An electrosurgical system having first and second units, the second unit being detachably connectable to the first unit and including an electrode assembly. The first unit comprises a power supply, RF oscillator circuit for generating a radio frequency output, and an output stage adapted to supply an RF output to the electrode assembly. The second unit comprises an identification circuit 16 presenting, in an alternating manner, a parameter with a first finite non-zero value for a first time period, and a parameter with a second finite value for a second time period. The first unit includes a sensing circuit (18, Fig. 4) adapted to detect a characteristic of the identification circuit 16 and provide an output signal, and a controller connected to the sensing circuit (18)； upon receiving the output signal the controller adjusts the RF output to suit the particular electrode assembly. The parameter may be capacitance.
