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NTC Thermistores

Bead thermistors are made by carefully depositing a small quantity of semi-conductor paste on to closely spaced parallel platinum alloy wires. The material forms in an elyptical shape between the two wires resulting in a series of closely spaced beads. The wire and beads are sintered at a high temperature at which time the material forms a tight bond between the two wires. After preferential cutting of the wire, the unit is generally coated or encapsulated in a selected glass to provide a rugged protected unit that exhibits excellent stability.

Wafer thermistors are produced by casting thin sheets of material made up of powders of manganese, nickel, and other oxides combined in a binder. This material is sintered at elevated temperatures, silvered, and then diced to size. Leads are attached by soldering for final test. By careful control of the sintering temperature, powder preparation, and physical properties of the thermistors, close tolerances can be maintained. The units are finally coated in an epoxy for final protection and stabilization.

The nature of the thermistor material is such that for minute changes of body temperature, large changes of resistance can be measured. This characteristic sensitivity to temperature change can result in a thermistor resistance change of 10 million to one over an operating temperature range.

Practical use for this highly sensitive device has been found in many diversified applications. A few of these include liquid level measurement, photography, fever thermometers, blood analysis, motor winding compensation, intravenous catheters, thermo-plastic equipment, etc..

WUNTRONIC manufactures a complete line of NTC thermistor products. These products include low cost wafer thermistors, miniature through standard size beads, and a variety of assemblies to meet with customer requirements. All units are tested in carefully calibrated sensitive temperature control baths and all calibrations are traceable to the NBS. All our devices are tested in accordance with and meet or exceed the requirements as prescribed in MIL SPEC. #T23648

These NTC units are available in resistance ranges from 50 ohms to over 20 megohms. Whatever your needs, if they are not listed in this catalog, we encourage you to write or call. If we can make it - we will.

General Notes:

• All resistance measurements are referenced at 25°C. Other reference temperature points or resistance requirements are available.

• Standard tolerances are + 25% for the Sensorbead 14. All other Sensorbeads and Sensorprobes are standard at ±20%. Tolerance values may be specified as low as ±2%.

• Longer or shorter leads are available upon request

• Special lead material and/or insulation can be supplied

• Custon made assemblies or special mounting upon request.

Glossary of Terms:

Standard Reference Temperature: The thermistor body temperature at which nominal zero power resistance is specified.

Zero-Power Resistance (Ro): The dc resistance value of a thermistor at a specified temperature with negligible electrical power to avoid self heating.

Resistance Ratio Characteristic: The ratio of the zero power resistance of a thermistor measured at two specified temperature levels.

Zero Power Temperature Coefficient of Resistance (Alpha): The ratio at a specified temperature(T), of the rate of change of zero power resistance with temperature to the zero power resistance

Stability: The ability of a thermistor to retain specified characteristics after being subjected to designated environmental or electrical test conditions.

Resistance Temperature Characteristic: The relationship between the zero power resistance of a thermistor and its body temperature.

Temperature-Wattage Characteristic: The relationship at a specified ambient temperature between the thermistor temperature and the applied steady state wattage.

Maximum Power Rating: The maximum power which a thermistor will dissipate for an extended period of time with acceptable stability of its characteristics.

Thermal Time Constant: The time in seconds required for a thermistor dissipating zero electrical power to change 63.2% of the difference between its initial and final body temperature.

Current-Time Characteristic: The relationship at a specified ambient temperature between the current through a thermistor and time, upon application or interruption of voltage to it.

For more information's about Thermistors send us please an e-mail WUNTRONIC@wuntronic.de, use our Info Form, Fax or phone.

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