Chart Recorder - Marking Mechanisms

Marking Mechanisms

Many mechanisms have been adopted for marking paper. In the telegraphic siphon recorder of 1858 a fine capillary tube is connected to an ink reservoir and is deflected by the process signal. In modern strip chart recorders a disposable cartridge combining both a fiber-tipped pen and ink reservoir has been used. Other types of recorder use a heated stylus and thermally sensitive paper, an impact printer using a ribbon and an electrically operated hammer, or an electric spark that makes a visible spot on aluminized paper. One form of sensitive and high-speed recorder used beams of ultraviolet light reflected off mirror galvanometers, directed at light-sensitive paper.

The earliest instruments derived power to move the pen directly from the sensed process signal, which limited their sensitivity and speed of response. Friction between the marking device and paper would reduce the accuracy of the measurements. Instruments with pneumatic, mechanical, or electromechanical amplifiers decoupled pen movement from process measurement, greatly increasing the sensitivity of the instrument and the flexibility of the recorder. Directly-driven pens often moved in the arc of a circle, making the scale difficult to read; pre-printed charts have curvilinear scales printed on them that compensated for the path of the marking pen.