Application — Thermistors NTC thermistors decrease resistance with an increase in temperature and are the most common type of thermistor used in applications. PTC thermistors increase resistance with an increase in temperature. Thermistors come in a variety of resistance values. Resistance is typically specified at a room temperature of 25°C (77° F) to make it easier to test the resistance of a thermistor using a DMM before it is placed into a heated/cooled application. Although thermistors are available in numerous resistance ranges, standard NTC thermistors rated at 25° C (77° F) include the following resistance values: 2 kΩ, 3 kΩ, 5 kΩ, 10 kΩ, 30 kΩ, 50 kΩ, and 1 MW Changes in thermistor resistance are not linear with temperature changes. Manufacturers provide a chart showing the specific resistance at each temperature above and below the thermistor’s rating (typically 25° C). Photoconductive cells are used in many applications in which it is important to know whether light is present. Such applications include headlights that automatically turn on, automatic glare reduction on rear view mirrors, and security lighting.
TEMPERATURE vs. RESISTANCE—2000 Ω NTC THERMISTOR Temperature °F –40.00 –22.00 –4.00 14.00 32.00 41.00 59.00 77.00 95.00 113.00 131.00 149.00 167.00 185.00 203.00 212.00
°C –40.00 –30.00 –20.00 –10.00 0.00 5.00 15.00 25.00 35.00 45.00 55.00 65.00 75.00 85.00 95.00 100.00
Resistance Nominal Ohm 67,021 35,305 19,338 11,058 6,530 5,079 3,143 2,000 1,306 873 597 416 296 214 157 136
Minimum Ohm
Maximum Ohm
Resistance Tolerance +/– %
64,412 34,230 18,944 10,880 6,464 5,029 3,114 1,983 1,295 867 593 414 293 211 154 133
69,747 36,418 19,843 11,240 6,597 5,130 3,172 2,018 1,317 880 601 419 299 218 161 139
4.07 3.15 2.35 1.65 1.03 1.00 0.94 0.88 0.83 0.79 0.74 0.70 1.00 1.59 2.12 2.37
Resistance
Temperature Tolerance +/– °C 0.60 0.50 0.40 0.30 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.30 0.50 0.70 0.80
Application — Photoconductive Cells Photoconductive cells are used in many applications in which it is important to know whether light is present. Such applications include headlights that automatically turn on, automatic glare reduction on rear view mirrors, and security lighting.
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