Stopwatch and Timer Calibrations - National Institute of Standards ...
Stopwatch and Timer Calibrations - National Institute of Standards ...
Stopwatch and Timer Calibrations - National Institute of Standards ...
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Other Topics Related to Measurement Uncertainty <br />
Temperature is perhaps the most important factor that affects quartz crystal time<br />
base performance. The quartz crystals used in wrist watch time bases are cut in<br />
such a way as to make them most stable near body temperature. The time base<br />
acts as a thermally stable oscillator while it is on a person’s wrist. <strong>Stopwatch</strong>es,<br />
on the other h<strong>and</strong>, use quartz crystals that have been cut to be stable at or near<br />
room temperature. If they are used in very hot or very cold environments, the<br />
time base can vary by over 20 parts in 10 6 . Figure 24 shows the accuracy <strong>of</strong> a<br />
typical stopwatch over a temperature range <strong>of</strong> 0° C to 50° C (32° F to 122° F).<br />
As can be seen for the figure, the flat portion <strong>of</strong> the performance curve is near<br />
room temperature (23° C or 73° F), <strong>and</strong> drops <strong>of</strong>f as the temperature increases<br />
or decreases.<br />
Figure 24. <strong>Stopwatch</strong> accuracy versus temperature.<br />
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