Inductance Transducer Type

Passive Transducers is require external power
- Magnetic circuit transducer
operation = self inductance or mutual inductance of ac-excited coil is
varied by change in the magnetic circuit
- Reluctance pickup
operation = reluctance of the magnetic circuit is varied by change the
position of the iron core of a coil
- Differential Transformer
operation = the differnential voltage of two secondary winding of a
transformer is varied by positioning the magnetic core through an
external applied force
- Eddy current gage
operation = Inductance of a coil is varied by the proximity of an eddy
current plate
- Magnetostriction gage
operation = Magnetic properties are varied by pressure and stress

Capacitance Transducer Type

Passive Transducers is require external power
- variable capacitance pressure gage
operation = distance between two parallel plates is varies by an external
applied force
- capacitor microphone
operation = sound pressure varies the capacitance between a fix plate and
a movable diaphragm
- dielectric gage
operation = variation in capacitance by changes in the dielectric

Transducer Type

Passive Transducers is require external power,producing a variation in
Some electrical parameter which can be measured as a voltage or
current variation.

Resistance Transducer Type
- potentionmetric
operation = position of slider by external force varies the resistance in a
potentiometer or bridge circuit
- resistance strain gage
operation = resistance of a wire or semiconductor is change by compression
due to external appile stress
- pirani gage
operation = resistance of a heating element is varied by convection colling of
gas
- thermometer
operation = resistance of pure metal wire with a large positive temperature
coefficient of resistance varies with temperature.
- thermistor
operation = resistance of certain metal oxides with negative temperature
coefficient of resistance varies with temperature.
- hygrometer
operation = resistance of a conductive strip change with moisture content
- photoconductive cell
operation = resistance of the cell as a circuit element varies with incident

Constant current source circuit

We can use a voltage reference turn into a Constant current source
circuit and use pnp-transistors for current-boosting

By op amp action ,the voltage across R is away Vref , give
Ie = Vref / R

Ie = Ib + Ic = (Ic/B) + Ic

Ic = [B/(B+1)] *Ie

Io = Ic = [B/(B+1)] * Vref / R about Vref / R
VL = Io*RL
Where maximum voltage of Vl(max) <>

We can adjust output current by adjust current setting resistance R