SmartTag Tracking
SmartTag? is an RFID-based technology designed to allow tracking of ore from its source through blasting, run of mine (ROM) pads, crushers, intermediate stockpiles and finally into the concentrator. Here we look at current developments and the future direction of the SmartTag? ore tracking system.

Metso?s Process Technology and Innovation group is a world leader in mineral processing consulting. A significant amount of this consulting work involves Process Integration and Optimisation (PIO) studies, which inclu?des investigating the effects of drill-and-blast design and implementation on down?stream processing. Critical to these studies is the ability to track specific ore into and through the plant. To increase the accuracy of this ore tracking, Metso Process Technology and Innovation (PTI) deve?loped a system to track ore using RFID transponders called SmartTag?. Since its commercialisation in 2007, SmartTag? has been used in the majority of PTI?s consulting projects and several permanent systems have been installed world wide.

The benefits of using SmartTag? in?clude linking spatial mine data to time-based processing data; increased confidence in ore blending; proactive process changes for known ore types; and accurate measu?rement of residence times in stock piles and bins. Since 2007, there have been sig?nificant advancements with RFID tech?nology that has allowed PTI to extend the reach of SmartTag? beyond secondary crushing to tertiary crushing and beyond. This has been achieved by drastically reducing the size of the SmartTags from a diameter of 60 mm to 20 mm. The new smaller RFID tags have been successfully used in several studies.

The SmartTag? System

A SmartTag? RFID tag travels thro?ugh a mine and mineral processing plant in a series of simple steps. Initially, the tag and insertion location is logged using a hand-held computer or PDA, then it is inserted into the ore (eg, into a blast hole). The tag travels with the ore through dig?ging, transport and processing, before be?ing detected at detection locations (on con?v?eyor belts), when the time and specific tag is recorded. The RFID tag data is then loa??ded into a database and analysed as required. To achieve this, the SmartTag? system requires five main components. The first co?m?ponent in the SmartTag? system is a PDA, which allows the initial RFID tag in?sertion process to become more efficient and accurate. Each RFID tag is added to the database using one of three options; it is as?sociated with a GPS coordinate, a pre-defined point (such as a blast hole), or a new po?i?nt which can be accurately located later.

At present the system does not allow for high precision GPS but it can locate the nearest point in a series of predefined poi?nts, such as blast holes, and allow the user to associate RFID tags with these points.

The next component in the system, the antenna, is located at the conveyor belts. The antenna both induces a charge on the tag and also receives a transmitted signal back from the tag. The design of the antenna is decided by two parameters, which are its size and its robustness. The size of the antenna dictates the size and the strength of the field it radiates. For this application, the area of field strong enough to charge the tag should be as large as pos?sible; therefore, the antenna used for the SmartTag? system is the largest available for this frequency of RFID system.

An RFID reader then decodes the signal from the antenna and determines the ID of the RFID tag passing the antenna. Later versions of the readers also have auto-tuning capabilities which ensure that the maximum possible read distance is achieved at all time. In the SmartTag? system the reader then transmits the ID using serial communications.

A data logging or buffer stage improves the reliability of the systems and also makes movable systems possible. The data logger receives data directly from the RFID reader, stores the IDs with the time they were detected and monitors vital system parameters, such as the tuning state of the antenna. The data logging stage also makes SmartTag? less reliant on communication links (such as wireless) as the data is stored at the detection point until a link is established to the software applications. The critical communications links, like the one between the antenna and the reader, are all wired and very reliable.

The core of the SmartTag? software is an SQL (Structured Query Language) database. The database, located on a dedicated server, stores all the information about the detection points, detected RFID tags and original locations. There are several SmartTag? software applications which either input data into the database or use the data to output information. These include the SmartTagServer, which reads data from the data loggers, the SmartTagPDA, which exchanges data with the PDAs and translates site blast hole layout diagrams, and the SmartTagRes, which calculates the residence time between two detection points.

Mini RFID tags

To expand the applications of SmartTag? through and beyond secondary crushing a mini RFID tag was required. To incorporate the mini RFID tags into the SmartTag? system, PTI faced two significant challenges; firstly, the reduced read distance, and secondly, making the mini tags robust.

By reducing the size of the RFID tag, the size of the antenna in the tag is also reduced. The size of the antenna in the tag is directly proportional to the amount of charge that is induced, for a given field strength. Therefore, the read range of a
tag will be reduced as the size of the tag is reduced.

Through investigation, the 20 mm tags were found to have an insufficient read range for the standard SmartTag? installation. PTI trialed two methods for fixing this issue; one method was to use two antennas while the second method was to place the antenna closer to the RFID tags.

Both systems were tested at an iron ore mine. Both approaches, dual antennas or closer antenna distance, were found to have similar detection capability. However, based purely on the ease of installation, a single antenna located under the belt, was chosen as the new standard insta?llation method.

The second challenge faced when incorporating the mini RFID tags into the SmartTag? system was how to protect them sufficiently to survive a blast. A method previously used by PTI to achieve this was to encase the tags in a two part epoxy. The method works well for protecting the tags, and although it is time consuming and expensive it is currently the preferred method for protecting the tags. Different encasing materials, such as reinforced nylon, are still being investigated.

After encasing in epoxy, the mini-tags have a diameter of 20 mm and are shown, with a standard SmartTag? as reference, in Figure 1. The size of the mini RFID tags allows them to pass easily through screens with apertures down to 25 mm.

Conclusion

Metso PTI has successfully incorporated a smaller, or mini, RFID tag into their SmartTag? system. The changes to the system installation are minor and increase the reliability of the system as a whole. In several examples, the mini RFID tags have proven to be, on average, more robust than normal-sized RFID tags.

The PTI team envisage that with the successful incorporation of the mini RFID tags into the SmartTag? system it will allow applications for the system to be expanded. These new applications could include a wider use in the iron ore industry where size is the critical material quality. PTI is now working on proving the reliability of the next size of RFID tags, the even smaller micro RFID tag, which can pass through a 10 mm mesh screen.

With the decreasing size of RFID tags and the development of SmartTag? into a truly distributed system, it can be extended past the mine to cover the whole minerals supply chain. Detection points can now be located in the plant, the port and even at the location of the customer, such as a blast furnace.

CASE STUDY

Secondary Crushing Circuit

As part of a wider PIO study, a secondary crushing circuit was surveyed while being fed with a particular ore type. To determine the origin of the ore at any particular time and, most importantly, during the surveys, SmartTag? detection points were set up at three locations around the circuit. The three locations were primary crusher product, secondary crusher feed and secondary crusher product. A total of 384 mini RFID tags were placed on eight polygons (a polygon is defined as different ore zones within the mine block model) after the blast, the ROM pad and trucks as they tipped ore into the primary crusher.

Of the 384 tags placed onto either the muck pile or on the ROM pad, 45 per cent were detected. However, if this is compared with the percentage of each polygon that had been excavated by the end of the trial it is a fair conclusion that many of the RFID tags that weren?t detected were also not excavated during the trial. To determine the survival rate of the tags during secondary crushing, the number of tags detected before and after the secondary crusher were compared. Of the 128 tags detected before the secondary crusher, 97 were also detected after secondary crushing.

However, as there were 52 tags that were detected after the secondary crusher but weren?t detected before the secondary crusher, the real survival rate is difficult to determine. By just comparing RFID tags detected at both detection points, it can be concluded that at least 76 per cent of the mini tags survived secondary crushing, although this number is likely to be much higher. The screen immediately following the secondary crusher uses panels with 55 mm apertures and, as expected, none of the tags were recycled back through the secondary crusher.

The primary application for SmartTag? was to determine the origin of the ore being processed during the plant surveys. In this application, where the plant feed included ore from ROM mixing and stock piles, SmartTag? was essential for determining which materials were processed in the plant at the time of the surveys. Mini tags were required to enable the ore source to be tracked all the way through secondary crushing, and proved to be robust enough to survive both blasting and secondary crushing.