NTC temperature sensor and CP1H

[pszczepan 2]

I do not see card to read NTC sensor directly. How I can read by CP1H temperature using NTC sensor? Thanks for clue

[pfort 20]

I think NTC is a thermistor. Usually we find it on motor wirings to detect an overheating, and they must be connected to a special relay (ABB have it) or on a drive input dedicated to it. What is the application?

[pszczepan 2]

Yes you are right - it is thermistor I have such a sensor integrated with moisture sensor to control ground temperature. Could you write model of this ABB relay - is it analog converter to signal 0..10VDC or something? regards

[pfort 20]

No it is a relay that close or open a contact when resistance of a thermistor (PTC) go above a treshold. Not an analog signal. If you need a proportionnal signal that is not good for you. This afternoon i worked with a temperature controler that can handle PTC (positive), and it have an analog output, but i dont think it is good for NTC. (negative) It was a GEFRAN 800 temp controler model. If you still want to know about this ABB relay, let me know and when i will be back to work tomorrow i will find that number.

[pszczepan 2]

Can I set switch threshold for the sensor in this ABB relay. Anyway please write model of this relay. Thanks in advance Pawel

[Geir 4]

Unlike the platinum sensors the dedicated temperature modules handle, the thermistors vary too much in characteristics to give accurate readings. The actual values of the resistors will vary according to the type of thermistor you have, but if you make a Wheatstone bridge like the one below and connect the +24V to the top and the voltage input terminals of a MAD11 across it, you will have a primitive but functional temperature measurement. As an example if your NTC is 10K at 25 degrees C, it would be 26K at 0 degC and 4,4K at 50 degC, if R3 and R2 are 10K and R1 is 26K, you would measure OV at o degC and approx. 8V at 50 degC. You would have to compare your thermistor with an accurate thermometer at various temperatures and and monitor the reading from the MAD11 to calibrate it. More about using thermistors Edited 8 Dec 2010 by Geir

[pfort 20]

1SVR550800R9300 It is for PTC it would not do the job for NTC

[BobB 58]

AARGHH!! I would strongly suggest you use 3 wire RTDSs and not thermistors. Any one involved regularly in temperature control activities hates them. They are inaccurate and unreliable - even in motors they can drift to the point where the over heating detection of a motor becaomes unreliable. I had one recently where the thermistor had drifted so far that the thermistor relay was tripping when the motor was running at a normal temperature.

[Leitmotif 0]

From what I have read either thermocouple TC or Resistance Temp Detecter (positive temp coefficient) are preferable to thermister (negative temp coefficient) 1. Both RTD and TC are built to a standard. Regardless of manufacturer a type K TC will be nearly same as another built by someone else. Same can be said for RTDs ie PT 100 is basically same regardless of source. This is not the case with thermisters - they are NOT built to a standard - so there is variation between manufacturers and who knows maybe even a particular production run. The moral here is it may be difficult getting a replacement thermister. 2. Thermisters are accurate (maybe better term would be proportional with predictabiltiy ??) only in a much tighter temperature band compared to the accuracy vs temp bands for TC and RTD. Dan Bentler