Dispositivo de diagnóstico de estado de señal para la activación de un medio de control externo cuando se alimenta con potencia eléctrica de accionamiento mediante una señal de activado/desactivado transmitida a través de un medio de aislamiento

This aims to provide a signal status diagnosing device for an external control means, which is enabled even by a simple constitution to prevent the rise of a production cost due to the increase in a parts count or the complexity of a circuit constitution, and which can perform a signal status diagnosis of an actuator (the external control means) such as an electromagnetic valve, a lamp, a relay or a small-sized DC motor precisely. The signal status diagnosing device comprises a switch circuit connected with an intermediate tap disposed on the primary side of a transformer, for sending a driving electric power to the external control means disposed on the secondary side, in response to an ON/OFF signal of the external control means, and a means connected with the switch circuit and driven by the external control means, for measuring the primary side electric current to flow in a manner to correspond to the electric current to flow to the transformer secondary side. The signal status diagnosing device diagnoses the signal status of the external control means in accordance with the measurement result of the current measuring means.