Get Ahead of the Curve

Understanding and then selecting the right temperature curve might seem like a daunting task. To a newbie, it might seem impossible but there is a logical, systematic method to selecting the right temperature sensor.

 

Basically, the thermistors we use in our systems have negative temperature coefficients meaning as the temperature rises, the corresponding resistance decreases; but, the relationship is far from linear.

 

We refer to thermistors by their resistance value at a specific base temperature, usually 77°F (25°C), and a “Type” number that designates the specific relationship of resistance to temperature throughout the relevant range.

 

This relationship depends upon the mix of materials from which the thermistor is made, and for simplicity’s sake, each recipe is assigned a different designation. These are listed in product specifications, ordering information, and the Technical Reference sections in both your Kele catalog and the technical reference section of Kele.com.  To make it easy, you can also click here..

 

For example, the Precon ST-S3E Executive wall sensor uses a high-quality Precon Model 3 thermistor. This sensor has a resistance value of 10 kΩ at 77°F (25°C), and varies according to the Type III temperature/resistance curve.

 

The important take-away from this is to make sure that both the base resistance and the type designation for a thermistor sensor match up with the BAS to which they’re connected.

 

RTD sensors have positive temperature coefficients, meaning as the temperature rises, so does the resistance value of the sensor. Like thermistors, RTDs are classified by a base resistance value, but at a different base temperature, 0°C (32°F). RTDs behave in much more proportional way than thermistors as the change resistance.

 

Each controller is designed and manufactured to use a specific temperature curve. Using the wrong curve will lead to poor control due to inaccurate temperature sensing. Easier still, call Kele and ask for Technical Sales. We’ll help you pick the sensor that’s right for your application!

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