SAMA Diagrams- IV

Rectangular blocks such as the , P, I, and D shown in this diagram represent automatic
functions. Diamond-shaped blocks such as the A and T blocks are manual functions which must
be set by a human operator. Showing even more detail, the following SAMA diagram indicates the
presence of setpoint tracking in the controller algorithm, a feature that forces the setpoint value to
equal the process variable value any time the controller is in manual mode:

Here we see a new type of line: dashed instead of solid. This too has meaning in the world of SAMA diagrams. Solid lines represent analog (continuously variable) signals such as process variable, setpoint, and manipulated variable. Dashed lines represent discrete (on/off) signal paths, in this case the auto/manual state of the controller commanding the PID algorithm to get its setpoint either from the operator’s input (A) or from the process variable input (the flow transmitter: FT).