General bases of work of measuring sensors of temperature - semiconductor thermo-resistors
Physical bases of work of thermo-resistor are described. Semiconductor thermo-resistor, methods of calibrating.
A thermo-resistor is name a device, consisting of explorer electric resistance of which depends on a temperature and which electric conclusions are connected to. A wideuse is found by semiconductor thermo-resistors. In this case as an explorer of electric current a semiconductor serves as tape on an insulating base or in by volume execution. Mostly apply such semiconductors: Ge, GaAs, Si. General sizes of thermo-resistors can be less than 1 mm^3, electric resistance from a few Ohm to 100 kÎhm, currents of feed, as a rule, 10 - 100mkÀ, sensitiveness from 5 %/Ê in area of room temperature to 100 %/Ê in area of cryogenics temperatures, an inertance can arrive at a few ten of milliseconds.
Semiconductor thermo-resistors sensors are widely used for measuring and control of temperature in a wide range, but, as a rule, not higher 200 °Ñ, because at a high temperature self-admittance and temperature dependence of resistance comes falls sharply, becomes not monotonous, not stable. In the wide range of temperatures dependence of resistance of semiconductor on the temperature of R(T) difficult character has and depends on the type of alloying admixture and alloying level. It is therefore impossible to express dependence of R(T) a simple formula which would allow to execute calibrating with high exactness. As a rule, all interval of temperature is broken up on separate areas on which dependence of R(T) is described by the interpolation formula.
The methods of calibrating can be considered on a next example. In area of room temperature dependence of R(T) for semiconductor thermo-resistors it is possible to express:
R=Ro * e ^ B/T ( 1 )
For calibrating of thermo-resistor (receipts of tables of dependence of electric resistance from a temperature) will transform a formula (1) :
lnR = lnRo + B ( 2 )
The got expression (2) is equalization of line in co-ordinates 1/T and LnR.
LnRî is a size of logarithm of resistance when Ò aspires to endlessness . Coefficient In equal to the tangent of angle of a slope of line to the axis 1/Ò. If at two fixed temperatures of Ò1 and Ò2 to measure resistances of thermo-resistor of R1 and R2 accordingly, then it is possible to build dependence of LnR(1/T) on two points:
Using a formula (2) and got chart it is possible to find for any value R from an interval from R1 to R2 corresponding to him value of temperature (to make calibration charts).
For the exact measuring of temperature calibrating of thermo-resistor is conducted in the specialized laboratories with the use of corresponding approximating formulas for the necessary range of temperatures, computer treatment of these and other. In the wide range of temperatures temperature dependence of resistance of semiconductor thermo-resistor has difficult enough character.