Editing Secondary frequency standard (section)

{{short description|Standards in electronics and telecommunications}}

In [[telecommunications]], a '''secondary frequency standard''' is a [[frequency standard]] that does not have inherent [[accuracy]], and therefore must be calibrated against a [[primary standard|primary frequency standard]]. 

Secondary standards include [[crystal oscillator]]s and [[rubidium standard]]s. A crystal oscillator depends for its frequency on its physical dimensions, which vary with fabrication and environmental conditions. A [[rubidium standard]] is a secondary standard even though it uses atomic transitions, because it takes the form of a gas cell through which an optical [[signal]] is passed. The gas cell has inherent inaccuracies because of gas pressure variations, including those induced by temperature variations. There are also variations in the concentrations of the required buffer gases, which variations cause frequency deviations.