ILX Lightwave LDT-5525 User Manual page 54

In the LDT-5525 Temperature Controller, the practical upper temperature limit is the temperature at which the
thermistor becomes insensitive to temperature changes. The lower end of the temperature range is limited by the
maximum input voltage of the LDT-5525 Temperature Controller. Thermistor resistance and voltage are related
through Ohms Law (V = I x R). The LDT-5525 Temperature Controller supplies current to the thermistor, either 10µA
or 100µA. As the thermistor resistance changes, a changing voltage signal is available to the thermistor inputs of the
LDT-5525. The LDT-5525's measurement system will over-range when the input voltage exceeds about 4.5 volts.
Figure B.1 graphically shows the lower temperature and upper voltage limits for a typical 10 K thermistor. (A 10 K
thermistor has a resistance of 10 kΩ at 25 °C). The practical temperature ranges for a typical 10 K thermistor with the
LDT-5525 are given in Table B.2, below. These temperature ranges may vary from thermistor to thermistor, even
though both thermistors are nominally 10 K. This is due to manufacturing tolerances in the thermistor, and is
compensated for by determining C1, and C2 (calibrating the thermistor). The practical temperature ranges for a 10 K
thermistor are also shown as solid bars at the bottom of Figure B.1.
10K Thermistor Practical Temperature Range
Sensing Current
10 µA
100 µA
Table B.2 10K Thermistor Temperature Ranges
B-2
Temperature Range
-30 to 30 °C
10 to 70 °C