Wednesday, August 16, 2017

Compact Electric Control Valve Actuators

electric linear control valve actuator
CML linear valve actuator
Image courtesy of Rotork
Rotork's CMA line of electric valve actuators are intended for use in industrial process control applications where precise response and positioning are key requirements. The variants of linear, rotary and quarter-turn actuators span a wide range of application requirements and support on-board programming and connection via any of several recognized communication protocols.

The compact actuators are available with enclosures rated for several environments, ranging from non-hazardous to hazardous. Low temperature operation to -40 degrees Celsius is provided with the inclusion of a low temperature option.

These are but a small recounting of the useful features incorporated into the product line. More detail is provided in the document included below. For best results, share your valve automation requirements and challenges with process valve automation specialists, combining your own process knowledge and experience with their valve automation expertise to develop effective solutions.


Tuesday, August 8, 2017

Rotary and Linear Drives for Damper Control on Combustion Air and Flue Gas Applications

pneumatic vane type damper drive
Pneumatic vane damper drive, one of several
variants available.
Image courtesy Rotork
Combustion air and flue gas damper drives fill a critical role requiring safety, accuracy and reliability above all else. It is critical to deploy the best drive technology to maximize combustion efficiency, minimize emissions and reduce installation costs.


Damper Operator (Drives) Types :


Damper drives can be one of three types: pneumatic, electric, or electro-hydraulic, as described below.
  • Pneumatic. These damper operators are used whenever controls rely primarily on compressed air (pneumatic) for moving operators.
  • Electric. These damper operators are used whenever controls rely primarily electricity as the power source.
  • Electro-hydraulic. These damper operators are the same as the electric type described above, but also have a hydraulic system to position the damper.
A very important part of damper design is determination of damper torque, and sizing and selection of the damper actuator for the maximum torque. Actuator torque should be selected to provide the maximum torque required to operate the damper as well as to provide margin and allow for degradation over the life of the damper. Actuators should be evaluated for damper blade movement in both directions, at the beginning of blade movement, and while stroking blades through the full cycle of movement.

The Goal for Selecting the Best Drive Technology:


Reduced emissions, lower fuel consumption and improved boiler draft control.

Ways to achieve this goal:
  • High speed continuous modulation of ID/FD fan and inlet guide vanes 
  • Improved modulation and control of secondary air dampers 
  • Improved automation and burner management 
  • Quick response to plant demand 
  • Improved reliability in high temperature environments 
  • Precise damper and burner positioning 
  • Simple commissioning and diagnostics 
  • Low running costs, virtually maintenance free 
  • Pneumatic, analog and bus network communications 
For more information, share your requirements and challenges with combustion experts. The combination of your facilities and process experience and knowledge with their application expertise will yield an effective solution.

Thursday, August 3, 2017

The Application of Heat in Industrial Settings

industrial shell and tube heat exchanger
Heat exchangers are found throughout industrial and
commercial settings in many sizes and types.
The measurement and control of heat related to fluid processing is a vital industrial function, and relies on regulating the heat content of a fluid to achieve a desired temperature and outcome.

The manipulation of a substance's heat content is based on the central principle of specific heat, which is a measure of heat energy content per unit of mass. Heat is a quantified expression of a systems internal energy. Though heat is not considered a fluid, it behaves, and can be manipulated, in some similar respects. Heat flows from points of higher temperature to those of lower temperature, just as a fluid will flow from a point of higher pressure to one of lower pressure.

A heat exchanger provides an example of how the temperature of two fluids can be manipulated to regulate the flow or transfer of heat. Despite the design differences in heat exchanger types, the basic rules and objectives are the same. Heat energy from one fluid is passed to another across a barrier that prevents contact and mixing of the two fluids. By regulating temperature and flow of one stream, an operator can exert control over the heat content, or temperature, of another. These flows can either be gases or liquids. Heat exchangers raise or lower the temperature of these streams by transferring heat between them.

Recognizing the heat content of a fluid as a representation of energy helps with understanding how the moderation of energy content can be vital to process control. Controlling temperature in a process can also provide control of reactions among process components, or physical properties of fluids that can lead to desired or improved outcomes.

Heat can be added to a system in a number of familiar ways. Heat exchangers enable the use of steam, gas, hot water, oil, and other fluids to deliver heat energy. Other methods may employ direct contact between a heated object (such as an electric heating element) or medium and the process fluid. While these means sound different, they all achieve heat transfer by applying at least one of three core transfer mechanisms: conduction, convection, and radiation. Conduction involves the transfer of heat energy through physical contact among materials. Shell and tube heat exchangers rely on the conduction of heat by the tube walls to transfer energy between the fluid inside the tube and the fluid contained within the shell. Convection relates to heat transfer due to the movement of fluids, the mixing of fluids with differing temperature. Radiant heat transfer relies on electromagnetic waves and does not require a transfer medium, such as air or liquid. These central explanations are the foundation for the various processes used to regulate systems in industrial control environments.

The manner in which heat is to be applied or removed is an important consideration in the design of a process system. The ability to control temperature and rate at which heat is transferred in a process depends in large part on the methods, materials, and media used to accomplish the task. Share your process control challenges with application specialists, combining your own knowledge and experience with their product application expertise to develop effective solutions.

Thursday, July 27, 2017

Pneumatic Control Valve Positioners

smart valve positioner for pneumatic process control valve
Smart valve positioner
Courtesy Rotork
Valve positioners can provide process operators with a precise degree of valve position control across the valve movement range, as well as information about valve position. A relationship exists between applied pneumatic signal pressure and the position of the valve trim. The relationship between the two elements is dependent upon the valve actuator and the force of the return spring reacting to the signal pressure. In a perfect world, the spring and pneumatic forces would reach equilibrium and the valve would return to the same position in response to an applied signal pressure. There are other forces, however, which can act upon the mechanism, meaning the expected relationship between the original two elements of pressure and position may be offset. For example, the packing of the valve stem may result in friction, or the reactive force from a valve plug resulting from differential pressure across the area of the plug may be another.
While these elements may seem minor, and in some cases they are, process control is about reducing error and delivering a desired or planned output. Inclusion of a positioner in the valve assembly can ensure that the valve will be set in accordance with the controller commands.

Each positioner functions as a self-contained small scale control system. The first variable in the positioning process is the current valve position, read by a pickup device incorporated in the positioner. A signal which is sent to the positioner from the control system, indicating the desired degree of opening, is used as the setpoint. The controller section of the positioner compares the current valve position to the setpoint and generates a signal to the valve actuator as the output of the positioning process. The process controller delivers a signal to the valve, and then the positioner takes that signal and supplies air pressure required to accomplish the needed adjustment of the stem position. The job of the valve positioner is to provide compensatory force and to act as a counterbalance against any other variables which may impact valve stem position.

Magnetic sensors can be employed to determine the position of the valve stem. The magnetic sensor works by reading the position of a magnet attached to the stem of the valve. Other technologies can be employed, and all have differing ways of overcoming degrees of inaccuracy which may arise with wear, interference, and backlash. In addition to functioning as a positioner, control valve positioning devices can also function as volume boosters, meaning they can source and subsequently ventilate high air flow rates from sources other than their pneumatic input signal (setpoint). These devices can positively affect and correct positioning and velocity of the valve stem, resulting in faster performance than a valve actuator solely reliant on a transducer.

The inclusion of a positioner in a control valve assembly can provide extended performance and functionality that deliver predictable accurate valve and process operation. Share your valve automation requirements with a knowledgeable valve automation specialist and combine your process knowledge and experience with their product application expertise to develop an effective solution.

Wednesday, July 19, 2017

Condensate Return in a Steam System - Basic and Essential

food and dairy production plant
Efficient production of steam and return of condensate
are essential to the operation of this and many other
industrial operations.
Many industrial processes and plants, as well as commercial buildings, utilize steam in their operations. The generation and use of steam is one of the oldest industrial processes and is so well understood that it may be considered more of a utility than part an industrial process. Whatever the case, if your process or installation uses steam, then steam is a necessary input for successful operation. Keeping your steam system performing at capacity frees up time and resources for the more complex aspects of your work.

If steam is not consumed directly by the process as a component input, it is steam's heat of vaporization that is utilized by the operation. Efficient use of steam as a heating medium results in the conversion of vapor to liquid (water). Returning the liquid condensate back to the boiler for conversion to vapor again is a necessary step in the efficient operation of a closed loop system.

Condensate return systems are certainly not high technology, but keep in mind that a steam system may be the lifeblood of not just one, but many operations throughout a plant. Avoiding downtime in the steam system, of which the condensate return system is an integral part, ranks highly on the list of "Important Things for Plant Operations". Condensate return is critical.

Three general methods are employed to move the condensate from a collection vessel, a trap, to the feedwater side of the boiler. Gravity can be used when conditions permit. A pressure motive return arrangement uses steam pressure and a coordinated valve sequence to drive the condensate through the piping system and back to the boiler. Condensate pumps can also be employed as a positive means of moving condensate through the return piping system.

What are some strong attributes of a good and reliable condensate return pump?
  • Minimize or eliminate cavitation at high temperatures. Cavitation will impede pump performance and cause premature deterioration of pump and drive components.
  • Ability to handle a high load during cold starts through motor and pump design.
  • Design and configuration to handle high temperatures without deterioration of pump and motor.
  • Develop higher pressure at lower motor speeds for extended service life.
  • Avoidance of mechanical seals below water line.
  • Consider a single unit with dual pumps for handling high loads and extending service life.
Specifying and installing a solidly designed and built condensate return pump may require an investment of your time and consideration. The return on that investment will be reduced maintenance, repair, and downtime. hare your steam system challenges, from end to end, with knowledgeable application specialists. Combining your intimate operational knowledge and experience with their deep product knowledge and experience with many installations will yield a good solution.

Monday, July 17, 2017

Filled Impulse Lines With Pressure Sensors

industrial process measurement and control pressure transmitter
Pressure sensors or transmitters are installed directly to
process lines or vessels, or remotely using impulse lines.
Image courtesy Azbil NA, Inc.
Pressure sensors intended for use in industrial process measurement and control applications are designed to be robust, dependable, and precise. Sometimes, though, it is necessary or beneficial to incorporate accessories in an installation which augment the performance of pressure sensors in difficult or hazardous environments. There are some scenarios where the sensor must be isolated from the process fluid, such as when the substance is highly corrosive.

A way to aid pressure sensing instruments in situations where direct contact must be avoided is by using a filled impulse line. An impulse line extends from a process pipe of vessel to a pressure measurement instrument or sensor. The line can have a diaphragm barrier that isolates the process fluid from the line, or the line can be open to the process. There are best practices that should be followed in the design and installation of an impulse line to assure that the line provides a useful transmission of the process pressure to the sensor and whatever degree of isolation or protection is needed remains in effect.

The filled impulse line functions via the addition of a non-harmful, neutral fluid to the impulse line. The neutral fluid acts as a barrier and a bridge, allowing the pressure sensing instrument to measure the pressure of the potentially harmful process fluid without direct contact. An example of this technique being employed is adding glycerin as a neutral fluid to an impulse line below a water pipe.

Glycerin’s freeze point is lower than water’s, meaning glycerin can withstand lower temperatures before freezing. The impulse line connected to the water pipe may freeze in process environments where the weather is exceptionally cold, since the impulse line will not be flowing in the same way as the water pipe. Since glycerin has a greater density and a lower freezing point, the glycerin will remain static inside the impulse line and protect the line from hazardous conditions.

The use of an isolating diaphragm negates the need for certain considerations of fill fluid density, piping layout, and the need to create an arrangement that holds the fill fluid in place within the impulse line. System pressure will be transferred across the diaphragm from the process fluid to the fill fluid, then to the pressure sensor. It is important to utilize fluids and piping arrangements that do not affect the accurate transference of the process pressure. Any impact related to the impulse line assembly must be determined, and appropriate calibration offset applied to the pressure sensor reading.

An essential design element of a filled impulse line without an isolating diaphragm is that the fill fluid must be compatible with the process fluid, meaning there can be no chemical reactivity between the two. Additionally, the two fluids should be incapable of mixing no matter how much of each fluid is involved in the combination. Even with isolating diaphragms employed, fluid harmony should still be considered because a diaphragm could potentially loose its seal. If such a break were to occur, the fluids used in filled impulse lines may contact the process fluid, with an impact that should be clearly understood through a careful evaluation.

Share your pressure measurement requirements and challenges with experienced application specialists, combining your own process knowledge and experience with their technical expertise to develop an effective solution.

Friday, July 7, 2017

Industrial Uses of Steam - Part 2

industrial steam boiler gas fired
Steam is used throughout commercial, institutional, and industrial facilities in various ways. In addition to other direct pressure and propulsion/drive applications, steam can be utilized as ‘motive fluid’ to assist in the movement of liquid and gas streams in a piping system. Jet ejectors can pull vacuum in equipment like distillation towers, allowing for the separation and purification of vapor streams. Continuously removing air from surface condensers via steam results in the desired vacuum pressure on condensing turbines to stay uniform. The entrance and subsequent diffusion of the steam through an inlet nozzle results in a low pressure zone, where the air from the surface condenser gets transferred. Similarly, steam serves as the primary motive fluid for secondary drainers, which pump condensate out of vented receiver tanks, flash vessels, and other process control components susceptible to stall conditions.

Steam is applicable to a process called atomization, wherein steam mechanically separates a fluid. Burners use steam for atomization by having steam injected into the fuel, thus maximizing the efficiency of the unit’s combustion while concurrently minimizing soot production. These steam generators and boilers, powered by fuel oil, use steam atomization to partition viscous oil into smaller droplets. Flares, similarly, utilize steam atomization as an exhaust pollutant reducer. In said flares, typically, the waste gas mixes with the steam prior to combustion.

Along with motive fluid and atomization, steam is also a fantastic cleansing tool. The soot in soot blowers gets removed via a steam cleaning process. Oil or coal fuel sourced boilers need soot blowers to cyclically clean the furnace walls and eliminate combusted deposits. These regularly scheduled cleanings allow for the capacity, durability, and effectiveness of the boiler to remain consistent. The nozzle of the soot blower directs the steam, dislodging dry, sintered ash and slag. Hoppers then catch the dislodged substances and they are expelled with other combusted gases.

Steam can also add moisture to a process while simultaneously acting as a heat supply source. In paper production, paper moving over rollers at high speed is moisturized by the steam, ensuring that no miniscule breaks or tears are suffered during the production process. Pellet mills, which produce animal feed, directly inject steam to heat and, concurrently, add to the water content of the feed as the feed passes through the mill’s direct conditioner section. The water softens the feed and then partially gelatinizes the starch content, leading to firmer pellets overall.

Lastly, commercial and industrial facilities utilize low pressure steam as a primary source of seasonal heating and humidification. Finned or bare coils, coupled with steam humidifiers, condition the facility air, keeping the temperature regulated for both comfort and preservation of items like books and records. Steam coils heat the cool air, resulting in the relative humidity dropping. The controlled injection of dry, saturated steam allows for moisture addition to regulate the relative humidity in a smooth and precise manner via steam humidifiers installed in air ducts.

Share your steam generation and use challenges with steam system and combustion experts, combining your own knowledge and experience with their expertise to develop effective solutions.

Monday, June 26, 2017

Industrial Uses of Steam – Part 1

gas fired boiler in equipment room
Boilers are the most common production equipment
for industrial steam applications
Steam is used throughout industrial process control operations in various ways. The ability of steam to serve as a means to deliver heat and provide motive power to a facility or process keeps it in wide use throughout many industries.

Heating with steam can by of a direct or indirect nature. Direct heating uses steam distributed into or onto a substance to directly affect its temperature. In order to ensure success in direct heating, mixing needs to occur so that the temperature of the substance is uniformly impacted. Indirect heating uses one of the many available forms of heat exchangers to transfer heat from steam to process fluid across a physical barrier that isolates the process fluid from the steam.

Industries employ steam for many valuable uses. Food processing factories, refineries, and chemical plants utilize positive pressure steam. In most instances, steam is delivered to equipment, typically, at pressures above atmospheric and at a temperature exceeding 100°C. Process fluid heat exchangers, reboilers, air preheaters for combustion, and a range of other heat transfer equipment uses steam as the heat source. A shell and tube heat exchanger raises product temperature on its passage through the unit. Ideally, the heat exchanger expels condensate after removing the latent heat from the steam. Condensate can be collected and returned to the steam generation portion of the system, conserving much of the energy used to originally heat the water.

Hot water was the main agent traditionally used for heating at temperatures below 100°C. Using steam to heat at temperatures below the 100°C benchmark is an increasingly popular technique. Vacuum saturated steam can be applied in the same way as positive pressure saturated steam, but the steam temperature is adjustable by altering the pressure. The ability to change the pressure (and the temperature) allows for more precise temperature control when compared to using hot water. Another advantage of using steam over hot water is that the steam heating system is fast and precise. The desired temperature can be reached quickly and uniformly.

Another popular use for steam in industrial settings is as a propulsion or drive force. Steam turbines generate electricity in thermal power plants. A recent trend, developed to minimize wasted energy, is applying steam at increasingly higher temperatures and pressures. Superheated steam, used in steam turbines, acts as a counter to potential damage to the equipment resulting from condensate in the turbine section. Less chance of condensate in the turbine translates into a reduced risk of equipment damage or failure. Nuclear power plants, though, cannot utilize the advantages of superheated steam because of complications arising involving the steam and the turbine material. To combat this problem, high pressure saturated steam is utilized instead, with upstream separators installed to remove condensate from the steam flow. In addition to power generation, steam acts as the force behind turbine driven compressors and pumps, including gas compressors and cooling tower pumps.

Depending on the process being controlled and the specific industry’s demands, the simplicity and various applications of steam make this reliable medium a first choice for industrial operations. Share your steam system and use challenges with combustion and steam experts, combining your own knowledge and experience with their specialized expertise to develop effective solutions.

Tuesday, June 20, 2017

Wireless Transmitters In Process Measurement and Control

oil refinery
Industrial process instrumentation connectivity can present
substantial challenges.
In process control, various devices produce signals which represent flow, temperature, pressure, and other measurable elements of the process. In delivering the process value from the measurement point to the point of decision, also known as the controller, systems have traditionally relied on wires. More recently, industrial wireless networks have evolved, though point-to-point wireless systems are still available and in use. A common operating protocol today is known as WirelessHART™ , which features the same hallmarks of control and diagnostics featured in wired systems without any accompanying cables.

Wireless devices and wired devices can co-exist on the same network. The installation costs of wireless networks are decidedly lower than wired networks due to the reduction in labor and materials for the wireless arrangement. Wireless networks are also more efficient than their wired peers in regards to auxiliary measurements, involving measurement of substances at several points. Adding robustness to wireless, self-organizing networks is easy, because when new wireless components are introduced to a network, they can link to the existing network without needing to be reconfigured manually. Gateways can accommodate a large number of devices, allowing a very elastic range for expansion.

In a coal fired plant, plant operators walk a tightrope in monitoring multiple elements of the process. They calibrate limestone feed rates in conjunction with desulfurization systems, using target values determined experientially. A difficult process environment results from elevated slurry temperature, and the associated pH sensors can only last for a limited time under such conditions. Thanks to the expandability of wireless transmitters, the incremental cost is reduced thanks to the flexibility of installing new measurement loops. In regards to maintenance, the status of wireless devices is consistently transmitted alongside the process variable. Fewer manual checks are needed, and preventative measures may be reduced compared to wired networks.

Time Synchronized Mesh Protocol (TSMP) ensures correct timing for individual transmissions, which lets every transmitter’s radio and processor ‘rest’ between either sending or receiving a transmission. To compensate for the lack of a physical wire, in terms of security, wireless networks are equipped with a combination of authentication, encryption, verification, and key management. The amalgamation of these security practices delivers wireless network security equal to that of a wired system. The multilayered approach, anchored by gateway key-management, presents a defense sequence. Thanks to the advancements in modern field networking technology, interference due to noise from other networks has been minimized to the point of being a rare concern. Even with the rarity, fail-safes are included in WirelessHART™.

All security functions are handled by the network autonomously, meaning manual configuration is unnecessary. In addition to process control environments, power plants will typically use two simultaneous wireless networks. Transmitters allow both safety showers and eyewash stations to trigger an alarm at the point of control when activated. Thanks to reduced cost, and their ease of applicability in environments challenging to wired systems, along with their developed performance and security, wireless industrial connectivity will continue to expand.

Share your process measurement requirements and challenges with application specialists, combining your own process knowledge and experience with their product application expertise to develop effective solutions.


Friday, June 16, 2017

Common Industrial and Commercial Process Heating Methods

Gas fired boilers in industrial facility
Gas fired boilers used the combustion of fuel to produce
steam which is utilized by other process equipment
Many industrial processes involve the use of heat as a means of increasing the energy content of a process or material. The means used for producing and delivering process heat can be grouped into four general categories.
  • Steam
  • Fuel
  • Electric
  • Hybrid
The technologies rely upon conduction, convection, or radiative heat transfer mechanisms, soley or in combination, to deliver heat to a substance. In practice, lower temperature processes tend to use conduction or convection. Operations employing very high temperature rely primarily on radiative heat transfer. Let's look at each of the four heating methods.

STEAM

Steam based heating systems introduce steam to the process either directly by injection, or indirectly through a heat transfer device. Large quantities of latent heat from steam can be transferred efficiently at a constant temperature, useful for many process heating applications. Steam based systems are predominantly for applications requiring a heat source at or below about 400°F and when low-cost fuel or byproducts for use in generating the steam are accessible. Cogeneration systems  (the generation of electric power and useful waste heat in a single process) often use steam as the means to produce electric power and provide heat for additional uses. While steam serves as the medium by which heat energy is moved and delivered to a process or other usage, the actual energy source for the boiler that produces the steam can be one of several fuels, or even electricity.

FUEL

Fuel based process heating systems, through combustion of solid, liquid, or gaseous fuels, produce heat that can be transferred directly or indirectly to a process. Hot combustion gases are either placed in direct contact with the material (direct heating via convection) or routed through tubes or panels that deliver radiant heat and keep combustion gases separate from the material (indirect heating). Examples of fuel-based process heating equipment include furnaces, ovens, red heaters, kilns, melters, and high-temperature generators. The boilers producing steam that was described in the previous section are also an example of a fuel based process heating application.

ELECTRICITY

Electric process heating systems also transform materials through direct and indirect means. Electric current can be applied directly to suitable materials, with the electrical resistance of the target material causing it to heat as current flows. Alternatively, high-frequency energy can be inductively coupled to some materials, resulting in indirect heating. Electric based process heating systems are used for heating, drying, curing, melting, and forming. Examples of electrically based process heating technologies include electric arc furnace technology, infrared radiation, induction heating, radio frequency drying, laser heating, and microwave processing.

HYBRID

Hybrid process heating systems utilize a combination of process heating technologies based on different energy sources or heating principles, with a design goal of optimizing energy performance and overall thermal efficiency. For example, a hybrid steam boiler may combine a fuel based boiler with an electric boiler to take advantage of access to low off-peak electricity cost. In an example of a hybrid drying system, electromagnetic energy (e.g., microwave or radio frequency) may be combined with convective hot air to accelerate drying processes; selectively targeting moisture with the penetrating electromagnetic energy can improve the speed, efficiency, and product quality as compared to a drying process based solely on convection, which can be rate limited by the thermal conductivity of the material. Optimizing the heat transfer mechanisms in hybrid systems offers a significant opportunity to reduce energy consumption, increase speed and throughput, and improve product quality.

Many heating applications, depending on scale, available energy source, and other factors may be served using one or more of the means described here. Determining the best heating method and implementation is a key element to a successful project. CTI Controltech specializes in combustion applications and the industrial production and use of steam. Share your process and project challenges with them and combine your facilities and process knowledge and experience with their engineering expertise to develop effective solutions.

Friday, June 9, 2017

Dual Input Industrial Temperature Transmitter - What You Can Do

dual input advanced industrial temperature transmitter
Dual input advanced industrial transmitter
has many built in functions
Courtesy Azbil
You will likely find temperature measurement to be a part of almost every industrial process. It is a mainstay of commercial and industrial processes and operations globally. Accurate measure of process, equipment, or product temperature provides operators with useful information that is utilized in countless ways. The range of available instruments and equipment for measuring temperature in industrial process settings is extensive, with devices or varied types, performance, and form factor to accommodate every application.

There are a variety of instruments and methodologies for measuring temperature, the most common of which is probably direct contact between the target substance and an appropriate temperature sensor. Industrial process applications are commonly served by thermocouples or resistance temperature detectors (RTD), chosen for their cost, accuracy, and flexibility of installation.

Every operating process is "critical" to some group of stakeholders. The process may be of great importance for a number of reasons:
  • The process output may serve as an input to another process with great value.
  • The process output may be of great direct value to the stakeholders.
  • The process may have significant levels of hazard associated with improper or out of control operation.
  • Out of control operation may result in substantial financial loss to the stakeholders.
When temperature is an important indicator of process function, whether for financial or safety reasons, the operator cannot tolerate a loss of the temperature signal. One manufacturer has an advanced solution in the form of a dual input temperature transmitter with built in functions that:
  • Switch to the backup sensor if the primary has a failure indication.
  • Alert the operator if the deviation between the two sensor readings indicates sensor drift. 
  • In wide range temperature applications, switch between sensors with differing measurement ranges for better accuracy.
Along with HART communications and other useful features, these advanced temperature transmitters can help reduce risk and increase performance and safety. Assess how these advanced devices can enhance your process performance. A product data sheet is included below. Product specialists can help with product configuration and selection, along with any application concerns you may have.


Tuesday, May 30, 2017

Rack and Pinion Style Pneumatic Valve Actuator

pneumatic rack and pinion valve actuator
One example of a pneumatic rack and pinion valve actuator
Courtesy Rotork
Three primary kinds of valve actuators are commonly used: pneumatic, hydraulic, and electric.
Pneumatic actuators can be further categorized as scotch yoke design, vane design, and the subject of this post - rack and pinion actuators.

Rack and pinion actuators convert linear movement of a driving mechanism to provide a rotational movement designed to open and close quarter-turn valves such as ball, butterfly, or plug valves and also for operating industrial or commercial dampers. The rotational movement of a rack and pinion actuator is accomplished via linear motion and two gears. A circular gear, known as a “pinion” engages the teeth of one or two linear gears, referred to as the “rack”. Pneumatic actuators use pistons that are attached to the rack. As air or spring power is applied the to pistons, the rack changes position. This linear movement is transferred to the rotary pinion gear (in both directions) providing bi-directional rotation to open and close the connected valve.
rack and pinion gears animation
Rack and pinion gear
Courtesy Wikipedia

The actuator pistons can be pressurized with air, gas, or oil to provide the linear the movement that drives the pinion gear. To rotate the pinion gear in the opposite direction, the air, gas, or oil must be redirected to the other side of the pistons, or use coil springs as the energy source for rotation. Rack and pinion actuators using springs are referred to as "spring-return actuators". Actuators that rely on opposite side pressurization of the rack are referred to as "direct acting".

Most actuators are designed for 100-degree travel with clockwise and counterclockwise travel adjustment for open and closed positions. World standard ISO mounting pad are commonly available to provide ease and flexibility in direct valve installation. NAMUR mounting dimensions on actuator pneumatic port connections and on actuator accessory holes and drive shaft are also common design features to make adding pilot valves and accessories more convenient.

Pneumatic rack and pinion actuators are compact and effective. They are reliable, durable and provide good service life. There are many brands of rack and pinion actuators on the market, all with subtle differences in piston seals, shaft seals, spring design and body designs. Some variants are specially designed for very specific operational environments or circumstances.

Share your process valve control and automation challenges with application experts, and combine your process experience and knowledge with their product application expertise to develop effective solutions.

Wednesday, May 24, 2017

Desuperheating and Attemperation of Steam

electric power plant
Electric power generation plant
Steam heats or powers a respectable swath of industrial operations, plus there is electric power generation. Steam is an important sort of "back office" component of the lives of many dwellers in modern economies.
What is steam?
Sorry, but we need to get everybody on the same page here. Steam is water vapor, produced by the application of heat to water. In order for steam to do work and serve as a useful energy source, it must be under pressure. There can be applications that employ steam at atmospheric pressure, but most are pressurized.

The heat goes on, the water boils, steam is produced and flows through the piping system to where it is used. Sounds simple, sounds easy. It is not. There are intricacies of designing and operating a steam system that determine its raw performance, as well as how efficiently it uses the fuel or other heat source employed to boil water. Steam utilization equipment is also carefully designed to provide its rated performance when supplied with steam of a given condition.

Steam at any given pressure has a saturation temperature, the temperature at which the vaporized water content of the steam is at its maximum level. Heat steam above its saturation temperature and you have superheated steam. Cool it below the saturation temperature and vapor will start to condense. The way in which the steam is to be used determines whether, and how much, superheat is desirable or necessary.

  • Turbine operations benefit from properly superheated steam because it avoids exposure of the turbine to liquid water droplets, generally a source of surface erosion and other accelerated wear.
  • Heat exchanger performance is based upon certain inlet conditions, one of which is the degree of superheat.
  • Maintaining sufficient superheat throughout a continuously operating steam system minimizes the need for, and size of, a condensate return system
Processes are designed to deliver a predictable output when provided with known inputs. In the case of steam, the temperature of the steam may be an input requiring control. This brings us to attemperation, which in the case of steam most often refers to lowering the temperature of a steam supply. Attemperation and desuperheating (reducing the degree of superheat) are accomplished in a similar fashion, but with differing objectives. Attemperation involves simply controlling the temperature of the steam, without any direct regard for the level of superheat. Desuperheating, as a control operation, is not directly related to the temperature of the steam, just the degree by which it exceeds the saturation temperature at the current condition. For attemperation, steam temperature measurement is all that is needed. For desuperheating, pressure and temperature measurements are needed. Decreasing the temperature of superheated steam will naturally reduce the amount of superheat.

Some process requirements may focus on temperature of the delivered steam, without regard to superheat level. Others will rely on a specified level of superheat. The application scenarios are vast, with equipment available to accomplish whatever is needed. 

Either operation can be accomplished with some sort of heat exchanger that extracts heat from the steam. A more flexible option relies on the addition of atomized water to the flowing steam to manage temperature or superheat level. Share your steam system challenges with experts, combining your own facilities and process knowledge with their product application expertise to develop effective solutions.

Tuesday, May 16, 2017

Shell and Tube Heat Exchangers

diagram of shell and tube heat exchanger
Shell and tube heat exchanger diagram
Cars are something which exist as part of the backbone of modern society, for both personal and professional use. Automobiles, while being everyday objects, also contain systems which need to be constantly maintained and in-sequence to ensure the safety of both the machine and the driver. One of the most essential elements of car ownership is the understanding of how heat and temperature can impact a car’s operation. Likewise, regulating temperature in industrial operations, which is akin to controlling heat, is a key process control variable relating to both product excellence and operator safety. Since temperature is a fundamental aspect of both industrial and consumer life, heat management must be accurate, consistent, and predictable.

A common design of heat exchangers used in the oil refining and chemical processing industries is the shell and tube heat exchanger. A pressure vessel, the shell, contains a bundle of tubes. One fluid flows within the tubes while another floods the shell and contacts the outer tube surface. Heat energy conducts through the tube wall from the warmer to the cooler substance, completing the transfer of heat between the two distinct substances. These fluids can either be liquids or gases. If a large heat transfer area is utilized, consisting of greater tube surface area, many tubes or circuits of tubes can be used concurrently in order to maximize the transfer of heat. There are many considerations to take into account in regards to the design of shell and tube heat exchangers, such as tube diameter, circuiting of the tubes, tube wall thickness, shell and tube operating pressure requirements, and more. In parallel fashion to a process control system, every decision made in reference to designing and practically applying the correct heat exchanger depends on the factors present in both the materials being regulated and the industrial purpose for which the equipment is going to be used.

The industrial and commercial applications of shell and tube heat exchangers are vast, ranging from small to very large capacities. They can serve as condensers, evaporators, heaters, or coolers. You will find them throughout almost every industry, and as a part of many large HVAC systems. Shell and tube heat exchangers, specifically, find applicability in many sub-industries related to food and beverage: brewery processes, juice, sauce, soup, syrup, oils, sugar, and others. Pure steam for WFI production is an application where special materials, like stainless steel, are employed for shell and tube units that transfer heat while maintaining isolation and purity of a highly controlled process fluid.

Shell and tube heat exchangers are rugged, efficient, and require little attention other than periodic inspection. Proper unit specification, selection, and installation contribute to longevity and solid performance.

Wednesday, May 10, 2017

High Pressure Valves for Industrial Processes and Operations

engineer working on pump and piping system oil refinery
Industrial operations present substantial
challenges to engineers and equipment
I am convinced that there is a valve out there for every conceivable application. Of course, that is not literally true, but there is an enormous array of manufacturers producing countless valve variants to meet specific requirements of the many industrial fluid processing applications.

A valve installed in a fluid process needs not only to perform its intended control function, but to stand up to the impact of several physical challenges.
cutaway view of high pressure angle valve for industrial process control
Cutaway view of high pressure angle valve
Courtesy Flowserve - Kammer
  • Temperature
  • Pressure
  • Corrosion
Any combination of these factors in the extreme can call for the use of a severe service valve. A good match between the valve ratings or capabilities and the demands imposed by the process conditions is essential for achieving safe operation and a reasonable useful valve lifespan.

Valves designed to handle very high pressure will exhibit specific attributes designed to accommodate the imposed physical stress. Body construction, assembly hardware, seats, and trim will all be noticeably heavier, stronger.

Rely on a valve specialist to contribute product expertise to the valve selection process. Combine your own process knowledge and experience with their product application expertise to develop an effective solution.



Tuesday, May 2, 2017

Operating Principles and Application of Vortex Flowmeters

vortex flow meter for steam gas or liquid
Vortex Flow Meter
Courtesy Azbil NA
To an untrained ear, the term “vortex flowmeter” may conjure futuristic, potentially Star Wars inspired images of a hugely advanced machine meant for opening channels in warp-space. In reality, vortex flowmeters are application specific, industrial grade instruments designed to measure an important element of a fluid process control operation: flow rate.

Vortex flowmeters operate based on a scientific principle called the von Kármán effect, which generally states that a fluid flow will alternately shed vortices when passing by a solid body. “Vortices” is the plural form of vortex, which is best described as a whirling mass, notably one in which suction forces operate, such as a whirlpool. Detecting the presence of the vortices and determining the frequency of their occurrence is used to provide an indication of fluid velocity. The velocity value can be combined with temperature, pressure, or density information to develop a mass flow calculation. Vortex flowmeters exhibit high reliability, with no moving parts, serving as a useful tool in the measurement of liquid, gas, and steam flow.

While different fluids present unique challenges when applying flowmeters, steam is considered one of the more difficult to measure due to its pressure, temperature, and potential mixture of liquid and vapor in the same line. Multiple types of steam, including wet steam, saturated steam, and superheated steam, are utilized in process plants and commercial installations, and are often related to power or heat transfer. Several of the currently available flow measurement technologies are not well suited for steam flow applications, leaving vortex flowmeters as something of a keystone in steam flow measurement.

Rangeability, defined as a ratio of maximum to minimum flow, is an important consideration for any measurement instrument, indicating its ability to measure over a range of conditions. Vortex flowmeter instruments generally exhibit wide rangeability, one of the positive aspects of the technology and vortex based instruments.

The advantages of the vortex flowmeter, in addition to the aforementioned rangeability and steam-specific implementation, include available accuracy of 1%, a linear output, and a lack of moving parts. It is necessary for the pipe containing the measured fluid to be completely filled in order to obtain useful measurements.
Applications where the technology may face hurdles include flows of slurry or high viscosity liquids. These can prove unsuitable for measurement by the vortex flowmeter because they may not exhibit a suitable degree of the von Kármán effect to facilitate accurate measurement. Measurements can be adversely impacted by pulsating flow, where differences in pressure from the relationship between two or more compressors or pumps in a system results in irregular fluid flow.

When properly applied, the vortex flowmeter is a reliable and low maintenance tool for measuring fluid flow. Frequently, vortex flow velocity measurement will be incorporated with the measurement of temperature and pressure in an instrument referred to as a multivariable flowmeter, used to develop a complete measurement set for calculating mass flow.

Whatever your flow measurement challenges, share them with a flow instrument specialist, combining your process knowledge with their product and technology expertise to develop effective solutions.

Saturday, April 29, 2017

Scotch Yoke Valve Actuators

Scotch Yoke Pneumatic Valve Actuator
Courtesy Flowserve - Automax
A Scotch yoke is a mechanical linkage arrangement that converts linear motion into rotational motion. A common usage of the mechanism found in modern industry is valve actuators for quarter turn valves with high torque requirements. These applications would emerge most frequently in chemical and oil and gas industrial installations.

Quarter turn valves, such and ball, plug, or butterfly valves, only require a 90 degree rotation from their fully closed to fully open positions. In this case, the Scotch yoke is not used to produce continuous rotating motion, as it may in some engine applications. For the valve actuation case, the Scotch yoke functions much like a hand on a lever. The pneumatic variants use air pressure to drive the slider in one direction until a preset stop position is reached. Usually, a spring provides a counterforce that will drive the valve to a desired fail-safe stop position in the absence of air pressure. Other combinations of driving force and fail-safe operation are available to suit differing application needs.
Diagrammatic representation of Scotch yoke valve actuator
Illustration excerpted from Automax RG Standard Pneumatic Valve Actuator IOM 
with text added
The drive assembly consists essentially of a slider, a pin, and the yoke. The slider is moved laterally by whatever power sources are appropriate for the unit (pneumatic, hydraulic, spring, hand wheel, etc.). The pin is affixed to the slider and extends through a slot in the yoke. One end of the yoke is mounted to the valve shaft. As the slider is driven through is range of motion, the pin moves with the slider and forces movement of the yoke. This movement of the yoke translates into rotational force on the valve shaft and the repositioning of the valve trim.

Selecting and configuring the right actuator and valve for any application benefits from consultation and cooperation among the process engineers and valve automation specialists. Share your process valve and automation challenges with experienced professionals, combining your own process knowledge and experience with their product application expertise to produce an effective solution.

Wednesday, April 19, 2017

Introduction to Flowmeters

magnetic-flow-meter-flowmeter
Electromagnetic Flow Meter
Courtesy Azbil N.A.
Flowmeters measure the rate or quantity of moving fluids, in most cases liquid or gas, in an open channel or closed conduit. There are two basic flow measuring systems: those which produce volumetric flow measurements and those delivering a weight or mass based measurement. These two systems, required in many industries such as power, chemical, and water, can be integrated into existing or new installations. For successful integration, the flow measurement systems can be installed in one of several methods, depending upon the technology employed by the instrument. For inline installation, fittings that create upstream and downstream connections that allow for flowmeter installation as an integral part of the piping system. Another configuration, direct insertion, will have a probe or assembly that extends into the piping cross section. There are also non-contact instruments that clamp on the exterior surface of the piping and gather measurements through the pipe wall without any contact with the flowing media.

Because they are needed for a variety of uses and industries, there are multiple types of flowmeters classified generally into four main groups: mechanical, inferential, electrical, and other.

Quantity meters, more commonly known as positive displacement meters, mass flowmeters, and fixed restriction variable head type flowmeters all fall beneath the mechanical category. Fixed restriction variable head type flowmeters use different sensors and tubes, such as orifice plates, flow nozzles, and venturi and pitot tubes.

Inferential flowmeters include turbine and target flowmeters, as well as variable area flowmeters also known as rotameters.

Laser doppler anemometers, ultrasonic flowmeters, and electromagnetic flowmeters are all electrical-type flowmeters.

The many application classes throughout the processing industries have led to the development of a wide range of flow measurement technologies and products. Each has its own advantages under certain operating conditions. Sorting through the choices and selecting the best technology for an application can be accomplished by consulting with a process instrumentation specialist. The combination of your own process knowledge and experience with their product application expertise will develop an effective solution.

Tuesday, April 11, 2017

CTi Controltech In-House Capabilities and Solutions for Combustion, Automation, and Instrumentation

CTi Controltech has operated in northern California and Nevada for many years, satisfying customers and building their capabilities into today's top flight provider of equipment and services to industrial and commercial markets. The short piece included below is a synopsis of the company's range of products and services.

Share your combustion, emission, steam, process control, and automation challenges with experts in the field. The combination of your own process knowledge with the expertise at CTi Controltech will produce effective solutions.


Tuesday, March 28, 2017

Oil and Gas Wellhead Valves Meet Special Application Challenges

oil and gas industry slab gate valve
Slab Gate Valve
Courtesy Flowserve - Valbart
Industrial valves are manufactured in a huge array of configurations to accommodate the specialized needs of a broad range of industrial process applications. The oil and gas industry is but one segment of many throughout the industrial sphere that presents its own set of application specific criteria.

Oil and gas production, essentially pulling raw material from the earth, has unique valve performance challenges. Extreme pressure and abrasive or erosive material are common elements of oil and gas production at the wellhead. The valves also need to tolerate the range of outdoor temperatures at the production site. Safe and reliable operation throughout these and a range of other conditions are part of the design criteria for these valves. Here are some of the specific valve variants and configurations applied in the oil and gas industry at the production wellhead.

oil and gas industry rising stem ball valve
Rising Stem Ball Valve
Courtesy Flowserve - Valbart
  • Slab Gate Valve - Provides metal to metal seal and employs parallel gate and seal with a preloaded means of assuring positive upstream and downstream seal. Full port design allows for pigging.
  • Expanding Gate Valve - A parallel expanding gate seals positively against both seats, which are protected from the flow medium in the open and closed positions.
  • Mud Gate Valve - Designed to provide positive closure under rigorous field conditions with abrasive media. 
  • Adjustable Choke Valve - Designed to regulate production well flow and downstream pressure. Different trim configurations provide appropriate levels of control.
  • Needle Adjustable Choke Valve - Utilizes different trim arrangement than other types to provide good flow management, abrasion resistance, erosion resistance, and reliable service over a long life with low maintenance requirements.
  • Check Valve - Check valves of various types are utilized throughout practically all fluid flow operations, essentially anywhere that fluid is supposed to flow in only one direction. Oil and gas production presents some special conditions of abrasion, erosion, and pressure that call for special accommodation in design and materials of construction.
There are other specialty valves employed at or near the wellhead, but the key take away here is that oil and gas production generally cannot be accommodated by general purpose valves. Share your oil and gas production challenges with a valve specialist. The combination of your process and production field experience with their product expertise will produce effective solutions.

Thursday, March 23, 2017

Electric Control Valve Actuators

electric valve actuator quarter turn
CVQ Electric Valve Actuator
For quarter turn valves
Courtesy Rotork
Many process control valve installations present the option of selecting either electric or pneumatic actuators as part of the control component train. Pneumatic actuators have been in use for many years, but advances in electric motor design that delivered greater torque and more precise operation have brought electric valve actuators into a prominent market position.

Electric actuators are compact and comparatively self contained, requiring only cable connections and none of the additional devices sometimes needed for a pneumatic installation. There are some points of advantage to consider with electric actuators. Rotork introduced their CVA line of electric actuators almost ten years ago, making it something of a mature product now. Here are some advantageous points about the CVA actuators that likely apply generically as well.

  • Setup is accomplished with a Bluetooth enabled device which provides quick calibration of open and closed positions, as well as establishment of valve setup parameters.
  • A separately sealed electrical connection compartment keeps motor and mechanical compartment isolated from the environment while electrical connection section cover is removed.
  • An on board datalogger records thrust and position data over time for use in asset management and service functions. Data can be downloaded by Bluetooth or transmitted by common protocol to another station.
  • Change in setpoint produces a rapid and precise change in valve position with high resolution accuracy and repeatability.
  • Actuator can be programmed to move to a preset condition in the event of a loss of electric power. The energy to achieve the failsafe position is stored in the actuator.
  • Force balance positioning used in pneumatic valves, with spring force vs. air pressure, has resilience that can result in a change in position of the valve trim in response to a bump in system pressure. Resistance from the gear train on electric drives prevents this movement.
  • Static friction of the valve packing and other parts increases the amount of force to intially get the valve moving toward a new position. The additional time required to build air pressure and force to overcome static friction results in delayed valve response, then overshoot of the new setpoint. A combination of a sensor system and the mechanical drive section of an electric actuator eliminates overshoot and delayed response.

Electric actuators can be had in quarter turn and linear versions, with torque ranges suitable for a broad range of process control applications. The datasheet below, from Rotork, provides useful illustrations of the actuator interior, along with additional detail about electric actuators. Share your process control valve requirements and challenges with product application specialists, combining your own process knowledge and experience with their product application expertise to develop the best solutions.



Friday, March 17, 2017

Innovative Boiler Water Level Gauge Delivers High Visibility

The Simpliport boiler water level gauge provides the type of performance always wanted by operators. It is visible from great distance at angles up to 180 degrees. The brightly illuminated display clearly shows what portion of the boiler contains water and what portion contains steam.

The short video provides a good demonstration. More information is available from steam system specialists. Share your combustion and steam system requirements and challenges with experts, combining your own knowledge and experience with their product application expertise to develop effective solutions.

Thursday, March 9, 2017

Clean Steam Trap Ball Valves

cutaway of sanitary ball valve on clean steam trap piping assembly
Cutaway view of sanitary ball valve on clean steam trap piping
Courtesy PBM Valve Solutions
The use of clean steam generally implies that there are substantial concerns regarding sanitary aspects of an application. Clean steam systems, from production through distribution and return, differ in many respects from systems where clean steam is not the medium.

A major consideration for sanitary applications is the practical reduction or outright elimination of dead areas in piping systems. Any section, regardless of size, that can trap liquid is considered a potential harbor of contamination.

PBM Valve Solutions addresses some challenges posed by the use of ball valves at trap locations in a clean steam system. The valve materials and design modifications make them well suited for the intended application and reduce the pipe and fitting requirements for the trap installation.

The common design for a ball valve allows some amount of fluid to be retained within the port area of the valve when it is closed. This is undesirable for a clean steam system where the steam may come in contact with manufactured product. There can also be a requirement in such a system to maintain a minimum temperature throughout the steam distribution system under all conditions, to assure sterility is maintained. The specialty clean steam trap valve has  purge holes that drain the port area to the valve outlet that leads to the steam trap. Other features of this specialty valve support the effective use of clean steam in sanitary processing.

The document below, from PBM Valve Solutions, provides more detail on the operating features of the clean steam trap ball valve. Share your steam system and fluid processing challenges with application specialists, combining your own process and facilities knowledge with their product application expertise to develop effective solutions.



Wednesday, March 1, 2017

Boiler Feedwater Deaerator

spray type feedwater deaerator for boiler
Spray type feedwater deaerator
Courtesy Williams and Davis Boilers
Boiler feedwater can require treatment in order to minimize corrosion and scaling which lead to steam system performance reduction or eventual failure and repair. There are various technologies, methods, and units of equipment which process boiler feedwater for differing challenges. One of those equipment items is a deaerator.

The purpose of a deaerator is to reduce the amount of dissolved oxygen and carbon dioxide in the feedwater. Both of these dissolved gases contribute to corrosion in the boiler and steam system. Oxygen will promote the formation of oxides with metal surfaces, commonly steel, found in most steam systems. Dissolved carbon dioxide in the feedwater will promote the formation of carbonic acid (H2CO3) which is also corrosive to metals.

Feedwater deaerators come in two basic forms. The tray type deaerator will generally have two sections, an upper domed section where feedwater is heated by system steam and dissolved gases liberated from the water, and a lower shell vessel that serves as a collecting reservoir for the degassed water. The spray type deaerator employs a single vessel or tank, with feedwater sprayed into the vessel and heated by system steam. The steam strips the dissolved gases from the feedwater, then maintains the stored feedwater at a temperature high enough to prevent gases from re-dissolving in the feedwater. Both tray and spray systems vent the removed gases.

Williams and Davis Boilers, in addition to manufacturing a broad line of steam boilers, also manufactures spray type deaerators in vertical and horizontal configurations, as well as other steam system ancillary equipment.

Share your steam system challenges with the combustion and steam experts at CTI-Controltech, combining your own process and facilities knowledge with their steam system expertise to develop effective solutions.

Tuesday, February 21, 2017

Learning From Catastrophe - Case Study of Heat Exchanger Failure

shell and tube heat exchangers in industrial plant
Shell and tube heat exchangers at industrial plant
Industrial accidents, whether minor or catastrophic, can serve as sources of learning when analyzed and studied. Operators, owners, and technicians involved with industrial chemical operations have a degree of moral, ethical, and legal responsibility to conduct work in a reasonably and predictably safe manner without endangering personnel, property, or the environment. Part of a diligent safety culture should include reviewing industrial accidents at other facilities. There is much to learn from these unfortunate events, even when they happen in an industry that may seem somewhat removed from our own.

The U.S. Chemical Safety Board, or CSB, is an independent federal agency that investigates industrial chemical accidents. Below, find one of their video reenactments and analysis of an explosion that occurred at a Louisiana chemical processing plant in 2013. A portion of the reenactment shows how a few seemingly innocuous oversights can combine with other unrecognized conditions that result in a major conflagration.

Check out the video and sharpen your sense of awareness for potential trouble spots in your own operation.

Tuesday, February 14, 2017

Continuous Liquid Level Measurement Technologies Used in Industry

Industrial pressure transmitter
Pressure measurements can be utilized to determine liquid level
Courtesy Azbil
Although continuous level measurement technologies have the ability to quantify applications for bulk solids, slurries, and granular materials, liquid level technologies stand out as being exceptionally crucial to many facets of the process control industrial sphere. Called “transmitters,” these continuous liquid level measurement devices employ technologies ranging from hydrostatic to magnetostriction, providing uninterrupted signals that indicate the level of liquid in a vessel, tank, or other container.

Hydrostatic devices focus on the equilibrium of dynamic and static liquids. There are three main types of hydrostatic transmitters:
  1. Displacer
  2. Bubbler
  3. Differential pressure
The displacer transmitters utilize a float placed within the liquid container. With its buoyancy characterized to the liquid and the application, the float, a connecting stem, and a range spring or similar counterbalance represents the liquid level in terms of the movement of the displacer (float). The displacement, or movement, of the assembly is converted into an electric signal for use by the monitoring and control system.

Bubbler transmitters are used for processing vessels that operate at atmospheric pressure. This method introduces a purge gas or an inert gas, e.g. air or dry nitrogen, into a tube extending into the liquid vessel. Precise measurement of the pressure exerted on the gas in the dip tube by the liquid in the tank is used to determine the height of the liquid.

Differential pressure (DP) transmitters rely directly on, in a basic explanation, the pressure difference between the bottom and top of the container. Precise pressure measurement is used to determine the height of the liquid in the tank. One of the most advantageous aspects of DP transmitters is that they can be used in pressurized containers, whereas displacer and bubbler transmitters cannot.

Other examples of level transmitter technologies––which are not hydrostatic devices––are magnetostrictive, capacitance, ultrasonic, laser, and radar.
magnetic liquid level indicator gauge with guided wave radar transmitter
Guided wave radar liquid level transmitter
joined with magnetic liquid level gauge
Courtesy Jerguson

In magnetostrictive level transmitters the measuring device, a float, has a series of magnets that create a magnetic field around a wire enclosed in a tube. Electrical pulses sent down the wire by the transmitter head product a torsional wave related to the position of the float, which moves with changes in liquid surface level. The transit time of the torsion wave back to the sensing head is measured and the depth of the liquid, as indicated by the float position, can be determined.

Capacitance transmitters are best applied to liquids that have high dielectric constants. Essentially, changes in the capacitance of the sensor / tank / liquid assembly will vary proportionately with the liquid level. The change in capacitance is measured and converted to an appropriate electrical signal.

Ultrasonic level transmitters emit ultrasonic energy from the top of the vessel toward the liquid. The emissions are reflected by the liquid surface and them time required for the signal to return to the source is used to determine the distance to the liquid surface.

Laser level transmitters operate similarly to an ultrasonic level transmitter. However, instead of using ultrasound signals, they use pulses of light.

Radar level transmitters involve microwaves emitting downward from the top of the container to the liquid’s surface and back again; the measurement is the entire time-frame. One variable radar level measurement echoes capacitance measurements: they both involve dielectric contact of liquid.

The precise measurement of transmit time for a wave or pulse of energy is employed in several of the technologies, the measurement of pressure in others. Each technology has a set of attributes making it an advantageous selection for a particular range of applications. Share your liquid level measurement challenges with an application expert, combining you process knowledge with their product application expertise to develop effective solutions.