| 摘要 |
PURPOSE: To enable frame detection simply at low cost by outputting signals which represent scopes of a first and a second frame current levels. CONSTITUTION: A circuit 10 makes a capacitor 50 generate a voltage which is increased as time elapses at a rate which is substantially proportional to the magnitude of a frame current IF which passes through from an electrode 12 to an electrode 14. A processor 38 samples a condition of a port 49 per cycle of a supply device 18 and judges that a frame 16 is between the electrodes 12 and 14 when the condition becomes from low level to high level (threshold value) in a scope of a predetermined number of cycle. Really, the processor 38 judges that the current IF exceeds a predetermined ampere level (the second level) above the threshold value. The processor 38 makes an LED 28 emit light continuously when the current IF is above the second level, makes it flicker when the current IF is above the first level (threshold value) which is below the second level, and turns it off when the current IF is below the first level. |
