Customers over the world are searching for simplication and integration of their gas, liquid or vapour flow processes. They prefer integrated platforms that are compact, robust and reliable, and even containing different type of sensors.
In this blog I provide a sneak-preview of the ‘toolbox’ which is under development at Bronkhorst High-Tech B.V. One of the components which we are working on, a micro Coriolis mass flow sensor, is already shared with you in our previous blog ‘Miniaturization to the extreme’.
Why do we develop a next-generation toolbox?
On a daily base, our customers tell us their need for miniaturization and the need to control a complex set of different parameters to meet the stringent demands of their customers. These types of customers include the life-science market, analytical device manufactures but also markets in which online gas-concentration levels are measured.
MEMS based technology
These types of requests triggered us to work on the next level of sensor development which can support the future need of our customers. This new development includes MEMS based technology (Micro Electro Mechanical System) which gives you the possibility to measure more than just flow alone on one customized system that can consist of one or a combination of sensors.
For instance, a measured physical property can be used to identify the type of medium, if that property is unique for that medium. Or, in case the medium consist of a mixture of 2 gasses, a property can be used to analyse the fraction of this binairy mixture.
Other parameters which can be thought of are the sugar content of a fluid, also referred to as the Brix number, or heat capacity that can be used to measure oil/water mixtures.
In short, these new concepts are under development to support our customers to solve their next generation technology challenges.
Multi-parameter sensor chip
An example of how a program was started to minimize the footprint;
Bronkhorst received the request to measure fysical gas properties in combination with several partners. The fysical properties included the:
• heat capacity (cp)
• density (ρ)
• thermal conductivity (λ) and
• viscosity (η)
To analyze these properties several individual sensors like a Coriolis-, Thermal-, Pressure- and Density sensor were needed. To proof that the combination of several sensors in combination with electronics could meet the needs of the customer, a demonstation model was developed. This demonstration model contained commercially available products which where combined in one system.
The learnings from the demonstration model support the project team to define the exact scope for the multiparameter chip alternative.
One important aspect of sensor performance is the stability, espacially when multiple sensors are combined to determine information about the medium in the system. In figure below it's shown that we can measure the viscosity with a combination of the massflow, density and differential pressure.
With the demonstration model shown above we have tested if the viscosity of a medium can be measured accurately over longer periods independent of room temperature changes. The measurement of viscosity can be interesting for some applications, for instance with natural gas where viscicosity and calorific value are strongly correlated. The test results are shown bellow for a test period of 84 hours, the histogram shows that all measurements values for the viscosity fall within a band of 0.5 %.
The next level will be to combine the same functionalities on a much smaller footprint. The concept below shows the possibities to combine the required parameter on chip level.
Bronkhorst® Flow Solutions
For machine builders all over the world who are searching for simplification and integration of their gas, liquid or vapour flow processes, Bronkhorst can already help in developing and supplying 100% customized flow solutions that fully meet the customer’s needs.
For information about our future toolbox concepts please contact our office [email protected]
In several earlier blogs the results of this co-creation process has been addressed:
• Miniaturization to the extreme: micro-Coriolis mass flow sensor.
• Bronkhorst, its share of a clean – solar – energy future: a collaboration between Tempress’ engineers and Bronkhorst
• Customized low flow measurement skids and the four reasons why customized skids are popular
In this blog I would like to share the development of a MEMS-based Coriolis instrument, currently the lowest flow measuring Coriolis mass flow sensor in the world. MEMS is short for Micro Electro Mechanical System. This unique Coriolis instrument is available for field tests now.
MEMS (Micro Electro Mechanical System) technology
MEMS technology is similar to semi-conductor technology, but it is applied for sensors and miniature mechanical components instead of electronic chips. Well known applications of MEMS technology are airbag sensors, inkjet heads, pressure sensors, microphones, compasses, accelerometers, gyroscopes and time-base oscillators. For instance, a smartphone contains a lot of MEMS components and thermal flow sensors are widely used in air conditioning systems.
Wafers, extremely flat circular discs
MEMS chips are made from wafers. Wafers are extremely flat circular discs, made from Silicon or glass. A typical wafer has a thickness of 0.5 mm and a diameter of 6 inch. MEMS technology is all about adding layers and removing those layers in certain areas. The layers that are applied can be of very high quality and robust materials. Silicon Nitride is an example of such a material, which is applied by Low Pressure Chemical Vapor Deposition (LPCVD) and it is performed around 800˚C.
Photo-lithography is used to define the areas that need to be removed. In photo-lithography, a layer of photo-resist is deposited on the surface of the wafer. The photo-resist is chemically altered by shining light on its surface and is selectively removed in a development solution.
Advantages of a Coriolis sensor
Most MEMS flow sensors are based on a thermal measurement principle. It has been demonstrated that such sensors are capable of measuring liquid flow down to a few nanoliter per minute. Advantages of these sensors are that they are fast and very stable. A disadvantage is that they need to be calibrated for each specific fluid.
A Coriolis type of flow sensor, i.e. flow sensors containing a vibrating tube in which a mass flow is subjected to Coriolis forces, do not have this problem. The Coriolis forces are directly proportional to the mass flow and independent of temperature, pressure, flow profile and fluid properties since Coriolis flow sensors measure true mass flow.
Coriolis flow sensor
Coriolis flow meters are mostly used for measuring large flow rates (>1 kilogram per hour), since the relatively weak Coriolis forces are correspondingly harder to detect for small flows. In order to gain enough sensitivity to measure ultra low flows below 2 gram per hour, the sensor size and tube wall thickness needs to be minimized to the extreme, which is not possible by conventional machining of stainless steel.
Here MEMS technology comes into play. A process called “surface channel technology”, which we developed in close collaboration with the University of Twente, allows for the fabrication of tubes with 1 micrometer thin Silicon Nitride walls. The choice of material renders these tubes mechanically stable even at this extremely thin wall thickness.
Principle of operation, MEMS based Coriolis sensor
In picture 3, the principle of operation of the MEMS based Coriolis sensor is explained. The sensor that is built into the demonstration model is based on this technology. The demonstration model can measure and control gas and liquid flowrates from 0.01 up to 2 gram per hour.
The Coriolis flow sensor tube. The tube is brought into resonance by Lorentz actuation. The Coriolis force Fc is a result of the mass flow Φm through the tube
As an additional advantage of MEMS technology, the Coriolis tube inside the instrument has such small dimensions that the resonance frequency of the tube is in the kHz range. This results in a lower susceptibility to external vibrations than conventional stainless steel Coriolis instruments.
Demonstration models micro-Coriolis technology for field tests
We currently offer demonstration models of the micro-Coriolis sensor technology equipped with an on-board communication interface allowing integration into any application available. This demonstration model is called the BL100 and is available with and without valve for flow control. We see applications for the BL100 in microfluidics, such as life science, lab on a chip, medical dosing, chemical micro-reactors, catalyst dosing, pump calibration. We are also eager to learn more about applications from customers.
Interested in receiving a demonstration model?
Please contact us at [email protected] to request more information or a demonstration unit of this technological breakthrough in Coriolis mass flow measurement and control.
BL100; demonstration model micro-Coriolis technology for field tests
Sneak preview next MEMS blog: Surface channel technology
The “surface channel technology” that is used to create the micro-Coriolis sensor chip allows for other types of sensors as well. Examples are: pressure sensors, density sensors, viscosity sensors and thermal mass flow sensors.
Stay tuned for new blogs regarding this technology!
Read more about using MEMS technology in gas chromatography equipment in our November blog.