difference between detectors

[mona123]

what is the difference between voltage peak detector, voltage rms detector and power detector? Any reference? Thanks.

 

[KlausST]

Hi,

you don´t tell in what context...

But the names tell almost everything:
* voltage peak detector: detects the peak value of a voltage signal
* voltage RMS detector: detects the RMS (root-mean-square) value of a random signal. It represents the DC value that generates the same power on an ohmic load as your random input signal.
* power detector: P = U x I. Either it calculates the power for a specified resistance (50 Ohms) or it calculates the (avaerage) from U x I

Klaus

 

[mona123]

Hi,

you don´t tell in what context...

But the names tell almost everything:
* voltage peak detector: detects the peak value of a voltage signal
* voltage RMS detector: detects the RMS (root-mean-square) value of a random signal. It represents the DC value that generates the same power on an ohmic load as your random input signal.
* power detector: P = U x I. Either it calculates the power for a specified resistance (50 Ohms) or it calculates the (avaerage) from U x I

Klaus

Thanks Klaus. I was asking in general for a wireless transmitter or a receiver. Is there any reference for power detection through vxi? Why someone will use it and Why voltage rms detection won't be sufficient for power detection? Thanks.

 

[chuckey]

For transmission it is inconvenient to measure the current as you would need to put a current meter in series with a live feed. It is sometimes done inside the transmitter at lower frequencies (LW & MW) using a current transformer.
Frank

 

[c_mitra]

what is the difference between voltage peak detector, voltage rms detector and power detector? Any reference? Thanks.

The peak voltage: The maximum positive value of the voltage in a given cycle. The cycles are expected to be identical.

The RMS voltage: the square root of the sum of the squares of the voltage values in a cycle: this is defined in the form of an integral. The cycles are expected to be identical.

power detector: non-standard term.

 

[albbg]

As already said voltage peak detector will detect the maximum voltage of a waveform. It can be done charging a capacitor through a diode. Ideally the capacitor is never discharged so the maximum reached by the waveform is stored for infinite time. A switch that shorts the capacitor can be used to reset it.
A quasi-peak detector has a resistor (R) in parallel to the capacitor (C) that is used to discharge it, so the output will be close to the peak if the frequency of the signal is high enough with respect to the time constant RC.
The voltage RMS detector will detect the root-mean-square value of the voltage
A power detector will detect the voltage but will be converted to a power, using for instance a diode operating in the "square region", so that the output voltage will be Vo=Vin^2. We know that the power is given by P=V^2/R, this means the output of the detector will be proportional to the power with proportionality 1/R that can determined after a calibration. However there are other methods for RF power detectors.
A power detector can be true RMS or not. In case of a true RMS detector, the output will be the RMS power of the input signal regardless to its waveform, otherwise the output will be the RMS only fo CW signals (sinewave) and correcting coefficients are needed in case of different waveforms.

Sometimes RMS detection is not enough. For example if it is required to detect the crest factor of a signal, that is the ratio between the peak and the mean (RMS) power.

 

[c_mitra]

A power detector will detect the voltage but will be converted to a power, using for instance a diode operating in the "square region", so that the output voltage will be Vo=Vin^2. We know that the power is given by P=V^2/R, this means the output of the detector will be proportional to the power with proportionality 1/R that can determined after a calibration. However there are other methods for RF power detectors..

I would assume that a power detector simply detects the presence of voltage that can potentially deliver some power. An example will be a simple neon lamp line tester.