Flow Measurement Instrumentation Used in Engineering Design of Processes

Flow Measurement Instrumentation Used in Engineering Design of Processes

Flow measurement is an action to measure the flow of liquids, gases and vapors using a flow measurement instrument or device, which measures the rate of flow or the quantity of flow. We measure flow in industrial processes, utility pipelines, HVAC systems, municipal water and wastewater, automotive, food and pharmaceutical plants, hospitals, commercial and retail stores, weather stations, our homes, and many more. Flow measurements indicate flow rate, flow total, flow velocity, the absence of flow, presence of flow, too much flow, too little flow, and flow direction.

Flow measuring instruments and their technologies

There are several different flow measuring instruments available, each with its own technology and application.

Differential pressure flowmeters correlate flow to the measured pressure differential across the in-line sensing elements listed here:

  • Flow nozzle
  • Orifice plates – concentric orifice, eccentric orifice, conditioning orifice
  • Pitot tube
  • Averaging pitot tube, annubar
  • Variable area flowmeter, rotameter
  • V-cone flow element
  • Venturi tube
  • Wedge flow element (slurries, heavy liquids)

Differential pressure transmitters have high and low pressure ports connected to a valve manifold so that impulse tubing is connected to any of the flow sensing elements shown here. Valve manifolds are available in three-valve and five-valve configurations and are suitable for most applications, providing an ideal low-cost solution for connecting a transmitter to its impulse tubing. The three-valve configuration provides span and zero calibration, with additional ports available to connect test instruments. The five-valve configuration provides the additional ports for draining or purging of the impulse tubing. The impulse tubing size is usually ½ inch. Sometimes impulse tubing is heat traced if the fluid freezes inside them.

In situations where the process fluid needs to be isolated from the sensor due to extreme temperatures, corrosiveness or sanitary reasons, differential pressure transmitters with valve manifolds and impulse tubing are replaced with differential pressure transmitters with diaphragm seals and capillary tubing. The diaphragm seals connect directly to the process. The transmitter, diaphragm seals and capillary tubing contain a fill fluid, the type of which is dependent on the application. There are several fill fluids to choose from, listed in the instrument manufacturers’ specifications. Food-grade fill fluids are used in food and pharmaceutical industries; other fill fluids are used in chemical industries.

Mass flowmeters correlate the volumetric flow and density of the fluid through the sensing elements listed below. Gases are most often measured by thermal mass flowmeters, whereas liquids are measured by Coriolis mass flowmeters but measure gases also. Solids are measured by impact flowmeters of several types.

  • Coriolis mass flowmeter correlates mass flow to the fluid’s inertia sensed when induced by vibration within the meter tubes. It is excellent for custody transfer measurements of fluids.
  • Thermal mass flowmeter correlates mass flow to the quantity of energy transferred from the heated probe to the flowing fluid.
  • Bulk solids measuring types
    • Weigh belt/feeder uses a combination of the continuous weighing system load cells and speed sensing of the belt or feeder to determine a mass flow rate.
    • Coriolis correlates mass flow rate to torque measured by a load cell on a motor-driven paddle wheel, rotating at a constant rate while solid particles are flowing onto an area slightly offset from the hub.
    • Impact plate and deflection chute correlates mass flow of falling bulk solids to the reactive force imparted to an impact plate or deflection chute, as measured by installed load cells.
    • Radiometric nuclear source correlates mass flow to the quantity of radiation absorbed by a receiver mounted opposite of a nuclear source.

Open channel flowmeters correlate flows that are open to the atmosphere to the measured levels and measured velocities of the fluid through flumes or weirs, by restricting the flow.

  • Parshall flume makes the channel narrower.
  • Weir forces the fluid over a plate in a channel or box.

Velocity flowmeters correlate flow to the measured flow velocities and other properties of the flowmeters sensing elements listed below.

  • Magnetic flowmeter correlates flow to the voltage measured when induced by fluid passing through a generated magnetic field.
  • Vortex flowmeter correlates flow to the frequency of vortices created within the flow element. It is excellent for steam, clean liquids and clean vapors measurements.
  • Swirl flowmeter is very similar to the vortex shedding flow meter, but it has a swirl element at the inlet and a de-swirl element at the outlet.
  • Turbine flowmeter correlates flow to the speed of the internal rotating turbine or gears, respectively. It is excellent for custody transfer measurements of fluids.
  • Both the Doppler ultrasonic flowmeter and the transit time ultrasonic flowmeter correlate flow to ultrasound either time of travel or reflected from the transmitter, respectively, but ultrasound must penetrate or reflect to work. There are two types: in-line, and clamp-on.

Other Types of Flowmeters

  • Positive displacement flowmeters correlate flow to the measuring of specific volumes and the speed of internal rotating turbine or gears, respectively. It is excellent for custody transfer measurements of fluids.
  • Target flowmeter correlates the deflection of a plate mechanism in the line by the fluid flow, which in turn generates an analog signal.

Flow switches correlate flows above or below a setpoint for the switch types listed below. Switches should be selected so that the normal process variable actuation setpoint lies between 40 and 60 percent of the maximum full scale range of the switch. These switches have contact closures or openings based on your failsafe operation. High flow switches use the normally closed contact, and it opens on high flow above the setpoint. For flows below that setpoint, the contact closes. Low flow switches use the normally open contact, and it opens on low flow below the setpoint. For flows above that setpoint, the contact closes. Confusing? Maybe not. Think of it as if you lose power or a wire breaks you want the circuit to open as if it is in the failsafe state. High flow opens and low flow opens.

Types of flow switches include:

  • Paddle
  • Vane
  • Rotor
  • Thermal
  • Differential pressure

Mechanical flow indicators correlate flow to the visual presence of the fluid through the in-line sensing elements listed below.

  • Rotameters
  • Vane
  • Piston
  • Turbine
  • Sight flow indicators/flow glasses

Flow measuring instruments are widely used throughout industry. Understanding the different types of flow measurement instrumentation is critical in industrial applications. Next time, we will look at the steps involved in specifying flow measuring instruments.

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our manufacturing operations management capabilities and manufacturing process control solutions, contact Bob Kurczewski, Technical Consultant, Process & Electrical Design Department.

© Matrix Technologies, Inc.

How a Finite Element Analysis Complements Your Flow Simulation

How a Finite Element Analysis Complements Your Flow Simulation

When prototyping or testing systems that involve the use of fluids or gasses, engineers use both computational fluid dynamics (CFD) and finite element analysis (FEA) to analyze the relationship between a fluid or gas and the structure it is flowing through. In a previous article, we discussed how engineers use CFD to analyze how liquids or gasses will respond to forces exerted upon them; for example, engineers can use CFD to examine turbulence in fluid as it flows, force exerted on equipment by gasses, possibilities of changes in state, and more.

But CFD is only one part of a more robust analysis that can determine equipment design or investigate system problems. While CFD allows for a detailed analysis of fluid flows, engineers use FEA to determine the effects of those fluid flows on the piece of equipment being analyzed and how that piece of equipment will hold up over time.

What FEA Can Tell Us

Finite element analysis is typically part of a multi-disciplined engineering approach. FEA can be used to test custom machine design, assess vibrations, analyze the effects of vortex shedding, conduct failure investigations, and evaluate individual components or complex pressure vessel design. Though FEA can certainly be used as part of a design process to virtually prototype equipment before it is built, Matrix engineers more often use FEA to analyze problems with existing systems and determine a piece of equipment’s fitness for service.

The first step in using FEA is determining when it is necessary. In some situations, some simple calculations can provide the analysis needed; in other cases, the problem requires the high level of detail FEA provides. FEA’s level of detail can help determine if a piece of equipment is able to withstand whatever forces are being exerted upon it, whether it be heat, pressure, vibrations, or more. Ultimately, finite element analysis can guide engineers in determining if a piece of equipment should continue in its use, be modified, or be taken out of service.

What Situations Call for FEA?

Using FEA to test equipment viability is a specialty of Matrix engineers. Company leaders will often call upon Matrix to validate their existing equipment design and find (and fix) weaknesses if they exist.

Here are some examples of problems that can be solved using FEA:

Analyze cavitation in a control valve

Engineers use CFD to evaluate the vibration and flow of liquid as a result of cavitation. Once they use this process to get the frequency of the force on the back of the pipe, they can then map that force into a solid model in FEA and determine if it puts excessive stress on the pipe and connected components. (Another name for this process is fluid structure interaction, or FSI.)

Evaluate performance in extreme pressure and temperatures

Imagine a jet engine test stand is being designed. High pressure and temperature air flows through the pipe out of the jet engine, and this pipe must contain the pressure from the jet engine or it will fail catastrophically. FEA is needed to ensure the flows modeled inside the pipe (with CFD) will not destroy the pipe or its components when the pressure and temperature are elevated to extreme levels during testing.

Prevent equipment from being damaged by environmental conditions

In a recent case, Matrix engineers were called upon to examine high stacks (attached to a boiler) that had been damaged in the wind. Throughout their use, vortex shedding causes an alternating change in air pressure on side of the stacks which made the stack sway back and forth to an excessive degree, cracking the concrete base. Matrix engineers used FEA to examine solutions to the problem and fix the existing design.

These are just a few of the ways engineers use FEA in combination with CFD to analyze and provide solutions for complex situations.

Rely on the Experts

Finite element analysis is a useful simulation tool that can improve system performance and save time and money in the long run. However, it’s also a complicated tool that requires knowledgeable and experienced engineers to perform well. This is where Matrix’s multi-discipline engineering services come in. FEA is certainly useful during the prototyping phase, but FEA can also be particularly helpful in validating existing designs—a specialization of our engineers. Our clients continually rely on Matrix to provide safe and efficient new designs utilizing CFD and/or FEA. In addition to our original designs, clients rely on Matrix to properly analyze and fix problems that arise in their existing systems so they can get back on track.

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our multi-disciplined engineering solutions or finite element analysis, contact Chris Mach, PE, Senior Consultant (Team Leader), Process Solutions Department.

© Matrix Technologies, Inc.

Earned value provides powerful forecasting tool

Earned value provides powerful forecasting tool

Earned value is a tool for tracking real progress of a project that allows for more accurate forecasting and provides a sense of urgency early in a project, before things have gotten out of hand. The key word in the previous sentence is “real.” In the past, project performance was measured by how much was spent versus the budget. What this method fails to address is the value of the work being done.

For example, let’s say there was a project with a scope of work to drive from Chicago to Cleveland in six hours spending $50 in gas. If we called the driver after an hour and they said they’ve gone 75 miles so far, we would say that was really good progress. However, what if they had driven 75 miles around the suburbs of Chicago but made no progress east? What if they had driven 75 miles west instead of east? Now, not only does the 75 miles they’ve gone so far count for nothing, they are actually 75 miles farther away from the goal, meaning they will be late and over budget.

What if they finally arrive in Cleveland on time and on budget, and then the customer asks where their package is? The driver says, “I didn’t know about any package!” To which the customer replies, “I told the project manager very clearly that I needed a package delivered. What is the point of your trip if it wasn’t to bring my package?!?”

Earned value measures real progress

Earned value attempts to measure the amount of real progress being made (i.e., a driver heading east with the right package in hand), quantify it, and compare it to baseline values relative to cost and schedule. In order to do this, there are three key values that need to be understood:

  • Earned value – how much have we actually accomplished?
  • Actual cost – how much have we spent to date?
  • Planned value – how much does the schedule say we should have spent to date?

Proper tasks in a work breakdown structure, integrated into a schedule, with accurate budgets for each task, and accurate manpower loading for those tasks, allow us to track and calculate these three key indicators needed for earned value analysis.


But it’s not just math; it’s common sense. Earned value is the ultimate forecasting tool because it provides a comparison of your current status against a baseline plan. The plan baseline is a graph of your planned value over the life of a project. Another way to portray this is as your projected spending curve.

How do you develop this initial plan and spending curve for a project? It starts at the beginning with a proposal.

The proposal provides the basis

The proposal needs to describe the project’s scope, schedule and budget in a clear way so that the client understands what they are getting, how much it will cost, and how long it will take. The proposal is your first chance to define your baseline and tell the client how long the project will take, how much it will cost, and what you can deliver within that time and budget. In our trip example, if the delivery of the package wasn’t included in the proposal and it should have been, this is the opportunity for the client to spot this and make sure it gets included.

Project plan makes expectations clear

Once we have the project, we pull the team together and lay out the project plan using the proposal as a basis, making sure all the stakeholder’s expectations are clear. Using this information, we assemble a schedule. By using the estimate and manpower loading the schedule, we get a budget for each task. Once we have an established baseline with this information, we can check and see if our proposal and expectations match. This is an opportunity to refine and put details into the schedule and baseline. The culmination of this is the planned value projection.

Planned Value

Doing an analysis

Once you have completed a portion of the work and are into the project, you can perform an earned value analysis. Doing an earned value analysis before you have significant portion of work done or the project team has not necessarily stabilized can lead to some misleading results at a given point in time.

There are two means to determine earned value: percent complete estimates and rules of credit.

Percent Complete – This uses a task-by-task basis for completing the work. We go down each item on the work breakdown structure and estimate percent complete, then aggregate that information into a percent complete of the total project. It’s essentially a weighted average.

Rules of Credit – Under rules of credit, we establish milestones and give credit on the basis of reaching milestones on an item-by-item basis. Let’s say the client does not trust percent complete estimates and wants tangible proof of progress. We work with them to establish rules of credit. These can be thought of as milestones within a task. Ultimately, the percentages are still estimates, but they are tied to subtasks and milestones.

An example

Using either of these methods, we arrive at the three key values at a given point in time: earned value, actual cost, and planned value. For example, let’s use the sample values below at 3:00 based on our planned value spending curve above:

  • Earned value = $350
  • Actual cost = $280
  • Planned value = $410 (what the curve shows at 3:00)

Now we need to use these numbers to evaluate our performance relative to budget (CPI), our performance relative to schedule (SPI), and our forecasted final totals. Let’s run the numbers

CPI = Cost performance index = earned / actual = $350/$280 = 1.25

SPI = Schedule performance index = earned / planned = $350/$410 = .85

ETC = Estimate to completion = (total budget-earned)/ CPI = ($500-$350)/1.25 = $120

EAC = Estimate at completion = actual cost + ETC = $280 + $120 = $400

Now we have some calculations that we can analyze. Let’s take them one at a time. First, if our CPI is 1 or greater, we are doing well on our budget. If our CPI is less than 1, we are behind on our budget.

Next, if our SPI is 1 or greater, we are doing well on our schedule. If our SPI is less than 1, we are behind on our schedule.

The last two numbers are our project projections based on the performance so far. Our ETC, or estimate to completion, is how much more we are projected to spend from this date forward based on our current performance. Our EAC, or estimate at completion, is how much total we are projected to spend on the project.


Earned value prompts the “why” questions

This analysis can provide us with some powerful forecasting tools that can be used to make informed decisions about the project throughout the project lifecycle and track real progress of project against a baseline plan. The real power here is not in the numbers, but in the fact that EV forces us to ask the “why” questions about the numbers we are seeing:

  • Why is my CPI what it is?
  • Why is my SPI what it is?
  • Why aren’t we complete with a certain task yet?
  • Why are we so far over/under budget on a task or on the project as whole?

Understanding the answers to these questions provides us with a clear understanding of the state of a project and ability to make educated decisions. An earned value analysis provides a sense of urgency early in a project when the projections are showing problems and allows us to form a corrective action plan to get things back on track.

This is the first of a two-part series on earned value analysis. The second part will focus applications of earned value analysis in project management.

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our manufacturing operations management capabilities and manufacturing process control solutions, contact Jason Perry, PE,  Senior Director of Operations.

© Matrix Technologies, Inc.