Starting to Focus on the Process Variable “Temperature”

The temperature’s rising….the fever is high...
(“Cold Turkey” by John Lennon, 1969)

Exactly how hot is hot and how cold is cold?

There’s not a definite answer to that question. Someone living in the polar regions of Norway and Greenland would give a different answer than someone living in Ecuador or Kenya through which the equator crosses.

What can easily be determined, though, is a relative sense of hotness or coldness. Thermometers are used for measuring a relative sense of hotness and coldness and display an outcome that PTOA Readers already recognize as a Temperature.

Your first exposure to the concept of determining a personal sense of hotness or coldness may have been when a caregiver shoved a thermometer in your mouth or put an electronic device up to your ear to determine your body temperature relative to the temperature expected of a normally healthy child.

Taking your temperature would not have been very useful without having a temperature scale to read in degrees Fahrenheit (°F) or degrees Celsius/Centigrade (°C).

99 deg F=37 deg C Either way a hot day!

The outside thermometer shown above indicates a right-side temperature of 99°F which is equivalent to the left-side temperature of  37°C. By either temperature scale it is a hot day!

PTOA Readers and Students interested in converting between  Fahrenheit and Celsius/Centigrade scales can do so by accessing this link: Universal Temp Converter


Thermometers are temperature scales that help define a normal range of hotness/coldness from a hotness/coldness range that would not be expected.  The main job of all Process Operators is to be sufficiently knowledgeable to recognize when an abnormal condition is present. Otherwise stated:

A Process Operator must have a sense of what the normal temperature of the process should be before s/he can recognize that an unexpected or abnormal temperature is being detected.”

Never forget that the “normally expected” temperature can change depending upon the season or if you are on top of a mountain or working deep down in a mine. So that means “normal” can change depending upon the environment.

103 deg F is normal in some locations

103 deg F is normal in some locations

-42 deg F is normal in some locations

-42 deg F is normal in some locations








There’s a fancy name for the temperature of your surroundings. Wherever you are right now reading the PTOA, the temperature of your environment is called the ambient temperature.

The outside ambient temperature changes depending upon the season and location. Many people are currently worried that outside ambient temperatures are varying too widely due to global warming.

An inside ambient temperature can be produced by artificial means. Air conditioning can be used to lower the inside ambient temperature of a room in a Dallas, Texas building during a sweltering hot August afternoon.

106 deg outside is hot! 71 deg inside is cool!

A 106 deg F outside ambient temperature is cooled to a 71 deg F inside ambient temperature!

Likewise, a room in a building located in Anchorage, Alaska can be heated to a comfortable level during a mid-January day.


In process technology jargon, the actual metal hardware device from which a temperature is observed is called a temperature gauge (not thermometer). However REAL Process Operators call the temperature indicating device a temperature indicator so that means PTOA Readers and Students will, too.

In fact, REALLY REAL Process Operators use the abbreviation “TI” (tee-eye) for a temperature indicator and that means PTOA Readers and Students will, too.

Doesn’t this industrial TI look a lot like the outside ambient thermometer in the below picture comparison?

Temp Indicator in Service

This TI indicates the temperature of the fluid inside the pipe is 187 deg F

This thermometer is indicating a 36 deg F outside temperature

This thermometer indicates the outside ambient temperature is 36 deg F








Both the thermometer and the TI are indicating the temperature of their location, or ‘local temperatures.’

Both the thermometer and the TI utilize the same type of mechanism to measure and indicate temperatures. The mechanism used to sense a temperature and transform that sensation into a display that appears on the dial of the gauge… and which can be understood by humans to be a temperature reading… is the subject of a much later PTOA segment so just don’t worry about that now.


A big difference between the thermometer and a TI is the source of the temperature that is being sensed, measured and displayed on the face of the gauge.

The below picture shows a Process Operator recording temperature and pressure readings. The temperature that he is recording is the temperature of the fluid that is flowing through the pipes of this processing plant.

This Process Operator is recording a TI reading

This Process Operator is recording a TI reading

The hardware that makes the temperature indicator (TI) work includes a thermowell which has been inserted into the pipe that the fluid is flowing through.


The thermowell protects the temperature indicator from directly contacting the flowing fluid. Don’t worry about the mechanics now. For now just understand:

A temperature indicator (TI) indicates the current temperature of the fluid that is flowing through the process unit pipes.

Also be aware that the temperature being recorded by the Process Operator has been artificially manufactured by process technology equipment. Temperature-changing process technology equipment is the subject of upcoming PTOA segments.

The outside ambient temperature is the temperature of the environment that the Outside Operator is feeling while on his rounds recording temperatures, pressures, flowrates and the liquid levels of tanks and other containers. Unlike the temperature of the fluid flowing through the pipes, the outside ambient temperature cannot be manufactured.

Take Home Messages: The ambient temperature is the temperature of your surroundings (indoor or outdoor) and can be measured by a common thermometer. Indoor ambient temperatures can be manufactured just like the temperatures in process pipes can be manufactured.

In the process industries, the temperature of a fluid flowing through the pipes of a processing plant is observed on a temperature indicator which all Process Operations personnel call a “TI.”

Both thermometers and TIs sense the temperature of where they are located, which is also known as the local temperature.

Temperatures can change from normal to abnormal expected ranges.

Monitoring local temperature indicators (TIs) is an activity that vigilant Process Operators routinely perform so they know if the fluid that is flowing through the process unit pipes is within the expected temperature range.

© 2015 PTOA Segment 00001
Process Variable Temperature



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