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A zero resistance ammeter (ZRA) is a current to voltage converter that produces a voltage output proportional to the current flowing between its to input terminals while imposing a 'zero' voltage drop to the external circuit. In corrosion test a ZRA is typically used to measure the galvanic coupling current between two dissimilar electrodes. An interesting application is when the coupling current between two nominally identical electrodes is measured. If both electrodes were identical then very little coupling current would flow. In real situations these electrodes will be slightly different, one being more anodic or cathodic than the other and a small coupling current will exist.
