In an actuator device for hard disks a suspension element carries a slider that is subject to undesired vibrations which give rise to rotations of the slider with respect to a nominal position. Credentials from one system are placed on a client, such as with a cookie on a browser, and the credentials are then extracted by another system, and used by system 1 to impersonate the client to system 2. The time constant of the time constant circuit comprising a R0 and C is adjusted according to whether a resistor R1 is present or not, and the signals of frequencies f1 and f2 coming out of the sawtooth wave generator 14 are sequentially switched to be sent to the comparator 12.