What is quasi peak?

Most radiated and conducted limits in electromagnetic compatibility (EMC) testing are based on quasi-peak detection mode. Quasi-peak detectors weigh signals according to their repetition rate, which is a way of measuring their "annoyance factor." They do this by having a charge rate much faster than the discharge rate. Therefore as the repetition rate increases, the quasi-peak detector does not have enough time to discharge as much, resulting in a higher voltage output (response on spectrum analyzer). For continuous wave (CW) signals, the peak and the quasi-peak response are the same. The quasi-peak detector also responds to different amplitude signals in a linear fashion. High amplitude low repetition rate signals could produce the same output as low amplitude high repetition rate signal.

Quasi-peak detector readings will always be less than or equal to the peak detection. Because quasi-peak readings are much slower, (by 2 or 3 orders of magnitude compared with peak) it is very common to scan initially with the peak detection first, and then if this is marginal or fails, switch and run the quasi- peak measurement against the limits.