This posed a number of engineering constraints since the chimney needed to be raised from its original height of some 36 to 46 meters to meet current legal requirements. This was achieved by inserting an exhaust tube for any smoke on the top of the chimney.

The plan also demanded that the chimney form a stand-alone structure located in an open pedestrian area within the new university campus. This made safety a very important consideration. However, the chimney had a weak load-bearing structure with masonry less than 15 cms thick so that swaying in high winds might cause unacceptable stresses.

To achieve these objectives, the Spanish company, Metiri – working in collaboration with HBM Ibérica – built internal collars at the top and bottom of the chimney so that five steel cables could be fitted and pre-stressed. Each of the wires is fitted with an HBM C6A load cell with a nominal load of 200kN. There are also two PT100 temperature sensors fitted at the base of the chimney.

All of the sensors are connected to HBM’s MGCplus multichannel amplifiercapable of handling both analog and digital input signals. The output signal is linked to a panel of five bicolor LEDs giving a quick visual indication that the system is functioning properly. There is also an alarm fitted that sounds if the pre-stressing force in any of the cables decreases by more than 20% compared to the initial pre-stress force.

Control of the system is by a PC running HBM’s catmanAP software that reads the data at 1 sample/sec. This is then automatically exported once an hour as an average data output to an ASCII file that is automatically sent through a 3G connection to a database server. The database server collects, processes and displays the data on a website programmed for the purpose. Users have an authentication code that permits the download of historical files into spreadsheet-readable format.

This system is due to be upgraded shortly with the PC and the 3G connections being replaced by MGCPLUS Profibus cards that will transmit data to the SCADA system at the customer's site. This upgrade will integrate the monitoring and management system for the chimney at the customer's SCADA system.