Frequently Asked Questions

Q1 What is a Thermistor?

Thermistors are thermally sensitive resistors, which show a precise and predictable response to resistance change in direct proportion to temperature change.

There are 2 main types of Thermistor:

NTC Thermistors (Negative Temperature Coefficient) whose resistance falls when the temperature increases.

PTC Thermistors (Positive Temperature Coefficient) whose resistance increases when the temperature increases.

Q2. When would you use a Thermistor?

Typical applications for thermistors include:

1. Temperature Measurement
2. Temperature Control
3. Temperature Compensation
4. Inrush Current Limiting
5. Overtemperature Switches

Q3. What is an NTC Thermistor?

NTC Thermistors (Negative Temperature Coefficient) whose resistance drops when the temperature increases. When the term thermistor is used, engineers generally refer to NTC thermistors.

These are generally used for temperature measurement as their RT (Resistance – Temperature) characteristic is very well defined and can be readily programmed.
They are used across a wide range of industries and products from miniature Semitec F Micro within catheters, to the Semitec 103AT-11, which.

They are manufactured from metal oxide semiconductor materials encapsulated in an impermeable material such as epoxy or glass. These coatings are used to protect both the thermistor bead and wire connections mechanically whilst providing protection against humidity.

An NTC thermistor has a high resistance at low temperature, and as the temperature increases the resistance decreases rapidly. These therefore these offer the benefit of highly accurate and quick response times to very small changes in temperature.

Q4. What are the key features of an NTC Thermistor?

• Highly stable and highly reliable, excellent repeatability
• High accuracy (Tc ~1s)
• Fast response (± 1% tolerance or better)
• Compact designs – allowing them to be fitted into very tight spaces.
• Low-cost – by purchasing a thermistor with an accurate RT curve no further calibration is required over the life of the product.
• Interchangeability – no recalibration required when replacing thermistors.
• Point matching – Thermistors can be supplied calibration at exact working temperature.
• Wide temperature range (-60°C/+300°C).
• Highly customisable to best fit your application.

Q5. Which applications would you typically use an NTC Thermistor?

NTC thermistors are used in a large number of temperature sensors in everyday life and include :-

• Home appliances
• Medical device
• Smart devices /IOT products
• Battery monitoring
• Automotive and E-Vehicle applications
• Temperature control within HVAC appliances
• Fire & Security market
• Office automation products

Some larger NTC disc thermistors are used for current inrush limiting as they offer a neat and cost- effective solution to surge currents arising from switching on certain electronic or electrical products, e.g. S.M.P.S.s (Switch Mode Power Supplies), LED driver circuits and halogen lamps/ heaters.

Q6 Do you offer a choice of housings/configurations?

NTC thermistors can be supplied in different configurations/housings depending on your applications:

• Epoxy coated generally for lower temperature use (-60°C to +150°C)
• Glass encapsulated ideal for use in high temperature applications ( -50°C to +300°C)
• In temperature probe assemblies – with IP67 or IP68 ratings if required.
• SMD (surface mount) packages down to 0201 size
• Threaded or boss mounted, metal encapsulated temperature sensors.

Q7 How do you choose the correct NTC Thermistor for your application?

Ring ATC Semitec on 01606 871680.

There is no easy formula in deciding which is the best NTC thermistor for your application as there are many different factors to take into consideration. Factors to take into consideration include levels of accuracy, resistance values, shapes and size.

At ATC Semitec we have more than 25 years of experience in providing thermal solutions for industry. Give us a call today for expert technical advice.