shape (crest factor). The RMS value, can have an averaging time associated with it, which is really the amount of time that we are going to use to determine the signal ENERGY (not power!!) (energy heats), (power applied for some amount of time). So to know the amount of heat that would generated (energy consumed) we would need to apply the signal for some amount of time, in order to determine the DC voltage that would generate the same heat, DC in the sense of the non changing voltage over the averaging time chosen. 50 mSec is usually chosen as the integration (or averging time) because it is one cycle of 20 hZ. One cycle is required to determine the RMS value for 20 hZ..... a 50 mSec averaging time would give incorrect results for a 5 hZ sine wave.. So... The RMS value is indicative of the amount of energy, energy transfered from the radiator into the absorber... Voltage into Current into magnetic field into air movment into ear drum vibration... all energy transfer... the amount of work done. The RMS value give you a quick way of determining how much work you can get out of a 'waveform' or signal.