Quasi-peak value

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


In contrast to the other measuring detectors such as peak value , mean value or effective value detector , this cannot be represented by a corresponding simple mathematical algorithm. This detector is defined in the CISPR standard CISPR 16–1–1, from which the name CISPR detector comes from. The quasi-peak value detector is a peak value detector with defined charging and discharging times. In addition, a time constant is defined for the critically damped display element, which also includes the inertia of old mechanical instrument displays. This ensures that continuous, narrowband sinusoidal signals are evaluated more strongly than broadband pulsed signals or noise of the same (peak) amplitude. This is due to the fact that z. B. Broadband interference signals in a radio are perceived acoustically as "less disruptive" than a corresponding sinusoidal signal.

Technical definition

The technical parameters of the quasi-peak value detector according to CISPR 16–1–1 are separate 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), whereby the requirements for frequency ranges C and D differ only minimally. In detail, there are requirements for input impedance , measurement accuracy , display behavior in the event of pulses , selectivity , shielding attenuation and the limitation of intermodulation effects , receiver noise and internal undesired signals.

Frequency band 6 dB bandwidth QP detector charging time QP detector discharge time Time constant instrument
CISPR A (9 kHz - 150 kHz) 200 Hz 45 ms 500 ms 160 ms
CISPR B (150 kHz - 30 MHz) 9 kHz 1 ms 160 ms 160 ms
CISPR C (30 MHz - 300 MHz) 120 kHz 1 ms 550 ms 100 ms
CISPR D (300 MHz - 1 GHz) 120 kHz 1 ms 550 ms 100 ms

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

Measurement detectors for other frequencies

The QPPM detector is defined in audio measurement technology for frequencies below 9 kHz . The quasi-peak value detector is not defined above 1 GHz. In EMC measurement technology, measurements are usually made with a combined peak and mean value measurement or only with a peak value.

See also


  • EN 55016-1-1, requirements for devices and equipment as well as definition of the procedures for measuring high-frequency interference emission (radio interference) and interference immunity - Part 1-1: Devices and equipment for measuring high-frequency interference emission (radio interference) and interference immunity - measuring devices.
  • C. Rauscher: Basics of spectrum analysis. Rohde & Schwarz
  • S. Braun, P. Russer Taking Time-Domain EMI Measurements According to International EMC Standards