Following the trend of big-data in today’s digitial world here at Bronkhorst, we see that it has also affected the world of flow measurement. The amount and speed of data transmission continues to increase and digital flow meters are employed in an even wider range of applications, such as at Universities and R&D institutes.
Thermal mass flow meters are a well-known instrument in this field. They measure the mass flow of gases, employing a combination of heated elements and temperature sensors, with thermodynamic principles used to derive actual flow. Mass flow meters need limited correction for changes in temperature, pressure or density and are extremely accurate, especially when measuring low and very low flow rates, and are no longer regarded as high cost.
Throughout the years, we’ve seen the technology improve, from a simple VA-meter to today’s ‘smart’ measuring device, like Bronkhorst’s EL-FLOW Prestige mass flow meter. Bronkhorst has used big-data to improve the technology within the mass flow meters and we still do, to keep the devices ‘intelligent’. The improved technology within the device makes it possible to select corresponding gas properties which are on-board, such as density and heat capacity, and to automatically adjust measurement values for environmental influences, for long-term sensor stability. Which, in turn, will directly relate to process yield.
There are many parameters, such as temperature and pressure, that have an influence on the accuracy, stability and reproducibility of a mass flow meter or controller. These are very important conditions within laboratory research.
Furthermore, to investigate the influence of as many gases as possible in a certain period of time, there is a need for short settling times as well as a quick change-over to a new gas with a very short downtime. Using a multi-gas/multi-range device can make a difference here, which offers the ability to use multiple gases at various process conditions with just one device.
Download white paper EL-FLOW Prestige mass flow controller
For those of you interested in how we used big-data to optimize our thermal mass flow meter, the EL-FLOW Prestige, we have written a white paper containing in-depth information about influential factors and the impact on the accuracy, stability, linearity and pressure correction.
Please fill out the form and you’ll receive the whitepaper.
EL-FLOW Prestige Website
Amongst various flow measurement techniques the thermal mass flow measurement based on the CTA principle is used for both gases and liquids. ‘CTA’ is the abbreviation of Constant Temperature Anemometry, which is also named ‘direct through-flow measurement’ or ‘inline measurement’. Mass flow meters based on the CTA principle cover a wide range of measurement and control applications in almost every industry sector. Examples of applications are burner control, aeration processes, gas consumption measurement, leak rate tests and environmental air sampling at atmospheric conditions. Within the Bronkhorst® portfolio, these reasonably priced flow meters enlarge the scope of mass flow measurement solutions for higher flow rates, for low pressure requirements and for conditions within an application and/or local work environment that would be unsuitable for another measurement principle such as Thermal by-pass.
Top 5 key reasons why to use flow meters and controllers based on the CTA principle:
- It is the preferred thermal measurement solution for high flow rates of gasses, where the technical efforts of a thermal by-pass measurement with capillary sensor and laminar flow element are exceeded. The inline CTA measurement is available from a few ml/min up to hundreds of thousands of m3/h and even more.
- Compared to traditional thermal MFMs and MFCs with by-pass, the construction of the direct measuring CTA devices is less sensitive to humidity and contamination.
- The compact and robust instrument design provides continuous mass flow measurement with an excellent repeatability. It is extremely versatile and is used within many different industries and applications.
- This CTA concept makes it possible to build and to calibrate an instrument with Air or Nitrogen and to then model it for almost any other gas or gas-mix.
- The pressure loss over the instruments is almost comparable to a straight length pipe and is thus usually negligible.
The working principle
The CTA sensor consists of two probes, the first being a heater and the second being a temperature sensor. A constant temperature difference is created between the probes. Regardless of actual flow-rate CTA is aiming to keep this delta-T or temperature difference (T) between both sensor pins at a constant level. The flow rate and the heater energy required to maintain this constant T are proportional and thus indicate the mass flow of the gas. The actual mass flow rate is calculated by measuring the variable power required to maintain this constant temperature difference as the gas flows across the sensor.
In many research and production processes the important variable is mass and not volume. Measurements of volumetric flow are not as reliable as mass flow measurement due to the effects that changes in temperature or pressure have on the density of a fixed volume of gas.
Unlike volumetric flow measurement devices such as purge meters (variable area meters) or turbine meters, thermal mass flow meters (MFM) and mass flow controllers (MFC) are relatively immune to fluctuations in temperature and pressure of the incoming flow. The MFM/MFC is capable of providing direct measurement of mass flow, as opposed to most other method that measure volumetric flow and require separate measurements for temperature and pressure in order to calculate density and, ultimately, the mass flow.
The MFM/MFC actually measures and controls the flow on a molecular level and so is able to provide an extremely accurate, repeatable, and reliable delivery of gas into the process.
Originally developed for the semiconductor industry, MFMs/MFCs are now widely used for applications in research laboratories, pilot plants, and continuous processes. The thermal mass flow meter and mass flow controller advantages of low flow accuracy and repeatability, relative immunity to fluctuations of inlet flow temperature and pressure, and a complete PID control loop in a compact package have helped to improve productivity and reduce costs in a variety of analytical, industrial process, and OEM applications.
Principle of Thermal mass flow measurement
EL-FLOW Prestige mass flow meter/controller product tutorial
Since the day of their introduction Instrumentation devices have always been required to evolve. One of the main reasons for this is to accommodate new, better and more complex communication protocols.
What a lot of people still do, due to ease of use and consistency is specify instruments with analogue or RS-232 serial communication. Analogue communication (4-20mA, 0-5v or 0-10v) and RS-232 which was the original way in which computers communicated was the original, mainly due to cost and available technology.
It is still a very robust and solid way to send and receive information over a small group of instruments however it does have some very practical set-backs. As a point-point communication protocol it requires a port both on the instrument and the controller, this can be very limiting in size affecting both the amount and length of cables needed.
The development of Fieldbus communications meant it became possible to have multiple (100’s) of instruments connected through only one communication port at the controller level. This means that you had a huge reduction in both the number and length of cables needed. This development allowed the complexity to increase and size decrease of instruments containing multiple sensors.
As with VHS and Betamax there will always be competing technologies and ‘bus’ development was no different. Of course everyone hopes for a single unified solution because it makes things simpler, cheaper and more efficient. However the reality is that most ‘buses’ are utilised differently in different industries.
Different industries are described as either; a ‘process fieldbus‘ used in many process automation applications (flow meters, pressure transmitters and other measurement devices) or a ‘device network’ which is a large number of discrete sensors are used, motion, position etc., the best example of this is in automotive manufacturing.
There is an IEC standard that was developed for the European Common Market and interestingly I have learnt that the common goal was not focused on commonality but more the elimination of restraint of trade between nations. This standard is IEC 61158, it is almost 4000 pages long. Issues of commonality are now left to the consortium that supports each of the standard fieldbus types.
What next is always a good question, Ethernet based communication systems are one area that has seen large development over recent years and its definitions are being added into the International standards.
In all of this, what is our involvement in Fieldbus. As you may know, we are mainly involved in Process and control industries. We support almost all of the major bus systems out in the market and also have our own in-house ‘Flow-bus’ system that can be used link multiple instruments together. You run them through a single PC running our Flow-Plot or Flow-View software.
The latest addition to the communication range is the ‘Gateway’ solution. This allows multiple or manifold instruments on a Flow-Bus network to communicate with PROFIBUB or PROFINET DP through a specific fieldbus interface. This can be a very cost effective solution as multiple PROFIBUB or PROFINET DP instrument can become very expensive, very quickly.
Bronkhorst Field-Bus Technology
At this time of year it is good to reflect on what has happened, what you have achieved and what you have enjoyed. This year I have very much enjoyed writing about our experience in Industry delivering Mass Flow Control and Metering Solutions. This week I look back at one of my first blogs, the potential possibility of switching from batch to continuous process production.
I hope you enjoy reading a second time as I enjoyed writing it.
One of the most common topics of conversation over the last few years in the chemical industry has been about the change from continuous to batch process production.
In the beginning of my involvement with the Chemical Industry I was an early advocate for switching to the batch process method. With the benefit of hindsight this was based on my perspective of the application at that time. Having worked in Operations I was heavily into data and numbers (letting the data speak), I believed they would tell you everything and provide the perfect foundation to make a decision. Develop what you have, invest in new kit or re-design an entire process.
So, the next step was to find the top 5 points that would encourage someone to discuss the change from batch to continuous production.
Quality: With greater control and automation in the production process it becomes easier to remove inconsistency in final product quality.
Waste: The better the quality and the higher the frequency of achieving that quality the less the product waste and re-work required. This has huge returns on baseline production cost.
Safety: Increasingly an important consideration in the modern workplace, reduction in contact with chemicals through increased automation and the inclusion of built in alarms can add significant safety advantages.
Space: In bulk manufacturing you have to store bulk products, both pre and post production, by moving to a lower volume continuous production method you can have smaller more frequent deliveries enabling you re-use the old storage facility for extra production lines.
- Cost: In each of these improvements brings a cost incentive to the business, with extra production space, reduced waste or improved quality cost efficiency can be realised in multiple areas.
With advances made in metering and control instrumentation it would be remiss to not investigate the potential benefit an investment in continuous production could bring. The potential is there to achieve more predictable final product quality resulting in less re-works and waste product. A reduction in production space would be required; safer work environment, greater control and flexibility on supply chain operations. The ability to deliver smaller volumes to order increasing your potential customer base and reducing supply chain costs.
This has been a great topic to discuss and learn about, I would be more than happy to talk with more professionals in the field of Chemical production and expand my understanding further.
Coriolis YouTube videos
Chemical Industry brochure
As with any inter-dependent parameters there are consequences for changing one parameter if the controller of the other is responsive.
For example; if you installed a mass flow controller and a digital pressure controller in-line, each with their own inputs and outputs, changing the set-point on the digital pressure controller would adjust the valve and therefore the flow. This reaction would be detected by the mass flow controller as either a decrease or increase in flow and the mass flow controller valve would adjust accordingly to achieve its given set-point. This second reaction would then be seen as a change in pressure by the digital pressure controller and you can see how quickly this would become a feedback loop of increasing instability.
One of the most frequent challenges that we come across, and one that people are always surprised we can solve, is the ability to control and meter flow and pressure in-line. Many of the applications we are involved in require control and measurement of the flow and pressure of the fluid. However, as the two parameters are different but inter-dependent it can make it difficult to determine the optimal process conditions in which both parameters are fully supporting each other. Our experience teaches us that each case has its own unique solution.
We learned by experience that it is very beneficial to draw together the process owners of the application under discussion. I/we use this ‘drawing’ skill to help identify which areas are critical and where value could be added through the use of digital instrumentation. This can make it easier to determine what the best course of action is.
Applications for use:
The need to control/meter both pressure and flow can be important in:
• Consumption reactions
• Fuel cell development
• Burner/Ignition lance applications
• AiR Permeability testing
If you need to measure the AiR permeability of medical packaging; you need to set a standard pressure while also metering and controlling the AiR required to maintain the standard pressure. This measure gives you the flow required to achieve stability and therefore the AiR permeability.
In consumption reactions you may want to hold your reaction vessel at a set pressure and control/meter the feed gas to maintain the set pressure. This set-up, with electronic instruments and PC/PLC communication software will give you total consumption, consumption rate and allow you to profile the life cycle of the reaction you are conducting.
Adding digital control can allow you to control maximum flow as you build up to desired pressure levels which can be important in certain applications.
As with all application solution requirements, talking the application aim through with your supplier can be crucial to getting the best result.
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