Page 133 - Advances In Productive, Safe, and Responsible Coal Mining

Developing effective proximity detection systems for underground coal mines 117

number of other factors that can influence the performance of proximity detection sys-
tems, such as conveyor elevation, cutting drum elevation, tramming, and mining mode
[19]. These factors should also be taken into consideration when designing zone con-
figurations for intelligent proximity systems.

7.6 Future developments

7.6.1 Proximity considerations for underground mobile
equipment

In 2015, MSHA issued a proposed rule that would require mobile machines on work-
ing sections (with the exception of longwall sections) to be equipped with a PDS. Cur-
rently available PDS for underground mining are all based on electromagnetic
technology and were originally intended for use on CMMs. In an effort to identify
the applicability and transferability of EM-based PDS onto mobile equipment, NIOSH
conducted field evaluations of PDS-equipped mobile haulage machines. These field
evaluations consisted of having an operator drive the mobile equipment toward
an MWC positioned in an entry or crosscut. In most cases, the PDS did stop the
machine before it struck the MWC. However, three primary concerns have arisen with
respect to EM-based PDS for use on mobile machines in underground coal mines:
environmental effects, electromagnetic interference (EMI), and general performance
characteristics.
Recent field evaluations [22] observed some phenomena not measured in previous
field studies, including diminished performance in the vicinity of metal mesh and
powered cables on the working section. These occur due to mutual inductance, which
is the linking or coupling of a magnetic field from the generator coil to metal objects or
wires in close proximity. It should be noted that these observations were discovered
during field evaluations, but were not tested under a peer-reviewed field test protocol.
NIOSH researchers have observed EMI from continuous personal dust monitors
(cPDMs) that hinder the performance of PDS significantly. The cPDM is a belt-worn
monitor that takes interval samples for respirable coal dust. It was discovered by mine
sites and brought to the attention of NIOSH that when miners wear their cPDM and
MWC close together, the MWC begins to behave erratically. In some cases, this would
permit the miner to walk all the way up to the machine without incurring a warning or
stop zone, which poses a significant safety hazard. This behavior has been observed
with the cPDM, but could potentially occur from other electronic devices that emit
spurious electromagnetic noise within the operating frequency of the PDS.
NIOSH conducted laboratory testing of one PDS manufacturer’s MWC to measure
its susceptibility to EMI, along with measurements to identify the EMI being produced
by a cPDM, and found that it was best to keep the cPDM and MWC at least 6in. apart
in order to prevent EMI. This finding correlates with recommendations from PDS
manufacturers [23,24] of maintaining a 6-in. (15.2cm) separation distance.
A prototype shielded pouch for the cPDM was developed by a PDS manufacturer in
an attempt to mitigate EMI effects. Lab tests showed that the pouch reduced the