Checking devices have to take a multitude of external factors into consideration. The device has to reliably ensure that a faulty container does not slip through without being identified even in exceptional situations such as an emergency stop when the bottles slip about on the conveyor.
The SPECTRUM TX devices must be constantly aware of the actual position of each and every container within their inspection area. The so-called shifting register is used for container tracking. The starting-point for the function of the shifting register is the exact tracking of the movement of the conveyor chains. The conveyor chain runs in accordance with the revolutions of the chain wheel equipped with a rotary pulse generator (encoder). The encoder always supplies the same number of pulses for each revolution of the chain wheel. In this way the SPECTRUM TX device can conclude a movement of the conveyor chain by counting these pulses.
A trigger photocell at the beginning of the inspection area sends a signal to the SPECTRUM TX when a container interrupts the photocell. Each container receives a data sheet in the shifting register at the time of the triggering. This is shifted synchronously to the container movement when the conveyor chain moves and with it the container. The position is checked at each further photocell and if necessary corrected if the container has slipped a little. Therefore the position of the container is known at every moment.
The possibility to make an entry is included on the container data sheet for each detection available in the SPECTRUM TX i.e. as a rule the two statuses "product fault - yes"; or "product fault - no". At first all incoming containers are declared to be faulty on the data sheet. The subsequent detections can change this status. Each container passes through all the detections and each detection carries out the corresponding entries on the container data sheet.
The decision is made at the rejector whether a container is good or faulty. Only a container which can prove that it has passed all the inspections correctly will be allowed through. A container is rejected if it has slipped so much on its journey between the first trigger photocell and the rejector that the data sheet can no longer be allocated to it with 100% certainty. In the end the person who has full control is the person who prefers to throw away a container about which he is uncertain rather than run the risk of circulating a faulty bottle amongst his customers.