1. The problem statement, all variables and given/known data AD590 is a temperature sensor, through which a current of 1µA/K flows. AD590 is a sort of temperature sensitive transistor and can be interpreted as a current source. With two such sensors, you would like to measure the difference between temperatures T1 and T2 using a DMM. How to connect the sensors if you only have resistors of any kind and the two supply voltages + 12 V and - 12 V at your disposal? Draw a circuit, as simple as possible. 2. Relevant equations Ohm's law, Kirchhoff's circuit laws. 3. The attempt at a solution I came up with this circuit. The temperature sensors are the double ring symbols. Vcc=12V. I imagine that depending on the current I1 from e.g. the sensor in the left branch, the potential will fall 1k*I1 over the resistor to the left. The corresponding thing happens in the right branch, but with a different current I2. So now you should be able to read the temperature as the potential difference U. The temperature difference should be the the value for the potential difference measured in mV. https://www.physicsforums.com/attachment.php?attachmentid=18447&stc=1&d=1239647527 But the correct answer is the following (temperature sensors are the circles with arrows inside): Questions 1) Is my solution also correct? If not, why? 2) I understand that due to Kirchhoff's current law, you will have the difference in currents through the horizontal branch in the second drawing above. But a) why do I need two voltage sources (batteries)?, and b) why do I need a grounding point?, and c) is this grounding point the real planet earth, or is it just a reference potential? and finally d) if it's a reference potential, where is it really connected to the rest of the circuit? (I'm always getting confused when talking about grounding...) Any help appreciated!