Information Technology Reference

In-Depth Information

2.2

Sensor Characteristics

In this chapter we introduce some of the important characters of sensors. Under-

standing of these is important when choosing the right sensors for your application.

2.2.1

Transfer Function

Transfer function is a mathematical representation of the relation between the input

and output of a system. In terms of sensors it represents the relationship between

the physical signal on the input, and the electrical output signal.

2.2.2

Hysteresis

A sensor should be capable of following changes in the input parameter, regardless

of what direction the parameter changes in (whether there is an increase or a

decrease in value). Some sensors do not return the same value for both directions

of change. Hysteresis is the measure of this property.

2.2.3

Linearity

Linearity of a sensor shows how much the measured curve deviates from the ideal

transfer function. There are several ways to interpret and represent linearity, the

most commonly used being:

End point linearity

•

•

Best-fit straight line (BFSL)

•

Least squares BFSL linearity

On the Input against Output graph a straight line is drawn from the zero point to the

full-scale output point. The point on the actual measured curve that deviates most

from this line is used to define the linearity of the sensor. This is usually quoted as

a percentage of the full-scale output of the sensor.

2.2.3.1

Best-Fit Straight Line (BFSL)

BFSL linearity is a measure of the most accurate overall results that can be obtained

for a given sensor. Instead of using a line that connects the full-scale point to the

end point, a different line is chosen so that the maximal deviation of the actual

measured curve is minimal. Note that this is simply a means of interpretation of the

results and relies entirely on the system, including the measuring equipment, being

set up to take advantage of this technique.

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