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Greg: Whether we are talking about analyzers or any sort of digital communication, control and processing, a dead time is created for unmeasured disturbances from the time interval. The actual dead time to detecting and reacting to an upset depends upon the relative timing of the read (input), write (output) and the upset. If the output is done right after the input, the dead time varies from nearly zero to one time interval for an upset that arrives just before and after the input, respectively.
On average, we can say the upset arrives in the middle of the interval, so the average dead time is 1/2 the time interval. For unsynchronized digital devices, the worst-case dead time could be the summation of the time intervals. If the output is done at the end of the time interval, the dead time varies from one to two time intervals for an upset that arrives just before and after the input, respectively. This is the case for chromatographs and other analyzers where the sample is processed, and the analysis is ready at the end of the cycle time. Here the average is 1.5 times the time interval (cycle time).
Stan: In practice, the scan time of DCS inputs is set to reduce jitter and aliasing. But exception reporting and data compression can cause a distorted view of the data and can make any trend look flat, particularly large plot scales or short time frames.
This Month's Puzzler
What Time’s the Execution?
10. You have taken to using one-word sentences and one-syllable words like “yep.”
9. You think John Wayne was too verbose.
8. You feel life is just a series of subtitles.
7. Friends take to using sign language around you.
6. Strangers think you have laryngitis.
5. Your parents keep turning up their hearing aids.
4. You run off to become a “roadie” for the Blue Man Group.
3. Your favorite entertainment is watching mimes.
2. You let your slides do the talking.
1. You are mistaken for a statue.
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