Broadcast control system on a dam

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March 2005 PLCs, DCSs & Controllers Products & Solutions

When the rainy season in Taiwan causes the water level in a dam to rise too high, the dam operators must release the water to protect the area. This sudden onrush of water is dangerous to people fishing or close to the downstream river. Previously, the dam operators would send a truck with a loudspeaker along the river edge to broadcast warnings for several hours before the release, warning people about the impending danger. In order to improve the situation, the dam management decided to replace the truck, which was labour-intensive and unreliable.

It was decided that a broadcast system was required, placing loudspeakers at focal points, every 200 m along the river. The operator would schedule the time the water had to be released, and three different warning messages would be broadcast before a release.

A PC is the control host for the system for scheduling water release times and for controlling the warning messages. Control of three tape recorders and an amplifier for broadcasting is done using an RS485 network employing an Adam-4050 digital I/O module. Eleven broadcasting stations are installed along the river. Each station consists of a speaker, a microphone, a magnetic sensor and an Adam-4050. The stations are daisy-chained to the control room with an eight-wire cable. The RS485 network, speaker, microphones and power for the Adam module use two lines each.

Just before the message is broadcast, the host PC activates necessary stations by sending the station numbers in ASCII on the RS485 line. The Adam-4050 in the control room turns on appropriate tape recorders and the power amplifier to broadcast the message.

The operator can monitor the broadcasting quality of any station with a microphone controlled by the Adam-4050. The broadcasting stations are also protected against tampering. Each station is equipped with an anti-tamper magnetic switch monitored by the Adam-4050. A program running on the PC checks all stations and sounds an alarm if a station is being tampered with.

By using the system, the management of the dam was able to reduce the labour required for warning the public of an imminent release of water and at the same time protect lives. Additionally, the system is easy to expand and maintain because of the multidrop design of the RS485 network and the hot-swapping facility in Adam-4000 series.

For more information contact Elton Prytz, ProMicro, 011 706 7913, [email protected], www.promicro.co.za

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Broadcast control system on a dam

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