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Instrumentation Documents - SAMA Diagrams

SAMA is an acronym standing for Scientific Apparatus Makers Association, referring to a unique form of diagram used primary in the power generation industry to document control strategies. These diagrams focus on the flow of information within a control system rather than on the process piping or instrument interconnections (wires, tubes, etc.). The general flow of a SAMA diagram is top-to-bottom, with the process sensing instrument (transmitter) located at the top and the final control element (valve or variable-speed motor) located at the bottom. No attempt is made to arrange symbols in a SAMA diagram to correlate with actual equipment layout: these diagrams are all about the algorithms used to make control decisions, and nothing more.

A sample SAMA diagram appears here, showing a flow transmitter (FT) sending a process variable signal to a PID controller, which then sends a manipulated variable signal to a flow control valve (FCV):




A cascaded control system, where the output of one controller acts as the setpoint for another controller to follow, appears in SAMA diagram form like this:


In this case, the primary controller senses the level in a vessel, commanding the secondary (flow) controller to maintain the necessary amount of flow either in or out of the vessel as needed to maintain level at some setpoint.

SAMA diagrams may show varying degrees of detail about the control strategies they document. For example, you may see the auto/manual controls represented as separate entities in a SAMA diagram, apart from the basic PID controller function. In the following example, we see a transfer block (T) and two manual adjustment blocks (A) providing a human operator the ability to separately adjust the controller’s setpoint and output (manipulated) variables, and to transfer between automatic and manual modes:



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).


• Click here for the front page of this Instrumentation Documents article

Click here for Process Flow Diagrams (PFDs)

• Click here for Process and Instrument diagrams (P&IDs)

• Click here for Loop diagrams (“loop sheets”)

• Click here for Instrument and Process Equipment Symbols

• Click here for Instrumentation Identification Tags


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Comments (5)Add Comment
written by mohammad, December 22, 2012
hi, thanks for you , please guide me how to download this notes bcs it very nice
written by AS, July 07, 2014
My boss wants me to write a SAMA diagrams but I had no idea what PFD, Loop D, and P&ID are ...

then i found your posts, and you saved my life!
written by Mahesh Kumar Dubey, August 28, 2014
I would like to get registered to view the various topics in instrumentation
written by J Leland Kallmyer, March 12, 2015
Require instructions on developing SAMA diagrams from PI&D.
Consultant Principal Instrument and Controls Engineer PE
written by jerry smith , October 22, 2015
Scientific Apparatus Makers ASSOCIATION. this APPROACH HAS BEEN GOING THROUGH AN EVOLUTION OF THE FUNCTIONS PROCESS FLOW DIAGRAMS. SAMAS REPLACE WRITTEN PROCESS CONTROL DESCRIPTIONS WITH A Functional Diagram of the required correct controls for the process and then converted into a DCS type configuration and or a PLC logic program. SAMAS Diagrams can be a stand a lone document or a bridging document with P&ID'S,FBD'S,LD'S but not PFD'S..

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