Plotter pen with indicator circuit

Abstract

A technical pen, in particular for use in a drafting instrument such as a plotter, with a writing tube (4) fixed in the front end of a pen tip (1, 2, 3), into which a cleaning wire (5), fastened to the front end of a drop weight body (6), extends, has a device (20, 23, 24) for monitoring the writing fluid level in a buffer chamber (15) disposed between the front end of the inner bore (7) and the back end of the writing tube (4) as well as for activating a conveying means (25) for transporting writing fluid from the inner bore (7) into the buffer chamber (15) when the writing fluid has fallen below a pre-determined level. The buffer chamber (15) is formed centrally symmetrical in relation to the center axis of the writing tube (4) and its inner and outer boundary walls (16, 17) converge from the front to the back. The front area of the buffer chamber (15) is connected with the writing tube ( 4) and the inner bore (7), while its rear area is closed. At least the backwards converging sections of the boundary surfaces of the buffer chamber (15) are made of an electrically conducting material and are each connected with a contact (23, 24) of an electric control circuit. The contacts (23, 24) can be electrically connected by means of the electrically conducting writing fluid, and, when the electrical connection between the contacts (24, 25) is interrupted, the control circuit activates the conveying means (25).