| 摘要 |
PURPOSE:To prevent the effect of high voltage noise and to protect the inside of a controller from a burn-out fault even when a transmission line is connected wrongly by connecting an overvoltage absorbing circuit to the transmission line and disconnecting the transmission line when an overvoltage takes place in the transmission line. CONSTITUTION:A switching element 29 is driven in response to a transmission data and a data is sent to an opposite controller through transmission lines 23, 24. Further, a data signal from the opposite controller is inputted via a photocoupler 27 and inputted to an electronic circuit in the inside of the controller and since a varister 25 is connected to the transmission line 24 is such a case, the overvoltage over the critical voltage of the varister 25 is not applied to the inside of the controller. Thus, burn-out of an electronic circuit in the inside of the controller is prevented. Further, if an overvoltage is fed to the transmission lines 23, 24 due to mis-wiring, a large current flows to the circuit of the varister 25, a fuse 26 is blown by the current and the controller is disconnected from the transmission lines 23, 24 being a cause to the application of overvoltage.
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