Stopwatch and Timer Calibrations - National Institute of Standards ...

More documents

Recommendations

Info

Stopwatch and Timer Calibrations Its stability as estimated with ADEV was near 7 × 10 -8 after one week, or about seven times better than its accuracy. Because of their slow aging rate, stopwatches tend to produce very repeatable results over long periods of time. When compared to the requirements for stopwatch calibrations discussed in Section 3, the small changes in frequency due to aging are usually insignificant. This makes it possible for a laboratory to allow long intervals (perhaps exceeding one year) between calibrations. 9.C. Factors That Can Affect Stopwatch Performance Many factors can cause a quartz crystal oscillator to change frequency. Some of these are shown in Figure 23. Sharp temperature changes, vibration, and shock are some of the more common phenomena that can affect the time base on a dayto-day basis. Also, if power is removed from an oscillator and later restored, there can be a shift in the frequency. This is true of quartz crystal stopwatches when the battery is changed. This frequency change is usually small when compared to the stopwatch’s time base specifications, usually less than 10 to 20 parts in 10 6 (~10 to 20 ms/day) and usually short-term, with the time base returning to its original frequency after a period ranging from a few hours to a few days. 62 Figure 23. Factors that can change the quartz time base frequency.
Other Topics Related to Measurement Uncertainty Temperature is perhaps the most important factor that affects quartz crystal time base performance. The quartz crystals used in wrist watch time bases are cut in such a way as to make them most stable near body temperature. The time base acts as a thermally stable oscillator while it is on a person’s wrist. Stopwatches, on the other hand, use quartz crystals that have been cut to be stable at or near room temperature. If they are used in very hot or very cold environments, the time base can vary by over 20 parts in 10 6 . Figure 24 shows the accuracy of a typical stopwatch over a temperature range of 0° C to 50° C (32° F to 122° F). As can be seen for the figure, the flat portion of the performance curve is near room temperature (23° C or 73° F), and drops off as the temperature increases or decreases. Figure 24. Stopwatch accuracy versus temperature. 63
Page 1:
NIST Recommended Practice Guide Sto
Page 4 and 5:
Certain equipment, instruments or m
Page 7:
Acknowledgements ACKNOWLEDGEMENTS
Page 10 and 11:
Stopwatch and Timer Calibrations Se
Page 12 and 13:
Stopwatch and Timer Calibrations Li
Page 15 and 16:
Section 1 Introduction to Stopwatch
Page 17 and 18:
Introduction s or 42.13 s, but tha
Page 19 and 20:
Introduction basic principles that
Page 21 and 22:
Introduction and their traceabilit
Page 23 and 24:
Description of Timing Devices Sect
Page 25 and 26: Description of Timing Devices Figu
Page 27 and 28: Description of Timing Devices Figu
Page 29: Description of Timing Devices One
Page 32 and 33: Stopwatch and Timer Calibrations
Page 34 and 35: Stopwatch and Timer Calibrations a
Page 36 and 37: Stopwatch and Timer Calibrations 3.
Page 38 and 39: Stopwatch and Timer Calibrations 3.
Page 41 and 42: The Direct Comparison Method Secti
Page 43 and 44: The Direct Comparison Method Pleas
Page 45 and 46: The Direct Comparison Method uncer
Page 47 and 48: The Direct Comparison Method the u
Page 49 and 50: The Direct Comparison Method path,
Page 51 and 52: The Direct Comparison Method When
Page 53: The Direct Comparison Method Table
Page 56 and 57: Stopwatch and Timer Calibrations To
Page 58 and 59: Stopwatch and Timer Calibrations Fi
Page 60 and 61: Stopwatch and Timer Calibrations di
Page 65 and 66: The Time Base Method Section 7 The
Page 67 and 68: The Time Base Method effectively t
Page 69 and 70: The Time Base Method 7.B.2. Using
Page 71 and 72: Required Uncertainty Section 8 How
Page 73 and 74: Other Topics Related to Measurement
Page 75: Other Topics Related to Measurement
Page 82: Stopwatch and Timer Calibrations [1
show all

Stopwatch and Timer Calibrations - National Institute of Standards ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?