SAMA drawing is a particularly important engineering drawing. Although there are some standard legends at present, each instrument company still has its own special graphic symbols in engineering design. SAMA legend is characterized by clear flow, especially complex circuits, which are easy to draw and read. The input-output relationship and flow direction of SAMA diagram are close to those of DCS control configuration diagram, and all control algorithms are clearly marked. Most international instrument companies use SAMA diagram to design control projects. Although SAMA legends of different companies are different, many symbols of SAMA diagrams are universal. There are four commonly used SAMA legends, which respectively represent the following meanings: (1)δ stands for measurement or signal reading function; It is usually used to represent information read from field sensors or transmitters. (2) □ stands for automatic signal processing: it is generally used to represent the functions of instruments (or algorithm modules) in the control station (cabinet). (3) ? 7? 0 stands for manual signal processing: it is generally used to indicate the function of the operating station (equipment). (4)