Page 68 - Handbook of Biomechatronics

Sensors and Transducers 63

Fig. 1 Dartboard example. (A) shows lows accuracy, high precision. (B) shows high accu-
racy, low precision. (C) shows high accuracy and high precision.

Accuracy and precision are often explained using a dartboard (Fig. 1).
A low accuracy, high precision thrower will have tight spread, but not
around the bullseye. A high accuracy, low precision thrower will have a
wide spread, but the spread will be centered around the bullseye. A high
accuracy, high precision thrower will have a tight spread around the
bullseye.
Resolution refers to how small the sensor can measure (Bolton, 2003a).
A ruler with gradations every inch has low resolution compared to the one
with gradations every 1/16 of an inch. Range refers to the useful spectrum of
measurement of the sensor (Bolton, 2003a). A yard stick has a range of 3ft.
Hysteresis is a characteristic most often observed in electrically powered
sensors and is the separation of the signal when testing the full range of the
sensor (Bolton, 2003a). The path of the sensor is different going from the top
of the range to the bottom than starting at the bottom and going to the top.
Fig. 2 illustrates the hysteresis of an electrically powered sensor.
This chapter is separated into four sections: passive sensors, standard sen-
sor elements, common sensors, and biological sensors. In the passive sensors

Fig. 2 Example of hysteresis of a sensor. As the sensor progresses from point A to
point B, the sensor tracks a different path than when going from point B to point A.