New statistic addresses long-term stability. (General Developments).The measurement of the long-term stability The long-term stability of an oscillator, the degree of uniformity of frequency over time, when the frequency is measured under identical environmental conditions, such as supply voltage, load, and temperature. of clocks and oscillators has been a long-standing problem for science and industry. The Allan deviation DEVIATION, insurance, contracts. A voluntary departure, without necessity, or any reasonable cause, from the regular and usual course of the voyage insured. 2. and another statistic statistic, n a value or number that describes a series of quantitative observations or measures; a value calculated from a sample. statistic a numerical value calculated from a number of observations in order to summarize them. called total deviation both require data runs twice as long as the desired averaging time interval. Thus, determining the stability at one month requires a two-month-long data run. Recently, NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. developed a new statistic that yields a measure of stability at the end-point of the data series. Moreover, the statistic retains all of the desirable features of the Allan deviation. The effect of this advance is to cut required measurement times in half, effectively cutting the cost of acquiring the most expensive data point in half. The total deviation has long been used by manufacturers and analysts in place of the Allan deviation, where calculations of frequency stability at long-term time intervals are needed. This statistic, developed earlier, yielded a better confidence interval confidence interval, n a statistical device used to determine the range within which an acceptable datum would fall. Confidence intervals are usually expressed in percentages, typically 95% or 99%. , but still suffered from the need for long data runs. Using the total deviation as a starting point Noun 1. starting point - earliest limiting point terminus a quo commencement, get-go, offset, outset, showtime, starting time, beginning, start, kickoff, first - the time at which something is supposed to begin; "they got an early start"; "she knew from the , we found that a more complex combination of frequency sums and differences could yield an Allan-like statistic clear out to the interval of the data run itself. As a test, the statistic has been used over the past two years for measuring the performance of the NIST time scale and the primary cesium-fountain frequency standard, NIST-FI. The results, which have clearly demonstrated the efficiency of the statistic, have served to reduce the time required for evaluating the accuracy of NIST-FI and to improve the performance of the time scale. CONTACT: David A. Howe, (303) 497-3277; d.howe@boulder.nist.gov. |
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