PTOA DEJA VU REVIEW: Numero Quatro, Part #2

Trying once more
One more chance to make it right
Never say never, let's rise up together, take on the world

("Once More" by Spandau Ballet, 2009)

PTOA SEGMENT #97: STRINGING THE PEARLS OF TEMPERATURE WISDOM

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order did not learn one darn new thing in PTOA Segment #97.

Nevertheless, PTOA Segment #97 was strategically important because it threaded the following integrated concepts about the Process Variable Temperature together after each concept had been separately introduced:

Real-world local temperature indicators were correlated to their ISA symbol representations found on P&ID excerpts.
Real-world temperature-changing equipment in the form of a shell and tube heat exchanger was correlated to its corresponding ISA symbol on a P&ID excerpt.
The local and automatic instrumentation devices that work together to control the process temperature of the shell and tube heat exchanger were reviewed as were the signal transmission types between the 4 devices in the control loop.

PTOA Readers and Students were thus reminded that the ability for Process Operators and Control Board Operators to effectively and efficiently convert raw materials into desired final products is totally dependent upon the accurate detection, measurement, indication, and transmission of sensed process stream temperatures.

By the conclusion of PTOA Segment #97, the pump had been primed for PTOA Readers and Students to learn all about temperature detecting and measuring instruments.

Specifically ..

PTOA Readers and Students were alerted to notice the variety of technologies that are used in the instruments which transduce ... meaning change ... the molecular movement caused by temperature changes into temperature indications that human beings can easily understand.

PTOA SEGMENT #98: I USED TO BE HALF EMPTY ... NOW I AM HALF FULL

PTOA Segment #98 focused upon the temperature detection and measurement technology that utilizes the corresponding changes in the physical property known as "volume" (aka: the 3-dimensional space that Stuff/Matter/Mass fits into).

Everybody on Earth is familiar with this technology because it provides the operating basis of all liquid-in-glass thermometers.

Then the content in this extra-long PTOA Segment #98 ramped up considerably to demonstrate how the same temperature-change/volume-change technology found in liquid-in-glass thermometers has been directly applied to detect, measure, and indicate industrial process stream temperatures when linked with a bourdon tube and dial face-with-pointer.

PTOA Readers and Students were reminded several times in this PTOA Segment #98 that changes in the volume of a contained fluid are also known as "density changes." Ergo, references to Volume/Temperature devices are sometimes called Density/Temperature devices.

Prior to reading PTOA Segment #98, most PTOA Readers and Students would not even have dignified the common liquid-in-glass thermometer with an assigned working technology; yet all PTOA Readers and Students would have agreed that no thermometer would be useful without the predictable expansion and contraction of the working fluid that directly corresponds to temperature changes.

The technology that converts the expansion and contraction of the thermometer's working fluid into a temperature indication that human beings can understand was determined to be nothing more than the graduations on the glass stem that enclose the bulb and capillary of any liquid-in-glass thermometer.

PTOA Readers and Students were reminded that one important industrial use of wet and dry bulb thermometers involves the optimization of Cooling Tower operations.

However, the primary use of liquid-in-glass thermometers will be within the Quality Control/Quality Assurance laboratory of the facility; many sampled process streams will have their temperature measured in the laboratory.

PTOA Readers and Students also learned why mercury (Hg) is a convenient and popular working fluid to use in liquid-in-glass thermometers and were also reminded that mercury is highly toxic to human health.

Quietly introduced in PTOA Segment #98 was the alcohol thermometer; it appeared in a bubble toy.

The ability for liquids like alcohol to boil at much lower temperatures than water will reappear in PTOA Segments that focus on how refrigeration and cryogenics work.

Your Mentor predicts that many PTOA Readers and Students were perplexed ... yes, perhaps even bored ... with the detailed explanation and visual aids that were devoted to telling the story of how heat absorption/heat loss results in expansion/contraction of the molecules ... and hence volume ... of the trapped working fluid.

The reason for the blow-by-blow, detailed explanation was to exploit the visual imagery that liquid-in-glass thermometers present because the next application of volume/temperature changes is not as visually obvious:

Fluid-filled detecting and measuring devices that are used to detect and measure process industry temperatures use the same volume changing (aka density changing) principles as liquid-in-glass thermometers ... but their bulbs and capillaries must be enclosed in protective coverings.

Instead of graduations on a glass stem, PTOA Readers and Students learned that the important translation of molecular movement ... first into a mechanical movement and also into a temperature indication ... is performed by a helix-shaped bourdon tube.

The mechanical movement of the bourdon tube (aka "displacement") is linked to a dial face that has a pointer that human beings can easily read and understand.

PTOA Readers and Students learned that the C-shaped bourdon tube shown above provides the crucial transduction function that converts displacement of the tube tip into a pressure indication that human beings can understand; helix-shaped bourdon tubes transduce the mechanical movement caused by volume expansion into temperature indications that human beings can understand.

By the conclusion of PTOA Segment #98 PTOA Readers and Students could figure out that the common liquid-in-glass thermometer was limited to use for spot checking a local temperature ... for example the fever of a sick little boy ... or of a sampled process stream.

Likewise the industrial use of fluid-filled systems to measure temperature was obviously limited to local temperature indicating and recording instruments.

PTOA Readers and Students were reminded that the capillary in an industrial fluid-filled temperature-measuring device had a unique ISA symbol comprised of equidistant Xs drawn on an instrumentation line.

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