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

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Stopwatch and Timer Calibrations is still small enough for the WWV tones to be used as a stopwatch calibration reference, because the uncertainty introduced by an operator starting and stopping the watch (human reaction time) is much larger, typically tens or even hundreds of milliseconds. In summary, as long as each link of the chain and its uncertainty are known, traceability to the SI can be established. Stopwatch and timer calibrations are among the least demanding of all time and frequency measurements. Relatively speaking, the instruments requiring calibration are low cost, and the acceptable measurement uncertainties can be quite large. Even so, for legal, technical, and practical reasons it is very important to establish traceability to the SI for these calibrations. If a valid traceability chain to the SI is established, it ensures that the working device was properly calibrated, and, if correctly used, will produce valid results. 8
Description of Timing Devices Section 2 Description of Timing Devices that Require Calibration This section describes the various types of stopwatches (Section 2.A. Stopwatches) and timers (Section 2.B. Timers) that are calibrated in the laboratory. These types of stopwatches and timers are often used as transfer standards to perform field calibrations of the commercial timing devices described in Section 2.C. 2.A. Stopwatches Stopwatches can be classified into two categories, Type I and Type II [5]. Type I stopwatches have a digital design employing quartz oscillators and electronic circuitry to measure time intervals (Figure 2). Type II stopwatches have an analog design and use mechanical mechanisms to measure time intervals (Figure 3). The key elements of Type I and Type II stopwatches are summarized in Table 3. Table 3 - Type I and Type II stopwatch characteristics. Description Operating principle Time base Case Crystal Minimum time interval Type I Stopwatch (digital) Time measured by division of time base oscillator Quartz oscillator Corrosion resistant metal Impact resistant plastic Protects display Allows for proper viewing May be tinted May employ magnification 48 hours without replacement of battery Type II Stopwatch (analog) Time measured by mechanical movement Mechanical mainspring Synchronous motor, electrically driven Protects dial/hands Allows for proper viewing Must be clear and untinted 3 hours without rewinding 9
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Other Topics Related to Measurement
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