Thermal Mass Flowmeters

Thermal dispersion mass flow meters provide an accurate means of mass flow measurement with no moving parts and little or no encroachment on the media flow path. There are a number of different configurations to be found among various manufacturers, but all function in basically the same manner.

Two sensors are exposed to the heat transferring effect of the flowing media. When the media composition is known, the mass flow can be calculated using the meter reading and the pipe cross sectional area. One of the flow meter sensors is heated, the other is allowed to follow the media temperature as a reference. The heat dispersion from the heated sensor is measured and used to calculate mass flow.

Some positive attributes of thermal dispersion flow meters:

• In-line and insertion configurations available to accommodate very small to large pipe sizes
• Rugged Construction
• No moving parts
• Measure liquid or gas in a wide range of applications
• Measurement not adversely impacted by changes in pressure or temperature
• Wide range of process connections 
• In-line versions provide unobstructed flow path
• Wide turndown suitable for extended flow range
• Flow rate and totalized flow
• 4-20 mA output interfaces easily with other instruments and equipment

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

Digital Bar Graph Process Displays Still Have a Place in Your Panel

Analog process value indicators are available in a wide
variety of form factors
Courtesy Ametek - Dixson

Analog indicators provide a graphic display of a process value. The value can be a setpoint for a particular operation, or the value returned from a sensor or transmitter. In the current digitally focused environment, we sometimes devalue analog displays. They do, however, have some attributes that set them apart from digital displays. Let's look at bar graph displays.

The ability of an analog display, such as a bar graph, to display useful information depends heavily on its graphical scale. The scale length and resolution should allow significant change in the process value to be displayed in a manner that is readily discernible to an operator. Bar graph displays are composed of illuminated segments, so any significant change in the process value should be sufficient to change the illuminated state of one or more segments.

The scale length and range of the display should extend across the whole of the process, and slightly beyond. An indicating range that far exceeds any possible process value can compromise the display resolution and fail to maximize the use of the instrument. For example, an operation with a maximum process value of 100 should not be paired with an indicating scale that extends to 2500. In this case, the entire range of possible process values indicated will only use four percent of the available indicating scale. A scale range extending to 150 would be more appropriate and deliver better performance.

Analog indicators, especially bar graphs, can provide rapid assessment of the state of a process value. As an illustration, it may not be necessary for an operator to know process temperature with resolution to a tenth of a degree. The key requirement may be to answer the question, "Is it too hot?". Analog displays excel at providing rapid answers to those types of decision-making questions. An onboard digital display of real time process value provides additional information about current process state.

Analog bar graph displays have a proven track record of accuracy and reliability over decades of field use. Modern units include programmable auxiliary functions and take advantage of their microprocessor based design to enable adaptation and setup for almost any application. More information is included in a data sheet below, or your can share your process indication requirements and challenges with instrumentation specialists. The combination of your own process knowledge and experience with their product application expertise will yield an effective solution.

Process Digital Bargraph Display for Industrial Control and Automation from Classic Controls, Inc.

Achieving Close Control of Process Temperature

Process Temperature Controller
Courtesy Yokogawa

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?

KNOW YOUR FLOW

First and foremost, you must have complete understanding of process fluid properties.

• 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.

MATCH SYSTEM COMPONENT PERFORMANCE WITH APPLICATION

• 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 opeartor.
• 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.

SAFETY CONSIDERATIONS

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.

Scenarios for Selecting Uninterruptible Power Supplies for Industrial Applications

UPS for industrial applications
Courtesy Ametek Solid State Controls

Process control runs on electric power. That is no secret. It follows that process uptime is first and foremost a function of the delivery of electric power. Uninterruptible power supplies provide backup power, filtering, and other functionality that helps assure the availability of clean electric power for control system operation. Even if machinery power fails, maintaining control system operation to monitor and document process conditions, and take any corrective action needed to maintain safe conditions, is paramount.

Ametek Solid State Controls manufactures world class UPS equipment and systems for industrial use. The company authored a white paper outlining three primary situations where a UPS is needed. The paper is included below for you to read.

Share your industrial power requirements with a product application specialist. Combine your facilities and process knowledge with their product application expertise to develop an effective solution.

Scenarios for Specifying an Uninterruptible Power Supply for Industrial Applications from Classic Controls, Inc.

Valve Control Monitor Adapts to Wide Range of Actuators

Valve monitor control mounted using cast NAMUR bracket
Courtesy Westlock Controls

Combining control components from various manufacturers can sometimes facilitate the most effective or desirable solution to a process control challenge. This can certainly be true when configuring a control valve installation. Getting the feature set and packaging that best fit the application requirements can yield benefits throughout the useful life of the equipment.

Westlock Controls, manufacturer of valve control monitors, provides a convenient mounting bracket that adapts the installation of their valve control monitors to actuators employing NAMUR mounting patterns. The cast stainless steel bracket is provided in one of three available mounting kits, each complete with all necessary hardware.

More detail about the adapter bracket is found in the datasheet included below. For more information, share your control valve project requirements and challenges with process control valve experts, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Stainless Steel Cast NAMUR Mounting Bracket from Classic Controls, Inc.

Pressure Measurement Handbook From Yokogawa

Pressure Transmitter
Courtesy Yokogawa

The impact of pressure on industrial processes would be difficult to understate. Pressure is an element of process control that can affect performance and safety. Understanding pressure concepts and how to effectively measure pressure within a process are key to any operator's success.

Yokogawa, a globally recognized leader in process measurement and control, has made available a handbook on pressure that covers a range of useful topics. The content starts with the very basic concepts and moves quickly to practical subjects related to process measurement and control.

The handbook will prove useful to readers at all levels of expertise. Share your process measurement challenges with application specialists, combining your process knowledge with their product application expertise to develop effective solutions.

Pressure Measurement Handbook for Process Control from Classic Controls, Inc.

Electro-Hydraulic Valve Acutators and Damper Drives

X2 Linear Acuator
Courtesy Rexa

Many valves employed in industrial processes are controlled from remote control stations. They may have a manual override mechanism in the form of a lever or handwheel, but the primary operating mechanism, or actuator, is a powered unit that responds to a control signal and provides necessary torque or linear force to position the valve appropriately.

There are several power sources used to drive valve positioning mechanisms, one of which is electro-hydraulic. This self-contained system provides the operating characteristics of a hydraulic drive system by incorporating an electrically powered fluid system into the actuator package.

The video below provides some additional detail. Consider the electro-hydraulic actuator as a candidate for your valve control applications, then share your requirements and challenges with product application experts. The combination of your process knowledge and their application expertise will yield an effective solution.