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)

PTOA Readers and Students should not be overly concerned about understanding the P&ID excerpt at the top of this PTOA segment.

The primary focus of this segment is about learning to recognize ISA P&ID symbols for DCS architecture.

Not so long ago, PTOA Readers and Students began their PTOA self-study by learning about monitoring the process variable Temperature with TIs that look just a whole bunch like the common thermometer.

Building upon this fundamental understanding of Temperature as a sense of hotness or coldness, PTOA Readers and Students have learned important information about how Process Operators and Control Room Operators use control technology to turn raw materials into desired final products.

Anybody feeling a bit overwhelmed? Not to worry!

A "PTOA Deja Vu Review" is coming up and will help put the maze of information into perspective!

PROCESS PIPING AND EQUIPMENT DOES NOT EVOLVE
AS FAST AS INSTRUMENTATION TECHNOLOGY

Figuring out where the pumps and pipes, valves, vessels, towers, etc. are located in a processing facility has always been an easy exercise; just walk out to the processing area and there they stand.

For example, the above P&ID excerpt from a real P&ID features a piece of temperature-changing equipment with the tagname 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 picture to the right.

A new Process Operator would not have a problem finding E-1004, even if the process stream lines flowing into and out of it were not painted in bright colors.

Otherwise stated, the "P is for Piping" part of a Piping and 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 and Instrumentation Diagram changes as fast as computer technology does.

The ISA is challenged to update P&ID symbols to keep up with the ever evolving high-tech Distributed Control Systems (DCS) in use at process facilities.

Furthermore, the expansion of ISA P&ID symbols for DCS must mesh with the existing detecting and measuring hardware that has not evolved as rapidly.

THE NEED TO INCORPORATE
OLD WITH NEW PROCESSING TECHNOLOGIES

PTOA Readers and Students are already aware that the automation of process control has evolved from relying on outside Process Operators to be responsible for local control instruments into centralizing the indicating, controlling, and recording functions with board-mounted instruments located in a control room.

PTOA Readers and Students are also already aware that computer age technology resulted in upgrading automated process control systems to Distributed Control Systems (DCS).

The many benefits of DCS systems were discussed in previous PTOA segments. Any new processing facility would incorporate DCS control.

Just like remodelling an existing house, the effort to retrofit a control room from a board-mounted to DCS architecture is more costly and complicated than starting with a DCS system from the beginning. For these reasons, most facilities that upgrade their processes to incorporate DCS do so in a step-wise plan.

Depending upon the age of the automated process control in use at a facility, today's modern Process Operator must be aware that process control components 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.

ISA DCS SYMBOLS

ISA decided that DCS instrumentation would be differentiated by drawing square boxes around instruments that were part of a DCS system.

PTOA Readers and Students are already aware 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.

An illustrated example of a P&ID DCS Temperature Indicating Controller is below. The example also reviews local and control room instruments and transmission signal types.

TEMPERATURE CHANGING EQUIPMENT
AND ISA DCS SYMBOLS FOR TEMPERATURE CONTROL

E-1004 is a temperature-changing piece of equipment called an Exchanger. All instruments involved with temperature control for E-1004 have the tag number 10045.

The P&ID excerpt at the top of the page is shown again at the right for easy reference (however, the bigger version up top is much more clear).

There is a process flow line that appears to come out of the left-side top of E-1004.

On the drawing, the flow appears to take a left hand turn and then flows downward and off of the page. In the real plant, of course, the real piping doesn't necessarily turn as shown on a P&ID schematic.

TE 10045 senses the process stream temperature and transmits an electrical signal to the controller.

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 drawing to the left.

PTOA Readers and Students will eventually learn exactly how TE 10045 senses temperature.

PTOA Readers and Students already know that TE 10045 is located in the processing plant area because the tag name is written into a clear circle.

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.

TE 10045 transmits an electrical signal to Temperature Indicating Controller 10045 (TIC 10045). A capital letter "B" points to TIC 10045 in the graphic on the right.

PTOA Readers and Students know the signal between TE 10045 and TIC 10045 is electrical because it is drawn with dashed lines.

TIC 10045 is 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 alerts the P&ID reader that the controller can be interacted with on multiple computer screens that are located in the control room. 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 function of TY 10045 is to change the input electrical signal into a pneumatic signal.

The TIC 10045 Output signal is sent to Temperature Transducer 10045 (TY 10045). A capital "C" shows where TY 10045 is in the control loop.

As shown in the graphic to the right, the output signal from TIC 10045 to TY 10045 is electrical. How do PTOA Readers and Students know that?

TY10045 is also a local instrument, meaning it is located in the processing area. How do PTOA Readers and Students know that?

The function of TY 10045 is to take the incoming electrical signal and change it into a pneumatic signal. Transducers are very interesting control loop components that PTOA Readers and Students will learn about later.

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

The pneumatic output signal from TY 10045 is the input signal to Temperature Valve 10045 (TV 10045, shown by the capital "D" in the diagram on the right).

PTOA Readers and Students know the output signal from TY 10045 is pneumatic because this line is drawn with double hash marks at spaced intervals.

TV 10045 is a pneumatically actuated valve. The air line is drawn to the mushroom cap at the top of the valve.

PTOA Readers and Students will eventually learn exactly how the components of Temperature Control Loop 10045 work together with Exchanger 1004 to keep the process temperature where desired.

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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