Indicators of Ferromagnetic Objects – HFT

Indicators of the ferromagnetic objects of the HFT series are computer-controlled magnetometric digital devices, equipped with the algorithms for the recognizing of the presence of the ferromagnetic objects on the belt conveyors. They are designed for the extremely difficult environmental, vibrational, dusty and above all magnetic operating conditions.

The main task of the HFT system is to protect the belt conveyors and the technological devices from the damage caused by the pieces of iron found in the transported material. The HFT system was developed in cooperation with the heavy industry partners based on our magnetometer with the patented physical principle.

The functional principle of the HFT system is based on the pair of groups of sensors and exciters, which are located in the axis of the conveyor belt. The system also includes a conveyor belt movement sensor. Computer signal processing is used to evaluate the magnetic phenomena in the proximity of the sensors in the real time. This configuration enables the detection of the presence of the ferromagnetic objects on the conveyor belt.

Digital signal processing gives the system an exceptional resistance to the interference, impulses and transient phenomena from the switching of the power devices. The system also stands out for its extremely stable parameters. As long as the properties of the transported material do not change, there is no need to set and change the system settings.

The HFT system is equipped with a single-board industrial computer with a semiconductor memory. The basic modes are signalized optically, and the information is also available on the switching relay contacts. The HFT systems are self-diagnostic. During the entire time of operation, the correct operation of the individual sensors, electronic blocks, switching on of the relays and the presence of the supply voltage are tested. The software also includes a diagnostic block for the comprehensive verification of the system functionality, for the reviving after the general repairs or a possible malfunction. The software evaluates the interference conditions and recommends the optimal settings of the operating parameters to the operator. The HFT system records the entire operating information into its memory (when it was switched on, when the system reported the presence of iron and gave a signal to the technological process, when the operator responded, or when and in which part of the system a malfunction was detected). In case of a power outage, the system regularly switches off, blocks the belt motion, and makes an operational record.

Thanks to the hardware and software modularity, the HFT system provides multiple configuration options. The basic system contains a fully functional set of electronics, sensors, excitors and software ready for the operation. Based on the customer’s requirements, the system can be supplemented with the option of the sensing sensitivity switching. In this variant, up to three different sensitivity levels can be saved in the system settings, among which it is possible to switch smoothly during the system operation. Another optional part of the HFT system is the communication module. This allows the HFT system to be connected to a local computer network, where the system sends information about its activity and status. In some specific cases, when bulk ferromagnetic material is transported on the conveyor belt, in which it is necessary to detect the piece iron (iron works and smelters), the system can be equipped with the special frame sensors.

The photo shows the placement of the magnetic sensors under the conveyor belt of the excavator in the surface mine. Such a location is suitable for the difficult operating conditions and protects the system from the damage which can be caused by the transported material. Special digital filters ensure the protection against the interference from the rotating rollers of the conveyor belt.

Photo of the installation of the frame sensors on the conveyor belt of the agglomeration stacker. The transported bulk material does not represent a risk to the frame sensors, as it is in the case of overburden and coal excavators. The low speed of the conveyor belt and the need to detect the piece iron in the ferromagnetic material require the use of the frame sensors with the appropriate selectivity.

The photos show the pieces of iron captured thanks to our HFT systems in the Třinec Iron and Steel Works. The first photo shows the amount of the pieces of iron collected during one week of the trial operation of the new agglomeration stacker at the homologation landfill. The second photo shows the pieces of iron captured in front of the sintering furnaces at a time when the HFT systems were not deployed on the homologation landfills.