Safety device at remote control of hydraulic or pneumatic machine tools

A safety device at the remote control of hydraulic or pneumatic machine tools where electric signals are used for controlling hydraulic or pneumatic valves, typically in machines comprising a selector valve for different hydraulic functions, which is provided with a plurality of spring-centered slides and two electrohydraulic or electropneumatic converters (N) connected to each slide, where a control unit is provided to transfer orders to a receiver unit (H), which in its turn controls said converters, and the output of said receiver unit is connected to signal converters (L) and amplifiers (M) for amplifying received signals and controlling said converters (N), wherein the output of the receiver unit also is connected to a zero-detector (P), which is capable, after a certain predetermined time from detection that there is no output signal from the receiver unit (H), to detect whether or not there is an output signal from the respective amplifier (M), and when there is an output signal from the respective amplifier (M) although there is no corresponding signal on the output of the receiver unit (H), to break the current supply to said amplifier (M).