The present invention provides a process for removing metals from aqueous solutions. If no external entrapment device is connected to the controller, the controller automatically sets maximum control limit values which will effect stopping or reversing of the motor if an obstruction is encountered by the barrier. The device is provided with electronic means, a body, a transmitting transducer and at least two receiving transducers, mutually spaced apart in a first transducer array along an array direction that is directed substantially parallel to the device axis. One or more records may be retrieved from a statistics memory based on the memory pointer. The controller stores the specific data of the target objects acquired by the camera module and the model data of the target objects related to the specific data in the storage unit in association therebetween such that the specific data and the model data are callable from the storage unit.