A method of initializing a sensor for monitoring a patient, comprising: driving, by a patient monitor, an oximetry sensor at a first current level, the oximetry sensor comprising an LED; measuring, by the patient monitor, a first voltage across the LED at the first current level; driving, by the patient monitor, the pulse oximetry sensor at a second current level; measuring, by the patient monitor, a second voltage across the LED at the second current level; and determining, by the patient monitor, a voltage/current curve for the LED using the measured first voltage and measured second voltage; characterised in that the method further comprises: projecting, by the patient monitor a next sensor voltage based at least on the first and second voltages by projecting the voltage/current curve for the light emitter to a point that it intersects a voltage/current curve for voltage available from the patient monitor to drive the LED; identifying a third current level that could produce the projected next sensor voltage, wherein the third current level is a maximum emitter drive current that can be provided by the patient monitor to the LED in the sensor;comparing, by the patient monitor, the determined maximum emitter drive current to a check value for the sensor, the check value comprising a lowest acceptable maximum current for driving the LED; and producing an alarm in response to the comparison. driving, by a patient monitor, an oximetry sensor at a first current level, the oximetry sensor comprising an LED; measuring, by the patient monitor, a first voltage across the LED at the first current level; driving, by the patient monitor, the pulse oximetry sensor at a second current level; measuring, by the patient monitor, a second voltage across the LED at the second current level; and determining, by the patient monitor, a voltage/current curve for the LED using the measured first voltage and measured second voltage; characterised in that the method further comprises: projecting, by the patient monitor a next sensor voltage based at least on the first and second voltages by projecting the voltage/current curve for the light emitter to a point that it intersects a voltage/current curve for voltage available from the patient monitor to drive the LED; identifying a third current level that could produce the projected next sensor voltage, wherein the third current level is a maximum emitter drive current that can be provided by the patient monitor to the LED in the sensor;comparing, by the patient monitor, the determined maximum emitter drive current to a check value for the sensor, the check value comprising a lowest acceptable maximum current for driving the LED; and producing an alarm in response to the comparison. projecting, by the patient monitor a next sensor voltage based at least on the first and second voltages by projecting the voltage/current curve for the light emitter to a point that it intersects a voltage/current curve for voltage available from the patient monitor to drive the LED; identifying a third current level that could produce the projected next sensor voltage, wherein the third current level is a maximum emitter drive current that can be provided by the patient monitor to the LED in the sensor;comparing, by the patient monitor, the determined maximum emitter drive current to a check value for the sensor, the check value comprising a lowest acceptable maximum current for driving the LED; and producing an alarm in response to the comparison.