Technology
 News
 

No. 479 January 2000 

Ore Pass Level and Blockage Locator Device
 

Objective 

Develop a means of determining both the fill level of material in 

an ore pass or bin and the location of bridging material causing a 

blockage. 

Background 

Bridging of material in ore passes causes blockages in the flow 

of material. These blockages can be hazardous and must be 

removed before production can continue. Sensors are available 

that can determine fill level from the top of an ore pass, but there 

are presently no sensors that can determine both fill level and the 

position of a blockage. If information can be obtained regarding 

the location of a blockage, the depth of the material above the 

blockage and the distance from the outlet can be determined. This 

information is needed to determine the safest and most effective 

method for removing the blockage. 

Approach 

Because an ore pass is constructed in solid rock, there is no 

access to the outside of it, which presents significant challenges in 

designing a means of determining depth of the material. A second 

challenge is that any system internal to an ore pass must be rugged 

enough to withstand direct impacts from rock or other materials 

flowing through it. 

An inexpensive level-sensing system was designed to monitor 

the presence of material inside an entire ore pass. The sensor 

consists of simple steel strapping instrumented with strain gages 

that can detect the presence of material at discrete points along the 

length of the strapping. The steel strap can be attached to the 

interior of an ore pass or bin and can conform to the shape of an 

irregular opening. It can be from 3 to 30 m (10 to 100 ft) long as 

designed. Longer distances may be possible. Tests of a prototype 

in a 6-m- (20-ft-) tall bin have shown that the sensor works with 

various sizes of rock. 

How It Works 

The prototype consists of steel strapping 4.6 m long, 10 cm 

wide, and 3 mm thick (15 ft by 4 in by 1/8 in). Weldable strain 

gages are attached at equal intervals along the strap. Bolts with 

standoffs are inserted between each strain gage, and the steel 

strapping is bolted to the wall of the bin with the strain gages 

toward the wall. A slotted rubber hose protects the back of the 

strap from impacts and/or filling with material. 

As material fills the bin, hoop stresses cause a slight deflection 

in the steel strapping between the bolts. This deflection is 

measured by the strain gages. Where material is present, strain is 

indicated. In this way, the location of material can be resolved to 

within 0.6 m (2 ft). A microprocessor multiplexes and analyzes the 

data from the strain gages and outputs data to a user interface that 

indicates the presence or absence of material at each gage. While 

the sensor was originally developed for ore passes, it can also be 

used in bins and hoppers that might require a more rugged level 

sensor than currently exists. 

Patent Status 

A patent has been applied for under the name “Ore Pass Level 

and Blockage Locator Device,” application number 60/086,929. The 

patent will be available for licensing, and a cooperating mine is 

being sought at which to conduct full-scale tests. 

U.S. Department of Health and Human U.S. Department of Health and Human Services Services

Public Health Service
 

Centers for Disease Control and Prevention
 

National Institute for Occupational Safety and Health
 
 

For More Information 

Additional information can be obtained by contacting Todd 

Ruff at (509) 354-8053, e-mail ter5@cdc.gov, Spokane Research 

Laboratory, E. 315 Montgomery Ave., Spokane, WA 99207. 

To receive additional information about 

occupational safety and health problems, call 1­

800-35-NIOSH (1-800-356-4674), or visit the 

NIOSH Web site at www.cdc.gov/niosh 

Mention of any company name or product does not 

constitute endorsement by the National Institute 

for Occupational Safety and Health. 

Figure 2.—Device installed in bin.

 Figure 1.—Ore pass level and blockage locator 

device prior to installation in bin. 

Figure 3.—Level indicator with LED’s showing presence or 

absence of material at each gage.