| 摘要 |
PROBLEM TO BE SOLVED: To carry current in proper quantities, regardless of the surface state of window glass by detecting an inflection point changing from a state that a rate of change of current is comparatively small to a state that the rate is large after current carrying and interrupting supply current. SOLUTION: A device measuring a rate of change of current is constituted of a device 7 detecting current, an A/D converter converting the current values into digital values, an arithmetic unit 8 calculating a rate of change of current and a rate of change of the rate of change of current based on the digital values and an operation circuit 6 automatically interrupting supply current based on the result of the arithmetic unit 8. Current values are converted into digital values, a rate of change of current and a rate of change of this rate of change of current are calculated for every fixed time based on the digital values in a computer, the size of the rates of change are compared every time, a signal is transmitted when the value becomes larger and a supply circuit 4 is interrupted by a manual switch 5. A stoppage signal is transmitted by depending on whether the rate of change of the rate of change of current is larger than 1 or not. |
