Sensors frequently asked questions

Q: Why should I use an NTC thermistor as a temperature sensor instead of any other type of contact temperature sensor?

A: Resistance values of NTC thermistors tend to be high to very high, which means that low-current, 2 point measurements can be done with high precision.  They also offer one of the most cost-effective solutions vs other types of temperature sensors.  Eaton also has a variety of different packaging types that is suitable to meet the application requirements of a broad range of electronic applications.  

Q: Does the non-linearity characteristic of an NTC cause a problem for appropriate use?

A: The inherent non-linearity does not create an issue in the accurate measurement of temperature for one or several values.  In fact, this feature can help with temperature accuracy when selected appropriately.   To assist in providing proper temperature analysis on a measured resistance, resistance vs temperature tables can be stored and used for interpolation.  Another method is an algorithm that can be programed to give a precise temperature based on measured resistance.

Q: How stable is resistance of NTC thermistors over time?

A: Different thermistor families have different long term stability characteristics based on their construction and the environments that they are subjected to.  Hermetically sealed glass NTCs offer higher stability than epoxy coated versions.  Additionally, long term exposure to the temperature extremes of the respective family ratings can impact stability.  Eaton offers both epoxy and glass constructions to suit application needs.

Q: What type of NTC should I choose if I need temperature sensing in my application and low cost has been deemed the more important design goal versus stability and precision?

A: With low price being the most important, selecting a higher resistance and/or B tolerance, such as ±5%, can help reduce price.  Also, epoxy coated construction can help lower price.

Q: Does the datasheet specifications for NTC thermistors factor in any long-term stability considerations?

A: No. The specifications listed on Eaton’s datasheets do not include factors for stability given the wide range of possible environmental conditions that each individual device can be subjected to in the application.  The accuracy is specified when the product is manufactured.

Q: What resistance value should I select for my application?

A: Typically, a lower resistance sensor is designed for lower temperature (<0 C) applications and vice versa for higher temperature applications.  It should be desired to have high resistance rate of change in your temperature range of interest to take advantage of the non-linear characteristics.

Q: How do I obtain the resistance versus temperature characteristics or R-T tables of Eaton NTC thermistors?

A: The most common R-T information is posted on Eaton’s website; more specifics by part number can be provided.  Please use Contact Me form with Eaton part number information for requested information.

Q: Why would I want a high resistance of the NTC or a higher rate of change in resistance in my temperature range of interest?

A: The higher NTC resistance helps reduce any external noise that can cause nuisance issues or lead wire resistance contribution that would need to be offset.  Additionally, the higher rate of change can help provide a higher level of sensitivity in the application when there are small temperature changes.   Another way to state this or how its been referred to as is sensitivity resolution. 

Q: How is response time of NTCs defined?

A: This is established by the thermal time constant (τ) of the individual product.  This is defined as the time required by the thermistor to change to 63.2% of the difference between its initial and final temperature.  Each family has its thermal time constant listed on the respective datasheets.

Q: How much to NTCs typically cost?

A: Pricing is impacted on a couple of different aspects.   The first is related to the tolerances of resistance and B value, which is a result of yields.   Furthermore, the type of construction and additional materials required to properly package the thermistor chip also impacts the overall product cost.  Each of these aspects results in a range of prices.

Q: After selecting my NTC thermistor, are there any steps I can take to make sure I leverage the specified accuracy and speed?

A: Since an NTC is a temperature sensitive device and has its datasheet resistance defined as zero power resistance, designing a circuit to limit current through the thermistor to help ensure that there is not significant self-heating and artificial lowering of resistance.  Each datasheet includes a power dissipation value to offset the self-heating for a given power across the device.   

Q: Is there a specific NTC used for sensing temperature in Li-ion battery or supercapacitor applications?

A: Since there are no specific standards that govern temperature sensing in Li-ion battery packs or for supercapacitors, there are multiple different types of products that can be used based on footprint available, temperature range and assembly method.   This results in epoxy coated NTCs, PCB SMD thermistors and axial leaded NTCs being suitable for this application.

Q: Are there best practices for attaching an NTC to a surface requiring temperature sensing?

A: There are many commercially available adhesives used to attach a thermistor to support surface temperature sensing.  We recommend using a thermally conductive adhesive in order to provide best results and not greatly interfere with thermal performance of the NTC.

Q: Can I infer product technical information from Eaton’s NTC part numbers?

A: Yes. Outside of the part family I.D., the resistance, resistance tolerance, B value, B value definition and B value tolerance are all provided in the part number.  Additional information can be found on the respective product datasheets.

Q: Are Eaton’s NTC thermistors RoHS compliant?

A: Yes.  Eaton’s NTC thermistors are RoHS compliant.