When a knob is turned by a predetermined turning angle α and this angle is detected by a rotary encoder, an electromagnetic brake is activated by a controller and the rotation of the knob is locked. Then, while the knob is locked by the electromagnetic brake, the controller determines whether an operating force was applied to the knob in direction A in which the turning angle of the knob is increased. If the controller determines that the operating force was not applied to the knob in direction A (if the operating force was applied in direction B), the locking of the knob is released.

A force-feedback input device comprising an operating section, actuators to supply force-feedback by way of a transmission mechanism to the operating section, a movement quantity detector to detect a quantity of movement of the actuators and a controller to control the actuators by an output from the movement quantity detector. An initializing process is performed by the controller at startup utilizing an output from the movement quantity detector, and an output to the actuators is compensated after startup so that a fixed quantity of force-feedback is supplied to a quantity of movement of the operating section.

A protection device for electrical circuits comprises a frangible container (10) over which an electrical circuit path (14) extends and a substance in the container having a characteristic such that upon occurrence of a condition, such as a low temperature, the substance expands and fractures the container (10) thereby breaking the circuit path (14).

In Figure 1, an electrical circuit on a circuit board 9 can be controlled by operation of switches 2B, 3B, 4B. These are operated by removing portions of the board 9, effected by the snapping off of respective corresponding cover member portions 2A, 3A and 4A.

When used as a thermal log this control can respectively activate, deactivate and display the thermal data but avoid any tampering.