Thermocouples | Resistence Thermometers | Thermistor Probes | Hand Held Sensors

What is a Thermistor Probe?
Thermistors are solid temperature sensors that behave like temperature sensitive resistors; hence the name is a contraction of “thermal” and “resistor”. There are basically two broad types, NTC negative temperature coefficient, (resistance falls as temperature rises) used mostly in temperature sensing and PTC positive temperature coefficient, (resistance increases as temperature rises) used mostly in electric current control. They are resistors with a high temperature coefficient of resistance and their resistance is a function of absolute temperature. Thermistors are not new, they have been known about for about 160 years, but had very little use because they were considered to be unstable and nonreproducible. This is no longer true.

About 50 years ago Bell Telephone laboratories started investigating various materials and processing procedures to determine how to manufacture stable and reproducible Thermistors. They were quite successful in their investigations and actually put Thermistors into large scale telephone usage about 30 years ago. The units they developed were both stable and closely reproducible to standard specifications. It is only in the last 20 years, however that Thermistors have been generally available for large-scale industrial use.

Thermistors are made from small masses of complex oxides and materials, compressed and heat treated to a coherent nonporous mass. This process is what gives a Thermistor its basic resistance curve. The material is trimmed for proper resistance a 25˚C. Two leads are then attached and the sensor is then encapsulated in an epoxy resin.

Although not as reproducible as Platinum resistance thermometers, they are much more sensitive. Commonly the resistance falls exponentially with increasing temperature, (NTC) as a consequence OF high sensitivity the range and use of an individual Thermistor is comparatively narrow, hence a range of Thermistors are manufactured to suit a variety of applications

Standard Thermistor Probe	Lollipop Thermometer
Solar Panel Thermometer	T-Bar Thermometer