Designs Unique, in conjunction with Thermotron of Wadeville, Germiston has recently commissioned a sophisticated data acquisition system for the Lesotho Highlands Water Project's "tunnel-boring machine".
The Lesotho Highlands Water project is one of the most ambitious multipurpose water schemes at present being undertaken in the world. Its sheer magnitude and ingenious engineering concepts have captured the imagination of water authorities and laymen alike the world over. When completed, the project will deliver approximately 70 m3 of high quality water per second into the Vaal River system, simultaneously making Lesotho self-sufficient in electric power and giving it a healthy injection of cash in the form of royalties from the sale of water.
Phase 1A, completed in 1998, included the construction of the Katse Dam, the highest dam in Africa, and the impressive hydroelectric power complex.
Phase 1B, to be completed by 1 January 2003, is now underway and includes amongst other components; a 145 m high concrete faced rockfill dam on the Senqunyane river at Mohale, forming the Mohale reservoir. A 32 km long water transfer tunnel is to be bored, connecting the Mohale Reservoir with the Katse Reservoir.
Two TBMs (tunnel boring machines) are used to drive the 4 m-finished diameter tunnel, one launched from the construction access at the Mohale intake and the other via the permanent aqueduct at the outlet at the Katse dam.
One of the TBMs has been completely refurbished and the pilot's control cabin equipped with some of the latest technology in data acquisition, supplied by Designs Unique, sole agents for the Intelligent Instrumentation range of data acquisition and control electronics.
The "lifetime warranted" data acquisition system now monitors the existing PLC controller, and performs the realtime logging and displaying of some 270 channels of Digital I/O, 160 channels of Analog I/O, and controlling the PLC critical status. These input signals are fed from the various sensors measuring torque, distance, pressures and temperature, etc, and if necessary the system will override and instruct the PLC to shut down critical equipment such as hydraulic pumps, etc.
The entire data acquisition system is PC-based, using Pentium II-450 systems and Microsoft Windows NT4.0. An external bus-extender housing with integral power supply and fans houses the data acquisition and control electronics. Due to severe space restriction in the pilot’s control cabin, two flat 17" (432 mm) high resolution, active colour LCD display screens are used, displaying the operational status of the entire TBM by means of video-splitting electronics and software in the PC. A graphical engineering image of the TBM and hydraulic systems is displayed across the two adjoining screens, with various dynamic displays in the form of panel meters, LEDs, graphs, etc, superimposed over the image for the pilot's observation and control.
Additional to the above signals, gas sensors are monitored across the length of the TBM (approx 350 m), for fire, or explosion-threat status, and the readings are continuously logged. The monitored gasses include oxygen, methane, hydrogen-sulphide, carbon dioxide, carbon monoxide, and nitrogen oxides.
In the event of hazardous gas detection, or undesirable gas levels in the tunnel, the 11 KV power supply line to the TBM is shutdown and an emergency explosion-proof power supply redirects power to the gas detectors. High-speed ventilation fans at the entrance to the tunnel would then force-feed air into the tunnel. Gas statuses are then logged at very high speed and these signals are transmitted via fibre-optic cable out to the tunnel engineer's office for realtime observation while the tunnel is evacuated of personnel.
Live video monitoring consists of four video cameras with operator-programmable pan/tilt/zoom capability, to monitor the various hydraulic and conveyor belt activities simultaneously on split-image format. These signals, in total, together with the data acquisition signals, telephone PABX system, and the laser guidance system are transmitted via a 12-core fibre-optic cable out of the bored tunnel back to the tunnel engineer's office. This will be some 18 to 20 km distant when this TBM reaches it's furthest point from the tunnel mouth. A 12-core fibre-optic cable was used to facilitate easy future expansion.
Identical images are produced on the tunnel engineer's PC system in his office, and all signals again continuously recorded and displayed. The data transmission is achieved by means of NetDDE and acquisition speeds have proved to be remarkably fast, typically 30 ms for all of the above signals. The data is then available for report generation, research and analysis on the routine daily shifts by the tunnel engineer.
The software program used for the data acquisition system is the award winning Visual Designer (a powerful application generator from Intelligent Instrumentation). It is a quick and simple task to modify, or change any parameter or function, with typical modifications taking a few seconds. This can also be done 'on the fly', without interruption of the boring process - an important feature of the software considering that the down-time costs of the TBM are in the order of R680 000 per day. Operator training requirements are minimal and no operator keyboard requirements are necessary. This software can also be modified, or adjusted, at will from the tunnel engineer's office or from the developer's offices in Johannesburg and the TBM progress monitored, or even updated, by means of Internet facility.
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