Sensor - The Electronic Nose Artificial Olfaction Technology - page 53

Table 2.9 Displacement sensor comparison by detection method

Type Eddy current Optical Ultrasonic

wave

Laser focus Contact

Detectable object Metal Most

objects

Most
objects

Most
objects

Solids

Detecting distance Short Normal Long Short Short

Accuracy High High Low High High

Response speed Fast Fast Slow Normal Slow

Environmental
resistance

Highly
durable

Normal Normal Normal Highly

durable

Detecting point Normal Small Large Small Small

Units In the region of 0.00001 in. or 0.001 lm minimum

Fig. 2.13 LVDT and its characteristics

coil. In operation, the LVDT's primary winding is energized by alternating current
of appropriate amplitude and frequency, known as the primary excitation.

Figure 2.13 shows the basic principle of LVDT and its characteristic.
The LVDT's electrical output signal is the differential AC voltage between the
two secondary windings, which varies with the axial position of the core within the
LVDT coil. Usually this AC output voltage is converted by suitable electronic
circuitry to high level DC voltage or current that is more convenient to use.