What is a Thermistor Probe?

What is a Thermistor Probe?

A thermistor probe consists of a thermistor sensor element (bare chip, DO-35 Glass, epoxy coated or other element style) attached to extension lead wires and potted into a thermowell with thermally conductive epoxy or other potting material as dictated by the application. They are built to monitor, measure or control temperature, and provide accurate, reliable, fast, and stable thermal monitoring, at a cost-effective price. 

Water heaters, HVAC controls, organ transport equipment, distillery equipment, battery chargers, coffee makers, electric vehicles, refrigerated supermarket displays…these are just some of the wide variety of applications in which thermistor probes have been proven invaluable for sensing temperature.  In our everyday life, they are crucial for our comfort, safety and well-being.

Looking at the individual aspects of thermistor probes, we’ll start with the thermowell.

Thermistor Probe StylesThermowells (or probe housings) are made from materials such as Stainless Steel, Copper, Brass, Vinyl or Plastic.  There are various mounting styles to choose from depending upon the needs of the application. Ring lugs, flag terminals, and pipe clip-on are commonly used for surface temperature sensing.  Threaded such as a pipe plug or NPT with a tube, straight with a radius or pointed end, flanged thermowells with mounting holes are often used to measure fluid flow/fluid temperature in the Pool/Spa, Industrial or Medical industries or air temperature in the HVAC and Building Automation sector. EI Sensor has a wide variety of thermowell styles available, if you don’t see your required size or style, we are confident we can fulfill your needs so be sure to contact us to discuss further.

The extension lead wires on a thermistor probe assembly are typically insulated. Insulation types such as Teflon, PVC, Kynar or XLPE are commonly used.  If warranted by the application, a higher temperature cable will be utilized. Single conductor, two conductor, solid or stranded, jacketed…there are many choices for your design.  The length of the wire will be cut and stripped to your requirements.

Many thermistor probes are provided with terminals and connectors as dictated by the customer.  Molex, TE, JST and Aptiv are just some of the many EI Sensor has supplied over the years.  Don’t hesitate to let us know if we can help you with this value-add service.

The ability to customize a probe for a specific application is crucial to the end product. Our highly experienced design engineers will ask many questions to help narrow down the physical style as well as the electrical properties needed.  Important characteristics we need to know include the size limitation(s) of the application, the operating temperature range, whether moisture will be present, the base resistance value and accuracy as well as if there are specific resistance vs temperature (RT) characteristics required.  As the design develops, our engineers will offer a drawing or drawings of a thermistor probe showing the thermowell dimensions, lead wire details and the electrical characteristics.  The customer can mark up the drawing if changes are needed and we will revise then resubmit for review.

Our website displays a subset of common thermistor probe styles. Our company prides itself on providing a customer with a solution that fits their needs so if don’t see your required style, contact us for further assistance at sales@ei-sensor.com. We will respond quickly to your inquiry.

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