TRANSISTOR

A transistor is formed by sandwitching p-type semiconductor material in between two n-type semiconductor material or n-type semiconductor material in between two p-type semiconductor material. It is also known as Bipolar junction transistor as in this device conduction takes place by motion of both polarity particles ie electrons as well as holes.
Every transistor has three terminals:
1.EMITTER : This terminal supplies large number of majority carriers and is heavily doped. This terminal is always forward biased wrt base in order to supply high majority carriers.
2.BASE : The middle sections forms two pn junctionsbetween emitter and collector is called base.It is lightly doped.
3.COLLECTOR : This section collects major portion of majority carriers supplied by emitter. The collecor base junction is always reverse biased. It is moderately doped.

Linear Variable Differential Transformer

Linear Variable Differential Transformer is used as inductive transducer to convert linear motion into electrical signals. The transformer consist of primary and two secondary windings wound on a cylinderical former. The secondary windings have equal number of turns and placed on either side of primary winding. The primary winding is alternatively connected to alternating current source. A movable soft iron core is inside former and displacement is measured with the help of movement of core.The output voltage obtained is the differential voltage of two secondary windings.
USES:
1. LVDT is used in all applications which include displacement ranging from fraction of mm to few cm.
2. It is used to measure force , weight and pressure etc.
3. Pressure of liquid in tank.

TRANSDUCER

Transducer is a device which converts one form of energy into other. As in measurement system , measurand can be any physical quantity like displacement , stress , pressure etc but it is calculated in terms of electrical signals so that they can be processed, calibrated and recorded easily. So transducer is used to convert these physical signals into electrical signals.We can also say that transducer is a device which converts mechanical force into electrical signal.
Few Examples of Transducer:
1. Thermocouple which converts heat into electrical voltage.
2. Photoconductor which converts light intensity into change in resistance.
3. LVDT converts displacement into voltage change.
Classification of Transducers:
Passive Transducer: These devices derive power from auxiliary power source for transduction of signal.
Example POT
Active Transducer : These devices do not require any auxiliary power source for transduction of signal.
Examples thermocouple , tachogenerators, photovoltic cells.