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Author Topic: Measurement errors.  (Read 29513 times)
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« Reply #15 on: February 09, 2011, 02:57:03 PM »


Just to be pedantic: sensitivity is the change of the reading of your measurement tool with respect to any change in the signal you monitor. Say you want to measure a voltage, and have a pointer on a scale, and the pointer moves over a 90 degrees angle. Let's say the maximum reading from the voltmeter is 10V, then the sensitivity of the voltmeter is 10V per 90, or 9/V.

This has little to do with the lower limit of detection (LLOD). At this limit, the noise of the measurement tool (chain) becomes so large, that you cannot distinguish one value from the same value plus or minus the measurement error. In the case of the voltmeter, the smallest voltage you could measure is not limited by the sensitivity (alone), but by the noise in your measurement tool chain: say your pointer vibrates a little, then when you approach the zero reading, eventually the pointer will go into or even across the zero. At that point you cannot distinguish your reading from zero any longer: you have reached the LLOD.
The LLOD is a function of both, the sensitivity and the precision of the measurement tool chain.


« Last Edit: February 09, 2011, 02:59:54 PM by KLD » Logged
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« Reply #16 on: February 10, 2011, 10:16:53 PM »

Thanks for all useful and informed comments/corrections. If anyone else feels inclined to add relevant comments, please feel free - hopefully this thread will prove useful (without being too boring!) for anyone thinking of setting up a scientific experiment or comparison, and not wanting to make fundamental mistakes.
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