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

ISA Nomenclature for "Field-Mounted" Instruments

The ISA realized that P&ID symbols needed to evolve so that they could alert P&ID readers which instruments were in the processing area and which were located in a control panel of a Control Room.

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.

 

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.

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 graphic to the left is a simplified P&ID that shows flow through a piece of PV Temperature-changing equipment called a Shell-and-Tube Heat Exchanger.

PTOA Readers and Students will soon understand the graphic completely so do not fret about that now.

Focus on the ISA symbol with the Tag Name TC1. Smart PTOA Readers and Students know the Tag Name translates into "Temperature Controller 1."

What features of the ISA symbol for TC1 can be decoded by PTOA Readers and Students so that they know the hardware of TC1 is in the processing area?

 

ISA Nomenclature
for Control Room Instruments

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...

the ISA symbol would be slightly altered.

 

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 identified this FIC from every other FIC in the processing plant.

 

Just like with local instruments are shown on a P&ID, a faint line would be drawn from the circle to the place where the control room instrument was located...like on a process flow line or on a piece of equipment.

.

Would the FIC 55 hardware be just randomly hanging around and hard to find in the control room? Heck no!

The symbol infers that FIC 55 would logically be found in a control panel like the ones shown in PTOA Segment #10, perhaps in a Control Room as shown in the nearby photo.

Another way of describing the whereabouts of the instrument is to say it is "board-mounted" because the instrument will be found on one of the control board panels in the Control Room.

 

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

The nearby list of ISA symbols indicates some of the hardware is located in the Control Room.

For example …

PTOA Readers and Students already decoded that FIC 55 is board-mounted and will be found in a control panel in the Control Room.

The ISA symbols also reveal that Pressure Indicating Controller 105 (PIC 105) and Level Transmitter 65 (LT 65) are also board mounted in the control panel of a Control Room.

The ISA symbols on the chart hint that seven other instruments on the list below are 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.   

 

©2015 PTOA Segment 00011
Process Industry Schematics

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