Abstract: A device and process for determining the uniformity of a superconducting film's critical current density and transition temperature over a large area uses an array of ac coils placed in close proximity to a superconducting film. A variable ac current is passed through each coil which induces a proportional current in the superconducting film. A lock-in amplifier set to the third harmonic of the ac current is put in parallel with the ac current source. When the current in the film exceeds the critical density of the film then the third harmonic is picked up by the lock-in amplifier. In this way one can measure the critical current density of the film at each of the coils. The above coils are mounted within a flat plate (the film side of the substrate is placed against the plate). The entire assembly is cooled within a cryostat so that the temperature can be precisely controlled.