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Analog: Accuracy is expensive, Resolution is cheap

One of the most common misconceptions we see is the belief that high resolution in an analog measurement is the same as high accuracy. That is simply not so. For example, you might buy a thermistor that is accurate to ±2°C and use it in a circuit that can resolve 0.1°C changes. The 0.1°C resolution does nothing to improve the accuracy, it simply allows you to detect small changes (which may be very useful indeed).
 
In digital systems resolution is usually measured in bits. 8 bits is 0.4% of full scale, 10 bits is 0.1%, 12 bits is 0.025%. You can buy an analog to digital converter chip with 12 bit resolution for a few dollars. A little more will buy you 18-bits (0.0004%). It's no big deal as such things go. But to achieve 18-bit accuracy you would have to talk to the good folks at the national standards laboratories and probably mortgage your house.
 
The corollary is that you need to be careful when specifying the analog accuracy you need in a system. Over-specify and you may at best waste money and at worst price your product out of the market. Perform a careful analysis of what you need to measure and the bad things that may happen if the measurement is not accurate enough. Then source a solution that will provide sufficient performance with a modest margin of safety. If it looks as though you need a very expensive analog solution, ask yourself if your should find a different way of getting the result you want.
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