Sensor Notes
What is sensor linearity? Non-linearity plotted to output Lin. Error (%)
BSFL 0.15
10.00
0.1
8.00
0.05
6.00
0
4.00
-0.05
2.00
-0.1
0.00
-0.15
Voltage
12.00
Non-Linearity % FSO
Voltage (VDC)
0
2.0
0
1.8
0
1.6
0
1.4
0
1.2
0
1.0
0
0.8
0
0.6
0
0.4
0
0.0
Displacement
Most analog output sensors have general specifications such as linearity (or non-linearity), repeatability, and resolution, as well as environmental specifications such as operating temperature or shock and vibration, and dynamic specifications like response or bandwidth. All of these specifications represent limits of error or sources of uncertainty related to the sensor’s output compared to its input. Many of these terms are fairly easy to understand by their wording alone, but linearity error or nonlinearity is not in that category. Linearity, or more correctly, non-linearity, is a measure of the maximum deviation of the output of any sensor om a specified straight line applied to the plot of the data points of the sensor’s analog output versus the input parameter being sensed (which is called the measurand) under constant environmental conditions. The more linear the sensor’s output, the easier it is to calibrate and to minimize uncertainty in its
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output scaling. However, understanding a sensor’s non-linearity specification requires understanding the nature of the reference straight line. There are several possible reference straight lines that could be used to express a sensor’s linearity error. The optimum choice based on statistics would be a “best fit line.” But just what is the criterion for best fit? Both experience and statistics favor a line calculated by the method of least squares, where the sum of the squares of the deviations om the desired line is mathematically DESIGN WORLD
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