Clear PET
Near-IR backlight
Near-infrared light passes through clear PET. Where there is liquid, the light is bent at the surface and absorbed by the product, so the liquid reads dark and the headspace reads bright. Usually the simplest setup.
Station
Fill level inspection station.
An IR backlight shines through every clear PET or amber bottle, so the liquid reads as a dark band and the headspace above it reads bright. The station measures that edge on every bottle and rejects any bottle outside the tolerance set on the HMI.
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Full write-up: Fill level inspection in clear, amber and opaque bottles
The method
How does the IR backlight method work?
The light sits behind the bottle and the camera in front, so the camera sees each bottle as a silhouette.
Amber and tinted
Through the tint
Near-IR gets through amber and tinted plastic and glass better than visible light does, so the same backlight method works on amber bottles.
Measurement
The fill line on every bottle
The fill line is the edge between the dark band and the bright headspace. The station measures that edge against the nominal fill height on every bottle, short fills and overfills alike.
Other bottles
Opaque HDPE needs SWIR
Opaque HDPE scatters near-IR light, so it needs a SWIR light and camera instead of the IR backlight.
Tolerance and rejects
How is the fill tolerance set?
Tolerance
Set per customer, adjustable on the HMI
The plant sets a nominal fill height and a tolerance on the HMI. The right tolerance depends on the customer and the product. It is part of the recipe, so it changes when the MES pushes a changeover over EtherNet/IP or TCP/IP.
Reject
Encoder-tracked air reject
An encoder-tracked pneumatic reject, driven by a PLC output, removes the exact bottle that failed. Each result is logged with a timestamp and the measured level.
Trends
Drift shows before rejects
Every measured level is kept, not just the rejects. A level creeping toward the edge of the tolerance over a shift shows on the HMI, so maintenance can look at the filler first.
Fitting it to your bottles
What changes from one bottle to the next?
Shape
Front light on some shapes
On some bottle sizes and shapes, a front light gives a cleaner fill edge than a backlight, for example where the shoulder curves sharply at the fill height. We pick it per bottle.
Product
Tested with real product
Foam and a moving meniscus can blur the fill edge on some products, so we test with real product at line speed before we commit to a light.
Setup
Calibrated to known levels
The station is calibrated against bottles filled to known levels at setup and re-checked at changeover.
Next step
Start with your line.
Tell us what you make and what is getting through. Start with a feasibility study.
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