EVER EVOLVING ISA SYMBOLS

You say you want a revolution,
Well you know, we all want to change the world.
You tell me that it's evolution...
Well you know, we all want to change the world.

("Revolution," by the Beatles, 1968)

DECODING THE ISA P&ID SYMBOLS FOR A DISTRIBUTED CONTROL SYSTEM (DCS).

Fred the Stickman is a PTOA Student.

Guess what, Fred?

The fact is that the "P is for Piping" part of a Piping & Instrumentation Diagram (P&ID) has always been relatively straightforward to match up to the real-world hardware.

But the "I is for Instrumentation" part of a Piping & Instrumentation Diagram changes as rapidly as technology does.

Brilliant PTOA Readers and Students ... meaning those who are reading the PTOA Segments in the intended, sequential order ... are "knowed-up" regarding how Outside Process Operators and Control Room Operators use control technology to turn raw materials into desired final products.

PTOA Readers and Students acquired a fundamental understanding of the PV Temperature as a sense of hotness or coldness in PTOA Segment #1.

The modern control room.

PTOA Readers and Students learned in PTOA Segment #9 how the evolution of the modern-day Control Room centralized the indicating, recording, and controlling of Process Variables like the PV Temperature. Simultaneously, the evolution of the modern-day Control Room "invented" the Control Room Operator.

In PTOA Segments #12, PTOA Readers and Students learned how computer-age technology upgraded the automation of process control systems into Distributed Control Systems (DCS). The many benefits of DCS systems were featured in PTOA Segment #13.

ISA Symbols used to decode Piping and Instrumentation Diagrams (P&IDs).

Most recently, PTOA Segments #14 and #15 featured how the hardware and software components in a control loop send signals to each other, which makes it possible to control Process Variables

While all this control technology evolution has been ongoing, the ISA has been challenged to update P&ID symbols to keep up in real-time.

A Distributed Control System.

Currently, Wi-Fi and satellite technology can be incorporated to transmit the status of a PV Pressure or PV Level hundreds of miles away.

And the evolution never stops; the "automizing" of "smart controls" that "talk to each other" would be the way to maximize efficiency and productivity for a brand-new processing plant built today. The role of AI in process control is yet to be determined.

Regardless, the worldwide investment in DCS predicts that the Distributed Control System will be around for a while before it, too, goes the way of the Pneumatic Transmitter and is considered a "legacy control system."

The primary focus of this PTOA Segment is to apply the P&ID decoding skills that PTOA Readers and Students have acquired to this point and extend that knowledge to include how ISA Symbols delineate instruments that are located within a Distributed Control System (DCS).

PROCESS PIPING AND EQUIPMENT DOES NOT EVOLVE QUICKLY
BUT PROCESS INSTRUMENTATION TECHNOLOGY EVOLVES FAST!

A P&ID snippet featuring the Temperature Control Loop surrounding Exchanger E-1004.

The nearby P&ID snippet features a Shell and Tube Heat Exchanger with the tag name E-1004 (Exchanger 1004).

All the gray tubular looking things in this picture are shell and tube heat exchangers.

In real life, E-1004 looks like the gray, tubular pieces of equipment in the nearby photo.

The tubular structure of the Shell and Tube Heat Exchanger has not evolved much at all because its geometry is optimized for its job function.

A spanking new Outside Process Operator would not have a problem finding E-1004, even if the process stream piping were not painted in bright colors as shown.

However, decoding the process instrumentation that helps E-1004 do its job requires more effort.

All of the instrument tag names begin with a "T." The Process Variable Temperature is of great concern to a Shell and Tube Heat Exchanger.

The ISA symbols shown around E-1004 indicate that the PV Temperature is the Process Variable of most concern because all of the instrument tag names begin with "T" ... and "T is for "Temperature!" (refer to PTOA Segment #8).

Brilliant PTOA Readers and Students are aware that the components in Temperature Control Loop 10045 could be located:

in the processing area (local instruments).
in the control room mounted on a panel board.
in a cabinet of a DCS system with modules outside the control room.
as part of the DCS system on a computer screen in the control room.

IDENTIFYING ISA DCS SYMBOLS

Drawing a square box around the tag name of an Instrument means the instrument is part of a Distributed Control System (DCS).

PTOA Readers and Students learned in PTOA Segment #11 that the tag name of an instrument found mounted on the board of a control room has a horizontal diameter drawn through the circle.

DCS components that are visible on screens of the Human-Machine Interface are drawn the same as board mounted instruments...and then a square box is drawn around the circle of the tag name.

Fred, are you ready to figure out which instruments on a P&ID can be found in a DCS?

TEMPERATURE CHANGING EQUIPMENT
AND ISA DCS SYMBOLS FOR TEMPERATURE CONTROL

Temperature Control Loop 10045 controls the Temperature of the process stream that exits the shell side of Heat Exchanger 1001.

Focus on Temperature Control Loop 10045 shown in the nearby P&ID snippet.

Note the process flow line that appears to come out of the top left-side of E-1004. PTOA Readers and Students will eventually learn that this process stream is flowing out of the "Shell Side" of Shell and Tube Heat Exchanger E-1004.

The process flow appears to take a left-hand turn and then flows downward and off of the page. Of course, in the Real-World plant, the Real-World piping doesn't turn as shown on a P&ID schematic. The P&ID schematic is just a schematic!

Point A in Temperature Control Loop 10045: TE 10045 senses and measures the process stream's temperature and then transmits an electrical signal representing the magnitude of the measured Temperature to the Controller, TIC 10045.

Before taking the downward turn, the process stream temperature is sensed by Temperature Element 10045 (TE 10045). TE 10045 is shown near the capital "A" on the nearby P&ID snippet.

PTOA Readers and Students will eventually learn exactly how TE 10045 senses and measure the Process Variable Temperature.

Brilliant PTOA Readers and Students ... those who are reading the PTOA Segments in the intended, sequential order ... already possess the core competency to decode the following information about Temperature Control Loop 10045:

Point B in Temperature Control Loop 10045: The box drawn around TIC 10045 means that it is located in a DCS system. The Control Board Operator interacts with TIC 10045 by a computer screen and keyboard. The Control Board Operator will enter a Set Point Temperature into the TIC 10045.

TE 10045 is located in the processing plant area because the tag name is written into a clear circle.
A capital letter "B" points to TIC 10045 in the nearby graphic. TIC10045 must be located in the control room because a horizontal diameter line divides its tag name circle.
TIC 10045 is also part of a DCS system because a box is drawn around the tag name circle. The box around TIC 10045 also alerts the P&ID reader that the controller can be interacted with on multiple computer screens that are located in the control room.
TE 10045 transmits an electrical signal to Temperature Indicating Controller 10045 (TIC 10045). The signal from TE 10045 to TIC 10045 must be electrical because it is drawn with dashed lines.

Guess what?

The Control Board Operator will interact with TIC 10045 by using a keyboard, or a mouse, or maybe even a touchscreen that is part of the Human-Machine Interface.

The Control Board Operator will perform the important action of entering a Set Point Temperature into TIC 10045. The Set Point Temperature is the value of the Process Variable Temperature ... the PV Temperature ... desired at TE 10045.

A capital "C" in the nearby P&ID snippet shows where some kind of mysterious piece of control hardware called TY 10045 is located between TIC 10045 and Temperature Valve TV 10045.

Point C in Temperature Control Loop 10045: The function of TY 10045 is to change the input electrical signal into a pneumatic signal.

The tag name of TY 10045 infers this instrument is physically located "in the field" out with the pumps and pipes because the tag name is in a clear circle.

The function of TY 10045 is to take the input electrical signal and transduce the signal (aka "transform the signal") into a pneumatic signal. The input signal is most likely a 4-20 mA signal. The output signal is mostly likely a 3-15 psig Instrument Air signal.

Transducers are very interesting control loop components that PTOA Readers and Students will learn about later in the PTOA Instrumentation Focus Study Area.

The pneumatic signal to the actuate on TV 10045 will make it open more, close more, or hold its current position.

Focus on Point "D" in the nearby P&ID snippet. The pneumatic output signal from TY 10045 is the input signal to pneumaticallly actuated Temperature Valve 10045, aka TV 10045. The mushroom-shaped top represents the Pneumatic Actuator that uses Instrument Air to open and shut the valve.

Keep up the great work!

PTOA Readers and Students will eventually learn exactly how the components of Temperature Control Loop 10045 work together with Exchanger 1004 to keep the PV Temperature at the desired Set Point Temperature.

Take Home Messages: Today's modern Process Operator must be aware that, depending upon the age of the processing facility, components of automatic process control can be distributed throughout the processing facility.

ISA P&ID symbols will inform the Process Operator and Control Room Operator where the control components are located.

DCS control components that are viewable and/or accessible on DCS screens will have ISA symbols with square boxes drawn around them.

Exchangers like the one featured on the P&ID and in the picture are temperature-changing equipment.

The P&ID excerpt featuring E-1004 also illustrated electrical and pneumatic signal transmission and differentiated local from control room instruments.

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