Events such as explosions or rock falls inside a mine can be catastrophic because of the time to pinpoint the location of trapped miners. Their chances of survival may dramatically increase with the knowledge of their location and number. The locator system is used for the detection of trapped underground mine workers and allows the rescue team to reach the trapped workers much more quickly than the normal process of random searching.
How the detection system works
The transmitter unit is located at the mine workers’ cap lamp batteries and emits a low frequency radio wave. The transmitter is capable of transmitting though rock and other debris. The receiver unit which is carried by the rescue team is to catch the transmission. The rescue team turn the antenna in the direction of the maximum signal strength. The rescue members then move towards the direction of the signal during the rescue operation.
Different types of tags:
This type of tag contains its own power source. It’s used in trapped miner location. An active radio tag normally consists of a radio transmitter attached to a cap lamp battery that radiates EM energy as a beacon. The operational life of this active radio tag is limited to 30-50 hours.
This type of tag does not contain its own power source. A passive receiver accumulates energy over time which is received from a search receiver and uses this energy to transmit a location signal. The operation life is indefinite, but its location distance is limited by the power and duration of the transmission cycle of the search receiver.
This method is a combination of a passive or active receiver with an active transmitter which increases the detection range. This method provides an accurate location of trapped miners in respect of position, distance and direction.
Methods to increase detection distance:
- Selection of operational frequency which provides the lowest channel (through rock)
- Increase radiated power on a tag
- Increase the searching receiver sensitivity
- Increase antenna efficiency.
There are a number of devices for locating trapped miners that have been developed. Booyco Electronics
introduced a Trapped Miner Locator in South Africa developed by Selectronics of Germany with positive feedback from the mining sector.