Key Applications of Thermal Mass Flowmeters

Thermal mass flowmeters work on the principle that when you place a heated object in the midst of a fluid flow stream and measure how much heat the fluid transfers away from the heated object, then you can be able to determine the mass flow rate. Industrial thermal mass flowmeters consists of a specially designed flow tube with two temperature sensors inside: One that is heated and one that is unheated. The heated sensor acts as the mass flow sensor (cooling down as flow rate increases) while the unheated sensor serves to compensate for the “ambient” temperature of the process fluid.  The following diagram shows an example of a thermal mass flowmeter from Magnetrol.

Magnetrol Thermal Flowmeter

An important factor in the calibration of a thermal mass flowmeter is the specific heat of the process fluid. Fluid with high specific heat values make good coolants because they are able to remove much heat energy from hot objects without experiencing great increases in temperature. Since thermal mass flowmeters work on the principle of convective cooling, this means a fluid having a high specific heat value will elicit a greater response from thermal mass flowmeter than exact same mass flow rate of a fluid having a lesser specific heat value. Therefore it is paramount that you know the specific heat value of the fluid you plan to measure with a thermal mass flowmeter and be assured that its specific heat value will remain constant. For this reason, thermal mass flowmeters are not suitable for measuring the flow rates of fluid streams whose chemical composition is likely to change over time.

Another potential limitation of thermal flowmeters is the sensitivity of some designs to changes in flow regime. Since the measurement principle is based on heat transfer by fluid convection, any factor influencing the convective heat-transfer efficiency will translate into a perceived difference in mass flow rate. Turbulent flows are more efficient at heat convection than laminar flows. Therefore, a change in flow regime from turbulent to laminar will cause a calibration shift for this design of thermal mass flowmeters.

So what are some of the applications where thermal flowmeters are used?

Generally thermal flowmeters are used in applications where the composition of the fluid is known especially in purified gases. Having said that, lets look at some of the areas where thermal flowmeters are commonly used:

Natural Gas

Flow measurement of natural gas fuel usage is important for combustion efficiency as well as general energy management projects for both industrial and commercial facilities. Thermal mass flowmeters will monitor the flow to individual combustion sources.

Air Efficiency

In combustion applications, thermal mass flow meters can ensure repeatability of air flow measurements to obtain an efficient air-to-fuel ratio. On compressed air, it is common to measure for plant allocation or to determine leaks.

Tank Blanketing

Nitrogen is frequently used to maintain an inert environment in the vapor space of a tank. Thermal meters are ideally suited for measuring the flow of nitrogen in such applications because they support mass measurement, they are easily installed into the pipe & are excellent at measuring low flow rates.

You can also read: 

• The Ultimate Guide to Industrial Flow Instruments
• How Pitot Tubes are used In Flow Measurement

Flare & Vent Gas

Thermal mass meters are a particularly good fit for flare measurement. Flares can range from vent gases at atmospheric pressure to high flow applications needing extended turn down. Oil and Gas is a common industry here.

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Biogas

Both the landfills and anaerobic digesters at wastewater plants produce a mixture primarily composed of methane and carbon dioxide. Excellent low flow sensitivity, hot tap capabilities and mixed gas calibration make thermal mass flow measurement a popular technology.

Source: Magnetrol

Types of Proximity Sensors used in Industrial Control

Almost every automated manufacturing operation has sensors that ensure that the system is working correctly.

Examples of Sensors that are used in industrial control are:

Non-Contact Presence Sensors (Proximity Sensors)

Contact sensors are often avoided in automated systems because wherever parts touch there is wear and a potential for eventual failure of the sensor. Automated systems are increasingly being designed with non-contact sensors. The three most common types of non-contact sensors in use today are:

• Inductive proximity sensor
• Capacitive proximity sensor
• Optical proximity sensor

The above sensors are actually transducers, but they include control circuitry that allows them to be used as switches. The circuitry changes an internal switch when the transducer output reaches a certain value.

Hall Effect Limit Switch

The inductive Sensor

This is the most widely used non-contact sensor due to its small size, robustness, and low-cost. This type of sensor can only detect the presence of electrically conductive materials.

The DC power supplied is used to generate AC in an internal coil, which in turn causes an alternating magnetic field. If no conductive materials are near the face of the sensor, the only impedance to the internal AC is due to the inductance of the coil. If however, a conductive material enters the changing magnetic field, eddy currents are generated in that conductive material, and there is a resultant increase in the impedance to the AC in the proximity sensor. A current sensor, also built into the proximity sensor detects when there is a drop in the internal AC current due to increased impedance. The current controls a switch providing the output.

Inductive Sensor

 

Capacitive proximity Sensors

These sensors sense the target objects due to the target’s ability to be electrically charged. This works both on conductors and non-conductors.

Inside the sensor is a circuit that uses the supplied DC power to generate AC, to measure the current in the internal AC circuit, and to switch the output circuit when the amount of AC current changes. Unlike the inductive sensor, the AC does not drive a coil, but instead tries to charge a capacitor. The AC can move current into and out of this plate only if there is another plate nearby that can hold the opposite charge. The target being sensed acts as the other plate.

Capacitive Proximity Sensor

If this object is near enough to the face of the capacitive sensor to be affected by the charge in the sensor’s internal capacitor plate, it will respond by becoming oppositely charged near the sensor, and the sensor will then be able to move significant into and out of its internal plate.

Optical Proximity Sensors

These are widely used in automated systems because they have been available longer and some can fit into small locations. They are commonly known as light beam sensors of the thru-beam type or of the retro-reflective type. A complete optical proximity sensor includes a light source, and a sensor that detects the light. The light source is supplied because it is usually critical that the light be tailored for the light sensor system. The light source generates a light of a particular frequency which is able to be detected by the light sensor in use. Infra-red light is used in most optical sensors. To make the light sensing system more foolproof, most optical proximity sensor light sources pulse the infra-red light on and off at a fixed frequency. The light sensor circuit is designed so that light that is not pulsing at this frequency is rejected.

Optical Proximity Sensors

The light sensor is a semiconductor device such as a photo diode which generates a small current when light energy strikes it or more commonly a photo transistor or a photodarlington that allows current to flow if light strikes it.

You can also read: Use of Smart Sensors in Industrial Measurement and Control Systems

Some of the manufacturers of proximity sensors include:

• Siemens
• Omron

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Programmable Logic Controllers (PLC)

Programmable logic controllers (PLC) play an important role in automation sector. Various industries like Food & Beverage, Chemical, Petrochemical, Power generation etc.  use PLC.

We have several types of PLC designs:

Compact PLC: This is built by several modules within a single case. The I/O capabilities are decided by the manufacturer and not the user.

Modular PLC: This is built with several components that are plugged into a common rack or bus with extended I/O capabilities. It contains power supply module, CPU and other I/O modules that are plugged together in the same rack, which are from the same manufacturers or from different manufacturers.

Soft PLC: This is an advanced PLC system that consists of compact, rack mounted components such as power supplies, I/O modules and a CPU which embeds a powerful PLC Control software.

Programming Languages of PLC

There are several programming languages used to write programs in a PLC. They include but not limited:

• Ladder Diagram
• Instruction List
• Functional Block Diagram
• Sequential Function Chart
• Structured Text

So what are some of the components that make up a Programmable Logic Controllers?

PLC  System

Functions of each component:

CPU – This the unit that contains microprocessors

Input and Output Sections – This is where the processor receives information from external devices and communicates information to external devices.

Power Supply Unit– It converts the Main AC voltage to low DC voltage.

Programming device – Used to enter the required program into the memory of the processor.

Memory Unit – This is where the program is stored that is used to control actions.

The Operation of a PLC

Check the input status: First the PLC takes a look at each I/O to determine if it is on or off.

Execute Program: Next the PLC executes the program one instruction at a time. 

Update output status: Finally the PLC updates the outputs. It updates the outputs based on which inputs were on during the first step. 

 

The Working of a PLC system

Advantages of PLC:

• More flexibility
• Lower cost
• Increased reliability
• Faster response
• Easier to troubleshoot
• Communication capability
• Remote control capability

Disadvantages:

• They can render some jobs redundant
• They have a high initial cost
• If a Programmable logic controller stops, then the production stops 

Industrial Applications of PLCs

• Food and Beverage industry
• Gas and Water Filling Stations
• Power Sector
• Bottling Plants

You can also read: 

• How to Integrate PLC into your Control System
• The Transition from Relays to PLC systems

Some of the Top PLC Brands in the world include:

• General Electric
• Toshiba
• Siemens
• Allen Bradley
• Omron

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How to upgrade your Legacy Equipment for industry 4.0

Scholar and leadership expert Warren Bennis once said, “In life, change is inevitable. In business, change is vital.” This wisdom resonates with every business owner, but none more than the manufacturer.

We are in the midst of a new industrial revolution, one which will significantly impact the manufacturing industry. Experts are calling it Industry 4.0, the fourth wave in the industrial revolution behind steam power, electricity and computing.

According to TechRadar, Industry 4.0 is “the label given to the gradual combination of traditional manufacturing and industrial practices with the increasingly technological world around us.” Industry 4.0 is ushering in a new era of production where automation and data exchange are integrated into the manufacturing process to streamline productivity.

Sounds great, right? It is, if you can upgrade your legacy equipment. Nobody enjoys the process of upgrading, let alone talking about it, but this is a revolution you don’t want to miss. Here’s how you can upgrade your legacy equipment to successfully ride the wave of Industry 4.0. 

Industrial Internet of Things

The Industrial Internet of Things (IIoT) is the interconnection between manufacturing and production equipment. This equipment uses sensors and internet connectivity to communicate with themselves and one another to create a more efficient production output. As a result, equipment can consider factors like stress on the electrical grid and projected weather to determine the most efficient way to operate at any given time.

According to Gartner, a leading research and advisory company, more than half of major new business processes and systems will incorporate some element of the IIoT by 2020. What’s more, McKinsey Global Institute reported that in the last five years, the number of connected machines has grown by 300 percent.

These businesses are onto something; there are many benefits of integrating the IIoT into manufacturing processes. Information gleaned from the IIoT provides access to real-time data and insights on equipment’s performance and use. Operators can also closely track the lifespan of their machinery in order to proactively plan for maintenance and upgrades. IIoT integration also aids in the automation process. Digitally connecting the machinery creates a mesh that seamlessly translates into full automation. Finally, clients can more readily track the progress of their order with insights provided by the IIoT.

Integrating the IIoT with existing equipment can be challenging, but it isn’t impossible. Most legacy equipment can be retrofitted with sensors and other online monitoring devices.

Smart Factories

In the past, many manufacturing facilities relied on Manufacturing Operations Management (MOM) software to integrate the many independent facets of the production process. Unfortunately, this technology is not able to manage production processes in real-time.

Smart Factory software integrates every part of the production process, including production, resources, supply chain, maintenance and human resources, in order to create a single, efficient output.

This technology enables factory managers to examine data once unavailable, informing decisions about production and other business processes. With Smart software, operators can be more responsive to several factors, including resource availability and cost, consumer demand, market fluctuations, and more. 

An Example of Wireless HART mesh network

Digital Supply Chains

Digital supply chains aren’t simple A to B, B to C, C to D processes. In these systems, relationships between different parts of the overall production process are affected by changes or events elsewhere in the system and able to adapt to those changes.

To create a truly digital supply chain, the facility must consider all factors that could potentially impact each part of the supply chain, all the while remedying any issues that may impede the supply chain from operating as designed. Insights from a digital supply chain give manufacturers a real-time overview of every link in the supply chain. As a result, they can quickly respond to problems and simulate scenarios to proactively plan for the future.

To do this well, factories must integrate every step of the product life cycle. This includes everything from sourcing and shipping raw materials, to ordering packaging, advertising the product, and scheduling employees on the factory floor. The digital supply chain system acknowledges that creating a product isn’t black and white. It is a highly sophisticated process that involves many interconnected variables.

 You can also read: Introduction to Industrial Automation

Industry 4.0 is here to stay. Upgrades can cause growing pains, but in the end, change is almost always a good thing. Be a part of the next industrial revolution. Integrate your equipment and transform your business.

About the Author:

Page Long is the Marketing Operations Director at PDF Electric & Supply, which is based out of Cary, NC. PDF Electric & Supply is an automation supplier specializing in Legacy GE PLCs.

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Key Considerations when Specifying Displacer Level Transmitters

Displacer level transmitter is used in Process measurements of liquids across many process industries. In this article we discuss the Principle of operation and industrial level applications that displacer transmitter technology offers.

Principle of Operation

Operation is based on buoyancy force. The buoyancy force works on the displacer which will vertically move in (increasing liquid level) and out (decreasing liquid level) the linear differential transformer (LVDT). Due to this movement, voltages are induced in the secondary winding of the LVDT. These signals are then processed in the electronic circuitry and used to control the output signal.

Industrial Applications

Displacer transmitters are ideal solution for liquids or slurries, clean or dirty and light hydrocarbons to heavy acids with a specific gravity (SG) of 0.23 to 2.20.

Displacer transmitter technology works well in a variety of vessels including process & storage, bridles, bypass chambers, interfaces, sumps and pits up to unit pressure and temperature ratings. They can also handle most liquid conditions including varying dielectric, vapors, turbulence, foam, buildup, bubbling or boiling and high fill/empty rates.

Some of the specific industrial applications include:

Boiler control – The displacer unit provides a stable output signal for valve control on turbulent surface applications, such as feed water heaters, flash tanks, and reactors. 

Interface control on storage tanks – The displacers are tolerant of emulsions. They can track towards middle of emulsion, and are tolerant of unstable interface. They also ignore vapor/liquid interface point above displacer.

Mixing Tank – The displacer transmitter can also be used in harsh production environments like those in a mixing tank. It provides a stable output, easier to configure and is resistant to heavy surging caused by the mixer.

Water elevation – The displacer can be used to maintain a water elevation at a given height by sending out a proportional 3-15 PSIG signal (over a 14 ″ control band) to a control valve to maintain water level at midpoint by regulating the water flow rate out of the separator. The control valve is fully open at 15 PSIG input and fully closed at 3 PSIG input.

You can also read: Ultrasonic Level Measurement Technology

In Summary the advantages and limitations of Displacer transmitter include:

Advantages

• Stable signal in turbulent applications
• High Pressure/Temperature capabilities
• No flexure of pressure boundary part

Limitations

• Shifting SG can affect this technology

Some of the manufactures of Displacer level transmitters include:

• Magnetrol
• Emerson-Fisher
• Schneider Electric-Foxboro

Sources: Magnetrol

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How to Troubleshoot Servo Drives

Servo drives are used to control devices including robotics, model airplanes, aerospace technology and multiple industrial applications. The drive is a component in a closed-loop system, and uses an amplified control signal to send power to the device motor. They are primarily used to control the output torque, speed and position of a motor shaft.

Most servo drives in use in 2017 are digital, and like all other electronic equipment, they can malfunction at the most inconvenient times. A breakdown can disrupt an entire production schedule and cause significant loss of revenue, or it can cause problems like overheating and result in damage to the systems it supports.

Common Problems with Servo Drives

Most of the typical servo drive issues you’re likely to experience have common causes, which helps to make troubleshooting less frustrating. Here are some malfunctions to watch for:

•  System instability: If any of your settings are incorrect, the servo drive may not operate correctly. There are numerous parameters to check related to motor tuning as well as speed and current loops.   If you’re getting noise transmitted into the control wiring, you’re likely to see erratic movement of the motor shaft.
• Inability to reach the right levels of acceleration or deceleration: This can occur for several reasons, such as when the servo amplifier’s capabilities are insufficient for the system inertia, or the friction is excessive.
• Not responding to a velocity command: The reason for a lack of response is usually easily identifiable, and common causes are problems with the control interface, system or motor malfunctions, incorrect voltage supply (or none at all), or the motor thermal protection has tripped.
• Noise on signal wires: This is typically caused by incorrect wiring or grounding, but can also be caused by electromagnetic interference from nearby equipment.
• System runs uncontrollably: This issue develops when there are problems with the velocity command signal, when the motor speed/position feedback signal is erratic or missing, or when there is an internal malfunction in the servo drive.

AN EXAMPLE OF A MOTOR DRIVE SYSTEM

Troubleshooting: What to Look For 

Correct identification of the problem is critical for effective troubleshooting of your servo drives. Here are some tips on how to go about determining causes of common issues, and measures you can take to try and resolve them.

#1: Review the display on the drive. If it doesn’t come up, check the power supply. If you see an alarm on the display, use the instruction manual to investigate the possible causes.

#2: Verify that the feedback device (resolver, encoder, etc.) is functioning properly.  Use an oscilloscope to check waveforms and pay special attention to noise, missing channels, incorrect wave shapes, or low levels. Look for breaks or bad splices in the feedback cable.

#3: Check the line voltage to ensure that the incoming  power to the drive is balanced and the correct voltage. For common DC bus systems, check the intermediate dc voltage as well.  Use an oscilloscope to check for noise, voltage fluctuations, etc.

#4: Don’t forget the possibility of a mechanical problem. Problems such as friction or vibration in the machine can cause issues in the servo drive and motor.

Run all the tests recommended in the manual and record the results for future reference. If these initial measures don’t work, it’s time to consider getting a professional service company to help.

You can also read: Stepper and Servo motors

About the Author

With over 25 years of experience in the industrial automation repair industry, Jeff Conner is the Dallas Service Manager for Control Concepts and serves on the Advisory Committee for the Electronics Technologies Department at Texas State Technical College. Control Concepts offers around the clock service and support anywhere you need it. To learn more, visit http://www.controlconceptstexas.com

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