METHOD FOR DISCRIMINATING KIND OF PRINTING SHEET IN SERIAL PRINTER

PROBLEM TO BE SOLVED: To discriminate the kind of a printing sheet correctly by judging the kind of the printing sheet by judging whether the difference in the approach quantity of a print head is more than or equal to a prescribed value or not when the change quantity of pulse frequency associated with the change of the distance of a pair of magnetic substances exceeds the first and second standard values by the approach to a printing sheet. SOLUTION: During non-printing, the distance between a magnetic coil sensor 5 and a magnetic piece is kept constant, the pulse frequency from an LC oscillating circuit 15 connected to the sensor 5 changes when a ribbon protector contacts a printing sheet. A count circuit 13 counts the pulse from the circuit 15 and outputs the count value to a control part 11. The control part 11 compares the value with a standard value and judges whether the difference is a prescribed value or not, and judges whether the change quantity of the pulse frequency exceeds the first and second standard values. When the quantity exceeds both standard values, the difference in the approach quantity of a print head at that time is calculated, and the kind of the printing sheet is judged by judging whether the difference is more than or equal to a prescribed valued or not.