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THERMORESISTANCES
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The measurement of temperature by thermoresistance, is based on the property that metals have to vary their ohmnic resistance with temperature. These change is more accentuated deppending on the metal used.

The change of relative resistance with temperature is known as temperature coefficient.

Amongst metallic conductors, pure metals present a greater change in resistance, that is, they have a higher temperature coefficient.

Despite to select a metal for a thermoresistace, it's not enough to base the selection on its temperature coefficient, there are other factors that have the same importance as its repeatability of electrical constants and its stability.

Metals used in industrial applications are mainly two:

Níckel

MEASUREMENT RANGE -60.....a.....180ºc

Platinum

MEASUREMENT RANGE –220...a...630ºc

 


Construction:

In general we use nickel or platinum probes with pyrex crystal or ceramic isilation placed in a stainless steel tube filled with magnesium oxide.

The prolongation between the sensor and the connection terminal can be made with copper or silver threads, all them under ceramic beads.

other current models consist in the use of conductors embedded and isolated with magnesium oxide, with metallic continuous sleeve.

 

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