| 摘要 |
PROBLEM TO BE SOLVED: To prevent a pointer from swinging out by connecting one coil of a meter drive circuit in parallel with a Zener diode to provide a bypass circuit operating at a voltage higher than a predetermined level. SOLUTION: Coils L1, L2 are wound around a coil bobbin while intersecting perpendicularly. The coil L1 is connected through a resistor R with a power supply voltage Vcc and fed with a constant current I. The coil L2 is connected with a current type sensor providing a current corresponding to the power supply voltage Vcc and a measurement and a current Ic flows through the coil L2 when a current Is is provided from the current type sensor. A bypass circuit 2 comprises a Zener diode and connected in parallel with the coil L2 in the direction for blocking passage of current under normal voltage. When the resistance Rc of coil L2, the current Ih of coil L2 at full-scale, and the Zener voltage Vz are set to satisfy a relationship Vz<=Rc×Ih, the pointer does not swing out for any magnitude of current Is being fed from the sensor.
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