This article looks at thermistor probe types and their uses. Thermistor basics are covered in this introductory thermistor guide
Custom Thermistor probes
If a specific application requires a custom thermistor probe then please view the Custom Temperature Sensor Design Guide and get into contact for our probe design services.
The problem with exposed Thermistors and why thermistor probes are used
Raw thermistor elements are delicate electronic components , therefore a protective housing that is called a probe is placed over it to expand its usability to external harsher conditions.
However because of their exposure to the environment these small elements can break.
normally the better the protection the worse the thermal response. This is because the protective materials will insulate it from the temperature , the thermistor will still react to the temperature but will take longer.
Thermistor elements that have legs can break off causing an open circuit, or if this thermistor is a surface mounted component it means the PCB has to be exposed (sometimes this can be done intentionally but that is covered else where)
The environment may seem safe but airflow and humidity slowly erodes thermistor legs.
Thermistor probes offer varying levels of protection
Thermistor probes are the raw thermistor element shown above enclosed into a protective enclosure. Different levels of protection are provided depending on the type of probe however with this protection comes a cost THERMAL RESPONSE.
A rule of thumb is the better the protection the slower the thermal response.
Types of Thermistor Probes
Pipe Thermistor probes -TT0P
These thermistor probes are examples of a specific application .This are perfectly suited to measure the pipe temperature. Their thermal response is good enough for their application and can be further improved with thermal paste. although this has good mechanical protection and water ingress rating it is specifically design for one purpose for measuring the pipe temperature.
103AT-11 TPE Thermistor probe
The 103AT-11 Thermistor probe is a common TPE tipped probe that offers rugged protection with an IP67 rating .This is an excellent choice for optimal protection against the elements. This probe ha a good mixture between protection and response time.
- IP67
- TPE
- Cost effective
- Flexible
Metallic enclosure – TT08
This is a popular thermistor probe that offers mechanical and water ingress protection with an impressive IP68 rating. The metallic enclosure will offer great protection but at a cost , this cost is thermal response but this may not matter because its most common use case is water temperature monitoring which is a slow moving thermal environment, for a waterproof temperature sensor it is the most used type.
- IP68
- Stainless steel
- impressive protection
- Waterproof temperature sensor
- Flexible cable
Epoxy Leaded – AT-4
AT-4 has good thermal response qualities and reasonable protection against most non harsh environments and airflow making it a great choice for most applications that don’t require prolonged exposure to water.
- Fast response time
- Cheap
- protection against moisture and dust
M4 Ring mechanical – C3
The C3 thermistor probes are designed for mechanical applications that need to monitor the temperature by securing the sensor mechanically , this Thermistor probe uses the universal and popular M4 bolt size. Along as the back of the thermistor is in contact with the surface to be measured the thermal response is decent and can be further improved with thermal paste.
- M4 application specifica
- Mechanical protection
- Precuations need to be taken to ensure good thermal contact
Thin film – JT
This Thermistor probe has limited environmental protection and needs to be handled with care during install but offers the best thermal response out of the probes listed here . Due to its low mass and thin construction the temperature sensor with react quickly to temperature changes.
