"You know, my temperature's risin'
The juke box is blowin' a fuse.."

("Roll Over Beethoven," by Chuck Berry, 1965)

In the previous PTOA segment, two different ISA representations of temperature-monitoring hardware that appear on P&IDs were compared. The "Temperature Indicator" had a tag name that included the initials "TI." The "Thermowell" had a tag name that included the initials "TW."

PTOA Readers and Students will notice two common patterns between these two examples of ISA symbols for temperature-related hardware:

• The ISA symbols related to temperature monitoring hardware begin with the letter "T."
• The last letter that follows "T" identifies what kind of hardware the instrument is. 

The "I" in the TI informs P&ID readers that the hardware is an Indicator.  The "W" in the TW informs P&ID readers that the hardware is a Well in which the temperature sensing device is inserted.

The first letter of an ISA tag name is logically associated to whatever is being monitored or controlled. 

The last letter of an ISA tag name will identify what kind of device the hardware is (for example, "W" for "Well").

 

More ISA Tag Names for Temperature Instruments
That Are Located in the Processing Area

A list of temperature-related ISA symbols for temperature instruments is shown at the top of the page and repeated for easy reference in the graphic at the right.

All of the ISA temperature symbols in the list are drawn with clear circles.

ISA symbols drawn with clear circles inform the P&ID reader that the instrument is located in the processing area of the plant and not in the control room.

PTOA Readers and Students are well aware what a real temperature indicator and thermowell look like and their corresponding ISA abbreviations, TI and TW.

But what about TT, TR, and TC?

What do the ISA abbreviations mean and what does the hardware for TT, TR, and TC look like?

Temperature Controller (TC)
and Temperature Transmitter (TT)

Process Operators perform many more tasks than recording temperature and other status readings.

Sometimes gathering readings at specified intervals is not sufficient to keep the process fluid at the desired temperature to maximize yield and maintain safety.

In that case a Temperature Controller (TC) is installed out by the pumps and pipes in the processing area. The ISA tag name for a Temperature Controller uses the ISA abbreviation "TC".

A local Temperature Controller (TC) empowers the outside Process Operator to make a process temperature change that will maintain the desired operating temperature. How the Process Operator makes the process change will be explained in future PTOA segments.

A picture of a real temperature controlling instrument that could be located in the processing area is to the right.

In this picture at the right the temperature controlling instrument has its protective cover closed.  The outside Process Operator would have to open the door to make a change that would maintain the desired operating temperature. A picture of this temperature controlling instrument with the door open is below and to the left.

The vast majority of Temperature Controllers (TCs) are going to have an assigned Temperature Transmitter (TT) situated between the temperature measuring device and the TC.

Temperature Transmitters (TTs) are very interesting pieces of instrumentation hardware.The job of a transmitter is to transmit the current status of the process temperature to the Temperature Controller (TC) using a signal type that the TC can understand.

How the TT works will be explained in future PTOA segments. For now PTOA Readers and Students just need to know that usually every Temperature Controller (TC) is paired with a Temperature Transmitter (TT).

At this point the PTOA focus is on how ISA symbols are used to represent real process temperature instrumentation hardware on P&IDs.

Temperature Indicating Controller (TIC)

Sometimes the Temperature Indicator and the Temperature Controller are built into the same instrument housing. The photo above is a TIC with the protective door closed. The photo to the left is the same TIC with the protective door open. This TIC would be located in the processing area.

The ISA symbol for an instrument with duo functions is adjusted thus:

The first letter of an ISA tag name is logically associated to whatever is being monitored or controlled (for example, "T" for "Temperature"). 

The second letter in a duo-function device informs the P&ID reader what the function of the device is (for example, "I" for "Indicating").

The last letter of an ISA tag name will identify what kind of device the hardware is (for example, "C" for "Controller").

P&ID readers would instantly understand that this local TIC gives the outside Process Operator the responsibility of observing and controlling the process temperature at the spot where the TIC was located. 

Temperature Recorder (TR)

A local Temperature Recorder (TR) would visually show how process temperature changes over a period of time. The picture to the right shows a typical local chart recorder.

A pen draws on the chart as the chart rotates over a specified time interval, like a day. The outside Process Operator would change out the charts; s/he would remove the completed one at the conclusion of the time interval and insert a fresh chart to begin a new recording time interval.

Note that the TR is not a controlling device.

Nor does a TR have a dial that easily indicates the temperature to a Process Operator as a TI would do.

A TI is limited to showing the current process temperature just when the Process Operator observes it.

The purpose of the TR is to show the trend of temperature changes over a period of time.

A TR records process disturbances as a bump in pen movement. The bump would alert the outside Process Operator that the process had been upset at some point since the current chart had been inserted. The cause of the bump would then be investigated.

TRs are useful because they continually record the history of process operations.

Take Home Messages: All field-mounted instruments (meaning instruments in the processing area) are shown on a P&ID with tag names written into clear circles.

All temperature-related instruments/hardware will be represented on a P&ID with an ISA tag name that begins with "T."

When there is a second initial in an ISA tag name, the P&ID reader knows that the instrument is a duo-function device with both parts built into the same housing. The middle initial will reveal what the FUNCTION of the instrument is. Some examples of function abbreviations are:  "I"=Indicating, "R"=Recording).

The last initial in an ISA tag name reveals the type of instruments. For "I" for "Indicator," "W" for "Well," "C for "Controller."

© 2015 PTOA Segment 00008
Process Industry Schematics

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