“Yes we can” check cans inside a box using Contrinex long-range analogue inductives

To ensure that sealed cardboard cartons have the required number of tinned food cans inside them, a packaging company trusts Contrinex’s analogue inductive sensors. Using an analogue sensor enables this final pre-shipment quality check to process different sizes of can as well as manage with different material grades of can.

Customer application

Canned products and their labels are protected during delivery by being tightly packed into sturdy sealed cardboard boxes. This poses a challenge to food packaging companies because retailers, particularly supermarkets require absolute accuracy in the contents of the carton, but at final inspection, the carton is already sealed and so the contents can not be visually inspected.

Therefore to eliminate the risk that product faults that may have occurred during upstream processes are shipped out to the customers, the packing company needed a way to verify what tins are inside the sealed box. Because the packaging line handles a variety of cans of different sizes and materials, a conventional on-off switching inductive proximity sensor could not be used.

An additional challenge is that the sensor needs to be part of a verification process integrated into a fast-moving automated packaging and pre-shipment line, accepting or rejecting each carton instantly.

Customer solution

Analogue inductive sensors from Contrinex’s 509 Series, available from PLUS Automation, are ideal for this application because their Condist oscillator technology ensures excellent environmental stability, especially to temperature. This is key in providing sensing distances up to 3 times the standard (in this case 40 mm from the M30 sized sensor).

This extra sensing distance ability enables them to obtain a good signal not only through multiple layers of cardboard but also from different conductive metals at varying distances, depending on the can type.

The customer mounted the M30 sized inductive analogue sensors which yield the greatest sensing distance above and below the passing lanes of cans so that the double layer of cans in each carton can be checked through the cardboard walls of the box.

The continuous analogue current or voltage output from these sensors is connected directly to a PLC with a high-speed analogue input card. Resolution is in the µm range and repeat accuracy is very good. The solution excels because it is durable, adaptable, reliable and simple to install.