Abstract: A method for thermal environment sensing utilizing superconducting materi finds utility in the production of low power cryogenic flow meters, bolometers, level detectors and other types of thermal environment sensors. A device for determining the first and second derivatives (dV/dI and d.sup.2 V/dI.sup.2) utilizes a ramped current until a set value of the first derivative (dV/dI) is achieved, the current supply being placed in a feedback mode to maintain the first derivative constant and monitoring any changes in the second derivative (d.sup.2 V/dI.sup.2) which indicate changes in the thermal environment. Alternatively, the second derivative is maintained constant and the first derivative is measured. Any parameter which is indicative of the non-linearity of the relationship between the voltage and the current can be utilized instead of the second derivative.