Lightwave Communications LDT-5525 manual 1/T = A + B * ln R Equation

C H A P T E R A

For the LDT-5525, the Steinhart Hart equation has been simplified to a first order polynomial:

1/T = A' + B' * ln R Equation 2

This equation is easier to solve and provides adequate results. Table A.1 also shows that the use of Equation 2 introduces temperature errors of less than 0.3oC over the range -20oC to 50oC, with accuracies of up to 0.06oC over smaller temperature ranges near room temperature2.

1 Resistance of a 10 kW, Dale 1T1002-5 thermistor
2 Constants A' = 0.99 * 10-3, B' = 2.57 * 10-4(C1 = 0.99, C2 = 2.57).
			THERMISTOR R/T CURVES
		FOR VARYING ROOM TEMP. RESISTANCES
50.00
40.00
30.00
k Ω
20.00
	1 k	2.5 k 5 k		10 k	25 k 50 k		100 k
10.00
0.00	-40						80				160
-60		-20	0	20	40	60		100	120	140
			TEMPERATURE (DEGREES C)
Figure A.1 Thermistor Resistance vs. Temperature

Once the constants A' and B' are determined, the LDT 5525 Temperature

Controller is programmed with the following values of C1, and C2:

C1 = A' * 10+3

C2 = B' * 10+4

28 LDT-5525