Page 114 - Electromechanical Devices and Components Illustrated Sourcebook

76 Electromechanical Devices & Components Illustrated Sourcebook

resistors. Figure 4-120 shows a high-current rheostat. The coil
form is in the shape of a horseshoe with a wiper mounted on
an axle that allows it to be adjusted to any position on the coil.
Schematic Symbol Normal rheostat configuration calls for the wiper to be elec-
trically connected to one of the coil terminals. In this manner
Pivot
the unit acts as a simple variable resistor.
Potentiometers are variable resistors that are generally
used for more sensitive applications. Just about any electronic
Resistive Coil control knob that you might encounter is connected to a
Coil Form potentiometer. Much like standard resistors, potentiometers
are generally available with carbon or wire wound elements.
Copper Strips
Figure 4-121 shows a typical carbon film potentiometer and
Figure 4-122 shows a wire wound unit.
Terminals

Base
Wiper
Handle
Figure 4-117 Bench Built, Variable, Wire Wound Resister
Schematic Symbol

Wiper

Nichrome
Coil
Base
Schematic Symbol
Ceramic Plate
Coil Form
Center Tap
Terminal Axle
Exposed Coil

Ceramic Coating Terminals
Mounts
Figure 4-118 Center-Tap Resistor
Jumper
Figure 4-120 Rheostat

Schematic Symbol
Schematic Symbol

Plastic Case
Substrate
Wiper
Shaft Carbon Element

Solder
Adjustment
Screw Terminal

Terminals
Figure 4-119 Ten Turn PC Board Mount Wire Wound
Potentiometer Figure 4-121 Carbon Film Potentiometer