instrulab.co | Temperature Measuring, Temperature Monitoring, Sensors
From petroleum plants to food processing facilities, accurate and consistent temperature measuring and monitoring are vital to the health and well-being of both equipment and personnel.
Depending on the industry, spoilage and equipment failures may occur when temperatures fluctuate or stray beyond safe operating ranges. Worse yet, environments may become dangerously unstable.
Advanced Sensing Equipment
Fortunately, the technology surrounding industrial temperature monitoring has evolved to where process, product and machine temperatures can be scrutinized precisely and perpetually. The latest generation of temperature sensors are extremely accurate and reliable, as are the logging and reporting devices with which they are integrated.
Modern-day temperature probes come in a variety of styles and are designed to satisfy the requirements of just about any industrial endeavor. The thermocouple, for instance, is built to withstand some of the most exacting conditions, including temperatures exceeding 1,600 degrees Celsius.
What the thermocouple offers in temperature range, the thermistor and the resistance temperature detector (RTD) offer in accuracy. Both thermistors and RTDs are more accurate than thermocouples. However, they do not come close to the range of temperatures that thermocouples are capable of measuring. Thermistors are slightly more accurate than RTDs. But RTDs are able to measure temperatures at almost twice the range as thermistors.
Thermistors are generally the most cost-effective of these three “smart sensors.” But depending on the “type” of thermocouple used, these sensors can also be relatively inexpensive. RTDs are generally more costly due to the equipment that must be incorporated with their use in order to ensure accuracy.
In situations where temperature monitoring equipment is required, the three main considerations that a production plant must weigh when choosing sensors are temperature range, accuracy and cost. Temperature calibrators, signal conditioning equipment and other controlling and temperature indicating devices must also be factored into the equation.
In any industry, work stoppages and accidents can be extremely costly on multiple levels. But the temperature sensing and data transmission equipment of today provide an effective safeguard against the hazards associated with temperature-sensitive processes and environments.
Accuracy and stability in the monitoring and reporting of machine and process temperatures is critical in many industrial environments. Special temperature monitoring equipment is needed in situations where such devices are exposed to harsh and sometimes extreme conditions on a continual basis.
The wrong temperature sensors in the wrong locations can negatively impact operations and lead to circumstances that threaten both the efficacy of equipment and safety of surrounding personnel. Therefore, temperature measuring probes and sensors must be carefully selected for their level of endurance and ability to perform consistently within a given setting.
The “Big Three”
There are a number of different temperature probes as well as measuring and monitoring devices specifically built for hard-working industrial machinery and processes that generate intense heat. But the industry-wide “mainstays” are the thermistor, thermocouple and the resistance temperature detector (RTD).
Thermocouples are rugged and accurate. They are constructed of various metal alloys and contain two contact points made from disparate metals. Temperature readings are generated from the difference between the measurements of the two contact points and then delivered to a temperature indicator. Thermocouples can measure temperatures at a wider range than thermistors or RTDs, but are less accurate and more prone to noise interference.
Thermistors are very accurate at limited temperature ranges, but are not as sturdy as thermocouples. RTDs also offer a high degree of precision and durability. But like thermistors, they are incapable of withstanding the exceedingly high temperatures and mechanical strains under which thermocouples are able to perform.
Each of the smart sensors mentioned above can be customized for increased durability, accuracy and a wider temperature-measuring range. This can be accomplished through the use of protective sheathing and “signal conditioning” among other techniques.
With each type of sensor having its own set of advantages and disadvantages, operations managers and engineers must be discerning in their choice of which device to use in a particular situation.
Many temperature-sensitive industrial applications require precise and durable temperature monitoring equipment to ensure their efficient and stable performance. Of the temperature probes and sensing devices used in these situations, the thermocouple is the most popular due to its cost effectiveness and universality.
Thermocouples contain a “hot” and a “cold” junction. The hot junction consists of two distinct types of metal that are separated. At the cold junction end, the metals are joined together. The temperature differential between these two junctions generates a voltage that is converted to digital information that is sent to a temperature indicator to be read.
Signal Conditioning Enhances Performance
Often times, there is a loss of accuracy that occurs during the analog-to-digital information conversion process. Therefore, signals must be “conditioned” or enhanced to provide for increased precision. Other temperature monitoring devices such as thermistors and programmable RTD temperature sensors also require signal conditioning. However, in many situations, thermocouples are especially in need of conditioning due to their non-linear nature.
In the case of thermocouples, conditioning will amplify weak voltage levels; mitigate and filter noise levels; and “linearize” or better interpret signals being transmitted from the sensor. Signal conditioning is all but imperative for thermocouples in circumstances that call for extreme accuracy and consistency in temperature measuring and monitoring.
“Cold junction compensation” is another aspect of thermocouple signal conditioning. Often times, ambient temperatures will fluctuate and cause inaccurate temperature readings from the cold junction end of a thermocouple. To correct this, cold junction temperatures are read by another temperature measuring device and a compensating signal is sent to the instrument.
Signal conditioning technology that increases temperature reading accuracy even further has now been incorporated into “smart sensors.” With the flexibility and level of synchronization these sensors now offer, temperature data gathering and the transmission of that information to monitoring equipment occurs faster and more efficiently than ever before.
Gas-powered turbine engines are used in a wide array of applications including power plants, helicopters, ships and jets. Whether these powerful engines are used on a large or small scale, it is essential that sturdy, accurate and reliable temperature monitoring equipment is in place to protect against overheating.
The Gas Turbine Engine
Basically, a gas turbine engine is an “internal combustion” engine that uses a combination of air and fuel such as kerosene or specially-formulated jet fuels. Intense heat is generated from the burning of the fuel within the engine. This causes the air to heat up, expand and ultimately create enough pressure to spin the turbine blades at a high rate of speed.
The Importance of Temperature Monitoring
Because multiple stages are involved in the generation of power from a gas turbine engine, each stage must be carefully monitored for temperature stability. This is accomplished by using a variety of rugged-yet-sensitive temperature probes such as the thermistor and the thermocouple.
These temperature sensors monitor turbine inlet and outlet temperatures, interstage temperatures and overall friction or “windage” temperatures. Any overheating within these various stages could cause damage to turbine blades and rotors. If not immediately addressed, overheating could lead to equipment failures, shutdowns or in some cases combustion.
Many passenger jets have “dual detection” systems in place to minimize the chances of false overheating or fire warnings. These systems consist of two temperature measuring instruments that are located together. If one of these temperature detectors is activated, a “fault” will be indicated. But if both are activated at the same time, a warning will be initiated that will trigger system switchovers and overrides.
With so much literally riding on the sound operation of turbine engines, faulty temperature measuring and temperature indicator equipment is unacceptable. Aside from the potential hazards presented to personnel and property within stationary facilities that use these engines, a turbine engine malfunction on a ship or jumbo jet in the course of transporting passengers could prove disastrous. Therefore, only the toughest and most dependable temperature monitoring equipment is used to ensure turbine engine health and safety.
Wind storms, lightning storms and system overloads within power equipment are often major culprits when it comes to prolonged area-wide power failures. But increasingly effective controls have been developed to help prevent and minimize damage that can occur within equipment providing us with power.
Power Equipment Safeguards
Voltage irregularities, damage to equipment and overheated system components such as cables, connectors and switching devices are some causes of power failures. With regard to overheating issues within substation and stand-alone power equipment, the installation of warning systems consisting of sensitive-yet-sturdy temperature monitoring devices is one highly effective safeguard.
Strategically-placed temperature measuring equipment includes temperatures probes and “smart sensors” such as the thermocouple and the thermistor. These sensors give utility company personnel the ability to remotely monitor power equipment for temperature stability. Temperature monitoring equipment can also be programmed to generate alerts if contingencies should arise.
Other protective measures include infrared thermography where color-coded images indicating temperature are displayed on a computer screen. Monitoring power equipment can visualize heat radiating from equipment as well as note when temperature thresholds are close to being reached.
Power equipment safeguards also include:
- Sensors and temperature indicator devices for measuring oil temperatures within transformers
- Software applications for power outage avoidance and restoration
- Special circuit breakers and other such devices that help limit and isolate areas affected by power outages.
From food spoilage to loss of productivity, power outages can be costly and inconvenient to everyone in an affected area. But the technology surrounding the monitoring of power equipment and the detection of potential problems is becoming increasingly advanced. This will go a long way toward keeping us “out of the dark” as we move into the future.
Due to the precision and stability required of industrial temperature measuring and temperature monitoring instruments, it is necessary to have specific guidelines clearly outlined in regard to the testing and calibration of such equipment. Especially within highly sensitive, meticulously controlled and potentially volatile environments such as in the nuclear and petrochemical industries, an inaccurate or faulty thermocouple, thermistor or other type of temperature sensor could negatively impact operations or even lead to disaster.
Therefore, international standards have been created to ensure the effectiveness and integrity of testing procedures and to foster consistency surrounding laboratory processes and conditions. ISO/IEC 17025 standards apply to laboratories carrying out the testing and calibration of industrial instruments such as temperature sensors. It establishes the criteria that a testing laboratory must comply with in order to become accredited and certified.
ISO/IEC 17025 Promotes Quality, Consistency
Technically, compliance with ISO/IEC 17025 is not mandatory. However, most calibration and testing labs — and their potential customers — understand the benefits of ISO/IEC 17025 accreditation. An ISO/IEC 17025 certification not only legitimizes a testing facility, but is also required by many customers and government entities before they enlist the services of a particular testing and calibration lab.
There are two main sections within ISO/IEC 17025: “Management Requirements” and “Technical Requirements.” Management requirements apply to the quality management aspect of a facility, including organizational structure and quality assurance. Technical requirements apply to staff competence, the equipment and procedures used for testing, and the reporting and documentation of test results.
ISO/IEC 17025 replaced ISO Guide 25 in 1999 and was reissued in 2005 with updated management requirements and guidelines. To qualify for ISO/IEC 17025 accreditation, a testing facility must first go through an implementation process before being subjected to evaluation and assessment by an accreditation team.
This process can be somewhat lengthy and at times challenging. However, the time, effort and associated costs are well worth it to testing facilities that desire to increase their customer base. Industries that require the most rigid of standards to be met when it comes to the calibration and testing of temperature probes, smart sensors and other equipment used to measure temperature would have it no other way.
Precision temperature monitoring is critical within countless industrial processes and vital to the safe and efficient operation of a wide range of industrial machinery. Over time, rugged and reliable temperature sensors such as the thermocouple, thermistor and a variety of resistance temperature detectors (RTDs) have been developed to provide accurate and consistent temperature measurement under conditions that are often extreme.
Precision temperature measuring instruments are a major contributor toward the stability and effectiveness of industrial operations. They have a direct impact on aspects such as energy output, production and even emissions control.
Today’s temperature probes are sturdy, sensitive and precise in their ability to measure temperatures. They also offer more accuracy and convenience than ever before in the areas of data logging and reporting. However, there is always room for improvement.
Improving Temperature Sensor Performance
Faulty or inefficient industrial temperature monitoring equipment can be costly on multiple levels. For instance, the high-temperature thermocouple has a tendency to de-calibrate or “drift” during operations, especially in harsh environments. But the mineral insulated metal sheathed (MIMS) cable has been created to protect these sensors and to guard against drift; providing added stability to these instruments and greatly increasing their lifespan.
Additionally, “dynamically self-validating sensors” are enhanced, self-diagnostic thermocouple-type sensors that essentially eliminate erratic temperature readings. They are also capable of generating a warning before a signal begins to drift.
Within some systems, low frequency noise that can offset signals from a sensor is also a concern. But this has been addressed by methods such as “correlated double sampling” that acts as a filter to reduce noise in the signal processing phase.
Temperature calibrators are used to set thermocouples and other sensors to read temperature information with extreme precision. But factors such as extended use and extreme conditions can negatively affectinitial calibration. Fortunately, advances in technology have allowed us to circumvent many of these issues and have provided a new and improved generation of temperature sensors.
Countless industries rely on precision temperature monitoring equipment to ensure the safety and efficacy of their products and processes. Petrochemical plants, nuclear facilities and medical laboratories are just a few of the sectors in which accurate, reliable temperature measuring, monitoring and reporting are critical functions.
Temperature probes, temperature sensors and data logging equipment have been in a continuous state of refinement. As a result, these devices are now more durable and dependable than ever.
Preventing Contingencies
Unfortunately, some difficult lessons have been learned in the area of industrial temperature monitoring that have added a sense of urgency to the importance of its role.
As a result, a greater emphasis has been put on creating more consistent and durable temperature monitoring infrastructure within many industries. To that end, the engineering behind smart sensors such as the thermocouple, thermistor and their associated reporting equipment has taken a turn for the better.
Additionally, agencies such as the American Society for Testing and Materials and the National Institute of Standards and Technology (NIST) are more closely involved with the development and testing of industrial temperature monitoring equipment and have established more stringent guidelines in these areas. The International Temperature Scale of 1990 (ITS-90) also makes a considerable contribution toward temperature-measuring accuracy by defining standards for temperature calibrators and overall equipment calibration.
The standards are rigid in the temperature measuring and monitoring arena, and for good reason. Lives, property and the environment are in the balance; anything less than extremely stable and reliable equipment used to monitor temperatures within industrial settings could lead to calamitous consequences.
Bearings are critical to the functionality of countless industrial applications. Coming in a wide variety of shapes and sizes, bearings can be found in apparatuses such as generators, large turbine engines and paper mill machinery.
The negative effects of extreme heat on bearings are well understood within manufacturing and industrial circles. Intense or sustained heat on machine bearings can cause accelerated degradation, equipment failure and even severe damage to equipment in extreme cases.
Monitoring Bearing Temperatures
Vibration analysis and constant temperature monitoring are methods used to determine the health and stability of machine bearings. Thermistor, thermocouple and various resistance temperature detector (RTD) probes are among the devices used for machine bearing temperature measuring. These temperature sensors are built to stand up to harsh environments and provide accurate and consistent temperature readings.
Many “smart sensors” use wireless technology to report temperature data to monitoring stations. These devices are capable of triggering warnings and alerts if temperatures should exceed a prescribed range. They can also initiate system shutdowns if machinery reaches a point where damage will result if it continues to run.
Keeping Bearings Cool
One of the main methods of keeping bearings cool is using lubricants such as oil and grease. Bearings can be lubricated continuously as machinery is running or added when bearing temperatures reach a particular stage.
This is another area where temperature probes come into play. Some systems are set up to automatically inject lubricants when sensors detect that bearing temperatures threaten to surpass safe thresholds.
Various factors can contribute to bearing wear and tear. But attentive temperature monitoring can prolong the usefulness of bearings; which in turn will enhance the overall health of machinery that rely heavily on bearings to operate.
The “cold chain” is the system in which products and supplies that must be maintained within a prescribed temperature range from origin to destination are distributed. In order to preserve their integrity, it is crucial for products that are extremely temperature-sensitive — such as vaccines and pharmaceuticals — to be kept within certain temperature boundaries during storage and transit.
The lives and health of people all over the world depend on the safe delivery of medicines, blood products and biomedical materials. To that end, special shipping containers have been developed within the cold chain industry. These containers are well-insulated and built to hold temperatures for relatively lengthy periods of time under conditions often less than favorable.
An Intensive Qualification Process
With the life-and-death implications attached to the temperature stability these containers must provide while in transit, they must undergo rigorous testing before being qualified to enter the field. This validation process is meticulously regulated and overseen by agencies such as the Parenteral Drug Administration (PDA) and the International Safe Transit Association (ISTA).
Testing takes place in industry-approved laboratories where containers are exposed to extreme environmental conditions and subjected to vibration, compression and “drop” scenarios among other physical hazards. Temperature monitoring equipment must be sound and reliable as it measures temperature hold times during the qualification process.
Thermocouple temperature probes and thermistor temperature sensors are used in conjunction with temperature indicator and data logging equipment to measure and document internal container temperatures during testing. Temperature calibrators are used to adjust the monitoring equipment to ensure accuracy. If there are any inconsistencies or discrepancies detected during qualification procedures, the container in question will not be validated.
Precision in temperature measuring and monitoring is the most critical aspect within cold chain container testing. Not only is the efficacy of cold chain packaging relied upon for the successful delivery of life-saving products, but the potential financial loss is sizeable when these products are spoiled or rendered ineffective upon arrival.
