18/11/2013 Disc & Chip Thermistors Search Products Applications Industries Partners Support About Us You are here: Home > Products > NTC Thermistor Elements > Disc & Chip Thermistors Temperature Measurement and Control Devices DISC and CHIP Style NTC Thermistors DISC & CHIP Negative Temperature Coefficient (NTC) thermistors are thermally sensitive STYLE semiconductor resistors which exhibit a decrease in resistance as absolute Features temperature increases. Change in the resistance of NTC thermistor can be brought about either by a change in the ambient temperature or internally by self-heating Wide Ohmic resulting from current flowing through the device. Most of the practical applications of Value Range NTC thermistors are based on these material characteristics. Accurate & NTC DISC & CHIP Style Devices Stable RTI manufactures DISC & CHIP style thermistors in resistance values ranging from 1.0 Fast Thermal ohm to 500,000 ohms. These devices are suitable for a range of resistance values Response Time and temperature coefficients from relatively low resistance and temperature Tight Tolerances coefficients to very high values. Precision resistance tolerances are available to 1%. High Sensitivity Standard resistance tolerances are from 5% to 20%. All tolerances are specified at 25C or may be specified at any temperature within the operating temperature range of the thermistor. Thermistor Terminology for Temperature Measurement & Control Devices D.C. - The dissipation constant is the ratio, normally expressed in milliw atts per degree C (mw /C), at a specified ambient temperature, of a change in pow er dissipated in a thermistor to the resultant change in body temperature. T.C. - The thermal time constant is the time required for a thermistor to change 63.2% of the total difference betw een its initial and final body temperature w hen subjected to a step function change in temperature under zero-pow er conditions and is normally expressed in seconds (S). Alpha ( ) or Temperature Coefficient or Resistance - The temperature coefficient of resistance is the ratio at a specified temperature, T, of the rate of change of zero- pow er resistance w ith temperature to the zero-pow er resistance of the thermistor. The temperature coefficient is commonly expressed in percent per degree C (%/C). Applications NTC DISC & CHIP Time and temperature are two of the most frequently measured variables. There are Selection numerous ways of the measuring temperature electronically, most commonly by Considerations thermocouples and negative temperature coefficient (NTC) thermistors. For general purpose temperature measurement, NTC temperature sensors can operate over a Select Req d. wide temperature range (-55 to +300C). They are stable throughout a long lifetime, Resistance and are small and comparatively inexpensive. Typically, they have negative Value & temperature coefficients between -3.3 and -4.9%/C at 25C. This is more than ten Temperature (10) times the sensitivity of a platinum resistance thermometer of the same nominal Coefficient resistance. RTI s DISC & CHIP style thermistors are used in many applications that Determine require a high degree of accuracy and reliability. Accuracy Some of the most popular applications of NTC thermistors include: Req d. Review Pow er Temperature Compensation Dissipation www.rtie.com/category-s/91.htm 1/518/11/2013 Disc & Chip Thermistors Temperature Compensation Dissipation Determine Temperature Measurement & Control Operating Fan Motor Control Temperature Fluid Level & Temperature Sensors Range Review Thermal Time Constant Selection considerations for NTC DISC & CHIP Devices Power dissipation is a common problem in the use of thermistors as they can only dissipate a certain amount of power. If the power dissipated exceeds the dissipation constant (D.C.) rating of the sensor it is likely that it will exhibit self heating. Most thermistors dissipate from 1 to 25 mW/C nominal. This means that the resistance changes by an equivalent of 1C for each D.C. rating (mW/C) for the selected device. To maintain a higher degree of accuracy, temperature error caused by self- heating should be an order of magnitude less than the required sensor accuracy. For many applications, this degree of accuracy is not required and a less stringent de- rating may be adequate. Several options to reduce the thermistor power are to increase the thermistor resistance, lower the source voltage and/or increase the series resistor in the divider circuit. As an example, if the D.C. of the thermistor selected is 5 mW/C and the power dissipated by the device is 20 mW/C, then a 4C error is induced due to the effect of self-heating. To minimize this effect, a factor can be derived simply by taking the DC -1 rating times 10 (one order of magnitude lower) and use it in the power equation to produce a good approximation of the maximum allowable power. For instance, if the desired accuracy is 1C, and the rated D.C. of the device selected is 5 mW/C, adjusting the specified D.C. rating in the power equation to 0.5 mW/C compensates for self-heating error and effectively predicts the maximum power the device can dissipate without significantly affecting the desired accuracy. The resulting maximum power that should be applied would be calculated as 1C*0.5mW/C = 0.5mW. NTC DISC & CHIP - Selection Process Select R Value Determine R T Calculate DEV for R T Evaluate Power Rating (D.C.) Review T.C. Requirements NTC Standard Chip Thermistor Specifications Resistance R-T THK Part Number 25C D.C. T.C. Curve (in.) (Ohms) 10% 05CA101K 100 A 0.020 2 2 05CA151K 150 A 0.025 2 2 05CA201K 200 A 0.030 2 2 05CA251K 250 A 0.040 2 2 05CA301K 300 A 0.050 2 3 05CA401K 400 A 0.070 2 3 05CA501K 500 A 0.080 2 3 05CB102K 1,000 B 0.020 2 2 05CB152K 1,500 B 0.025 2 2 05CB202K 2,000 B 0.030 2 2 05CB302K 3,000 B 0.050 2 3 05CB402K 4,000 B 0.070 2 3 05CB502K 5,000 B 0.080 2 3 05CC802K 8,000 C 0.020 2 2 05CC103K 10,000 C 0.025 2 2 05CC153K 15,000 C 0.035 2 2 05CC203K 20,000 C 0.050 2 3 05CC253K 25,000 C 0.060 2 3 05CC303K 30,000 C 0.075 2 3 05CE104K 100,000 E 0.030 2 2 05CE154K 150,000 E 0.045 2 2 05CE204K 200,000 E 0.060 2 2 05CE304K 300,000 E 0.090 2 3 05CE404K 400,000 E 0.120 2 3 05CE504K 500,000 E 0.150 2 3 www.rtie.com/category-s/91.htm 2/5