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Sensors LMT Temp Sensors Slide 6

While this slide refers specifically to the LMT84 thru 87, this is fundamentally accurate for all TI’s analog LMT temperature sensors.Thermistors have a very narrow range of linearity. The graphs on this page show this. The graph on the left side indicates output voltage versus temperature. The output is highly linear across the entire operating temp range of the device. This means sensitivity, or gain, also stays the same across temperature.The graph on the right side of the page shows 3 graphs of output voltage versus temperature for an NTC thermistor. Only a small temperature range can be addressed with each R Bias value, and in each case the sensitivity changes, requiring both a circuit and look-up table change to measure across wider temp ranges. This is because thermistors have a narrow range of linearity and good sensitivity. For example, when R Bias is 1 mega ohm, -20°C to -5°C is approximately linear in output, with meaningful sensitivity. At higher temperatures, both linearity and sensitivity become degraded. For example, differentiating between the output voltage representing 80°C and 90°C is challenging. Different R Bias and lookup tables must be used for different temperature ranges. Analog temp sensors are far more linear and easier to use than thermistors.

PTM Published on: 2013-07-25