An Introduction to Fringe Effect Level Technology

Dr. Temoc Rodriguez, Principal Engineer at Cambridge Consultants talks to AZoSensors about Accurate Liquid Measurement with Fringe Effect Level Technology.

How is this new fringe effect level technology (FELT) cost-effective for accurately measuring liquid levels?

When you look at the available options, you find that retail prices go very quickly from £100 all the way up to £1000.

The more accuracy and immunity from the interference, the higher the price you need to pay, which in some applications can be a big obstacle.

There are some options that are in their budget range, but the price you pay is low accuracy. We’ve had a bit of brainstorming with the solutions for this and the reason this technology is cost effective is because the materials that have been used to engineer this device are quite inexpensive.

All the physics are behind printed electrodes that create an electric field and these could be part of our printed circuit board, for example, or for larger assembly technology where the electrodes could be stamped onto a sheet of metal.

The electrodes are encapsulated in plastic housings such as polypropylene that when manufactured in bulk is economical; therefore, all of the materials to build this technology and the electronics to drive this technology are low cost.

The reason why this technology is accurate is based on the ratiometric measurement calculated by the electronics (i.e., there is a ratio calculated between the measurement sensor and a reference sensor which are part of the same probe, and directly relates to the fill level).

We take this ratio and so we are able to cancel out variations in the fluid due to temperature or composition. The two sensors are in the form of three electrodes in the probe that are used to measure the fringe electric field flowing through the fluid.

What fluids are monitored by this novel technology and how?

Fluids need to have a dielectric constant or permittivity higher than air, typically above 20. This includes water based fluids, alcohols, acids, and solvents. The technology still works for fluids with low dielectric constant, but calibration would be required.

In both cases the probe works better when immersed in the fluid as this minimises interference from the environment.

We’ve been looking at a few industries that have working fluids or reagent bottles typically in instrumentation, or that have appliances or machines dealing with waste water that will benefit from the application of this technology.

This technology is also useful in industries where fluids are mixed together. In terms of the chemicals that we can use, we’ve tried using solvents that have worked well with this technology.

However, when you start focussing on a range of fluids you need to think about the robustness of the sensing element (e.g., a solvent will start to attack the plastic) and so there needs to be a fair amount of customisation of the housing and the material that gets into contact with these fluids to make sure that it remains a robust solution throughout the lifetime of the product.

How have you designed this technology to be immune to changes in fluid composition?

This is based on the ratiometric measurement. The electric field established between the electrodes is directly proportional to the permittivity of the fluid.

Fluid dielectric constant changes with temperature and composition. We can compensate for this because our electronics calculate the ratio of a measurement to a reference electrode, thereby cancelling the dielectric constant of the fluid. This only holds true when such a constant is much higher than air.

Fringe Effect Level Transducer by Cambridge Consultants.

What parameters are measured using this technology?

The electric field directly relates to fluid levels. A majority of the electric field gets deployed through the fluid because this gives low impedance, and so when the fluid level goes up, more and more of the electric field will be deployed in the fluid resulting in a higher current flowing through the electrodes which we are able to detect.

How does this novel technology compare to similar technology currently on the market?

We use two electrodes, one reference and one measurement on the same probe element, which means designers only need to worry about deploying a single probe.

Other solutions in the market do not compensate for changes in fluid and require calibration.

Some other solutions require the deployment of two sensors where one sensor will always be submerged in the fluid as a reference and the second sensor will measure the level and so with two sensors deployed in the vessel, they then are able to calculate a ratio.

However, as a designer, you need to worry about deploying two sensors - one which is always immersed and, therefore, has a dead volume in the vessel.

Are there any major level sensing problems that could be solved using a customized version of this technology?

Yes, the geometry of the sensors allows their deployment in the smallest spaces, which do not have to be perfectly flat.

We could think of reservoirs that contort and the electrodes could be part of a flexible assembly, or printed on the tank that follows such curvature (i.e., conform to the curves of the fluid vessel).

The electrodes can also be printed on the vessel, which is unique compared to any similar applications in the market; however, this requires a level of customisation.

What are the main benefits of using this technology for the end-user?

For a range of fluids, this sensor works off-the-shelf. All the calibration is done at the factory and therefore, the user needs only to design it into their system and they’ll get the information out.

Where do you see the biggest demand for this technology and why?

The biggest demand for this technology is in the design of instrumentation, appliances, or any other equipment with fluids vessel requiring continuous level sensing in ranges up to 1 metre.

Can you think of any design and development challenges with this technology?

Fluids that have low permittivity may become a problem which raises the question of what happens when the composition changes so much that the dielectric constant collapses.

When fluids change their composition drastically and push the mix towards a low dielectric, the output may become erroneous.

We are concerned about this issue and are currently researching algorithms that would prevent this. So we need to focus on making this application more robust.

Where can we find further information on your work?

We are currently drafting a specification sheet that will become available by the time we present the product at Hannover Messe in April.

In the meantime they can contact us at Cambridge Consultants.

About Dr. Temoc Rodriguez

Temoc Rodriguez has a Ph.D. from Cambridge University, an M.Sc. from McGill University, and a B.Sc. From the Monterrey Institute of Technology, all in Electrical Engineering.

Temoc has been with Cambridge Consultants for six years and he is currently a Principal Engineer.

Temoc's work focuses on the design of instrumentation, particularly low-noise analogue electronics and sensors, power electronics, and control systems. Before this, he worked at Enecsys, where he was a Senior Engineer and inventor of their micro-inverter technology.