Minesight Tutorial
Cristy Borovetz
The Mine Improvement and New Emergency Response Act of 2006 (MINER Act) requires mine operators to adopt underground communications and electronic tracking (CT) systems that meet specific performance goals. The MINER Act was signed into law on June 15, 2006. It amends the Federal Mine Safety and Health Act of 1977 and is intended to improve the safety of miners. Among other things, it provides updated requirements for emergency response, incident command and control, mine rescue teams, and incident notification.
One of the goals of the MINER Act is to provide wireless communications and location information between underground workers and surface personnel following an underground accident. The CT technology that is available, or anticipated to be available soon, to meet these goals may be unfamiliar to the mining professionals who need to purchase or use this technology. The purpose of this tutorial is to introduce the different types of CT technologies, describe how they work, and provide guidelines that allow the reader to evaluate and compare systems.
The term system describes a collection of components that must be connected or operated together to make a working arrangement - in this case a communications system or a tracking system. A mine may have a communications system that is completely separate from the tracking system. An integrated system is a single system that provides both communications and tracking. Communications systems and electronic tracking systems have similar principles of operation, but because they address different needs, they are best understood if discussed separately. Therefore, this chapter breaks CT systems into five parts: Communications Basics, Communications Systems Principles of Operations, Tracking Systems Principles of Operations, Network Options, and the Mine Operations Center.
All modern communications and electronic tracking (CT) systems depend on the transmission and reception of energy. Electromagnetic energy is energy associated with nearly all modern CT systems, and for all of the systems discussed in this tutorial. Electromagnetic energy is everywhere in the environment and examples include radio waves, visible light, and x-rays. Many common devices depend upon sending or receiving electromagnetic energy for their operation. Some examples are televisions and radios, cell phones, automatic garage door openers, and remote keyless entry fobs for cars. Electromagnetic energy can be visualized as a traveling wave of electric and magnetic energy. All waves are characterized by their wavelength and amplitude.
The wavelength is the distance between adjacent peaks of a wave. Notice that the wavelength of the dashed line wave in Figure 2-1 is longer than that of the solid line wave. The unit of measure for wavelength is meters or feet. The amplitude is a measure of how tall the wave is. The dashed line wave in Figure 2-1 has greater amplitude than the solid line wave.
In discussing their CT systems, manufacturers will typically mention the frequency at which the systems operate. The frequency relates directly to the wavelength. Frequency is a measure of the number of up and down oscillations or repetitions of the wave over a fixed length of time. The fewer oscillations that a wave has within a fixed period, the lower the resulting frequency will be (and the longer the wavelength). The dashed wave in Figure 2-1 has fewer oscillations than the solid wave, so it has a lower frequency. Cycles per second, or Hertz (Hz), is the measure of frequency. Low frequency waves have longer wavelengths while high frequency waves have shorter wavelengths. The maximum amplitude of a wave is the peak of the wave, labeled in Figure 2-1, whereas the amplitude of a wave is its value at any time, labeled on the y-axis.
The frequency (or wavelength) of a particular CT system is a very important factor in its design and operation because certain wavelengths lend themselves well to travelling through a given transmission media. For instance, very long wavelengths can travel a significant distance through the earth. Radio communications use short wavelengths, which travel well through the air or down tunnels, while extremely short wavelengths are required to travel within fiber optic cables.
Communications technology involves electronic devices that allow people to talk or send information to each other. In its most elementary form, a communications system is made up of a transmitter, transmission medium, and a receiver. Figure 2-2 shows these basic components. The transmitter is the device that sends out the signal, and the signal contains the information in the form of an electromagnetic wave. The information could be part of a conversation or a text message. The signal travels through or along a transmission medium such as air, wires, metallic pipes, fiber optic cable, or even the ground. A receiver then picks up the signal and a physical communication link is accomplished.
In the example shown in Figure 2-2, there is only one transmitter and receiver pair involved in the communications path, or one physical communication link. Obviously, for two people to talk back and forth a transmitter and receiver are required on both ends of the communication. A transceiver is a device that combines the transmitter and receiver into one unit; a walkie-talkie is a good of example of such a device.
Whether the cause is dissipation of energy in the transmission media, noise, or a combination of both, eventually the range of a single physical communication link becomes limited. Adding a node between the transceivers can increase the allowable distance between them. Among other functions, the node acts as a repeater, which relays the message from one transceiver to the next (in either direction) by automatically retransmitting the signals it receives. This retransmission may also involve converting the transmission frequency so that it can transmit across a different transmission medium, such as a wire. The retransmission may also involve sending the signal to multiple destinations or amplifying the signal. With the additional device of a node in the communications link, the result is a simple communications network. A communications network is a system of interconnected pieces of communications equipment used to transmit or receive information.
Figure 2-3 shows a simple network with two physical communications links: one from the radio to the node (repeater) on the left, and the other from the repeater to the radio on the right. Generally, the same antenna on the node receives and retransmits the message, but there may be separate antennas dedicated to each function. In Figure 2-3, the node receives the radio frequency (RF) signal from the radio on the left. The signal travels into the node where internal electronics process the signal, amplify it, and then retransmit it. The radio on the right then receives the signal. In this case, the situation is more complicated than simply connecting two radios by an air medium.
The communications path between two radios can be referred to as direct point-to-point (involving only one physical communication link), or it can be achieved through a complex network that connects the source and destination (involving multiple physical communications links). The interconnection between the nodes in the network can be wireless or wired. Fiber-optic cable or other means can also be used to connect the nodes. Figure 2-5 shows three examples of network configurations for interconnected nodes.
The solid lines in the above diagrams (Figure 2-5) represent physical communications links between the nodes. A well-designed network configuration increases the survivability of communications (the potential for the system to continue operating after an accident) should one or more of the nodes fail. For example, if one of the nodes in the ring configuration fails, the remaining communications can survive by reversing the direction of traffic in the region of the failed node. In the star configuration, the failure of an outlying node does not disrupt the rest of the network, but the failure of the center node will shut down the entire network.
Primary communications systems are characterized as those that have a transceiver small enough to be comfortably worn (carried) by a miner throughout an entire shift. Primary communications systems typically function at conventional radio communications frequencies, use small antennas, have a long battery life, and provide sufficient radio channels for general operations. Of the systems that will be discussed in this tutorial, the leaky feeder and node-based systems are considered primary systems.
Secondary communications systems require a larger and heavier antenna, making these systems still portable, but less manageable for wearing throughout a shift. Secondary communications systems typically operate at lower, non-conventional radio frequencies and generally have only a single channel for communications, and do not have sufficient throughput capacity for general operations. Of the systems discussed in this tutorial, the medium frequency (MF) and through-the-earth (TTE) systems are considered secondary communications systems.
Many underground coal mines use some form of telephone as the primary means of communications between the surface and the underground miners. It is easy to imagine two phones (or transceivers, as introduced in Section 2.1.1) directly connected by wires to form the physical communications link. Relating to the previous discussion of Figure 2-2 in Section 2.1.1, the energy from the transmitter directly couples into the transmission medium, which in this case is a wire or cable. For mine pager phones, which are the most common form of communications in underground mines, two wires are typically used. Connecting additional phones into the same wires forms a network of phones. With this network configuration, the phones operate in a page mode in which all the telephones broadcast simultaneously when a button is pressed on the transmitting pager phone. The system works well in the case of an emergency when all miners must be notified. However, there is no capability for private or simultaneous conversations.