Quasi-peak detector

The quasi-peak, quasi-peak or CISPR detector is mainly used in EMC measurement technology of special weighted peak value detector for measuring electrical signals in the frequency range from 9 kHz to 1 GHz. The term quasi-peak can be understood as "fast- peak ".

Background

Unlike other measurement detectors such as peak, average or RMS detector that can not be represented by a corresponding simple mathematical algorithm. Defines is this detector in the CISPR CISPR 16-1-1, thus the term CISPR detector originates. The quasi-peak detector is a peak detector with defined charge and discharge times. In addition, a time constant for the critically damped display element is defined, which includes, among other things, the inertia of old mechanical instrument displays. This ensures that continuous, narrowband sinusoidal signals are rated stronger than broadband pulsed signals or noise equivalent (peak) amplitude. This is due to the fact that, for example in a radio broad-band noise signals are acoustically perceived as " less disruptive " than a corresponding sinusoidal signal.

Technical definition

The technical parameters of the quasi-peak detector according to CISPR 16-1-1 are separated for four different frequency bands A (9 kHz to 150 kHz ), B ( 150 kHz to 30 MHz ), C ( 30 MHz to 300 MHz ) and D (300 MHz to 1 GHz ), wherein the differing requirements for the frequency bands C and D are minimal. In detail, among other requirements, the input impedance, measurement accuracy, display behavior in pulses, selectivity, shielding effectiveness and the limitation of intermodulation effects, receiver noise and internal unwanted signals are provided.

The values ​​given in the table three time constants for Edition 3 (2010) of CISPR 16-1-1 no longer part of the actual definition of the quasi-peak detector. This change was made because it has been shown that for today's digital measuring receiver, there is a discrepancy. The original time constants refer to analog receiver with additional parasitic effects, such as an inductive behavior of the charging diode. To solve this issue, there are different approaches to measuring digital receivers. Due to the backward compatibility of the now normative requirements of the pulse rating this table values ​​are still only valid for the historical analogue heterodyne receiver concept.

Measuring detectors for other frequencies

For frequencies below 9 kHz, the QPPM detector is defined in the measurement audio. Above 1 GHz, the quasi-peak detector is not defined. Here is measured in the EMC measurements instead usually with a combined peak and average measurement or only with peak value.