Company insight
Time to learn about CQV non-invasive level sensors
With a plethora of liquid level sensors available in the medical devices market, Frank Pellicano, project engineer at Strain Measurement Devices, talks to Medical Devices Development about what makes his company’s CQV technology so unique, what it does, how it works, and why SMD’s clients trust the company to provide effective products.
There are a lot of liquid level sensors out there in the marketplace. What makes the CQV technology unique? Frank Pellicano: There are several unique features. Unlike many liquid level sensors, CQV is non-invasive. Since it is adhered to the outside of the container, there is no physical contact between the process liquid and the sensor. The sensor is able to provide continuous liquid level measurement, outputting from 0–100%. This means that when combined with timestamp data, one can have a low-cost and effective flow metre. The last unique item is cost. This is priced for the disposable market. We received many sensor requests for “smart disposable containers and bags”, management decided to invest in this technology.
Why is it called ‘CQV’? Our sensor uses capacitance to achieve non-invasive liquid level measurement. Capacitance (C) is calculated by dividing charge (Q) by electrical potential (V), thus we decided to pay homage to this equation in our product number.
How does it work?
CQV is composed of two parts: a sensor and a control board. The sensor provides an accurate and repeatable output of liquid level measurement from 0% (empty) to 100% full by utilising the liquids’ permittivity across the container to non-invasively determine whether liquid is present inside the vessel. The control box processes signals from a CQV sensor and precisely calculates the liquid level using a proprietary algorithm which compensates for a variety of environmental and physical factors which could influence the output. The sensor has a FFC (Flat Flexible Connector) and is simple to connect to the board and is powered by
Frank Pellicano, CQV technology project engineer, SMD
USB or 5–24VDC. The sensor uses PSA adhesive to adhere to the container.
What type of accuracy is there, and how fast does it measure liquid level?
Accuracy is 5% or better, outputting continuous liquid level measurements at regular intervals as fast as 50ms per update. The control board is capable of easy recalibration to compensate for drastic changes in environment, vessel, liquid or other factors which normally impact capacitive level sensors.
Are there any special requirements for the sensor? Yes, due to the capacitive nature of this sensor, the container must not be made out of any metallic material. A container material with a relative permittivity between 2.0 and 8.0 can be used with this sensor. A table of some common materials within their permittivity is provided in the manual. Generally, plastic and glass vessels work best for this sensor. To improve performance, the vessel should be made as thin as possible. In general, containers with minimum bend radius of 5/16” and those containers with a constant liquid surface area from empty to full are preferred.
Some containers, and most bags, have conformal shapes. How does the CQV handle these applications? The sensor is on a flexible PCB, thus it is naturally able to conform to certain bends
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and curves. For conformal shapes and bags which are more extreme, we would adjust the algorithm to “conform” the output to the container shape. SMD engineering is known for custom designs, whether that is custom geometries, mounting features or electronics.
Do I need to calibrate the sensor prior to use? To achieve the highest accuracy, performing a calibration prior to use will allow the device to perform best in a given environment. We are able to perform a factory calibration prior to sending out the control board if the customer is interested in a more ‘plug-and-play’ approach. However, assuming each container is the same, once one sensor is calibrated, other sensors/ containers should have an accuracy no worse than 10%. In either case, calibration is quick and easy. Please see the manual for more information.
How can someone test the CQV product line? Can you describe the project inquiry process? As there are so many container shapes out there, we decided to offer a DEV (Development) Kit. The kit has everything one needs to test our CQV product. We provide a small plastic bottle, a control box, USB cable, and two sensors with PSA peel-away adhesive as well as two sensors without adhesive. We also provide a quick start guide and our manual and data sheets are found on our website.
After “test driving” the sensor using our DEV Kit, we suggest you send us samples of your containers as well as completing the CQV Technical Survey. Someone will contact you promptly for follow up. ●
www.smdsensors.com 103
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