Page 107 - Concise Encyclopedia of Robotics

Electromechanical Transducer
much as 1000 Ah. Spacecraft cells are made in packages that can withstand
extraterrestrial temperatures and pressures.
NICAD batteries are available in packs of cells that can be plugged into
equipment to form part of the case for a device.An example is the battery
pack for a hand-held radio transceiver.
NICAD cells and batteries should never be left connected to a load after
the current drops to zero. This can cause the polarity of a cell, or of one
or more cells in a battery, to reverse. Once this happens, the cell or battery
will no longer be usable.When a NICAD nears full discharge, it should be
recharged as soon as possible.
Nickel–metal-hydride (NiMH) cells and batteries can directly replace
NICAD units in most applications.
See also POWER SUPPLY and SOLAR POWER.
ELECTROMAGNETIC SHIELDING
Electromagnetic shielding is a means of preventing computers and other
sensitive equipment from being affected by stray electromagnetic (EM)
fields. Computers also generate EM energy of their own, and this can
cause interference to other devices, especially radio receivers, unless
shielding is used.
The simplest way to provide EM shielding for a circuit is to surround
it with metal, usually copper or aluminum, and to connect this metal to
electrical ground. Because metals are good conductors, an EM field sets up
electric currents in them. These currents oppose the EM field, and if the
metal enclosure is grounded, the EM field is in effect shorted out. Inter-
connecting cables should also be shielded for optimum protection
against electromagnetic interference (EMI). This is done by surrounding
all the cable conductors with a copper braid. The braid is electrically
grounded through the connectors at the ends of the cable.
One of the biggest advantages of fiber-optic data transmission is the
fact that it does not need EM shielding. Fiber-optic systems are immune
to the EM fields produced by radio transmitters and alternating-current
(AC) utility wiring. Fiber-optic systems also work without generating
external EM fields, so they do not cause EMI to surrounding circuits
and devices.
ELECTROMECHANICAL TRANSDUCER
An electromechanical transducer is a device that converts electrical energy
into mechanical energy or vice versa. Electric motors and electric generators
are the most common examples. A motor works by means of magnetic
forces produced by electric currents; the generator produces electric cur-
rents as a result of the motion of an electric conductor in a magnetic field.

