Abstract: In an automatic recording instrument having a thermal recording-pen to record on a heat sensitive recording-paper, an operational amplifier output supplies the heating current to the thermal pen through a resistor. A non-linear transfer element receives the output voltage of the amplifier and delivers a voltage having a predetermined non-linear relation to its input. The voltage difference between the output of the non-linear transfer element and the junction point of the thermal pen to the resistor is feedback connected to the input of the amplifier. When the relative velocity between the pen and the paper is increased, the input voltage of the amplifier is increased to increase the output voltage, and when the output voltage is increased, the resistance of the thermal pen is increased to balance to the output of the non-linear transfer element for reducing the input to the amplifier.

Abstract: A thermal pen of thick film type comprises a thermal pen tip and a thermal pen tip holder connected to the thermal pen tip for holding the thermal pen tip. The thermal pen tip comprises a high resistance substrate formed in the form of a pen point, a heater element formed in the form of a thick film on the end of the pen point of the high resistance substrate and an electric conductor formed in the form of a thick film so as to connect to the heater element. The thermal pen tip is preferably provided with a heat-resistant protective coating to cover the end of the pen point. A heat- and wear-resistant heat-sensitive recording piece is preferably provided in a heat conductive relation to said heater element.