NTC Thermistors - Components101

1 VISHAY BCCOMPONENTSR esistive ProductsApplication NoteNTC ThermistorsAPPLICATION NOTE Revision: 24-May-121 Document Number: 29053 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT APPLICATIONSNTC temperature sensors are widely used in motor example: Inlet air-temperature control Transmission oil temperature control Engine temperature control Airco systems Airbag electronic systems Temperature detection of laser diode in CD players forcars Frost sensors ABSDOMESTIC APPLIANCESNTC temperature sensors are in virtually all equipment in thehome where temperature plays a role. This includes Fridges and freezers Cookers and deep-fat fryers Washing machines and dish washers Central-heating systems Air conditioningINDUSTRIAL, TELECOMMUNICATIONS, CONSUMERIn switching, measuring and detection systems Process control Heating and ventilation Air conditioning Fire alarms Temperature protection in battery management/chargingsystems LCD contrast control in flat-panel displays, mobile phonesand camcorders Temperature compensation of quartz oscillator frequencyin, for example, mobile phones Ink-jet printer head temperature detection Video and audio equipmentSELECTION CHARTPRODUCT RANGEOPERATING TEMP.

2 RANGE( C) R ( %)OR ON T ( C)BTOL. ( %)RESP. TIME (s)MAX. (mm)LEADDOCUMENT NUMBER (mm)L(mm)Accuracy lineNTCLE203E3- 40 to + 125(1 , 2, 3, 5) % to 40 to + 125(2, 3, 5) % to 40 to + Ctwo-point 55 to + Ctwo-point versionsNTCS0603E3- 40 to + 150(1, 2, 3, 5) %1----29056 NTCS0402E3- 40 to + 150(1, 2, 3, 5) %3----29003 NTCS0805E3- 40 to + 150(1, 2, 3, 5) %1----29044 Miniature accuracy lineNTCLE300E3- 40 to + 125 40 to + 125 40 to + 125 to 1 temperatureNTCSMELFE3- 40 to + 1505 % 40 to + 3005 % max. long-leaded (UL2468 PVC insulation): NTCLS100E3- 40 to + 853 % to 3158 AWG2440029060 NTCLP100E3- 40 to + 853 % to 3106 AWG2440029060 NTCLE400E3- 40 to + 853 % to 376 AWG2440029060 Ring Tongue SensorsNTCALUG02 series- 55 to + 125(1, 2) % series- 40 to + 125 (2, 3) % to series- 40 to + 150 5 % ThermistorsAPPLICATION NOTEA pplication BCcomponents Revision: 24-May-122 Document Number: 29053 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE.

3 THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT SUMMARYACCURACY LINENTCLE203E3 and NTCLE100E3 The flagship of our ranges. The accuracy Line sensors offerreal value for money. They have low tolerances (as low as 1 % on the R25-value and % on the B-value) and anoperating temperature range from - 40 C to + 125 C. Inaddition, they are very stable over a long MOUNT TEMPERATURE SENSORSNTCS0402, NTCS0603 and NTCS0805 seriesOur surface mount NTC sensors for temperature sensingand compensation embody all the qualities of VishayBCcomponents NTC technology. The sensors come in a fullrange of R25-values from 2 k to 680 k with standardtolerances from 1 % to 5 %.HIGH-TEMPERATURE SENSORSNTCSMELFE3 and NTCLG100E2 This range of high-quality glass-encapsulated NTCtemperature sensors are price-competitive for general only can theleaded sensor be used at up to 300 C, buttheir glass encapsulation makes them ideal for use incorrosive atmospheres and harsh environments.

4 This makesthem an attractive alternative to other more expensivesensing methods. Two types of small glass envelopes areavailable: SOD 27 for sensors with leads, and SOD 80( MELF execution) for leadless, surface mount components are designed for all automotiveapplications (especially ECT sensors). Their coating iswithstanding harsh potting conditions. These componentsare compliant to the AEC-Q200 CHIP ACCURACY LINENTCLE201E3 NTCLE300E3 NTCLE305E4 These sensors combine the features of the accuracy linewith non-insulated or insulated leads for remote LONG-LEADED SENSORSNTCLS100E3 NTCLP100E3 NTCLE400E3 For special applications we can supply three types oflong-leaded sensors: water-resistant sensors for use inhumid conditions, pipe sensors for use in corrosiveatmospheres and epoxy-coated sensors for general TEMPERATURE SENSORSNTCALUG01 NTCALUG02 NTCALUG03 HOW NTC TEMPERATURE SENSORS WORKNTC temperature sensors are made from a mixture of metaloxides which are subjected to a sintering process that givesthem a negative electrical resistance versus temperature(R/T) relationship such as that shown in figure 1.

5 Fig. 1 - Typical resistance as a function of temperature for an NTC temperature sensor. The relatively large negative slope means that even smalltemperature changes cause a significant change inelectrical resistance which makes the NTC sensor ideal foraccurate temperature measurement and main electrical characteristics of an NTC ceramictemperature sensor are expressed by three importantparameters and their tolerances (see below).RESISTANCE R25 AT 25 C ( K)The resistance at 25 C (substantially at room temperature)provides a convenient reference point for on R25 are due mainly to variations in ceramicmaterial manufacture and tolerances on chip the use of highly homogeneous materialcompositions and proprietary ceramic sawing techniquesallowing precise control of chip dimensions, products areavailable with tolerances on R25 lower than 1 %.

6 IMPORTANT NTC PARAMETERSPARAMETERDESCRIPTIONR25 The resistance of the sensor in at the reference temperature of 25 CB-valueA material constant, expressed in Kelvin The temperature coefficient of resistance expressed in %/K or in %/ CMSB236 - 1R25B = 3740 KB = 4570 K0 - 25 0 25 50 75 100 125T ( C)log R ( )NTC ThermistorsAPPLICATION NOTEA pplication BCcomponents Revision: 24-May-123 Document Number: 29053 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT CONSTANT BB is a material constant that controls the slope of the RTcharacteristic (see figure 1) which can, at least to a firstapproximation, be represented by the formula: (1)Where T is the absolute temperature of the sensor. In practice, B varies somewhat with temperature and istherefore defined between two temperatures 25 C and85 C by the formula: (2)B25/85 (expressed in K) is normally used to characterize andcompare different ceramics.

7 Tolerance on B (or B25/85) iscaused mainly by material composition tolerances andsintering conditions. The latest materials offer tolerances aslow as % on some specific B25/85 most cases, better fitting curves than pure exponential arerequired to measure the temperature accurately; seeformula (1). That is why each NTC material curve is definedby a 3rd order polynominal, as shown below:(3)or inversely expressing T as a function of RT:(4)The two approximations (3) and(4) represent the real materialcurves with an error smaller than % at any values of the coefficients A, B, C, D, A1, B1, C1 and D1are given in some datasheets as NTCLE100E3 and in theR-T computation sheets, which can be downloadedfrom the TOLERANCESThe total tolerances of the NTC sensor over its operatingtemperature range is a combination of the tolerances on R25and on B-value given by the formula: (5)Figure 2 is a graphical representation of this formula whichshows a minimum at 25 C since this is the temperature atwhich the sensor is calibrated.

8 Above and below thistemperature, the tolerances increase due to the increasingtolerances on B-value, giving the graph a butterfly shape. Fig. 2 - Typical resistance change as a function of temperature for a 1 % Vishay NTC temperature sensor compared to a1 % sensor with a higher B-toleranceThe exceptionally low B-value of the VishayBCcomponents sensor compared with those of typicalcompetitors (see figure 2) gives a flatter R/R butterfly curve which means you can get more accurate temperaturemeasurements using Vishay BCcomponents NTCtemperature COEFFICIENT OF RESISTANCEThe temperature coefficient of resistance expresses thesensitivity of a sensor to temperature changes. It is definedas:(6)Using formula to eliminate R this can be re-expressed as:(7)Which means that the relative tolerance on is equal to therelative tolerance on STABILITYThe stability of an NTC temperature sensor is expressed interms of the maximum shift in its electrical properties, R25and B-values after it has been subjected to an extendedperiod at its limit operating conditions.

9 Figure 3, forexample, shows the long-term deviation of R25 and B-valuefor a standard lacquered component from the NTCLE100E3series with an R25 of 10 k . exp=B25 85 lnR85R25--------- =RTR25 ABTCT2DT3 + + + exp=T1A1B1 RTR25--------- C1ln2 RTR25--------- D1ln3 RTR25--------- ++ln+----------------------------------- ---------------------------------------- ---------------------------------------- ------= RR-------- R25R25------------- +=108- 50 MLC7296420 R(%)- 250255075100 125T ( C)competitorVishay 1R---- x R T--------= BT2--------=NTC ThermistorsAPPLICATION NOTEA pplication BCcomponents Revision: 24-May-124 Document Number: 29053 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT Fig. 3 - Aging characteristics (dry heat at 150 C of aNTCLE100E3 series NTC temperature sensor with an R25 of 10 k TEMPERATURE CYCLINGA nother important criterion for assessing the performanceof an NTC sensor throughout its operational life is itsresistance to thermal cycling.)

10 To assess this, products aresubjected to rapid temperature variations covering theextremes over which they are expected to operate untilfailure is tests fully demonstrate the high reliability of ourproducts: our soldered types (for example NTCLE300E3types) withstanding more than 5000 cycles, and our glassencapsulated types (NTCLG100E2) more than 100 000cycles without TIME CONSTANT AND RESPONSE TIMEThe speed of response of an NTC sensor is characterized byits time constant. This is the time for the sensor stemperature to change by % ( 1 to 1/e) of the totalchange that occurs when the sensor is subjected to a veryrapid change in conditions under which the time constant is measuredare important. Two are normally considered: Ambient change: the component is initially in still air at 25 quickly immersed in a fluid at 85 C.