To connect thermistors directly to the T100MD+ or T100MX+ PLC analog inputs to measure temperature, we recommend using the 10K ohm NTC thermistor due to the low self heating which result in good analog voltage range that can be connected directly to the PLC's 0-5V analog inputs. However, since thermistor R-T (resistance-temperature) graph is non linear accurate temperature measurement can most efficiently be achieved using a look up table.
An application note on how to use the T100MD+ PLC and 10K ohm thermistor as well the sample .PC6 program that perform the lookup table task quickly can be found at the following link:
http://www.tri-plc.com/appnotes/ThermistorSensor.zipNote: PT100 is a positive temperature coefficient thermister. However, its low resistance of 100 ohm at 0 degree C means that to avoid self heating only low excitation current should be allowed to pass through the sensor. The resulting low voltage drop across the PT100 would require pre-amplification before you can connect it to to the 0-5V analog inputs range on the M-series PLCs. (The 2 channel of 0-1V analog input on T100MD1616+ could allow a PT100 with a resistor divider network to generate voltage output range of less than 1V if the accuracy is not too critical).
