Process Temperature Sensors: Basics of Thermocouples and RTDs

Industrial Thermocouple
(Ashcroft)

Proper temperature sensor selection is key to getting useful and accurate data for maintaining control of a process. There are two main types of temperature sensors employed for industrial applications, thermocouple and resistance temperature detector (RTD). Each has its own set of features that might make it an advantageous choice for a particular application.

Thermocouples consist of a junction formed with dissimilar metal conductors. The contact point of the conductors generates a small voltage that is related to the temperature of the junction. There are a number of metals used for the conductors, with different combinations used to produce an array of temperature ranges and accuracy. A defining characteristic of thermocouples is the need to use extension wire of the same type as the junction wires, in order to assure proper function and accuracy.

Here are some generalized thermocouple characteristics.

• Various conductor combinations can provide a wide range of operable temperatures (-200°C to +2300°C).
• Sensor accuracy can deteriorate over time.
• Sensors are comparatively less expensive than RTD.
• Stability of sensor output is not as good as RTD.
• Sensor response is fast due to low mass.
• Assemblies are generally rugged and not prone to damage from vibration and moderate mechanical shock.
• Sensor tip is the measuring point.
• Reference junction is required for correct measurement.
• No external power is required.
• Matching extension wire is needed.
• Sensor design allows for small diameter assemblies. 

RTD sensors are comprised of very fine wire from a range of specialty types, coiled within a protective probe. Temperature measurement is accomplished by measuring the resistance in the coil. The resistance will correspond to a known temperature. 

Industrial RTD
(Ashcroft)

Some generalized RTD attributes:

• Sensor provides good measurement accuracy, superior to thermocouple.
• Operating temperature range (-200° to +850°C) is less than that of thermocouple.
• Sensor exhibits long term stability.
• Response to process change can be slow.
• Excitation current source is required for operation.
• Copper extension wire can be used to connect sensor to instruments.
• Sensors can exhibit a degree of self-heating error.
• Resistance coil makes assemblies less rugged than thermocouples.
• Cost is comparatively higher.

Each industrial process control application will present its own set of challenges regarding vibration, temperature range, required response time, accuracy, and more. Share your process temperature measurement requirements and challenges with a process control instrumentation specialist, combining your process knowledge with their product application expertise to develop the most effective solution.

Metso Neles T5 Series Top Entry Rotary Ball Valves

Metso's Neles® T5 series top entry rotary ball valves are designed to meet the requirements of chemical, petro-chemical and refining industries with improved process safety and efficiency of plant.

T5 series valves with famous trunnion mounted Stemball® design are suitable with wide rangeability for demanding heavy duty rotary control applications such as crude oil, hot residual oil, LPG and other hydrocarbon gases and vapors under medium and high pressures. 

Unique Stemball® design combined with anti-cavitation and low noise Q-trim technology are making the T5 series valve most suitable with wide rangeability for demanding control applications like anti surge and blow down services. The new high noise reduction Q2-trim is available for gas applications.

Metso Neles T5 Series Top Entry Rotary Ball Valves from Mead O'Brien, Inc.

Process Control Basics: The Underlying Principle Behind Coriolis Flowmeters

The Coriolis effect, a derivative of Newtonian motion mechanics, describes the force resulting from the acceleration of a mass moving to (or from) the center of rotation. As this video demonstrates, the flowing water in a loop of flexible hose that is “swung” back and forth in front of the body with both hands. Because the water is flowing toward and away from the hands, opposite forces are generated and cause the hose to twist. Coriolis flowmeters apply this principle to measure fluid flow.

For more information on any process flow application, contact Mead O'Brien by calling
(800) 892-2769 or by visiting https://www.meadobrien.com.

Pharmaceutical and Biotech Valve Communication Networks

Valve Communication Network

Pharmaceutical and biotech companies are facing increasing competition, driving their need for increased efficiency, reduced costs, and agility.

Automated valve systems that help reduce installation costs through easy set up, faster commissioning, and enhanced valve identification are being embraced in these industries. Features such as bright electronic indication, combined with optional remote wireless access systems, provide enhanced risk management and improved safety, which subsequently lowers overall cost.

Demands for higher product purity and productivity is pressuring Pharma and Biotech companies to make investments in new technologies that deliver improved quality and competitive agility. Process control systems, and specifically valve communication systems, are evolving to support these changes. The most significant changes to valve communications systems are:

Size

Valve communication modules that offer smaller, lighter and more durable form factors, and modules that conform to the needs of moveable process skids and flexible manufacturing provide operators are very popular in these industries. Also, the use of integral solenoid valves lessen the amount of tubing and cabling required for valve packages, affording smaller overall envelope sizes on skids.

Precision

Solid state continuous sensors increase reliability and provide precise position measurement compared to legacy mechanical or proximity-reed technology. These solid state sensors also allow for more sophisticated valve diagnostics, leading to reduced maintenance costs over the valve system's life cycle.

Predictive Maintenance

The information available for critical valve operating parameters allow operators to see potential problems early, thereby reducing the risk and potential expense from lost production and downtime. Remote valve function monitoring, which includes sensor temperature and cycle count, extends the life of critical valves and helps maintenance staff circumvent a problem before it causes a dangerous situation.

Improved Safety

StoneL Axiom

Wireless communications and control modules allow operators to access difficult to reach valve systems safely, securely and conveniently. Critical situations are known and dealt with immediately from safe locations, and away from potentially dangerous areas or circumstances.

Remote Access and Data Collection

Typical modern valve communication networks provide tremendous advantages over traditional valve monitoring systems, namely:

• Access devices up to 50 meters, depending on obstructions
• Monitor on or off line and set open and closed switch positions
• Monitor and set the network address
• Operate solenoid valve(s) (if network- or power supply-enabled)
• Identify model and serial number (preset from factory)
• Identify valve automation components (entered by valve supplier)
• Log maintenance information
• Monitor diagnostics (valve cycle count, electronics temperature, and more)
• Lockout of settings automatically when in operation

Solutions

StoneL Prism PI

Combining components such as StoneL’s Prism or Axiom platforms with a DeviceNet or AS-Interface protocol system to interconnect your automated valves will lower your construction costs and install faster than conventional systems. Additionally, using valve monitoring apps such as StoneL Wireless Link with standard iPads or iPhones provide further cost savings and security is assured. Maintenance schedules based on calendar days are no longer required - with access to cycle count data, you can perform valve maintenance when it is truly needed and replace parts prior to wearing out.

Example of StoneL Wireless Link on iPhone.

To discuss any valve networking application, contact Mead O'Brien by visiting https://www.meadobrien.com or by calling (800) 892-2769.

Understanding Vortex Shedding Flow Technology

Foxboro Vortex Shedding Flowmeter.
Notice the shedder bar in the flow path.

Photograph of vortices
(credit Jürgen Wagner via Wikipedia)

Vortex shedding flowmeters are a type of flowmeter available to the process industry for the consistent evaluation of flow rates. These flowmeters measure the volumetric flow rate of media such as steam flowing in pipes, gases, and low viscosity liquids, boasting both versatility and dependability. Since they have no moving parts, they are impervious to the kind of wear turbine or mechanical meters experience.

Principles of Operation
A "shedder" bar (also known as a bluff body) in the path of

Animation of vortices
(credit Cesareo de La Rosa Siqueira
via Wikipedia)

the flowing fluid produces flow disturbances called vortices. The resulting vortex trail is predictable and proportional to the fluid flow rate. This phenomena is know as the "Von Kármán vortex street" (see illustrations to the right). Sensitive electronic sensors downstream of the shedder bar measures the frequency of the vortices and produce a small electrical pulse with every vortex created. The electrical pulses also also proportional to fluid velocity and is the basis for calculating a volumetric flow rate, using the cross sectional area of the flow measuring device.

Typical Areas of Use
Vortex shedding flowmeters are used on steam, cryogenic liquids, hydrocarbons, air, feed water, and industrial gases.

Applications to Avoid
Splitting higher viscosity fluids into concordant vertices is extremely difficult due to the internal friction present, so using vortex shedding flowmeters on high viscosity media should be avoided. Also, avoid applications with low flow rates and low Reynolds Numbers, as the vortices created are unstable.

Consideration for Use
Consideration must be given to applications with low Reynolds numbers, as the generation of vortices declines at critical points of reduced velocity. Low pressure can also be a problem in this regard. Users must take Reynolds number, velocity, and density into consideration before choosing a vortex shedding flow meter. As always, it's best to discuss your application with an knowledgable support professional before specifying, purchasing, or installing this type of flowmeter.

Watch the video below for more information on vortex flow technology.

For more information on  vortex shedding flowmeters, visit https://www.meadobrien.com or call (800) 892-2769.

Inverted Submerged Bucket Steam Traps: How They Work

Cutaway diagram of the Armstrong Inverted Bucket Trap.

The inverted submerged bucket steam trap is a mechanical trap that operates on the difference in density between steam and water. Steam entering the inverted submerged bucket causes the bucket to float and close the discharge valve.

Condensate entering the trap changes the bucket to a weight that sinks and opens the trap valve to discharge the condensate. Unlike other mechanical traps, the inverted bucket also vents air and carbon dioxide continuously at steam temperature.

This simple principle of condensate removal was introduced by Armstrong International in 1911. Years of improvement in materials and manufacturing have made today’s Armstrong inverted bucket traps virtually unmatched in operating efficiency, dependability and long life.

For more information on Armstrong steam traps, visit http://www.meadobrien.com or call (800) 892-2769.

Fixed Point Gas Monitoring

Fixed Point Gas Monitors (GfG)

In industry, the assessment and control of risk factors is a crucial element of process control. Commanding risk allows not only for peace of mind regarding environments involving hazardous materials, but also ensures ' and prioritizes - the safety of those who work with said materials. Fixed point gas monitoring tracks and repeatedly evaluates the levels of potentially toxic or flammable gases in an industrial environment, typically using electrochemical, infrared, or catalytic bead sensors. A central monitoring station allows for an entire facility to operate under consistent watch, as the array of gas monitors throughout a facility form a system. Typical environments which utilize fixed point gas monitoring include CNG filling stations, fleet maintenance buildings, wastewater lift stations and treatment plants, pipelines, and refineries, among others.

Due to the variation in facilities and associated industrial purposes, the applicability and customization of fixed point monitors must be adaptable. The gases typically monitored by fixed point systems are industrial staples. Natural gas (methane) and hydrogen are inherently dangerous to work with due to both their combustible nature and flammability. Carbon monoxide, hydrogen sulfide, and chlorine are especially dangerous to those who work in and around facilities where they are used or produced, while otherwise harmless gases such as nitrogen can cause oxygen displacement leading to asphyxiation. Around-the-clock is the only way to monitor and mitigate the potential impact of such volatile substances; thanks to automation, the ability to be constantly vigilant of threats related to gases is possible.

Sensing and evaluating these types of gases is a complex process, yet one which also showcases the powers of the associated technology. International certification standards like ATEX (derived from a French regulation acronym) and SIL (the safety integrity level) allow designers of gas detectors to match their products with the necessary parameters to ensure safe working environments. For example, one manufacturer's electrochemical gas sensor operates based on a principle involving two electrodes; the first electrode senses the toxic gas, and then the second electrode receives protons generated by the sensing electrode through an ion conductor. Output current which flows to an external circuit is proportional to the concentration of gas, therefore the current generated is measurable as an indicator of gas levels. Despite the fact that these sensors are primarily used in industry, there is also the potential for domestic applicability, automotive process control, and air quality control, among other uses. The different technological and practical applications of fixed point gas monitors allow for industry professionals to safely and capably navigate working environmental hazards for personnel and process protection.

For more information on fixed point gas detection, contact Mead O'Brien by visiting http://www.meadobrien.com or calling (800) 892-2769.