Negative temperature coefficient Temperature coefficient

most ceramics exhibit negative temperature dependence of resistance behaviour. effect governed arrhenius equation on wide range of temperatures:

r
=
a
⋅

e


b
t





{\displaystyle r=a\cdot e^{\frac {b}{t}}}

where r resistance, , b constants, , t absolute temperature (k). constant b related energies required form , move charge carriers responsible electrical conduction – hence, value of b increases, material becomes insulating. practical , commercial ntc resistors aim combine modest resistance value of b provides sensitivity temperature. such importance of b constant value, possible characterize ntc thermistors using b parameter equation:

r
=

r

∞



e


b
t



=

r

0



e

−


b

t

0







e


b
t





{\displaystyle r=r^{\infty }e^{\frac {b}{t}}=r_{0}e^{-{\frac {b}{t_{0}}}}e^{\frac {b}{t}}}

where




r

0




{\displaystyle r_{0}}

resistance @ temperature




t

0




{\displaystyle t_{0}}

. therefore, many materials produce acceptable values of




r

0




{\displaystyle r_{0}}

include materials have been alloyed or possess variable negative temperature coefficient (ntc), occurs when physical property (such thermal conductivity or electrical resistivity) of material lowers increasing temperature, typically in defined temperature range. materials, electrical resistivity decrease increasing temperature.

materials negative temperature coefficient have been used in floor heating since 1971. negative temperature coefficient avoids excessive local heating beneath carpets, bean bag chairs, mattresses, etc., can damage wooden floors, , may infrequently cause fires.