Process Tech & Operator Academy: T is for Temperature

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

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

"T" REALLY IS JUST FOR "TEMPERATURE"

PTOA Readers and Students were introduced to Piping and Instrumentation Diagrams (P&IDs) and ISA Tag Names is in PTOA Segment #6.

In PTOA Segment #7, PTOA Readers and Students became aware that the detail of ISA symbols on P&IDs depends upon whichever general contracting company generated the P&ID.

A P&ID excerpt that depicted Carbon Filter Vessels featured "Temperature Indicators." shown as TIs.

However, a P&ID excerpt that featured Heat Exchangers was more detailed; the "Thermowells" (denoted at "TWs") which protected the "Temperature Indicators" (denoted as "TIs") were shown.

Both of the P&ID excerpts had these things in common regarding temperature-related hardware:

The ISA symbols related to TEMPERATURE monitoring hardware begin with the letter "T."

The last letter in the ISA tag name identifies what kind of temperature instrument it is.

For example:

The "I" in the abbreviation "TI" informs the person decoding the P&ID that the hardware of interest is an "Indicator."

The "W" in the abbreviation "TW" informs the person decoding the P&ID that there is a "(Thermo) Well" in which the temperature sensing device is inserted.

ISA TEMPERATURE SYMBOLS
FOR INSTRUMENTS THAT ARE LOCATED IN THE PROCESSING AREA

These ISA symbols are for temperature-related hardware that is located in the processing area, not in the control room.

A short list of temperature-related ISA symbols for temperature instruments is shown nearby.

PTOA Readers and Students should notice that all of the ISA temperature symbols in the list are drawn with clear circles.

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

Brilliant PTOA Readers and Students … meaning those who are reading the PTOA Segments in the intended, sequential order … already know what a real-world Temperature Indicator and real world Thermowell look like and that their corresponding ISA abbreviations are TI and TW.

PTOA Readers and Students already learned that this TI and TW will be found in the processing area (not in the control room).

But what about TC, TT, and TR?

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

Temperature Controller (TC)
Temperature Transmitter (TT)
Temperature Indicating Controller (TIC)

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

Sometimes gathering readings at specified intervals … like every 4 hours … is not sufficient to keep the process fluid at the desired temperature to maximize process safety and yield.

For that reason, a Temperature Controller (TC) might be installed in the processing area … where all the pumps and pipes are. In other words, not where the cozy control room is.

The ISA tag name for a Temperature Controller uses the ISA abbreviation "TC".

A local Temperature Controller (TC) empowers the Process Operator to make a target process temperature change which will be automatically maintained by the controller.

How the Process Operator makes the process change will be explained in future PTOA Segments so don't stress about that now.

Temperature Indicating Controller (TIC)

This TIC made by Foxboro empowers the outside Process Operator to make temperature changes. The ISA symbol for this device on a P&ID would be a clear circle with "TIC" and the identifying instrument number.

More than likely, the Temperature Indicator and the Temperature Controller are built into the same instrument housing as shown in the nearby photo of a Foxboro brand TIC.

The Process Operator can clearly read the process temperature that is indicated on the scale seen through the glass door. The Process Operator could record the reading and move on to the next reading of interest.

Alternatively, the Process Operator could open the door and make a change in the controller's target process stream temperature.

All Temperature Controllers must have a Temperature Transmitter to translate the signal input to the TC.

The same Foxboro TIC with the cover door open.

For example, the Foxboro brand Temperature Indicating Controllers (TC) will have a Temperature Transmitter (TT) physically situated in the same protective box housing.

The nearby photo shows the same Foxoboro brand TIC with the protective door open. The TT hardware will be physically situated between the temperature sensing/measuring device and the Temperature Controller (TC). .

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

Duo-Function ISA Tag Names

The Foxboro brand TIC featured above had more than one process temperature function performed in the same piece of hardware.

The process temperature was "indicated" and "controlled."

The ISA tag bubble must be adjusted to inform the person decoding the P&ID that the process temperature can be indicated and controlled within the same hardware device. .

For Duo-Function ISA Tags:

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

The second letter in a duo-function device informs the P&ID decoder what additional function is found in 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").

Temperature Recorder (TR)

A local Temperature Recorder (TR) would visually show how process temperature changes over a period of time. The nearby photo shows a typical local chart recorder. Hard to read the units from here but it could be a TR!

A pen draws on the chart as the chart rotates over a specified time interval, like a day.

The Process Operator would change out the charts each day. 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 display 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 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.

In other words,

TRs are useful because they continually record the history of process operations that would otherwise go unnoticed.

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." In the industrial process world "T is for Temperature."

The next initial in an ISA tag name reveals the type of instruments. For example: "I" for "Indicator," "W" for "Well," "C for "Controller, " or "R" for "Recorder."

A third initial in an ISA tag name alerts the P&ID decoder that the instrument is a duo-function device with two functions found in the same device or device housing. The middle initial will reveal an incorporated function within the device. The last initial will reveal what type of device both functions can be found in. For this reason a "Temperature Indicating Controller" … a TIC … will never be a "Temperature Controlling Indicator" because an "indicating type of device" cannot "control."

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The Process Technology and Operator Academy

GIVE ME A “T” FOR “TEMPERATURE”!