| 摘要 |
PROBLEM TO BE SOLVED: To improve the reliability of the detection of disconnection in a burden resistor by connecting in parallel with the burden resistor a neon discharge tube the discharge starting voltage of which the voltage across the terminals of the burden resistor is below when the burden resistor is in normal operation, and making the neon discharge tube generate a voltage above the discharge starting voltage if the burden resistor is disconnected. SOLUTION: A neon discharge tube 7 the discharge starting voltage of which the voltage across the terminals of a burden resistor 2, connected across both the terminals of a direct current source 1, is below when the burden resistor 2 is in normal operation. When the burden resistor 2 is in normal operation, therefore, the neon discharge tube 7 does not start discharge and thus does not light up. If the burden resistor 2 is disconnected, a voltage exceeding the discharge starting voltage is applied to the neon discharge tube 7. Accordingly, the neon discharge tube 7 is actuated and emits light. Further, excessive voltage is prevented by the discharge operation characteristics of the neon discharge tube 7. In a small current range a lighting circuit 8 in parallel connection accumulates the lighting energy of the neon discharge tube 7 and intermittently lights the neon discharge tube 7. |
