colorofwind
Lifetime Supporting Member
Hello, we've had some troubles with measuring the resistance of thermister for a while. We use 2252 NTC Thermistors. For the PLC side, we use AB CompactLogx and the module connecting to thermisters is 1769-IF16V which read analog voltage input. From the resistance versus temperature for thermistors table, the reasonable resistance range is between 1740 to 9600 ohm. We designed the simple voltage divider circuit with 24V applied to it. Basically it's just adding a resistor in serial with a thermistor. We tried using 18K resistor. Some thermistors read a reasonable voltage, some don't (at first read fine, but later the voltage drop to about half the value as before). We suspect it may because of self heat. So we tried using resistor with higher resistance, like 50k and 100k but the problem persist. Am I missing something here? How will you connect the PLC to thermistors?
Thank you everyone!
Thank you everyone!