What Does “3950” Mean on an NTC Thermistor?
In many NTC thermistor descriptions, “3950” refers to a nominal B value of about 3950 K, not the thermistor’s resistance at 25 °C. Confirm the supplier’s data sheet and the temperature interval used to define the B value—for example, B25/50 or B25/85—because the interval and tolerance are part of the specification.
The nominal resistance, often stated separately as R25, is a different parameter. A part described as “10 kΩ, B3950” identifies both a resistance at a reference temperature and a temperature-resistance slope; “3950” alone does not tell you the nominal resistance, package, temperature range, or accuracy of a finished sensor.
How the B Value Relates to the R/T Curve
An NTC thermistor’s resistance falls as its temperature rises, and the curve is nonlinear. The B value summarizes the curve between specified temperatures. For design and calibration, use the manufacturer’s R/T table or coefficients over your working range rather than assuming one B value fully describes every part or production lot.
Resistance tolerance, B-value tolerance, measurement conditions, and circuit self-heating all contribute to the final temperature error. If the application needs interchangeability, specify the allowed resistance deviation at relevant temperatures or the required curve tolerance and verification method.
OEM Selection Checklist for a B3950 NTC
1. Specify both resistance and curve
State the R25 value and tolerance, B value and its reference interval/tolerance, and any required R/T data points. Confirm that the controller’s conversion table or coefficients match the selected component.
2. Define operating and storage conditions
Give the normal, minimum, maximum, and excursion temperatures at the sensing location. Include moisture, vibration, chemicals, thermal cycling, and other environmental exposures that affect the element and finished assembly.
3. Select the physical construction
Specify bead, chip, glass encapsulation, lug, or probe assembly only after confirming mounting and thermal contact. For a probe, provide sheath or encapsulation material, dimensions, insertion depth, lead length, connector, and sealing requirements.
4. Review electrical and response behavior
Share the measurement circuit, excitation, ADC or controller input, and desired response under stated test conditions. Ask the supplier to review self-heating and the full system error budget; component tolerance alone is not system accuracy.
5. Agree on production validation
Define sample quantities, incoming inspection, lot traceability, calibration or curve checks, change notification, and the records required for approval. Validate samples in the actual mounting and operating environment.
Information to Include in an OEM RFQ
- Nominal resistance at reference temperature and resistance tolerance
- B value, interval, tolerance, and manufacturer R/T table
- Operating/storage limits and environment
- Element, probe, wire, connector, dimensions, and drawing
- Controller or circuit details and response-time test conditions
- Prototype and annual quantities plus approval documents
Explore the NTC thermistor product range and our NTC working-principle guide. Send your application, curve requirements, and drawing through the OEM quote form for a configuration review.
Frequently Asked Questions
Does B3950 mean 3950 ohms?
No. In this context, B is a thermistor coefficient expressed in kelvins; resistance is specified separately, such as R25 in ohms.
Are all B3950 thermistors interchangeable?
No. Confirm resistance value, B-value interval and tolerance, R/T data, package, operating limits, and controller conversion before substituting a part.
Can I calculate temperature from B3950 alone?
Not reliably across all parts. Use the exact component’s resistance reference, B interval, tolerances, and preferably its manufacturer R/T table or coefficients.
For a design review, contact Starlight Sensors with your data sheet, circuit, and assembly drawing.
Reference: TDK Electronics, NTC thermistors: general technical information.
