NTC CHIP THERMISTORS AND CHIP IN GLASS THERMAL SENSORS

NTC Chip thermistors are extensively used for accurate temperature measurement and control in automobiles, medical field and electronic appliances. To meet the challenging demands in the latest devices, high accuracy, close tolerance and high sensitivity thermistors are required.

Now widely used thermistors are epoxy coated chip thermistors and glass sealed bead thermistors. Glass sealed bead thermistors are used for applications requiring small size, fast response time, high working temperature (up to 450^oC), reliability and stability, and/or self heated use. The glass coating provides a true hermetic seal, critical for device stability, especially at use temperatures above 150^oC but they have more unit-to-unit variation in resistance and Beta value than chip type thermistors. Individual calibration is usually required.

Epoxy coated NTC chip thermistors, with tight ‘resistance tolerance’ and ‘Beta characteristics’ can be used interchangeably for some applications eliminating the need for calibration but it do not have the hermetic glass seal, thus limiting their stability and working temperatures to 150 ⁰C or below.

Fast response Chip in glass NTC thermistor, an alternative to glass sealed bead and epoxy coated chip NTC thermistors combine the best characteristics of both the devices. The advantages are

• Small size: (0.5- 1 mm) diameter
• Wide range of standard resistances
• Excellent stability up to 250 ⁰C

• Intermittent operation up to 450 ⁰C
• Beta tolerances less than 1%
• Resistance tolerances 1 % to 15 %
• Available for high volume applications
• Lower cost

• Excellent stability of resistance

•  High Precision Temperature Measurement

Applications

The largest share of thermistors is used in automobiles (~40%)    and then in consumer electronics (30%.). The use in medical applications has been gradually gaining expression

1. Consumer electronics: Washing machines, refrigerators, electric cookers, hair driers, coffee makers, electric kettles, in building automation controls (e.g. fire alarms), home heating, air conditioning systems
2. Automobile: Temperature measurement of cooling water and oil, temperature monitoring of exhaust gas, cylinder head or braking system, controlling the air conditioning system
3. Health care: Haemodialysis, Disposable thermometers, Used to continuously measure the body temperature of infants in incubators, Disposable hypodermic needle sensors are especially critical during open-heart surgery and a hypodermic needle with a small NTCR thermistor can be inserted into targeted anatomical sites for temperature measurement and are well-suited for cancer research and treatment, particularly for brain tumors.

C-MET has developed different NTC compositions, chip thermistors and chip in glass fast response thermal sensors suitable for various temperature ranges of sensing applications