Advanced Tutorial on Wireless Communication and Electronic Tracking: Mine Operations Center (MOC)
6.0 Mine Operations Center (MOC)
Wireless communications must be established between miners and surface personnel as required by the MINER Act of 2006. Similarly, for tracking systems, the electronic location information must also be available at the surface. An obvious central location on the surface to meet both these requirements is the mine operations center (MOC). At least one dispatcher should always be in the MOC, monitoring operations, directing needed resources, and checking the status of sensor readings. The MOC must have computers to monitor network performance and to implement diagnostic tests. There would likely be displays giving the status of the network, health of the various CT components and possibly atmospheric monitoring sensors, and mine maps showing locations of workers. The following sections describe how a MOC should function to ensure effective communications and worker safety.
The dispatcher in the MOC should have access to the tracking information. An electronic tracking system requires software to manage and process the data sent to the MOC from the readers or nodes in the mine. This software runs on a computer server in the MOC and should include graphical capabilities to display the locations of underground personnel on a representation of the mine map. The software should also include database capabilities to allow personnel in the MOC to pull up detailed information and track individual miners. Tracking information will have to be periodically stored so that, in the event of an accident, the most recent pre-accident locations of mine personnel can be determined.
Ideally, displays in the MOC would indicate the locations of all miners by superimposing an icon representing each miner on a mine map. The icons would either have the miner’s name or some other unique identifier associated with each miner. The locations would be accurate to within a certain distance, which might vary depending on location (escapeway versus working section, for example). The required resolution will be stipulated by MSHA. Additionally, the locations would be updated at a regular interval, again as specified by MSHA.
An example of a mine worker tracking display is shown in Figure 6-1.
6.2 Surface Communications
As mentioned at the beginning of this chapter, communications from underground will likely be centralized at the MOC. During normal operations, the CT communications backhaul system will go directly to the MOC. Under emergency conditions, the CT system may be damaged and communications traffic may be routed through an alternate communications path (ACP).
ACPs involve communications and/or electronic tracking system links to the surface at locations that are remote from the MOC. Ideally, there would be an RF communications path on the surface from an ACP back to the MOC, so that information between the ACP access point and the MOC would be relayed with a minimum of delay. In the optimum system, messages and information would be relayed automatically. However, the message relay could be done manually by operators stationed at the ACP surface access point (i.e., any message to/from the ACP access point is received and repeated by the operator). The link should only be required in a rare emergency in which the normal backhaul has become inoperable. Measures should also be taken to ensure that the ACP access point is easily reached and periodically verified as operational.
Manual relay over an RF communications path could be accomplished by using commercial cellular phones or simple walkie-talkies. The use of cell phones requires the ACP access and MOC locations to be within the coverage area of a cellular base station. Walkie-talkies require relatively short distances between the ACP access point and the MOC. In the event that cell phones and walkie-talkies cannot be used, a wireless RF communications link could be established on the surface using a high-power transmitter or a high-gain antenna, or a hardwired twisted-pair cable could be strung. It should be noted that any RF link on the surface would need to be approved by the FCC to avoid EMI with any existing radios or TVs in the vicinity of the ACP access point and MOC.
Figure 6-2 presents three of the methods discussed for connecting the ACP access point to the MOC on the surface. Figure 6-2a shows an ACP for a leaky feeder system exiting an air shaft. At the surface, the ACP links to the MOC via a fiber-optic cable. Figure 6-2b shows a wireless transmission through the air used to link the ACP with the MOC. Figure 6-2c shows a manual link of the ACP with the MOC using miners with walkie-talkies, one at the ACP and the other at the MOC.
A fourth option (not shown in Figure 6-2), with widespread availability due to the proliferation of Internet Protocol (IP) capable devices and broadband networks, is to lease a connection that relies on the Internet. Such options include DSL modems through the telephone companies, cable modems through cable television companies, and satellite modems through satellite service providers. Although only a few mine communications systems currently support IP protocols, the equipment vendors will soon offer such an option, and there are converters available that will allow mine communications through the Internet. An advantage of using the Internet-based approach is that mines can remotely monitor their communications, tracking, AMS, and other data links. Some equipment vendors and third-party providers already offer services to monitor the systems, thus eliminating the burden of the local mine operations personnel of monitoring and troubleshooting the networks.