Page 69 - Instrumentation Reference Book 3E
P. 69
54 Measurement of length
Optical i l l l l lgauge I EM radiation travel-time for long distance
diffraction
k-q ElectromaGtic distance measurement *I---
RADIATION Ultrasonic transit-time
Sensor needed to measure whole length f
Input movement of
plate being monitored
'r Ends fixed to subiect
\ Optical probe
L-----I \ - (bl
Length change 10 be measured
by rhon-range Sensor Figure 3.3 Examples of contacting and non-contacting
length measurements. (a) Contacting, using variable
Figure 3.2 Absolute (a) and relative (b) length^ resistance (b) Non-contacting, using an optical probe.
measurement situations.
detect the small differences that occur (see Figure It is often possible to measure a large length by
3.2(b)). Absolute whole length measurement, adding together successive intervals, for example by
Figure 3.2(a), requires a sensor of longer range. using a single ruler to span a length greater than
