Continued from last article.
It needs to be noted that the δ value is the parameter of NTC thermistor before the secondary encapsulation by most of the manufacturers. Although the current determined by this parameter won’t produce self-thermal, but it affects the selection range of the parameter value. That’s because the max. non self-thermal power is increased after secondary encapsulation. The way to determine the current range by dissipation factor is to determine the accuracy of NTC thermistor first, and then the self-thermal power consumption allowed. For example, when the accuracy of NTC thermistor is 0.1°C, then the self-thermal temperature doesn’t exceed 0.1°C, that is to say, less than 0.1δ power won’t produce self-thermal power.
Other factors needed to be noted: 1. τa will be increased after secondary encapsulation. 2. It needs to pay attention to the medium of the parameter since δ and τa vary widely for the same one NTC thermistor in different media. 3. In flow air, it doesn’t influence the accuracy much that NTC thermistor produce some self-heat.
Physical photo of a typical NTC thermistor
There are various types of NTC thermistor in Analog Technologies, Inc., such as ATH10K1R25 and ATH100K1R25, etc.
To be continued…
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