Bullet Sensors & Transducers e-Digest, Vol. 113, Issue 2, February 2010: Product News

    (ISSN 1726-5479)


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New Liquid Level Sensor Technology Chosen By Major Supermarket Group


The UK's largest supermarket group has opted for the Optical Level Sensor to monitor liquid levels in its refrigeration packs. Invented and developed by Product Innovation, 500 units have been ordered and delivered with further orders expected in the near future and the company is now looking for exclusive distributors in the US.


The unique and patented OLS (Optical Level Sensor), measures liquid level directly rather than calculating it from secondary effects as in capacitance and ultrasonic devices. It accurately measures the liquid level regardless of dielectric constant, conductivity or temperature.


Product Innovation, trialled the sensor with the supermarket group over an eight month period. The supermarket giant also tested capacitance and ultrasonic based products to measure refrigerant liquid levels, and chose the OLS because it is simple to install and requires no calibration or set-up time. One major advantage for the supermarket is that the refrigeration control system can continuously monitor the liquid levels inside the refrigeration packs. This is crucial to check for leaks which allow gasses to escape that are harmful to both humans and the environment. A small leak anywhere in the system will slowly reduce the liquid level. Being alerted to this at an early stage will protect the environment and also save money on replacing lost refrigerant. If the leak were to persist the refrigeration equipment itself could be damaged.

'The company specified a sensor with 220 mm of sensing range and a resolution of 4 mm. The output from the sensor is 0 - 5 V," says Peter Frank, chairman, Product Innovation. "As the nature of the technology is modular it is possible to alter the range, resolution and output to suit customer requirements. 4 - 20 mA and digital outputs are alternative options. For example a product with a range of 444 mm is already in production and samples have been made of shorter units with increased resolution. If required 2 mm resolution can readily be achieved."


The sensor uses the known optical principle of Total Internal Reflection in a novel way that allows it to work in a continuous probe. A long narrow PCB incorporating a ladder of IR LEDs and sensors is encapsulated into a smooth clear rod, typically made from epoxy resin. The Infra Red components are arranged so that they can be powered in pairs (one transmitter and one sensor). The electronics scan these pairs until the point at which the Total Internal Reflection does not occur. This point is then interpreted as the liquid level. This level is of course independent of the type of liquid being measured. Unlike capacitance methods it does not depend on the dielectric of the liquid, nor does any conductivity affect the result.


The technology is designed in a modular form allowing customers to specify the length of probe and resolution required for their application. If
appropriate the LED/Sensor pairs can be concentrated in regions of particular concern to the customer. This gives high accuracy in these regions at very attractive costs.








Optical level sensor








Level sensors manufacturers






High pressure applications work equally well because the probe is fully encapsulated in a hard resin. And because the probe is smooth and solid it is ideal for use where no moving parts or ease of cleaning are important factors.


For more information visit






Debby Freeman


Riverview House,

The Waterhaven, Earith PE28 3RH

Tel.: +44 (0) 1487 843366

E-mail: debby.freeman@communicator-marketing.co.uk





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