Chapter 7

Transducers

7-1 Introduction Input Transducer

A device which converts a non-electrical signal into an electrical signal

A microphone converts a sound signal into an electrical signal.

Output Transducer A device which converts an electrical signal

into a non-electrical signal A speaker converts an electrical signal into a

sound signal.

7-2 Temperature

Thermistor a device constructed of a

metal-oxide or semiconductor material with a resistance that changes dramatically with temperature

Platinum Resistance Temperature Detector (PRTD) a resistor that has a resistance that increases linearly with temperature

Thermocouple Whenever a temperature gradient is established across a metal, a

potential develops. This is called the thermoelectric effect. A thermocouple uses the junction of two dissimilar metals to measure

temperature. See also Peltier Coolers.

7-3 Light IntensityPhotoresistor (a.k.a. photocell)

a device made of cadmium sulfide, a compound which exhibits a change in resistance when exposed to different intensities of light

Photovoltaic Cell (a.k.a. solar cell)a solid-state device composed of a p-

n junction that produces a voltage across its terminals when light shines on the device

Photodiodea device that is similar to a solar cell

except that it is manufactured to detect light, not to power devices

Phototransistor a two-terminal device which allows

current to flow proportionally to the intensity of light striking the surface of the unit

Photomultiplier (a.k.a. photometer) a device use to detect very low light

levels (e.g. astronomy) light strikes the cathode of this device

causing electrons to cascade through an array of anodes

7-5 Force Strain Gauge

a device whose change in resistance is related to changes in length

Piezoelectric Transducer a crystalline material that

generates a voltage when deformed

this device call also be deformed if a voltage is applied

7-6 PositionPotentiometer

the simplest form of a position transducer angular measurement is accomplished quite

simply

Variable Capacitor displacements may be measured capacitively

by attaching a plate to the object which is moving and another plate to a fixed point

7-9 Magnetic FieldHall Effect Probe

When a current-carrying conductor is placed in a magnetic field, charge is displaced from its path and collects on opposites sides of the conductor

7-10 Particle DetectorsGeiger-Muller Tube

a device used to detect ionizing radiationionizing radiation is very high energy

radiation associated with nuclear disintegrations

current "spikes" are counted

7-7 Sound

What do you need to make a speaker? Permanent Magnet Coil of Wire Flexible Cone on a Frame

Can speakers also be used as microphones?