An apparatus includes at least one sensor, a connector and a conversion unit. The sensor is coupled to a patient body so as to measure a physiological parameter of the body. The connector coupled to a patient monitor, which measures a value of the physiological parameter by applying a test signal via the connector and measuring a response signal on the connector in response to the test signal. The conversion unit is coupled between the at least one sensor and the connector, and is configured to determine a corrected value of the physiological parameter, to calculate an auxiliary signal that, in combination with the test signal produced by the patient monitor, causes the response signal on the connector to represent the corrected value of the physiological parameter, and to generate and output the auxiliary signal to the connector so as to cause the patient monitor to measure the corrected value.
