ISA SYMBOLS ARE TELL-TALE SIGNS

The ISA symbols with clear circles represent instrument hardware found in the processing area. The ISA symbols with lines at the diameter represent instrument hardware found in the control room.

Sign, sign...Everywhere a sign.
Blockin' out the scenery, breakin' my mind.
Do This! Don't Do That! Can't you read the sign?

("Signs," by Les Emmerson
sung by the Five Man Electrical Band, 1970-71)

ISA NOMENCLATURE REVEALS
WHERE THE INSTRUMENT HARDWARE CAN BE FOUND

This is a P&ID snippet of Temperature Control Loop T10045. Which instruments are located out with the pumps and pipes (aka, "local") and which instruments are located in the Control Room (aka, "remote")?

Brilliant PTOA Readers and Students ... meaning those who are reading the PTOA Segments in the intended, sequential order ... recently learned in PTOA Segment #9 that the invention of the Pneumatic Transmitter made it possible to concentrate control and oversite of a process plant in a cool thing called a "Control Room."

Thus, the ISA realized that P&ID symbols needed to evolve so that they could alert P&ID decoders which instruments were in the processing area with the pumps and pipes and which instruments were located within the control panel of a Control Room.

ISA Nomenclature for "Field-Mounted" Instruments

A "Field Mounted" Temperature Recorder (TR).

As PTOA Readers and Students learned in PTOA Segment #7, the ISA had already established that hardware located in the processing area would be drawn with Tag Names written into clear circles.

This list of ISA symbols represents PV Temperature instruments that "field mounted" ... out with the pumps and pipes ... because the letters are drawn in clear circles. Unfortunately there are no Control Loop numbers in the bottom half of the circle. A complete Instrument Tag Name will have a Tag Name abbreviation on top and a Tag Number on the bottom.

These instruments are also sometimes referred to as "field mounted" because they are located "out in the field" somewhere in the processing plant area.

The nearby chart of PV Temperature-related ISA symbols indicates that each of the instruments are located in the processing area … aka "field-mounted."

On a P&ID the Tag Name names would be more complete.

Fred the Stick Man is keeping up with the Process Technology and Operator Academy.

A unique Tag Number is part of the Tag Name. The Tag Number would typically appear in the lower half of the circle.

Uh-oh. Fred is confused! No stress, Fred. Just keep reading!

Simple Heat Exchanger P&ID
Shown with Local Temperature Controller

The nearby graphic is a simplified P&ID illustrating process flows through a piece of PV Temperature-changing equipment called a Shell-and-Tube Heat Exchanger.

Is Temperature Controller 1 located in the field or in the Control Room?

Focus on the ISA symbol with the Tag Name TC1.

Brilliant PTOA Readers and Students have already figured out that the Tag Name translates into "Temperature Controller 1."

The ISA Symbol for TC1 reveals whether it is out with the pumps and pipes in the processing area (aka "local") or in the Control Room (aka "remote").

Hint: The circle is clear.

ISA Nomenclature
for Control Room Instruments

A Pneumatic Control Room.

The ISA decided that when hardware …

like a Controller or a Recorder or an alarm in an Annunciator Panel …

was located away from the processing area...

which means in a Control Room ...

the ISA symbol would be slightly altered.

For example,

The nearby ISA symbol for Flow Indicating Controller 55 (FIC 55) is located in a Control room.

How do PTOA Readers and Students know FIC 55 is located in the Control Room?

A circle is drawn with a definite line across the horizontal diameter.
The letters of the Tag Name are written above the diameter line. Just like the local instrument tag names, the letters of control room instruments would indicate which process variable the instrument is dedicated to (T=Temperature, P=Pressure, F=Flowrate, or L=Level) followed by letters that defined the function and type of instrument.
The Tag Number of the instrument is written below the diameter line. The Tag Number "55" uniquely identifies this PV Flowrate control loop from every other PV Flowrate control loop in the processing plant.

Furthermore, and just like all local instruments shown on a P&ID, a faint line would be drawn from the circle to the place where the control room instrument was located. This information would hint at whether the instrument could be found on a process flow line or on a piece of equipment.

For example ....

Would the FIC 55 hardware be just randomly hanging around the Control Room and be hard to find? Heck no!

The hardware represented on the above list of instruments as ISA symbols with lines drawn through the horizontal diameter of the circle could be found in a control room like this one.

The ISA symbol infers that FIC 55 is a single unit Flow Indicating Controller and perhaps looks very similar to the "board-mounted" instruments found in the Control Room shown in the nearby photo.

What other Instruments on the nearby ISA Symbol List
Could Be Found in a Control Room?

Scan the nearby chart of ISA Tag Names.

Beside PIC 105 and LT 65, what other Instruments are located in the Control Room?

Brilliant PTOA Readers and Students are ready to decode the ISA nomenclature. FIC 55 once again appears at the bottom of the chart.

Like FIC 55, Pressure Indicating Controller 105 (PIC 105) and Level Transmitter 65 (LT 65) are board-mounted instruments which are located in the Control Room.

The ISA symbols on the chart hint that seven other instruments on the list below are also located in the Control Room.

Which instruments are they?

Simple Heat Exchanger P&ID
with Board-Mounted Controllers in a Control Board Panel

The below graphic is a simple P&ID of another Heat Exchanger. PTOA Readers and Students will soon know how to interpret the flows through the Heat Exchanger so do not fret about that now.

For now, PTOA Readers and Students just need to recognize that the ISA symbols reveal that FC 1 and FC 2 (Flow Controller 1 and Flow Controller 2) are located in the Control Room.

How do PTOA Readers and Students know the FC 1 and FC 2 are located in the Control Room?

What other instrument represented as an ISA symbol in the drawing can be found in a control room?

What Process Variable is this instrument concerned with and what is the function of the instrument?

Hint: T is for Temperature!

Take Home Messages: The ISA created P&ID symbols that inform the P&ID decoders where the instrument hardware can be found in the processing plant.

The ISA Tag Names of local (aka "field mounted") instruments are drawn in clear circles.

"Board-mounted instruments" are not "field mounted." "Board-mounted instruments" are located in a control panel in the Control Room.

Both local and Control Room ISA P&ID symbols use the same conventions for the letters of the Tag Name:

The first letter represents the process variable (T for Temperature, P for Pressure, F for Flowrate or L for Level)
The second and third letters indicate the function of the instrument and what kind of instrument it is. For example, the ISA tag name FIC 55 is translated as "Flow Indicating Controller #55."

The ISA Symbol for a "board-mounted instrument" is a circle with a horizontal line drawn at the horizontal diameter.

The Tag Name of a board-mounted instrument have the instrument identifying letters in the top half of the ISA symbol and the Tag Numbers below in the lower half of the ISA symbol. The Tag Numbers uniquely identify the instrument from all other similar-type instruments.

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