Patent ID: 8756933

Claim:
A method of determining the ambient temperature of an SMA actuation arrangement comprising an SMA actuator arranged on contraction caused by heating to drive movement of a movable element relative to a support structure, the method comprising: supplying drive current through the SMA actuator, wherein, when the SMA actuator is in an unheated state, the drive current is applied initially to cause a resistance of the SMA actuator to rise to a local maximum resistance; detecting a measure of the resistance of the SMA actuator and controlling the drive current on the basis of the measure of the resistance of the SMA actuator; and deriving a measure of an electrical characteristic of the SMA actuator that is representative of the ambient temperature, said electrical characteristic of the SMA actuator being the difference between the resistance of the SMA actuator in the unheated state when the drive current is initially applied and the maximum resistance of the SMA actuator.