I need to monitor a temperature of the outer surface of a copper dewar which is inside a thermos flask arrangement. The monitored temperature should be displayed continuously on a display outside. I also need to design a PCB circuit which can give out 10uA of current to the DT-670 temp. sensor. I have chosen the TI LM series constant current source for this purpose (Link to the datasheet www.ti.com/lit/ds/symlink/lm134.pdf). Also I need to get the voltage drop across the sensor to monitor the temperature and show it across the e-paper display. please suggest me if the IC chosen for the constant current source is fine. What is the best IC/MCU which I can chose to monitor the temperature across the diode so as to display it on the e-paper display continuously. How to calibrate the MCU for the temperature readings for those particular voltages. Is the dv/dt table given in DT-670 datasheet a source for me to do the calibration? Also do I need to insert a sense resistor in series with the diode sensor as suggested in one of the literature (Appendix E- Temperature Measurement system). I need to do all these things on a PCB and not using any external current source like model 121 DC current source. Please suggest me a right track to go ahead. I have attached the image of the set up where it is going to be used.
Post by Lake Shore Jeff M on Oct 16, 2017 14:46:58 GMT -5
Although the current source you have selected sounds like it can work, there are many other considerations that need to be taken into account. Exciting the sensor with a 10uA current source will produce voltage across the sensor that is dependent on the temperature the sensor is measuring. You will need to design a voltage measurement circuit that can feed the measured voltage into a processor which can perform a calculation to determine what temperature the sensor is measuring. This calculation is done by doing a straight line interpolation between the two sensor calibration curve breakpoints that are directly above and below the measured voltage. You would then need to have the ability to write that information to a display.
Other than trying to design a circuit, I suggest you consider purchasing one of the Lake Shore Temperature Monitors such as the Model 211 which can do everything you are trying to design.
Thank you for addressing my question and replying appropriately and also for the suggestion regarding buying one of your instruments. Please answer a few more doubts of mine, it would help take a right path further. I would like to know if you have relation defined between dv/dt, V and K(Temperature), or please suggest me some materials to find an equation or relation for the same. Also quoting from your reply: " This calculation is done by doing a straight line interpolation between the two sensor calibration curve breakpoints that are directly above and below the measured voltage." Please let me know the meaning of the above sentence, and also what do you mean by " a straight line interpolation between the two sensor calibration curve breakpoints" How to identify the sensor calibration curve breakpoints? Kindly do the needful. Thanks in advance.