User's Manual

28 LDT-5525
CHAPTER 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 0.3
o
C
over the range -20
o
C to 50
o
C, with accuracies of up to 0.06
o
C over smaller
temperature ranges near room temperature
2
.
1 Resistance of a 10 k
W
, Dale 1T1002-5 thermistor
2 Constants A' = 0.99 * 10
-3
, B' = 2.57 * 10
-4
(C1 = 0.99, C2 = 2.57).
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
-60
-40
-20
0
20
40
60
80
100 120
140
160
50.00
40.00
30.00
20.00
10.00
0.00
kΩ
THERMISTOR R/T CURVES
FOR VARYING ROOM TEMP. RESISTANCES
TEMPERATURE (DEGREES C)
1 k
2.5 k 5 k
10 k
25 k
50 k
100 k