A checkweigher or metal detector can be used during the filling and closure process or the pre-palletizing process. The checkweigher machine determines if the proper amount of product has been placed in a container. Too much or too little product weight will cause the container to be rejected. The metal detector ensures no foreign objects have fallen into the product. A photoelectric sensor can be used to verify that a package has entered the checkweigher or metal detector. The sensor will start or stop product flow as needed. Additional photoelectric sensors are used to verify a product was rejected.