| 摘要 |
PURPOSE:To inform the life of a head and to prevent a printing quality from being deteriorated by detecting the resistance value of the dot of the head at an upper limit thereof. CONSTITUTION:A com5 and a point A always communicate on a head terminal T, dot1 to dotn on the terminal T generate dot selection signal from a dot selector 10 by a dot selection command from a CPU 11, and select an AND circuit 8 from N1 to Nn. Thus, it communicates with B through an OR circuit 9. The points A, B are connected to points C12, D13. Here, when the initial resistance value of the head dot is Rh, this bridge is balanced under the condition of RhR2=R1R3, and a potential difference VEF between points E17 and F18 becomes zero. Since the VEF is the difference of the points E and F, it is represented by VEF=VE-VF. Then. an operational amplifier Op1(19) calculates VE-VF to obtain the VEF. Then, an operational amplifier Op2(20) compares the VEF with a reference voltage E2, and outputs a signal to G21 when the condition EEF>E2 is satisfied.
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