OVERVOLTAGE PROTECTION CIRCUIT, ESPECIALLY DETECTING A NUMBER OF PARAMETERS TO THE MEASUREMENT LINE

摘要

PURPOSE: An overvoltage protection circuit is provided to protect a measurement control circuit by suppressing spurious conductive noise of an overvoltage induced to a measurement line while transmitting physical parameter information by detecting a number of parameters to the measurement line. CONSTITUTION: The first protection circuit(201) suppresses the first intrusion of an overvoltage due to the ground of a commercial frequency AC voltage through a gas discharge tube. The second protection circuit(203) comprises a positive temperature coefficient resistor connected to each port of the line to prevent the self over-heating due to a residual over-current of the first protection circuit or over-heating state of the measurement control circuit. The third protection circuit(205) comprises a varistor connected to both ends of the line and between each port of the line and the earth ground to confine a residual over voltage of the first protection circuit and the second protection circuit within a fixed level. The fifth protection circuit(209) comprises an avalanche breakdown diode connected to both ends of the line and between each port of the line and the earth ground to prevent the inflow of a breakdown voltage by suppressing the residual voltage of the third protection circuit. And the fourth protection circuit(207) comprises a linear resistor to suppress the over current of the fifth protection circuit.