R&S®Power Viewer Plus Software Manual - Rohde & Schwarz

R&S Power Viewer PlusPower Sensor Technologiesusing the sensor's internal trigger feature. Decreasing the sensor'sbandwidth decreases the noise floor and, therefore, also decreases thelower trigger-level limit.5 Uncertainty CalculationThis chapter briefly explains how to calculate the measurementuncertainty based on the figures provided in the sensor's specifications.The data sheet lists the absolute uncertainty for power measurementsin dB depending on the power level and frequency. Other contributors,such as zero offset or noise, are provided in watts and can beconverted into dB using the following equation.e=10dB⋅log P P PThis equation uses P as the power level of interest and ΔP as therelative error. The result is the error e in dB.Uncertainties are statistical measures, and they must be added bysumming up the squared uncertainties and then calculating the squareroot:U =U 1 2 U 2 2 U 3 2 This equation can be used for uncertainties in logarithmic scale (dB) orin percent (%).Uncertainties are commonly provided in dB, but the following equationpermits conversion into percent:U %=100%⋅10U dB10 dB −1To gain a simple approximation, the following formula can be used:U %≈10⋅ln 10⋅U dB=23⋅U dBManual 16