Fiber-optic sensing with blue light source detects translucent target through blister packaging

Fiber-optic sensing with blue light source detects translucent target through blister packaging


A consumer packaging company supplies toothbrushes in individual blister packs to stores. Production quality checks include final verification that the intended product is present in each blister pack prior to shipment to the store shelf. A fiber-optic solution meets both the technical challenges and space constraints of this application.


The customer supplies retail companies with individually blister packed toothbrushes for direct sale to consumers. Before shipment, a final quality check is required to ensure a toothbrush is present in each blister pack and so guarantee zero-defect shipping to the retailer.

This application presents the technical challenge not only of penetrating the packaging and detecting through multiple levels of vacuum formed plastic material, but also of reliably sensing a relatively translucent object – the toothbrush. A further complication is the fact that the space available to the customer for a sensing system is rather confined.


A fiber-optic solution meets the special requirements of this application. Acting as the extended “eye” of the photo sensor, these small, flexible conductors solve the problem of sensing in inaccessible places. The amplifier’s exceptionally small housing (30x60x10 mm) allows for optimum DIN-rail stacking of multiple sensors. Use of space is further optimized by cutting the fibers on site to the specific length required and exploiting the special lateral sensing characteristic of the optical fiber used. Fibers are easily connected by quick-locking, and device operation is simple: distance is set using a 12-turn potentiometer with illuminated scale.

A red light source was originally selected, but proved unworkable because there was no sensitivity setting that afforded the margin of movement required for the target. However, by utilizing an amplifier with a blue light source and a relatively small diameter fiber through-beam pair, reliable detection of the translucent target through the blister packaging is ensured.

14th Apr 2019 S.Abd

Recent Posts