Setting Dwell Time for Optimal EMI Scan Measurements on SSA5000A Spectrum Analyzer
In EMI Measurement mode, the dwell time for the quasi-peak detector is an important consideration. Depending on how you set it up, a shorter dwell time may be set when the detector is first changed. But the detector requires a longer dwell time.
Jim Wilson
Last Update setahun yang lalu
CISPR standards with a swept mode EMI measurement using a Quasi-Peak detector like SIGLENT analyzers typically specifies a dwell time of 1 second per frequency point.
The dwell time can be customized depending on the nature of the pulse events you want to capture in your QP measurements. The standard operating procedure is to do a full scan using the Peak detector and then use the meter function to verify the QP value at key points where the peak is high enough for further evaluation. This is done primarily because of the longer dwell times which means a full QP sweep is quite time consuming.
The meter is shown here on the right. When the sweep is complete it does live measurements using peak, QP, and AVG detectors at a given frequency. This is a great tool for debugging and monitoring the difference between Peak detector levels and QP levels. When using in Scan, Search, and Measure mode these measurements are done on each signal identified in the list at the bottom of the image.
The digital QP detector matches the CISPR standard for rise time and decay time. Typically, for conducted measurements from 150 kHz to 30 MHz this specifies 1 ms rise, 160 ms decay time, and a RBW setting of 9 kHz. For most radiated emissions from 30-1000 MHz, the typical values are 1 ms rise, 550 ms decay, and 120 kHz RBW.
Dwell time should be set to at least as long as the rise plus decay time in order to get valid results. Using the full 1 second time will most closely match lab measurements.
This is how to change the Dwell time:
Change dwell time to 160 ms, 1 second, or longer.
The number of sweep points is typically set by dividing the span by the resolution bandwidth so that no frequency is missed.
Using the correct settings for EMI measurements makes it possible to get the correct results faster and make changes when needed.
Make sure to carefully set the dwell time which does not automatically reset to CISPR default values when you switch the detector.