30 Keysight 81618A/9A and Keysight 81620B/3B/4B/6B/8B Optical Heads User’s Guide3 SpecificationsDefinition of TermsThis section defines terms that are used both in this chapter andPerformance Tests on page 41.Generally, all specifications apply for the given environmental conditionsand after warm-up time.Measurement principles are indicated. Alternative measurement principlesof equal value are also acceptable.Averaging TimeTime defining the period during which the power meter takes readings foraveraging. At the end of the averaging time the average of the readings isavailable (display- or memory-update). Symbol T avg.LinearitySpecifies the relative diff erence between the displa yed power ratio, Dx/D0,and the actual (true) power ratio Px/P0 caused by changing the displayedpower level from the reference level, D0, to an arbitrary di splayed level, Dx.Excluding noise and offset. Powers expressed in Watts.if expressed in %if expressed in dBConditions: reference level 10 μW. Power range and range setting asspecified.Note 1: Ideally Linearity is 0%, or 0 dB respectively.Linearity D x D0⁄P x P0⁄----------------- 1– X 100( )=Linearity dB 10 D x D0⁄P x P0⁄----------------- log=
