scope:

The basic principle governing the physical measurement of time is demarcation of equal time intervals by observation of a repeating process such as oscillations of a quartz crystal or of the electromagnetic field that excites a transition in an atom (e.g., cesium). Such a repeating periodic process can be used as a frequency standard. Frequency standards include atomic frequency standards, laser and cavity resonators, and mechanical oscillators [including, e.g., quartz, dielectric resonator (DROs), cryogenic sapphire, microelectro-mechanical system (MEMS), and thin-film resonator (TFR) oscillators]. All types of frequency standards can be influenced by environmental sensitivities.

The following three different areas of concern exist for the environmental testing and specifications of frequency standards:

a) Fitness of a frequency standard for actual user needs in specific environments (tests attempt to mimic the anticipated environments)

b) Characterization of a frequency standard's environmental sensitivities (tests attempt to provide distinct sensitivity coefficients for variations in independent environmental parameters)

c) Reliability and survival (tests attempt to stress the unit by either going to extremes of operating ranges or by repeated application of stimuli, e.g., cycling)

This document puts emphasis on item b). It provides guidance and a conceptual framework rather than a prescription of procedures that must be followed. It emphasizes proper methodology and practice and cautions against pitfalls. In summary, this IEEE guide is not a specification document but a resource document for deriving specification statements.

This document often refers to the influence of random frequency fluctuations on the measurement and characterization of environmental sensitivities. Readers unfamiliar with frequency fluctuations, phase noise, and Allan deviations should refer to IEEE Std 1139.

Purpose

This document describes the nature of the environmental effects, as well as the test methods to evaluate, quantify, and report (i.e., in specifications) the sensitivity of a frequency standard's output frequency to environmental influences such as magnetic fields, atmospheric pressure, humidity, vibration, acceleration, temperature, ionizing radiation, and intermittent operation. Its primary purpose is to aid in defining specifications and to verify specified performance through measurement. In addition, this document will help to assure consistency and repeatability of environmental sensitivity measurements, as well as the use of consistent methods across the various segments of the time and frequency community.