Page 195 - Advances In Productive, Safe, and Responsible Coal Mining

174 Advances in Productive, Safe, and Responsible Coal Mining

minimal dilution extraction. In-seam seismic and acoustic sensors must be attached to
the coal itself requiring frequent remounting as mining progresses. This is inefficient
and defeats one of the main purposes for having an automated system. Their applica-
bility in Illinois Basin conditions may be limited for two reasons. First, vibration-based
CID determines the interface using differences in vibration characteristics, which
depend on both rock hardness and fracture. Since fracture characteristics in Illinois
are highly variable, it would be difficult to calibrate mining machines for any particular
seam. Frequent recalibration may also increase operational cost in addition to making it
unreliable. Second, IllinoisBasincoal is hard and in some caseshas higher compressive
strength than roof and floor strata. Thus, differences in vibration frequency may be
minimal.

9.4.2.3 Infrared CID
Different types of strata release varying amounts of infrared radiation during extrac-
tion. Infrared sensing devices can measure radiation emitted from the cutting zone and
detect changes in strata being mined. This method has the distinct advantage that radi-
ation readings can be captured from a remotely mounted sensor located behind the
cutterhead, and they function even when it is obscured by dust and water sprays. This
method can be used under any type of roof, and response time is instantaneous when
the coal-rock interface is reached [20].

9.4.2.4 Optical/video CID
This technology is based on the concept that different types of strata have different
light reflectivities. Optical sensing technology by itself is not very accurate, but is
greatly improved with the addition of video cameras and image analyzing equipment.
These sensors, like infrared sensors, can be remotely mounted and, with appropriate
video technology, can penetrate moderate dust and water spray obstructions; however,
heavy dust and water spray mist can cause problems. Another benefit of this system is
that video data can be employed for guidance purposes [22].

9.4.2.5 Radar-based CID
This technology utilizes a single antenna, which transmits and receives Doppler radar
pulses. A network analyzer controls signal frequency. Signals are attenuated as they
pass through coal and bounce off the density interface of the confining rock, which is
interpreted by the network analyzer to determine the distance to that interface. This
system has reliable accuracy and operates well under most roof conditions. It is also
suited for monitoring rib thickness between adjacent holes in highwall mining. Two
disadvantages of this system are that it does not work well in coal seams with wave-
dispersing properties and it requires the transmitter to be located within 4in. (10cm) of
the coal [23].