Evening star., 1924-06-09
Various Types Of Resistance Elements

One of the most commonly used
elements in both> electrical and radio
circuits is the element of resistance
to adjust the~eurrent characteristics
of a circuit.
Resistance come in various forms
and sizes, each especially adapted to
the work which it is called upon to
perform. Regardless of the type of
resistance material used, rheostatS
arc classified into two general classes,
namely, fixed and variable. Fixed re-
sistance, are those which have a def
ute resistance value that cannot be
varied, while variable resistances, as
resistance value can be adjusted over
= range usually varying from close
to zero to the greatest or maximum
resistance of the element.
Variable resistances are further
classified as continuously variable re-
siStance, in which the resistance can
be varied minutely from the minimum
to the maximum value, and step-by-
step variable resistance in which the
resistance is varied in small or large
steps depending on the construction
or the resistance unit.
Fixed resistances are usually termed
''resistors." while variable reSistances
are called 'rheostats."
There are various materials which
can be used as resistance elements,
each type having its own peculiar ad-
vantages and disadvantages. The ma
terial most commonly used is resist
ance wire. This wire IS especially
made for this purpose and is used
because of its high resistance
to the passage of electrical cur
rent. German silver or nickel silver,
is suitable for resistance elements
where a very high resistance is not
required. Its resistance varies from
125 to about fifty times that of cop
per, depending on it's composition.
Various Metals Used.
Various other materials, such as
compositions Of copper, manganese
and nickel, copper and nickel. nickel
and steel and nickel and chromium.
are used for resistance elements.
Compositions Of nickel and chromium
have resistance Of over one hundred
times that of copper.
Carbon in one form or another is
also used to a consid erable extent as
a resistance element.
Another form of resistance material
which is not commonly looked upon
as such is the liquid resistance ele-
ments. Water and many other liquids
have the property of onering resist
ance to the passage of an electrical
current, and this property is taken
advantage of in constructing some
forms of resistors and rheoSta.ts.
Ordinary water solutions of copper
sulphate, sulphuric acid, sodium sui
pilates, potassium hydroxide and
other such solutions are often used
as the resistance elements of liquid
rheostats and resistors.
Rexistances Classified.
Resistances are further classified
as inductive or noninductive, de-
pending on whether or not inductive
quency current is passed through the
resistance element Ordinarily when
a resistance is used in a. direct cur
rent circuit the inductive effects are
neglible and can be disregarded ed.
When, however, resistances are used
tance of the rheostat must be consid-
cred in the design or in the effects
which it is likely to have on the
operations OF the circuit.
The ordinary type of rheostat or
resistor, consisting of coil of wire,
is Of the inductive type. non
inductive wire-wound resistance can
be obtain ed by doubling up the wire
so that the beginning and end of the
wire are at one end with the middle
point of the wire at the other end
and then winding the double wire
into a coil
Carbon element rheostats and re-
and resistors are of the purely nom
inductive type and therefore espe-
cially adaptable for use in hight fire.
quency circuits.