PLC relay failure diagnosis circuit

摘要

PROBLEM TO BE SOLVED: To provide a failure diagnosis circuit of a PLC relay capable of diagnosing a failure of a diagnosis signal transmission circuit and a diagnosis signal reception circuit. A failure diagnosis circuit (10) includes a relay A (20A) and a relay B (20B) connected in series, a diagnosis signal transmission circuit (31) for transmitting a diagnosis signal to an output point (21), and the like. A transmission circuit diagnostic circuit (32) that receives a signal from the input point (22), a diagnostic signal reception circuit A (35A) that receives a signal from the detection point A (25A), and a reception that transmits a signal A to the detection point A. Circuit diagnostic circuit A (36A), diagnostic signal receiving circuit B (35B) that receives signals from detection point B (25B), receiving circuit diagnostic circuit B (36B) that transmits signal B to detection point B, and transmission. Diagnosis of failure of diagnostic signal transmitting circuit, diagnostic signal receiving circuit A, diagnostic signal receiving circuit B, relay A, and relay B based on the reception results of the circuit diagnostic circuit, diagnostic signal receiving circuit A, and diagnostic signal receiving circuit B. A control unit (38) is provided. [Selection diagram] Fig. 1