The three R’s of analog position sensor-based mechanical measurements: Page 3 of 5

July 12, 2019 //By Edward Herceg
position sensor
Those of us old enough to remember the “good old days” recall that grade school focused on learning the 3 R’s: reading, ‘riting, and ‘rithametic.

Like repeatability, resolution is often specified as a percentage of Full Scale/Full Span Output (FSO) but may also be specified in absolute terms like fractions of the units of the actual sensor measurement, or, in digitally-augmented measurements, in bits, which is just a fractional measure expressed in powers of 2, as found in computers. Thus 10-bit resolution is 1 part in 1024 (210), 12-bit is 1 part in 4096 (212), etc.

Response denotes a sensor-based measuring system's performance under dynamic input conditions, that is, when the system's mechanical input is changing rapidly. It is particularly important to recognize that response is a measuring system parameter, not merely a sensor parameter or specification.

In practice, there are several ways to characterize response, typically based on whether the system is a first order or second order system. Traditional analog systems have used Bode plots to show frequency response and phase lag for repetitive inputs. For step function response, three times the system time constant is a typical measure of dynamic performance. In digital sampling systems, the update rate for a specified number of bits is one of the preferred measures of response. Regardless of the choice of how to specify response, the ultimate purpose is to understand how well the measuring system can respond to a changing input before the system's output becomes inaccurate, unusable, or unstable.

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