Transducer impedance measurement for hearing aid

A hearing aid, comprising:

• a transducer that stimulates the anatomy of a patient;
• and
• an amplifier electrically connected to the transducer;
• wherein the hearing aid has an operational mode in which the transducer stimulates the anatomy of the patient in response to ambient sound from around the patient;
• wherein the hearing aid has a test mode at a predetermined test frequency;
• wherein in the test mode:
• the amplifier receives a periodic input signal at the test frequency;
• the amplifier produces a primary output signal electrically connected to the transducer;
• the primary output signal is periodic at the test frequency;
• the primary output signal has a predetermined peak primary output current;
• the primary output signal has a periodic primary output voltage flowing through the transducer;
• the amplifier produces a secondary output signal that is a scaled version of the primary output signal;
• a voltage is recorded from one of the primary and secondary output signals;
• a current is recorded from the other of the primary and secondary output signals;
• and
• an impedance of the transducer at the test frequency is determined from the recorded voltage and the recorded current.