| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of parts, which hardly affects the temperature change or reduce power consumption by connecting a resistor to a coil for detection in series, and by utilizing the transient phenomenon of a circuit that does not use capacitance portion. SOLUTION: A time pulse generator T, with a time constant that is the same as one that can be estimated in advance based on a calculation expression or is slightly shorter than that, is provided inside, a drive power supply E which is turned on by a switching element S by a drive signal D, and at the same time the generator T is started. A signal waveform from a coil L for detection once passes through a waveform-shaping circuit W for converting into a rectangular wave, and a polarity is inverted by an inverter I. Difference is generated in the time width of a detection signal corresponding to the presence or absence of a metal object on the coil L for detection. By comparing the signal with the signal of the time pulse generator using a gate circuit G, the presence or absence of the metal object can be detected, by the difference between the two signals. Especially, since a device for receiving the signal does not exist, stable operation can be made without mutual interference, even when the same devices are installed adjacent to each other. |
