How does SWIR liquid level inspection work?
There are many instances where the accurate measurement of a liquid within a container is required. While the production of household cleaning products may require a fill-level monitoring system to ensure consistency, laboratories increasingly employ automated systems to differentiate samples.
It is possible to backlight a plastic container with wavelengths known to be absorbed by the substance inside. Using this method, in conjunction with fixed-position SWIR cameras and machine vision computer software, an accurate measurement system can be devised.
A simple example would be that of a water bottling facility. Water absorbs SWIR wavelengths in the ~1450 nm region and returns a darker image; whereas any plastics or inks on the container itself will appear transparent. While the human eye would fail to gauge the fill-level in an opaque container, an SWIR liquid level inspector simply looks straight through it.
The machine vision software processes the imaging data, before instantly comparing it to a previously-defined, acceptable fill-level. Any containers with an unsatisfactory fill-level can then be automatically removed from the production line or returned to a prior stage for correction.
But, what if you need to detect more than one substance at the same time? Ushio has mastered the art of placing up to three different chips, measuring only a few square millimeters, into one package. The chips can be an assortment of LEDs and sensors, so each package effectively reduces its occupied space on a circuit board by two-thirds.
It is even possible to analyze various material components in great detail by cycling through different illumination wavelengths. By independently pulsing light-emitting chips at a subject being captured by a high-speed camera, it is possible to obtain spectroscopic images that tell the whole story.
How are Ushio’s SWIR LEDs used in liquid level inspection?
1450 nm LEDs match the spectral absorbency of water, but other substances can be identified by SWIR too. By using SWIR LEDs that are attuned to the specific wavelengths absorbed by each substance, even a liquid mixture can have its individual components identified. For example, LEDs commonly selected for ethanol detection emit 1500–1600 nm, while oils and fats are easily detected with wavelengths at around 1700 nm.
Typically, multiple SWIR LEDs are arranged in a linear or planar configuration to illuminate the entire bottle, including the target liquid. The aim is to transmit the SWIR wavelength, through the liquid and container, to an InGaAs image sensor on the other side.
The wavelength of 1450 nm is mostly absorbed by water, while it has a high transmittance through resin and glass, which are commonly used for bottles. As a result, the transmitted image shows a strong shadow caused by the water and its top surface is clearly defined.
The liquid level information extracted from the transmitted image can be used to automate a number of actions. For example, it is possible to continuously observe the liquid level while pouring liquid into the bottle and halt pouring when the preset liquid level has been reached.
Contact Ushio about liquid level inspection solutions
If you would like to make an inquiry regarding the role Ushio’s SWIR LEDs in liquid level inspection applications, contact Ushio’s regional experts via the following link:
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