Wednesday, April 19, 2017

Ultrasonic Flow Measurement Overview

clamp on ultrasonic flowmeter llow meter
Clamp-on ultrasonic flow meter does not contact
process media
Courtesy Micronics
Ultrasonic flow meters measure, via sound waves inaudible to humans, the velocity of fluid flowing through a conduit. The conduit can be a recognizable closed piping run, or open channels, flumes, or chutes. The technology is predominantly applied to liquids and gases.

There are three types of ultrasonic flow meters, differentiated by their means of measurement. An open channel flow meter derives liquid depth by computing geometrical distance, combining it with a velocity measurement and known dimensional properties of a flume or other channel. A Doppler shift flow meter reflects ultrasonic energy off sonically reflective materials and measures the frequency shift between emission and reflection to derive a fluid velocity measurement. The contrapropogating transit-time flow meter, more recognizably, the transmission flow meter. The transmission flow meter has two versions: the in-line and the clamp-on. The in-line configuration is intrusive, with flow meter hardware extending into and exposed to the measured media. A clamp-on style ultrasonic flow meter resides on the outside of the pipe, emitting and receiving the ultrasonic pulses through the pipe wall. These process measurement tools, using ultrasound technology, have the ability to measure fluid velocity and calculate volumetric, mass, and totalized flow. The use of ultrasonic flow measurement is prevalent in the oil and gas, nuclear, wastewater, pharmaceutical, and food and beverage industries. It is also employed in energy management systems as a means to measure energy demand.

For intrusive flow meters, sensors are fitted opposite one another and alternate bouncing ultrasonic signals back and forth in the pipe, in an almost tennis-like format. In an elementary explanation, by increasing the number of sensors, engineers are able to decipher flow proportions through calculations of velocity between sensory transmissions; thereby, the flow volume can be computed.

For externally mounted flow meters, a clamp-on device affixes the flow meter measurement elements to the pipe. One special characteristic of clamp-on flow meters is the ability to transmit ultrasonic signals through piping up to four meters in diameter, making them suitable for application in very large systems such as those found in hydroelectric or wastewater installations. The clamp-on arrangement also facilitates addition of a flow measurement point to an existing system without process interruption.

The technology is pervasive in the processing industries, having its particular niche of applications where it excels. Proper installation is a key element in producing reliable and consistent results. Ultrasonic energy flow technology is used for custody transfer of natural gases and petroleum liquids. Custody transfer usually entails following industry, national, and government standards and regulations. Other popular applications include compressed air system monitoring and energy usage metering.

Ultrasonic flow meters, with no moving parts, are comparatively low maintenance and self-diagnosing. Temperature and pressure measurements are needed to calculate mass flow of gases. When measuring liquid mass flow in pipes, it is generally necessary for the pipe cross section to be media filled in order to obtain reliable results.

Whatever your flow measurement challenge, share it with a process measurement specialist. Combine your process knowledge with their product application expertise to develop effective solutions.

Tuesday, April 11, 2017

Hile Controls of Alabama - Video

We made this short video to illustrate the markets and industries we serve. Please check it out and be sure and contact Hile Alabama and share your process control, instrumentation, and automation challenges with experts. Let's combine your process knowledge and experience with our product application expertise to formulate and effective solution.

Tuesday, April 4, 2017

Appropriate Application for Pressure Regulator Valve and Back Pressure Regulator

pilot operated sliding gate pressure regulator
Pilot Operated Sliding Gate
Pressure Regulator
Courtesy Jordan Valve
Fluids move throughout processes, driven by pressure produced with mechanical or naturally occurring means. In many cases the pressure generated by the driving source is substantially greater than what may be desired at particular process steps. In other cases, the operation may dictate that a minimum pressure be maintained within a portion of the process train. Both cases are handled by the appropriate valve type, designed specifically to regulate pressure.

A pressure regulating valve is a normally open valve that employs mechanical means, positioning itself to maintain the outlet pressure set on the valve. Generally, this type of valve has a spring that provides a countervailing force to the inlet pressure on the valve mechanism. An adjustment bolt regulates the force produced by the spring upon the mechanism, creating an equilibrium point that provides flow through the valve needed to produce the set outlet pressure. A typical application for a pressure regulator is to reduce upstream or inlet pressure to a level appropriate for downstream processing equipment.

self operated pressure regulator valve
Self-operated Pressure Regulator
Courtesy Jordan Valve

Back pressure valves are normally closed, operating in a logically reversed fashion to pressure regulators. Where pressure regulators control outlet pressure, a back pressure valve is intended to maintain inlet pressure. Similar internals are present in the back pressure valve, with the valve action reversed when compared to a pressure regulator. An inlet pressure reduction in the back pressure valve will cause the valve to begin closing, restricting flow and increasing the inlet pressure. A representative application for a back pressure valve is a multi-port spray station. The back pressure valve will work to maintain a constant setpoint pressure to all the spray nozzles, regardless of how many may be open at a particular time.

Both of these valve types are available in an extensive array of sizes, capacities, pressure ranges, and materials of construction to accommodate every process requirement. Share your fluid control challenges with a process control specialist. Combining your process knowledge with their product application expertise will produce effective solutions.

Wednesday, March 22, 2017

Standalone Process Temperature Controllers

process controller with PLC functions
Sophisticated process controller features
multiple inputs and control loops, plus
PLC logic functions
Courtesy Eurotherm 
The regulation of temperature is a common operation throughout many facets of modern life. Environmental control in commercial, industrial, and institutional buildings, even residential spaces, uses the regulation of temperature as the primary measure of successful operation. There are also countless applications for the control of temperature found throughout manufacturing, processing, and research. Everywhere that temperature needs to be regulated, a device or method is needed that will control the delivery of a heating or cooling means.

For industrial process applications, the temperature control function is found in two basic forms. It can reside as an operational feature within a programmable logic controller or other centralized process control device or system. Another form is a standalone process temperature controller, with self-contained input, output, processing, and user interface. Depending upon the needs of the application, one may have an advantage over the other. The evolution of both forms, integrated and standalone, has resulted in each offering consistently greater levels of functionality.

There are two basic means of temperature control, regardless of the actual device used. Open loop control delivers a predetermined amount of output action without regard to the process condition. Its simplicity makes open loop control economical. Best applications for this type of control action are processes that are well understood and that can tolerate a potentially wide variation in temperature. A change in the process condition will not be detected, or responded to, by open loop control. The second temperature control method, and the one most employed for industrial process control, is closed loop.

Closed loop control relies on an input that represents the process condition, an algorithm or internal mechanical means to produce an output action related to the process condition, and some type of output device that delivers the output action. Closed loop controllers require less process knowledge on the part of the operator than open loop to regulate temperature. The controllers rely on the internal processing and comparison of input (process temperature) to a setpoint value. The difference between the two is the deviation or error.  Generally, a greater error will produce a greater change in the output of the controller, delivering more heating or cooling to the process and driving the process temperature toward the setpoint.

The current product offering for standalone closed loop temperature controllers ranges from very simple on/off regulators to highly developed products with multiple inputs and outputs, as well as many auxiliary functions and communications. The range of product features almost assures a unit is available for every application. Evaluating the staggering range of products available and producing a good match between process requirements and product capabilities can be facilitated by reaching out to a process control products specialist. Combine your own process knowledge and experience with their product application expertise to develop effective solution options.

Friday, March 17, 2017

Positive Displacement Liquid Flowmeters

positive displacement liquid flow meter for industrial process measurement
Positive displacement flowmeter
Rotating gear type
Courtesy Flow Technology
Unlike other liquid flow measurement technologies that rely on the measurement of a physical property of flowing media to produce a volumetric or mass flow measurement, a positive displacement flowmeter provides a direct indication of actual volumetric flow rate. There are a number of different positive displacement flowmeter designs in use throughout industrial, commercial, and even residential installations.

  • Oscillating piston
  • Gear
  • Nutating disk
  • Rotary vane
  • Diaphragm 

Each of the designs, and any others that would be classified as positive displacement, contain a mechanical structure through which the fluid must travel on its path from source to target. The fluid motion drives the mechanical assembly, which contains pathways of known volume. As the fluid motion drives the positive displacement flowmeter assembly, its rotational, oscillating, or other regular movement is counted, often by electronic means using magnetic pickups on moving assembly. The counts can be used to indicate current flow rate, or totalized to measure total flow volume. Additional inputs about fluid properties can be used to calculate mass flow, as well.

Positive displacement flowmeters can be applied to liquid or gaseous media, with the selection of the mechanical internals being a significant factor in the suitability of a design for a particular application.

Rotating gear flowmeters are especially well suited for high viscosity liquids. As the fluid drives the gear assembly, liquid is trapped in the spaces between the gear lobes and the housing. The rotation of the gear moves the liquid from the inlet port to the outlet. The product datasheet provided below has a good illustration of the geared positive displacement flowmeter operating principle. In many cases, a positive displacement flowmeter appears similar to a positive displacement pump, with the primary difference being that the pump is provided with its own motive power (a motor) and the flowmeter is driven by the process fluid.

Share all of your flow measurement requirements and challenges with process instrumentation experts, combining your own process knowledge and experience with their product application expertise to develop effective solutions. 

Friday, March 10, 2017

Rolling Diaphragm Air Cylinders Provide Linear Motion

rolling diaphragm air cylinder for linear motion from air pressure
Diaphragm Air Cylinder
Courtesy ControlAir, Inc.
Linear motion is a mainstay of automation. A variety of methods, product designs, and power sources are employed in delivering linear motion in response to a control signal. A commonly used methodology is the pneumatically driven piston.

Air cylinders convert air pressure into linear motion using a piston sealed to the inner walls of the cylinder. The introduction of sufficient air pressure into the cylinder forces the piston to move, driving a shaft that is connected to process equipment or devices. A single acting air cylinder is provided with a mechanical means of delivering an opposing force to the motion caused by increasing air pressure. Often a spring, this mechanical force will move the piston in the direction opposite that of increasing air pressure. As the air pressure is reduced, the piston will move toward its normal, or default, position.

A double acting air cylinder enables the introduction of air pressure on either side of the piston, providing air powered movement in both directions. In this design, a loss of air pressure will result in the load driving the piston to a default position, but also provides some flexibility in operation not inherent in the spring return single action design.

The method used to create a seal between the piston and the cylinder wall impacts the operation and longevity of an air cylinder. A seal affixed to the piston that will slide along the cylinder wall as the piston is driven to each new position encumbers operation with friction and stiction. Friction will cause wear on the seal material, with its deterioration eventually impacting response of the cylinder to a control signal. Stiction, also called "static friction" or "stationary friction" refers to the resistance to relative motion of two bodies in contact with one another. In practice, we see stiction as the reason why it often takes more force to get the piston moving than it does to keep it in motion. This also causes inaccuracy in linear positioning of the load.

ControlAir overcomes both drawbacks with their Rolling Diaphragm Air Cylinders. Instead of a fixed seal between the piston and cylinder wall, a flexible diaphragm connects to the leading edge of the piston and the end of the cylinder. The piston diameter is sufficiently less than that of the cylinder, providing space for the diaphragm to roll up as the piston changes position. The design delivers negligible levels of resistance to piston movement, with resulting superior positioning capabilities.

The datasheet provided below has more detail and cutaway illustrations of both single and double acting versions, so you can see how the diaphragm concept functions. Share your linear motion and automation challenges with process control experts, combining your own experience and knowledge with their expertise to develop the most effective solutions.

Friday, March 3, 2017

Sanitary Steam Trap for Tank Heating Applications

sanitary steam trap with bypass
Mark 934 Sanitary Steam Trap
Courtesy Steriflow
Saving space, reducing parts count, minimizing potential leak points, delivering good performance under all anticipated conditions, and cost savings are all hallmarks of a successful product adaptation. The Mark 934 Sanitary Steam Trap from Steriflow accomplishes all of these things for tank heating operations in food, beverage, or biopharma settings.

The innovative steam trap is essentially two different sized traps built into a single unit. One path employs a large orifice to accommodate large flows during process heat-up, replacing the more traditional bypass line with its additional piping, fittings, and specialties. A smaller orifice handles flow required for maintenance of tank temperature. The activation of either path is automatically controlled in response to the load on the unit.

The video below provides a more in depth explanation, description, and illustration of how the Mark 934 Sanitary Steam Trap functions.

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

Thursday, February 23, 2017

Melt Pressure Measurement

section view of plastics extruder
Section view of basic plastic extruder
The manufacture of plastic parts, extrusions, and films are all similar in that they involve the melting of solid plastic, then the forming of it into some output product. In a common extrusion process, dry solid base material, plastic flakes, pellets, powder, or granules, is fed into a screw. The screw is within a tubular housing called a barrel and is driven rotationally by a motor. The machining of the screw, and its rotation, forces the plastic material into an continually decreasing volume as it moves along the length of the screw/barrel assembly. The friction and pressure induced upon the plastic, as well as some carefully controlled heating along the barrel, melt the plastic in a predictable fashion. The melted plastic is forced through a breaker plate supporting screens that serve as filters to retain particulate contaminates from the liquid plastic. The liquified plastic, called a "melt", is driven by the screw motion out the end of the machine and into a forming stage of the process.

Producing melt with the proper characteristics for the forming stage involves careful measurement and control of temperature along the barrel. Multiple PID controllers and heaters typically create several heat zones along the screw length. Monitoring the melt pressure is also an important element of process control.

One company, GP:50 Melt Pressure, manufactures temperature sensors, pressure transducers, and other measurement equipment specifically tailored for the plastics industry. The company's sharpened focus on a single industry has produced a range of specialized products that meet specific application requirements and interface well with the machinery and systems used in plastics forming. Pressure and temperature sensors and transmitters are configured with options that reflect the requirements of plastic forming operations, a reflection of the company's extensive experience in this arena.

Share your plastics forming requirement and challenges with a product specialist, combining your process knowledge with their product application expertise to develop effective solutions.
melt pressure and temperature sensors for plastic forming

Monday, February 13, 2017

Load Cell Application in Process Measurement

force weight load cell process instrument
The Model G5 can process signals from mulitple
load cells
Courtesy BLH/Nobel
In industrial application of process measurement and control, principles of the physical sciences are combined with technology and engineering to create devices essential to modern high speed, high accuracy system operation. Years of research, development, and the forward march of humanity’s quest for scientific knowledge and understanding yields packaged devices for process measurement that are easily applied by system designer and operators.

Load cells are the key components applied to weighing component or processed materials in modern industrial operations. Load cells are utilized throughout many industries related to process management, or just simple weighing operations. In application, a load cell can be adapted for measurement of items from the very small to the very large. 

In essence, a load cell is a measurement tool which functions as a transducer, predictably converting force into a unit of measurable electrical output. While many types of load cells are available, one popular cell in multiple industries is a strain gauge based cell. Strain gauge cells typically function with an accuracy range between 0.03% and 0.25%. Pneumatically based load cells are ideal for situations requiring intrinsic safety and optimal hygiene. For locations without a power grid, there are even hydraulic load cells, which function without need for a power supply. These different types of load cells follow the same principle of operation: a force acts upon the cell (typically the weight of material or an object) which is then returned as a value. Processing the value yields an indication of weight in engineering units. 

For strain gauge cells, deformation is the applied operational principal, where extremely small amounts of deformation, directly related to the stress or strain being applied to the cell, are output as an electrical signal with value proportional to the load applied to the cell. The operating principle allows for development of devices delivering accurate, precise measurements of a wide range of industrial products. 

Load cell advantages include their longevity, accuracy, and adaptability to many applications, all of which contribute to their usefulness in so many industries and applications. A common place to find a strain gauge load cell in use is off a causeway on a major highway at a truck weigh station. Through innovation, load cells have been incorporated in an efficient measuring system able to weigh trucks passing through the station, without having each stop. Aircraft can be weighed on platform scales which utilize load cells, and even trains can be weighed by taking advantage of the robust and dependable nature of the transducers. 

Thanks to their widespread incorporation and the sequential evolution of technology, load cells are a fantastically useful tool in process measurement and control. Share your process weighing challenges with application experts, combining your own process expertise with their product knowledge to develop an effective solution.

Thursday, February 9, 2017

Hile Adds New Programmable Automation Controller

modular programmable automation controller
One version of the Eurotherm T2750
Programmable Automation Controller
now offered by Hile Controls of Alabama
Hile Controls of Alabama recently added the Eurotherm T2750 line of programmable automation controllers to its already broad offering of Eurotherm process recorders and controllers.

The T2750 is a high performance modular control unit that provides redundancy and capability that are unmatched in a consolidated single unit. The controller backplane, of which there are several variants to accommodate the scope of I/O needed for a process, can be populated from an extensive array of I/O and function modules providing a customized setup that closely matches project requirements.

Unit functionality includes:

  • I/O Block
  • Communications
  • Signal Conditioning
  • Control
  • Timing
  • Logic
  • Math
  • Valve and Motor Control
  • Diagnostics
  • Recorder
  • More
There is much more to learn about the highly capable T2750 Programmable Automation Controller. A datasheet is included below, but your interest will be best served by contacting a product application specialist and sharing your process control challenges. The combination of your process knowledge and their product application expertise will develop effective solutions.

Wednesday, February 1, 2017

PLC Enhanced With Integrated HMI, PID, Recording, and More

PLC programmable logic controller with touchscreen HMI PID and recorder
E+PLC100 Precision PLC
Courtesy Eurotherm
Industrial process control applications can present multi-faceted challenges to those responsible for designing them. There can be many small operations that must coordinate and combine into a larger one. Selecting and configuring hardware to develop the necessary inputs, execute control functions, and connect with machinery via controller outputs may prove to be only one layer of several that comprise a well functioning online process operation.

For smaller scale projects, Eurotherm has developed a product that integrates many of the functions needed to develop and execute a process control operation. The E+PLC100 bundles multiple necessary hardware components into a compact unit.
  • PID control function
  • Touchscreen display
  • On board process recording
  • Analog inputs
  • Digital inputs
  • Relay outputs
  • Digital outputs
One can think of the unit as a PLC with built-in PID control and recording, or as a PID controller with logic control and recording. Whatever the case, it can simplify the hardware configuration for a project immensely. Instead of researching and specifying separate controllers, HMI, PLC, I/O, and recording devices and getting them all connected, powered, and coordinated, just configure and program the E+PLC100 with all the functions needed in a single unit. Space savings are substantial, as well as cost, by eliminating much of the time for design, assembly, and configuration of multiple hardware units.

The programming of the unit is intuitive, executed on a PC using the companion software. There is benefit to having the whole program for the process on a single need to coordinate the programming or operation of multiple hardware units.

There is much more to learn about the value and features of this truly capable precision PLC. A product brochure is included below, but best results will come from sharing your ideas and process control challenges with a product application specialist. Combining your process knowledge with their product application expertise can streamline your project completion time and move quickly toward an effective solution.

Friday, January 27, 2017

Insulation Blankets From Unitherm International

pipe insulation blankets jackets covers
Insulating covers for pipe, fittings, valves
Courtesy Unitherm International
Whether for freeze protection, energy conservation, or personnel safety, insulating blankets and jackets can provide adequate levels of insulating performance in a removable form.

Unitherm International fabricates an extensive array of standard shapes to accommodate almost every conceivable fitting, valve, strainer, or other device found in a piping system. Custom fabrications are available, as well. The insulation jackets are universal and modular in their application, simple to install, rugged and long lasting, delivering energy conservation values far in excess of their cost. Removal and reinstallation of the insulation assembly is easily accomplished when access to the protected fitting or device is required.

A similar assembly is also available as a heated jacket or blanket that delivers even and controlled heat to maintain minimum temperatures in the covered or enclosed item. There are almost uncountable applications for the standard and custom shapes available.

There is more to learn about how insulating jackets and blankets can be applied to improve energy performance and protect assets and personnel. Share your challenges with a product application expert, combining your process and facilities knowledge with their application expertise to develop effective solutions.

Thursday, January 19, 2017

Application of Pyrometers in Industrial Settings

Multi-wavelength Infrared Pyrometer
Courtesy Williamson
Pyrometers provide a means of measuring the surface temperature of an object from a distance and without having to physically contact the object. Clearly these are useful tools for many operations and industries. The ability to measure temperature without contact provides isolation of the sensor from the target, as well as the ability to take temperature readings from a distance. A pyrometer does not rely upon intimate contact between sensor and measurement point. This is helpful is scenarios where the shape, location, or content of an object does not accommodate the installation of a temperature sensor. Service technicians can make great use of portable pyrometers when diagnosing machinery or process operation issues.

Pyrometers rely upon the gathering of radiation emitted from the measured surface. The instrument collects the radiation through its optical system and focuses it onto a collector or measuring element. Further internal processing produces the temperature reading in engineering units. There are several variants of IR (infrared) technology applied to pyrometers, but all operate on the same general principle.

Obtaining reliable measurements with pyrometers can require some knowledge and awareness of the emissive properties of the material being measured. There are some applications that are better served through the use of a particular IR measurement technology.

Multi-wavelength pyrometers employ measurement across a number of wavelengths to offset the effects of what are referred to as "non-greybody materials" that adversely impact readings derived through the use of other IR technologies. Algorithms are developed for specific applications that will provide accurate emissivity and temperature readings. Some examples of non-greybody materials.

  • Aluminum
  • Magnesium
  • Stainless Steel
  • Brass
  • Bronze
  • Copper
  • Zinc
You can see from the list that many industrial and commercial applications will benefit from the use of multi-wavelength IR measurement. More detail about pyrometers for industrial use are in the document included below. Share your temperature measurement challenges with an application expert and combine your facility and process knowledge with their product application expertise to develop an effective solution.

Tuesday, January 10, 2017

Accurate Thermal Metering For Building HVAC Energy Management

energy management meter btu meter ultrasonic inline thermal energy meter
Ultrasonic In-line Thermal Energy Meter
Courtesy Micronics
The modern business climate has, for some now, been spooling up demand for accountability and, even more so, efficiency. Whether you think of efficiency as "doing more with less" or just avoiding the waste of financial, human, or natural resources the end result is the same and calls for similar prerequisites.

We live in a society of buildings, each with a mapped out function. Most buildings are predominantly occupied by people, bringing a requirement to maintain temperature, relative humidity, and air quality at levels of suitable comfort for human occupants. The energy consumption involved with providing that level of comfort stands as a bold line item in the operating expense ledger for any building. That is where accountability and efficiency come in. It is in the building stakeholders' interest to have knowledge regarding rates and quantity of thermal energy usage, as well as efficiency measures of delivered output per unit of input energy.

HVAC (Heating, Ventilation, Air Conditioning) primarily is an endeavor that generates and moves thermal energy throughout an enclosed space. Commercially available technology now allows a building operator to accurately measure that movement of thermal energy throughout a system or building. The process is generally called BTU metering and has a number of justifiable benefits.

  • Real time equipment performance measurement.
  • Sub metering can indicate specific areas of consumption.
  • Ability to directly bill multiple tenants in a single building for their thermal energy usage.
  • Monitor and balance energy flows.

BTU metering essentially involves inlet and outlet temperature measurement of heat transfer liquids, along with their flow rate. While the principle is simple, the intricacies of the measurement methods and equipment accuracy can have a substantial impact on the accuracy, and thus the benefit, of the measurement data. Additionally, adding more instrumentation to an already complex system can create an additional on-going maintenance and calibration burden to retain the necessary levels of accuracy and function. Success at gaining the benefit of the performance data while minimizing the additional maintenance burden due to the instrumentation should be the goal.

One solution calls for the use of clamp on or in-line ultrasonic flow meters to measure liquid flow, coupled with temperature measurement in a single unit that will perform necessary calculations and provide output data in useful engineering units. An overarching benefit of the clamp on meter is its non-invasive nature, allowing its retrofit to in-place systems with no disturbance to existing piping. Here are some other characteristics of a highly effective BTU measurement unit:
  • No wear mechanism as part of the flow measurement unit
  • Traceable accuracy of flow and temperature measurements
  • Simple installation in new or retrofit applications without disruption to system operation
  • Reliable and maintenance free operation
  • Accurate measurement from near zero flow rate to maximum system flow
  • Stable sensing with no zero drift
  • Communications protocol to match building energy management system
  • Large storage cache for data, in case of communication failure
  • Common output signals, 4-20 ma or other, usable with selected ancillary equipment
Selecting the right equipment or instrumentation is the most important step along the path of adding measurement capability to increase efficiency. Without a solid stream of reliable data, useful decisions become difficult. Contact a product application specialist and share your requirements and goals. Combining your process and system knowledge with their product application expertise will produce a good outcome.

Tuesday, January 3, 2017

Close Control of Temperature in Liquid Processes

industrial temperature sensors rtd thermocouple
Temperature sensor or transmitter assemblies for industrial use
Courtesy Weed Instrument
Temperature control is a common operation in the industrial arena. Its application can range across solids, liquids, and gases. The dynamics of a particular operation will influence the selection of instruments and equipment to meet the project requirements. In addition to general performance requirements, safety should always be a consideration in the design of a temperature control system involving enough energy to damage the system or create a hazardous condition.

Let's narrow the application range to non-flammable flowing fluids that require elevated temperatures. In the interest of clarity, this illustration is presented without any complicating factors that may be encountered in actual practice. Much of what is presented here, however, will apply universally to other scenarios.
What are the considerations for specifying the right equipment?


First and foremost, you must have complete understanding of certain characteristics of the fluid.

  • Specific Heat - The amount of heat input required to increase the temperature of a mass unit of the media by one degree.
  • Minimum Inlet Temperature - The lowest media temperature entering the process and requiring heating to a setpoint. Use the worst (coldest) case anticipated.
  • Mass Flow Rate - An element in the calculation for total heat requirement. If the flow rate will vary, use the maximum anticipated flow.
  • Maximum Required Outlet Temperature - Used with minimum inlet temperature in the calculation of the maximum heat input required.


Heat Source - If temperature control with little deviation from a setpoint is your goal, electric heat will likely be your heating source of choice. It responds quickly to changes in a control signal and the output can be adjusted in very small increments to achieve a close balance between process heat requirement and actual heat input.

Sensor - Sensor selection is critical to attaining close temperature control. There are many factors to consider, well beyond the scope of this article, but the ability of the sensor to rapidly detect small changes in media temperature is a key element of a successful project. Attention should be given to the sensor containment, or sheath, the mass of the materials surrounding the sensor that are part of the assembly, along with the accuracy of the sensor.

Sensor Location - The location of the temperature sensor will be a key factor in control system performance. The sensing element should be placed where it will be exposed to the genuine process condition, avoiding effects of recently heated fluid that may have not completely mixed with the balance of the media. Locate too close to the heater and there may be anomalies caused by the heater. A sensor installed too distant from the heater may respond too slowly. Remember that the heating assembly, in whatever form it may take, is a source of disturbance to the process. It is important to detect the impact of the disturbance as early and accurately as possible.

Controller - The controller should provide an output that is compatible with the heater power controller and have the capability to provide a continuously varying signal or one that can be very rapidly cycled. There are many other features that can be incorporated into the controller for alarms, display, and other useful functions. These have little bearing on the actual control of the process, but can provide useful information to the operator.

Power Controller - A great advantage of electric heaters is their compatibility with very rapid cycling or other adjustments to their input power. A power controller that varies the total power to the heater in very small increments will allow for fine tuning the heat input to the process.

Performance Monitoring - Depending upon the critical nature of the heating activity to overall process performance, it may be useful to monitor not only the media temperature, but aspects of heater or controller performance that indicate the devices are working. Knowing something is not working sooner, rather than later, is generally beneficial. Controllers usually have some sort of sensor failure notification built in. Heater operation can be monitored my measurement of the circuit current.


Any industrial heater assembly is capable of producing surface temperatures hot enough to cause trouble. Monitoring process and heater performance and operation, providing backup safety controls, is necessary to reduce the probability of damage or catastrophe.

High Fluid Temperature - An independent sensor can monitor process fluid temperature, with instrumentation providing an alert and limit controllers taking action if unexpected limits are reached.

Heater Temperature - Monitoring the heater sheath temperature can provide warning of a number of failure conditions, such as low fluid flow, no fluid present, or power controller failure. A proper response activity should be automatically executed when unsafe or unanticipated conditions occur.

Media Present - There are a number of ways to directly or indirectly determine whether media is present. The media, whether gaseous or liquid, is necessary to maintain an operational connection between the heater assembly and the sensor.

Flow Present - Whether gaseous or liquid media, flow is necessary to keep most industrial heaters from burning out. Understand the limitations and operating requirements of the heating assembly employed and make sure those conditions are maintained.

Heater Immersion - Heaters intended for immersion in liquid may have watt density ratings that will produce excessive or damaging element temperatures if operated in air. Strategic location of a temperature sensor may be sufficient to detect whether a portion of the heater assembly is operating in air. An automatic protective response should be provided in the control scheme for this condition.

Each of the items mentioned above is due careful consideration for an industrial fluid heating application. Your particular process will present its own set of specific temperature sensing challenges with respect to performance and safety. Share your requirements with temperature measurement and control experts, combining your process knowledge with their expertise to develop safe and effective solutions.