Distinguish carefully between the following terms: i) relative error and dynamic range.

ii) nonlineariy and hysteresis. [30%]

(b) Measurement errors can be broadly classified as random, systematic and parasitic. What techniques can you use to reduce the effects of these types of errors on measurement results? [40%]

(c) Measurement errors can be treated as random variables and characterised by their moments. Briefly describe what ordinary moments and central moments are, and give one example for each type of moment.

Air gauging sensors are used for high precision dimensional measurement. (a) Explain with the aid of a sketch the principle of an air gauging sensor. [20%]

(b) Given the following relationship between the nozzle pressure (back pressure) P and the supply pressure Ps: where k = 16d 2 /d 2dn is the nozzle diameter and ds the orifice diameter. Sketch the functional relationship between P and Ps. [20%]

(c) Given the above nonlinear relationship, which region should you use for measurement and explain why.

[30%] (d) Briefly compare an air gauging sensor with an optical encoder.