ELECTROMAGNETIC NOISE IN McELROY MINE 

M. Kanda 

J. W. Adams 

W. D. Bensema 

Electromagnetics Division 

Institute for Basic Standards 

National Bureau of Standards 

Boulder, Colorado 80302 

The views and conclusions contained in 

this document should not be interpreted 

as necessarily representing the official 

policies or recommendations of the lnterior 

Department's Bureau of Mines of the U. S. 

Government. 

June 1974 

Prepared for 

U. S. Bureau of Mines 

United States Department of the lnterior 

Pittsburgh, Pennsylvania 15222 

Working Fund Agreement HO 133005 

U.S. DEPARTMENT OF COMMERCE. Frederick B. Dent, Secretary 

NATIONAL BUREAU OF STANDARDS Richard W Roberts D~rector 
iii 

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LIST OF FIGURES 

Page 

Figure 2-1. 

Figure 2-2. 

Figure 2-3. 

Figure 3-1. 

Figure 3-2. 

Figure 3-3. 

Figure 3-4. 

Figure 3-5. 

Block diagram of portable instrumentation-- 7 

System for field recording data to obtain 

amplitude probability distributions-------- 8 

Block diagram of laboratory recording system modified for field use----------------- 9 

Map of portion of McElroy Coal Mine where 

first day measurements were made (April 10, 1973)----------------------------------- 20 

Map of portion of McElroy Coal Mine where 

second day measurements were made (April 12, 1973)----------------------------------- 21 

Spectrum at location C in power entry. 

Spectral resolution is 78.1 Hz------------- 22 

Expanded spectrum at location C in power 

entry. Spectral resolution is 3.91 Hz----- 2 3 

Spectrum at location D near operating 

miner. Spectral resolution is 78.1 Hz-.---- 2 4 

Figure 3-6. Spectrum at location E in crosscut. 

Spectral resolution is 78.1 Hz------------- 25 

Figure 3-7. Expanded spectrum at location E in crosscut. Spectral resolution is 3.91 Hz------- 2 6 

Figure 3-8. Spectrum at location F in middle of angle 

cut. Spectral resolution is 78.1 Hz------- 2 7 

Figure 3-9. Spectrum at location B with no equipment 

operating. Spectral resolution is 78 -1 Hz- 28 

Figure 3-10. Expanded spectrum at location B with no 

equipment operating . Spectral resolution 

is 3.91 H~--------------------------------- 29 

Figure 3-11. Spectrum at location B near operating miner 

and loader. Spectral resolution is 78.1 Hz 30 
LIST OF FIGURES (continued) 

Page 

Figure 3-12. Expanded spectrum at location B near operating miner and loader. Spectral resolution 

is 3.91 Hz--------------------------------- 3 1 

Figure 3-13. Spectrum at location F in return entry. 

Spectral resolution is 78.1 Hz------------- 32 

Figure 3-14. Expanded spectrum at location G in return 

entry. Spectral resolution is 3.91 Hz- ---- 3 3 

Figure 3-15. Spectrum at location A near operating 

machinery. Spectral resolution is 156 Hz-- 34 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Spectrum at location A near operating 

machinery. Spectral resolution is 19.5 Hz- 35 

Spectrum at location A near operating 

machinery. Spectral resolution is 156 Hz-- 36 

Spectrum at locat ion A near operating 

machinery. Spectral resolution is 156 Hz-- 37 

Spectrum at location A near operating 

machinery. Spectral resolution is 19.5 Hz- 38 

Spectrum at location A near operating 

machinery. Spectral resolution is 156 Hz-- 39 

Spectrum at locat ion A near operating 

machinery. Spectral resolution is 156 Hz-- 40 

Spectrum at location A near operating 

machinery. Spectral resolution is 19.5 Hz- 41 

Spectrum at location A of an impulse. 

Spectral resolution is 156 Hz-------------- 42 

Spectrum in haulageway near bottom of 

elevator shaft. Spectral resolution is 

78.1 Hz------------------------------------ 43 

Figure 3-25. Expanded spectrum in haulageway near bottom 

of elevator shaft. Spectral resolution is 

3-91 Hz------------------------------------ 44 

vii 
LIST OF FIGURES (continued) 

Page 

Figure 3-26. 

- - Figure 3-27. 

Figure 3-28. 

Figure 3-29. 

Figure 3-30. 

Figure 3-31. 

Figure 3-32. 

Figure 3-33. 

Figure 3-34. 

Figure 3-35. 

Figure 3-36. 

Figure 3-37. 

Figure 3-38. 

Spectrum at location B near train passing 

by. Spectral resolution is 78.1Hz-------- 4 5 

Expanded spectrum at location B near train 

passing by. Spectral resolution is 3.91 Hz 46 

Expanded spectrum at location B near empty 

train going by. Spectral resolution is 

3-91 HZ------------------------------------ 4 7 

Spectrum at location C at head piece with 

conveyor and car -pull operating . Spectral resolution is 78.1 Hz ---------------------- 4 8 

Expanded spectrum at location C at head 

piece with conveyor and car -pull operating. 

Spectral resoluti.on is 3.91 Hz------------- 49 

Spectrum at location A of haulageway. 

Spectral resolution is 156 Hz-------------- 5 0 

Expanded spectrum at locat ion A of haulage - 

way. Spectral resdution is 19.5 Hz------- 51 

Spectrum at location A which was the highest 

measured on April 12, 1973. Spectral resolution is 78.1 Hz-------------------------- 5 2 

Spectrum of operating arc welder 15 meters 

away. Spectral resolution is 78.1 Hz- ----- 5 3 

Spectrum of noise near powerline on surface 

above FlcElroy Mine. Spectral resolution is 

78 1 Hz------------------------------------ 5 4 

Expanded spectrum of noise near powerline 

on surface above McElroy ?4ine. Spectral resolution is 3-91 Hz---------------------- 5 5 

Spectrum of noise at surface above McElroy 

Mine. Spectral resolution is 156 Hz------- 56 

Spectrum of noise at surface above FlcElroy 

Mine. Spectral resolution is 156 Hz--- --- - 5 7 

viii 
Figure 3-45. 

Figure 3-46. 

Figure 3-47. 

Figure 4-1. 

Comparison of magnetic field strengths of 

Grace and Robena Mines as a function of 

distance from noise source----------------- 64 

Comparison of E-M noise levels near operating machinery from four mines. Vertical 

magnetic-field components are shown. 

Broken sections of the curves represent system noise------------------------------- 65 

Comparison of E-M noise levels along 

haulageways in four mines. Vertical 

magnetic-field components are shown. 

Broken sections of the curves represent 

measurement -system noise leve 1s - - - - - - - - - - - - 66 

APD, 10 kHz, vertical component, location B 

on figure 3-1------------------------------ 73 
LIST OF FIGURES (continued) 

Page 

Figure 

F i g u r e 

Figure 

Figure 

F i gure 

Figure 

Figure 

Figure 

F i gure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

APD, 30 kHz, vertical component, location B 

on figure 3-1------------------------------ 74 

APD, 70 kHz, vertical component, location B 

on figure 3-1------------------------------ 75 

APD, 130 kHz, vertical component, location B 

on figure 3-1------------------------------ 76 

APD, 160 kHz, vertical component, locat ion B 

on figure 3-1 .............................. 7 7 

APD, 250 kHz, vertical component, location B 

on figure 3-1------------------------------ 7 8 

APD, 500 kHz, vertical component, location B 

on figure 3-1------------------------------ 79 

API), 1 MHz, vertical component, location B 

on figure 3-1------------------------------ 80 

APD, 2 MHz, vertical component, location B 

on figure 3-1 .............................. 8 1 

APD, 6 MI-Iz, vertical component, location B 

on figure 3-1------------------------------ 82 

APD, 14 Ta-Iz, vertical component, location B 

on figure 3-1 ......................... - ---- 8 3 

APD, 10 kHz, horizontal component, (NE-SW) , location B on figure 3-1 ---------------- --- 8 4 

APD, 30 kHz, horizontal component, (NE-SW) , location B on figure 3-1 ---------------- --- 85 

APD, 70 kHz, horizontal component, (NE-SW) , location B on figure 3-1 -------- - ---------- 86 

APD, 130 kHz, horizontal component, (NE-SW) , location B on figure 3-1 ------------------- 8 7 

APD 160 kHz, horizontal component, (NE -SW) , location B on figure 3-1 ------------------- 8 8 

APD, 250 kHz, horizontal component, (NE-SW) , location B on figure 3-1----- ---------- ---- 89 
Figure 4-27. 

Figure 4-28. 

Figure 4-29. 

Figure 4-30. 

Figure 4 -31. 

Figure 4-32. 

, 

g

APD, 130 kHz, vertical component, quiet 

time, location B on figure 3-I------------- 99 

APD, 10 kHz, vertical component, location A 

on figure 3-1------------------------------ 100 

APD, 30 kHz, vertical component, location A 

on figure 3-1------------------------------ 10 1 

APD, 70 kHz, vertical component, location A 

on figure 3-1 ------ -- ------------ ---------- 10 2 

APD, 130 kHz, vertical component, location 

A on figure 3-1 ---------------------------- 103 

APD, 160 kHz, vertical component, location 

A on figure 3-1---------------------------- 104 
LIST OF FIGURES (continued) 

Page 

Figure 

- Figure 

- A Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

Figure 

APD, 250 kHz, vertical component, location 

A on figure 3-1---------------------------- 105 

APD, 500 kHz, vertical component, location 

A on figure 3-1 --------------------.----- --- 106 

APD, 1 MHz, vertical component, location A 

on figure 3-1 ---------- ------------------- 107 

APD, 2 MHz, vertical component, location A 

on figure 3-1 ---- - ------------------------- 108 

APD, 10 kHz, horizontal component (N-S), location A on figure 3-1------ ---- ----- ---- 109 

APD, 30 kHz, horizontal component (N-S) , location A on figure 3-I----- - ----- --- -- --- 110 

APD, 70 kHz, horizontal component (N-S), location A on figure 3-I------ ---- --------- 111 

APD, 130 kHz, horizontal component (N-S) , location A on figure 3-1--- ---- ------ -- ---- 112 

APD, 160 kHz, horizontal component (N-S), location A on figure 3-1----- -------------- 113 

APD, 500 kHz, horizontal component (N-S) , location A on figure 3-1------------------- 114 

APD, 1 MHz, horizontal component (N-S), location A on figure 3-I------------------- 115 

APD, 10 kHz, vertical component, quiet 

time, location A on figure 3-I------------- 116 

APD, 30 kHz, vertical component, quiet 

time, location A on figure 3-I------------- 117 

APD, 70 kHz, vertical component, quiet 

'time, location A on figure 3-I------------- 118 

APD, 130 kHz, vertical component, quiet 

time, location A on figure 3-I------------- 119 

xii 
Figure 4-57. 

Figure 4-58. 

Figure 4-59. 

Figure 4-60. 

Figure 4-61. 

Figure 4-62. 

APD, 6 MHz, vertical component, location B 

on figure 3-2------------------------------ 129 

APD, 14 MHz, vertical component, location B 

on figure 3-2------------------------------ 130 

APD, 10 kHz, vertical component, location A 

on figure 3-2 --------------- --------------- 131 

APD, 30 kHz, vertical component, location A 

on figure 3-2 ------------------------------ 132 

APD, 70 kHz, vertical component, location A 

on figure 3-2 ------------------------------ 133 

APD, 130 kHz, vertical component, location 

A on figure 3-2--- ---------------- --------- 134 

xiii 

. . a -- . ----.- 
LIST OF FIGURES (continued) 

Page 

Figure 4-63. 

... Figure 4-64. 

Figure 4-65. 

Figure 4-66. 

Figure 4-67. 

Figure 4-68. 

Figure 4-69. 

Figure 4-70. 

Figure 4-71. 

Figure 4-72. 

Figure 4-73. 

Figure 4-74. 

APD, 160 kHz, vertical component, location 

A on figure 3-2 - --- - -- -- ---- -- - - --- - ---- --- 135 

APD, 250 kHz, vertical component, location 

A on figure 3-2 -- 136 

APD, 50 0 kHz, vertical component, location 

A on figure 3-2- --------------------------- 137 

APD, 1 MHz, vertical component, location A 

on figure 3-2--------- ------------------ --- 138 

APD, 2 MHz, vertical component, location A 

on figure 3-2------ ---- -- ---------------- -- 139 

APD, 6 MHz, vertical component, location A 

on figure 3 - 2 - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - 140 

APD, 10 kHz, roof bolt measurements-------- 141 

APD, 150 kHz, roof bolt measurements- ------ 142 

Field strength excursions between 0.001 and 

99% of the time as a function of frequency, 

vertical component, location B on figure 3-1 ---------------------------------------- 143 

Field strength excursions between 0.001 and 

99% of the time as a function of frequency, 

horizontal component, (NE-SW) , location B 

on figure 3-1--- --------------------------- 144 

Field strength excursions between 0.001 and 

99% of the time as a function of frequency, 

vertical component, quiet time, location B 

on figure 3 - 1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 145 

Field strength excursions between 0.001 and 

99% of the time as a function of frequency, 

vertical component, location A on figure 3-1 ........................................ 146 

ELECTROMAGNETIC NOISE IN MCELROY MINE 

Two different techniques were used to make 

measurements of the absolute value of electromagnetic noise in and above an operating coal mine, 

McElroy Mine, located near Moundsville, Nest Virginia. 

The electromagnetic environment created by 300 volt 

dc and 480 volt ac machinery was measured. In one 

technique noise was measured over the entire electromagnetic spectrum of interest for brief time 

periods. The noise was recorded using broadband 

analog magnetic tape. The noise data was later 

transformed to give spectral plots. In the other 

technique, noise amplitudes were recorded at 

several discrete frequencies for a sufficient 

length of time to provide amplitude probability 

distributions. 

The specific, measured results are given in a 

number of spectral plots and amplitude probability 

distribution plots. 

Key words : Amp1 itude probability distribution; coal 

mine noise; digital data; electromagnetic communications; electromagnetic interference; electromagnetic 

noise; Fast Fourier Transform; Gaussian distribution; 

impulsive noise; magnetic field strength; measurement 

instrumentation; spectral density; time-dependent 

spectral density . 

INTRODUCTION 

This report gives data concerning electromagnetic noise 

in a coal mine that used dc shuttle-car and rail-haulage power; 

the remainder of the section machinery and belt haulage used 

ac power. In this section, background information and 

a brief mine description are covered. In Section 2, 

measurement instrumentation is discussed. In Section 3, 

spectral plots of data are presented. In Section 4, amplitude 

probability distributions (APD) of magnetic-field noise are 

given. The last two sections cover conclusions and recommendations. 
During operation, the electrical machinery used in mines 

creates a wide range of many types of intense electromagnetic 

interference (EMI) . This EM1 is a major limiting factor in 

the design of a communication system. 

The work reported here gives the results of comprehensive 

measurements of this EM1 in critical communication locations 

where miners extract coal, as well as along haulageways. 

There are several EM1 parameters that can be measured: 

magnetic field strength, H; electric field strength, E; conducted current, I; and voltage, V, between two conductors. 

One parameter was emphasized, magnetic field strength. There 

are several reasons. First, electric field sensors are very 
insensitive at lower frequencies, and hence probably will 

not be useful in any practical mine communication system. 

Second, at any air-earth interface, only the magnetic field 

is essentially undisturbed, while the electric field is 

- - severely reduced. Third, any currents will induce magnetic 

fields, and hence measurement of the magnetic field will 

-. directly sense currents. Fourth, power line voltages are 

propagated as transmission line phenomena, are directly 

related to transmission line currents, and hence to magnetic 

fields induced. Thus, measuring magnetic field strength 

gives a representative composite picture of noise from 

currents and voltages from most sources, as well as measuring 

the magnetic fields induced by arcing equipment. 

Although magnetic field strength measurements are emphasized, this parameter is difficult to measure meaningfully. 

The IEEE definition [2] of magnetic field strength, H (magnitude of the magnetic field vector), is used in this report. 

Since there are a multitude of different sources that generate 

all known types of noise, the resultant magnetic field strength 

noise vector is a function of frequency, time, orientation, 

and location. Small variations in these parameters can cause 

several orders of magnitude difference in measured field 

strength. 

1.2 Mine Description 

The results and data presented in this report are based 

on measurements made on April 10 and 12, 1973, in the McElroy 

Coal Mine, near Moundsville, West Virginia. The mine belongs 

to the Consolidation Coal Company. Room-and-pillar mining 

techniques are used. The measurements were made primarily 

in section 1-left, 1-north. The overburden in this area is 

200 to 275 meters. 

2. MEASUREMENT INSTRUMENTAT ION 

Two measurement techniques were used. In the first technique used, a large portion of the spectrum is covered as a 

"snapshot1' at one relatively short period of time. In three- . - 

dimensional form, several such "snapshots" can show how drasti - 

cally a signal varies, not only with frequency, but also 

with time. In the second technique, variations over a 20- 

minute time interval are measured at a single frequency. 

Usually, a set of twelve different frequencies was used. 

Both techniques were used to measure two orthogonal components of magnetic field strength. This was done either by 

using two systems simultaneously or by varying the orientation of one system; both techniques were used in as many 

different locations as possible. 

With the exception of the roof bolt APD plots, all measured noise is reported in absolute quantities (instead of 

relative) to allow others to make effective use of the data. 

For the magnetic field strength measurements, the NBS field 

calibration site was used with each complete measurement system to assure correct calibration [3] . A complication to making these measurements is the mine 

environment, which is generally humid, dusty, poorly lighted., 

and potentially explosive. Battery-operated, dus t-protected, 

permissible gear was used for most of our portable measuring 

equipment. 

There are two types of noise recorded in the spectral plots, 

and hence two different magnetic-field-strength parameters are 

required, Ii and Hd. Results are given as the rms value of one 

component of magnetic field strength, H, versus frequency for 

discrete frequencies, or as one component of magnetic-fieldstrength spectrum density level [2] , Hd, versus frequency for 

broadband noise in the spectral plots. In the amplitude 

probability distributions, results are given as the rms value 
variations, most commonly amplitude probability distribution; 

it is also permissible. The third system is not permissible 

but is portable (with considerable effort) ; it records data 

for both spectral plots and statistical presentations. 
SIGNAL MONITORS 

SYSTEM 

#I 

SYSTEM 

#2 

SYSTEM 

#3 

LOUD 

SPEAKER OSCl LLOSCOPE 

2OO-kHz CRYSTAL 

OSCILLATOR i 

------ 

Figure 2-1 Block diagram of portable instrumentation. FM 

tracks are used to record from 100 Hz to 100 kHz; 

direct tracks are used from 3 kHz to 320 kHz. 

Systems 2 and 3 are identical to system 1. When 

the direct tracks are used, the 100-kHz low pass 

filters are eliminated, and the amplifier bandwidth is increased from 100 kHz to 300 kHz. The 

microphone is used for occasional vocal comments 

by the operator. 

LOOP 

ANTENNA BROADBAND 

I 

AMPLIFIER 

. 

100-kHz 

TRACK 4 (DIR) 

TRACK 5 ( FM ) 

PORTABLE 

TAPE RECORDE R 

(30 ips, record) 

EDGE TRACK 

(VOICE) 

I - - 

. MICROPHONE I 

TRACK I (FM) I 

IMPEDANCE 

lo METERS 

OF CABLE 

LOW PASS 

FILTER A 

TRANSFORMER 
COLLAPSIBLE 

ANTENNA 

I SCOPE Lf=lOkH~-250kHz 

Figure 2-2 System for field recording data to obtain amplitude 

probability distributions. 

FIELD 

STRENGTH 

METER 

LOOP BW=l .4kHz 

ANTENNA 

CHANNEL 1 40kHz ~h~~~~~t 

25kHz 

OSC 

' 

CHANNEL 2 

CHANNEL 3 

PORTABLE 

TAPE 

RECORDER 

DIRECT 

- 

i 

MIXER 

, 

J 

L . FIELD 

STRENGTH 

j - 

f =I 50 kHz -3 2MHz 

455kH5 MIXER 40kHf 
0 COLLAPSIBLE 

LOOP 

ANTENNA 

F I ELD 

11t-OBALUN , STRENGTH ,455kHz MIXER 40kHz * 

METER 

10 kHz -25Oktk 

j 10 kHz 4 

HIGH PASS * I FILTER - 

LOOP 

ANTENNA 

(SENSITIVE AXlS VERTICAL) 

Q COLLAPSIBLE 

LOOP 

ANTENNA EQUIPMENT 

SIMILARTO3, 0- 

BUT WITH HORIZONTAL 

ANTENNA ORIENTATION 1 Sl%k&H/ 455 kHz 

METER 1w kHz-32MH 

20 kHz I LOW PASS 4 

FILTER . 

LOOP 

ANTENNA 

(SENSITIVE AXlS VERTICAL) 

RECORDER 

CHANNEL I (FM 

CHANNEL 2(D\F; 

CHANNEL 3 (DIR 

CHANNEL 4 (DIR 

CHANNEL 5 (DIR] 

CHANNEL 6 (D IR' 

ZHANNEL 7 (FM' 

30 ips 

Figure 2-3 Block diagram of laboratory recording system modified 

for field use. 
taken at five locations on the second day, four of which are 

designated by letters A through D on figure 3-2. 

3.3 Electromannetic Noise Spectrum Results 

3.3.1 Interpretation 

When reading values from the spectra in this report, 

the following points should be kept in mind: 

1. Field strength values above the upper roll-off 

frequency and below the lower roll-off frequency are 

not calibrated and are therefore not shown on most 

spectra. 

2. The correct units for the spectral peaks are micro 

amperes per meter (pA/m), as these are cw signals. 
3. The broadband noise between spectral peaks is as 

seen by a receiver having the same bandwidth as the Fast 

Fourier Transform (FFT) spectral resolution bandwidth 

used to compute the spectrum. The correct units for the 

background noise between peaks are microamperes per meter 

per square root x hertz [(p~/m)/m], where x is the 

spectral resolution of the FFT (x equals 78.1 Hz for the 

1-to-100-kHz graphs). 

An easy way to obtain the spectral density per (one) 

root hertz for broadband noise is to subtract the required 

number of dB, remembering that the units have now changed to 

(pA/m)/a. For spectra with a resolution bandwidth of 78.1 

Hz, subtract 10 loglO (78.1) or 18.93 dB. 

The Appendix gives the code key used in determining the 

meaning of the numbers in the header block at the top of 

each spectrum. The resolution bandwidth is also given on the 

ordinate of the plots. 

3.3.2 Uncertainties 

The spectra to 100 kHz, to 3 kHz, and to 20 kHz have 

uncertainties of 2 1 dB over the following portions of the 

spectra. The 100 kHz spectra are valid either from 1 to 100 

kHz or 10 kHz to 100 kHz as stated or shown. The 3 kHz spectra 

have a 4 1 dB uncertainty from 100 Hz to 3 kHz. The 20 kHz 

spectra have an uncertainty of 4 I dB from 750 Hz to 20 kHz. 

The spectra shown to 180 kHz have an uncertainty of 2 2 dB 

from 3 kHz to 180 kHz. 

3.3.3 Section Measurements 

Figure 3-3, upper curve, shows the magnetic field noise 

spectrum from 1 kHz to 100 kHz received at the antenna location identified as C (in figure 3-1). Location C is the section 
power center and contains the step-down transformer and 

rectifier. C is one of the noisier locations in the mine (a 

small band of frequencies around 10 kHz measured at location 

B on the second day was 8 dB higher). This steady background 

noise is made up primarily of harmonics of 360 Hz, produced 

when three-phase, 60 Hz power is full-wave rectified. Figure 

3-4 shows the expanded spectrum measured at location C. This 

spectrum is one of the strongest measured in the mine. Oddly, 

while multiples of 360 Hz (6th harmonic of 60 Hz) predominate 

elsewhere in the mine, in this case, harmonics 60 Hz on either 

side of multiples of 360 Hz predominate. 

Figure 3-5 shows the noise spectrum measured two meters 

from the continuous miner (location D on figure 3-1). This 

location was also a relatively noisy location in the mine in 

the frequency range from 20 kHz to 60 kHz. With the headloader operating, and the miner not operating, the noise 

spectrum is similar to figure 3-5. With both the miner and 

head-loader not operating, the noise above 10 kHz drops 6 

to 10 dB. 

Figures 3-6 and 3-7 show noise spectra measured at location E. A measurement made 30 minutes later showed a 10 dB 

increase from 8 to 12 kHz and a 3 to 5 dB decrease from 25 

to 60 kHz. Figure 3-8 shows the noise spectrum measured at 

location F. This spectrum was taken when most equipment in 

the mine was not working. The noise spectrum has about the 

same shape as shown in the previous location, but at location 

F, the noise is 5 to 14 dB less from 5 to 60 kHz. This figure 

also shows the signal from the 100 kHz mine phone. 

Figures 3-9 and 3-10 show the noise measured at location 

B on the first day, with no equipment running. Figures 3-11 

and 3-12 show the noise measured at the same location later 

when all the mining equipment was working and about 15 meters 

distant. The latter two figures show a noise increase of 

8 to 30 dB, depending on frequency, when the face machinery 

15 meters distant was working. 
The quietest location measured in McElroy mine was in 

the return air entry, during shift change. This area is 

designated by letter G on figure 3-1, and is located 55 meters 

from the power center. Figures 3-13 and 3-14 show one of 

the strongest of the three orthogonal components measured at 

location G. The antenna sensitive axis was horizontal and 

parallel with the return-air-entry. The spectrum taken with 

the antenna sensitive axis horizontal and perpendicular to 

the return-air-entry shows the harmonics to be within 6 to 

10 dB of those shown in figure 3-14. The spectrum of the 

vertical noise shows about 13 dB higher noise levels at the 

low end and about 22 dB lower at the high end of the spectrum 

than the horizontal, parallel spectrum shown in figure 3-14. 

The crossover occurs near 500 Hz. Measurements made in the 

same location 2 days later (letter D, figure 3-2) during 

shift change, and also after the mine had closed for a strike, 

show that the noise was within a few dB of that shown on 

figure 3-13. This return-air -entry location is unusual in 

that the noise received with the antenna axis horizontal 

was stronger than for the antenna axis vertical. 

The noise measured at the section power center with the 

mine running (noisy location), with the antenna axis vertical, 

is 40 to 60 dB stronger over the 1 to 100 kHz frequency range 

than the noise measured in the return-air-entry (quiet location), between shifts, with the antenna axis vertical. 

Measurements were taken with the third measurement system 

in a crosscut shown as location A on figure 3-2 in the immediate (one to three meters) vicinity of a continuous miner 

and supporting shuttle buggies. Figures 3-15 through 3-22 

show spectra of noise generated by this machinery. Figure 

3-23 shows field levels generated by an impulse in this same 

location. 
was measured as 47 dB pA/m. 

A second haulageway location where noise was measured 

was on the main-line haulage near section 1-left, 1-north. 

This location is lettered B on figure 3-2. Figures 3-26 

and 3-27 show the noise recorded during the passing of a 

rapidly moving train that was drawing power. The noise 

at this location was found to vary more than in other locations. Other spectra taken here showed 10 to 20 dB lower 

noise than figure 3-26 for trains moving slowly, or for the 

absence of trains. As an illustration, figure 3-28 shows 

the spectrum from 100 Hz to 3 kHz for a train of empty cars 
moving slowly. From this it can be seen that a transient has 

briefly raised the background level of the previous spectrum, 

figure 3-27. While at location B, second day, a 100 kHz 

trolley phone signal from a remote location was measured as 

. - 27 dB relative to 1 yA/m. 

The third location along a haulageway where noise was 

measured is lettered C on figure 3-2. This location is on 

the opposite side of the recirculating "run -aroundtt from 

location B. The left side of the run-around is kept supplied 

with empty coal cars. An automatic car-pull located at C 

moves the empty cars forward as the coal coming off the conveyor belt "headpiece" fills the cars. Full cars are then 

periodically removed from the right hand side of the runaround. Figures 3-29 and 3-30 show the noise measured at 

location C. At this time, the conveyor belt and the car pull 

were running. 

Data from measurements taken at the end of a rail haulage, 

location A in figure 3-1, are shown in figures 3-31 and 3-32. 

These data were taken with the third measurement system. 

3.3.5 Arc Welder Measurement 

On the second day in the mine, the face had advanced as 

shown in figure 3-2. Figure 3-33 shows the noise measured 

in location A in figure 3-2 (the arc welder was not operating). 

Later, a helium-gas-shielded arc welder began operation. The 

welder used ac input voltage, and delivered 250 amperes at 

30 volts to the welding rod. Figure 3-34 shows the spectrum 

measured with the welder drawing full current. The antenna 

was about 15 meters away. The spectrum with the welder 

operating is lower than with the welder off by as much as 

16 dB at some frequencies. A quiet crackling, sounding like 

grease frying, was heard on the audio monitor. This indicates 
that this particular welder produced no strong spectral components. It did produce some impulses, but they were generally 

of a smaller amplitude than those associated with switching 

transients from sect ion mining equipment. 

3.3.6 Surface Measurements - 

Noise measurements were made on the surface of the 

ground, above the mine, at 5:25 p.m. on April 11, 1973. The 

location was a rural hilltop over 1 left, 1 north. The 

antenna site was 12 meters from a rural, single-phase distribution power line. The site was about one kilometer from a 

large, high tension line. Figures 3-35 and 3-36 show the 

spectrum measured on the surface with the antenna sensitive 

axis pointing N-S and parallel to the local power line. This 

figure shows many man-made transmitted signals, as well as 

what appears to be some atmospheric noise in the region below 

30 kHz. The energy shown around 100 kHz is broadcast by a 

Loran-C navigation system. Note the signal from the National 

Bureau of Standards WWVB, frequency-and-time radio station 

transmission at 60 kHz. This transmitter is located near 

Fort Collins, Colorado. Surface noise measurements were made 

in all 3 orthogonal directions ; however, only one direction 

(N-S) is shown. The other orthogonal directions showed lower 

signal strengths from man-made carriers and more momentary 

broadband sferics . Other spectral plots taken with the third measurement 

system are shown in figures 3-37, 3-38, and 3-39. 
3.4 Miscellaneous Measurements 

3.4.1 Measurement of Voltage Between Roof Bolts 

Two roof-support bolt measurements were performed at 

- - location F on the first day. The voltage was measured using 

non-shielded copper wire clipped to the bolts. For the first 

measurement, the separation between bolts was 21.7 meters. 

Figures 3-40 and 3-41 show the spectrum measured. For the 

second measurement, the separation between bolts was reduced 

to 11.2 meters. Figure 3-42 shows the spectrum measured. 

No receiver system noise curve is available for these spectra. 

With the exception of the sixth harmonic of 60 Hz, the 

shorter distance between roof bolts shows higher power line 

noise than the longer separation. The second spectrum 

(shorter separation) shows an impulse that has been picked 

up. It is not possible to say that the voltage measured 

between bolts was induced by any single mechanism. It may 

be any combination of electric and magnetic fields acting 

on the copper wires connected to the bolts, as well as by 

any potential produced by current flow between the bolts. 

3.4.2 Shuttle-Car Current Spectrum 

While no calibrated current measurements were made in 

McElroy mine, one measurement was made with the loop antenna - 

placed directly adjacent to the shuttle-car power cable. 

This adjacent placement caused the loop to strongly couple 

to the current in the cable. Figure 3-43 shows the resulting spectrum. Note the strong 360 Hz fundamental and 

harmonics of this dc-driven machine. This spectrum gives 

the characteristic signature of dc-powered machinery supplied 

by three-phase, full-wave rectifiers. This figure shows the 

highest field strength values measured; this is due to the 

loop being unusually and artificially close to the current 

carrying cable. 
in the three mines shows: 

1. McElroy is quieter than Robena. 

a. The highest logarithmic average of section noise 

measured one meter from a cable in McElroy is 51 dB 

relative to 1 uA/m (power center). The noise in 

Robena at an "air split" on a haulageway is 16 dB 

higher and at a car pull during operation is 21 dB 

higher than this 51 dB value. 

b. The quietest location in McElroy is 26 dB 

quieter than the quietest location in Robena. 

2. McElroy is noisier than Grace. 

a. Most of the McElroy measurements in the section 

were noisier than the noisiest Grace measurement 

(the diesel -powered Load-Haul -Dump (LHD) vehicle) 

by as much as 10 dB. 
b. The quietest location in ?4cElroy is 12 dB 

noisier than the quietest location in Grace. 

The magnetic noise from 1 kHz to 3 kHz in the three 

mines compared to the noise measured on the surface above 

PJcElroy shows : 

1. All measurements in Robena were higher by 15 to 

78 dB. 

2. Most measurements in McElroy were higher by 14 to 

33 dB. 

3. The LHD measurement in Grace was higher by 22 dB. 

3.5.2 Summary of 3 kHz to 180 kHz Data 

Figures 3-46 and 3-47 are given to show how fieldstrength levels at McElroy compare with levels in some other 

mines (i .e . , Grace, Robena, and Itmann Mines) . Figure 3 -46 

shows levels near operating equipment while figure 3 -47 

shows levels in haulageways. The curves are shown to 200 kHz, 

but the 2 2 dB uncertainty is valid only from 3 to 180 kHz. 

The Robena curves are shown to 100 kHz. 
Mai in haulage - i - -inin - r 

(trolley) - 

II run around" 

Figure 3-1 Map of McElroy Coal Mine, section l-left, l-north 

for April 10, 1973, the first day of measurements. 
Face on 

April 12 \ 

Conveyor belt end 

"tai I piece" 

Rail end 

Return air 

entry 

Conveyor be1 t 

entry 

Main haulage ~nu

Figure 3-2 Map of McElroy Coal Mine, section 1-lef t, 1-nor th 

for April 12, 1973, the second day of measurements, 
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Figure 3-18 Spectrum of machinery-generated, horizontal (E-

noise at location A, fig. 3-2, McElroy Mine, A

Note modulated, 100 kHz trolley-phone signal. 

brated from 3 to 180 kHz and the spectral resol
-- = -LO 

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30 

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SYSTEM NOISE 

FREQUENCY, Hz 

Figure 3-19 Spectrum of machinery-generated, vertical, magnetic-fi

location A, fig. 3-2, McElroy Mine, April 12, 1973, 1:2

spectrum is calibrated from 750 Hz to 20 kHz and spect

is 19.5 Hz. 
W 

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sDectrum is calib

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1973, 12:08 p.m. 

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sensitive axis vertical, 2:10 p.m., April 12, 19

is 3.91 Hz. 
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to 100 kHz, 

day, antenn

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1 North, McElroy Mine

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Figure 3-39 Spectrum of surface, ve

of McElroy Mine, April 

from 750 Hz to 20 kHz a

a F: 

moo 
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Figure 3-45 Comparison o

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110 

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P 1 

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(GRACE) 

--7- 

APPRO

- 

1 I 1 1 

I 2 3 45 

DISTANCE TO NEARES

DISTANCE TO CRUS
F m= a= W 

ZO It- 0 WLL t-W 

= az t-az1 

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40 60 80 100 120 140 16

FREQUENCY, kHz 

Figure 3-46 Comparison of E-M noise levels near operating machiner

four mines. Vertical magnetic-field components are sh

Broken sections of the curves represent system noise. 
- 

w u e IW n 4, $ 22 1 

0 0 

P: mz 

U u u n 

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Figure 3-47 Comp

mines

secti
4. AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS 

4.1 Int roduct ion and Uncertainties 

Statistical representations are required since the variations of field strength are, in general, random. The amplitude 

probability distribution (APD) of the received noise envelope 

is one of the most useful statistical descriptions of the 

noise process for the design and evaluation of a telecommunicat ions sys tem operating in a noisy environment [5 ,6,7] . By plotting the cumulative APD on Rayleigh graph paper, 

one can show clearly the fraction of time that the noise envelope 

exceeds various levels. Rayleigh graph paper is chosen with 

scales such that a Rayleigh distribution (i .e., envelope distribution of Gaussian noise) plots as a straight line with 

slope of -1/2. Noise with rapid large changes in amplitude 

(e.g. , impulsive noise) then has a much steeper slope, 

typically -4 or -5, depending on the impulsiveness of the 

noise and the receiver bandwidth. 

With the exception of the roof-support bolt measurements, 

all APD measurements are reported in absolute quantities. 

The estimated limits of error for the APD noise measurements are + 5 dB. Several sources of error that are critical 

to the overall accuracy of our measurements are listed below: 

1. Use of a discrete, digital level counter (levels are 

6 dB apart) contributes t l-dB quantization error limit. 

One-decibel step attenuators aye used to achieve the 

+ one decibel. 

2. The system, i.e., recording, data transcribing, and 

data processing, has a calibration uncertainty of 

2 0.5 dB [3]. 

3. The estimated uncertainty involved in using the portable and the laboratory tape recorders for record and 

playback is + 0.5 dB due to harmonic distortion, flutter, 

dropout, cross-talk, etc. 
balanced loop antenna. An estimate is that an additional 

+ 5 dB uncertainty might be advisable. However, due to the 

complexity of the shielded loop in the mine environment, this 

uncertainty cannot be rigorously bounded without substantial 

additional analysis. 

4.2 Results 

4.2.1 Introduction 

APD measurements were made on April 10 and 12, 1973, 

during operation in the FlcElroy Coal Mine located near 

Moundsville, West Virginia. Descriptions of McElroy Mine 

are given in section 1.2. APD measurements were made at 

four locations. The first set of APD measurements of about 

eleven different frequencies was made on April 10, 1973, at 

68 
location B in figure 3-1. The second set of APD measurement 

of about eight different frequencies was made on April 10, 

1973, at location A in figure 3-1. In these two sets of 

APD measurements, both the vertical and horizont a1 components 

of magnetic field were measured. 

The third set of APD measurements of about nine 

frequencies was made on April 12, 1973, at location B 

in figure 3-2. The fourth set of APD measurements of about 

nine frequencies was made on April 12, 1973, at location A 

in figure 3-2. In these two sets of APD measurements, only 

the vertical components of magnetic field were measured. 

In addition to these four sets of measurements, APD 

measurements were made during a quiet time at locations A 

and B in figure 3-1. APD measurements between roof -support 

bolts were performed on April 10, 1973, at location B in 

figure 3-1. 

4.2.2 Measurement Results 

Figures 4-1 through 4-11 show the APD1s of vertical 

components of magnetic field noise and figures 4-12 through 

4-23 show the APD1s of horizontal components (NE-SW) of 

magnetic field noise measured at location B of figure 3-1 

on April 10, 1973. APD1s measured at quiet time at location 

B of figure 3-1 are shown in figures 4-24 through 4-27. Here 

only the vertical component of magnetic noise was measured 

at four frequencies ranging from 10 kHz to 150 kHz. Above 

250 kHz, the magnetic noise measured in the mine was below 

the system noise (i.e., 60 dB or more below one microampere 

per meter) since EIFS meter readings with and without an 

antenna were the same. 

Figures 4-28 through 4-36 show APD1s of the vertical 

component of magnetic field noise and figures 4- 37 through 

4-43 show APD1s of the horizontal component of magnetic 

field noise measured at location A in figure 3-1 on April 10, 
copper wire. It was a combination of electric field through 

a dipole with a lossy surrounding medium (i .e., coal) , of 

magnetic field through a lossy loop antenna, and of voltage 

induced by current flowing through the medium between the 

roof bolts. Therefore, relative voltage is the parameter 

given. The rms value is arbitrarily assigned the value 

0 dB. 

4.2.3 RfiIIS and Average Values 

The APD1s are integrated to give rms and average values 

of the field strength, according to the equations 
where H represents the magnetic field strength of the noise, 

and p is the probability that the measured field strength 

exceeds the value H. These quantities are also dependent 

upon the measurement bandwidth, the length of the data run, 

and possibly other parameters. Finite series are actually 

used for the numerical integration. The rms and average 

values so arrived at are identified on each graph and are 

time averages (23 minutes) of these time-dependent parameters. 

If the tapes are played into ordinary rms-reading meters, the 

meter readings will vary 10 to 20 dB over fractions of a 

second depending on the averaging time constants of the meter. 

The rms value is directly relatable to noise power. 

4.2.4 Summary Curves 

Excursions of field strength between 0.001 and 99 percent, 

as well as rms and average values, are shown in figures 4-71 

through 4-78. The predetection bandwidth for these APD 

measurements either is 1 kHz or is normalized to 1 kHz. Figures 

4 -1 through 4-11 (vertical , near the power distribution center) 

are summarized on figure 4-71; figures 4-12 through 4-23 

horizontal, near the power distribution center) are summarized 

on figure 4-72; figures 4-24 through 4-27 (vertical, quiet 

time, near the power distribution center) are summarized on 

figure 4-73. Figures 4-28 through 4-36 (vertical, near end 

of rail haulage) are summarized on figure 4-74; figures 4-37 

through 4-43 (horizontal, near end of rail haulage) are summarized on figure 4-75; figures 4-44 through 4-48 (vertical, 

quiet time near end of rail haulage) are summarized on figure 

4-76. Figures 4-49 through 4-58 (near intersection of main 

haulage and conveyor belt) are summarized in figure 4-77. 
Figures 4-59 through 4-68 (near operating continuous miner) 

are summarized on figure 4 -78. 1-lagnetic field strength 

generally decreases monotonically with increasing frequency 

at 20 dB per decade. Some long-term fluctuations in values 

occur because of different operating conditions during 

different times of the day. Although 20 minutes was determined 

to be a sufficient time to give validity to the statistics in 

a mine-section environment where the work cycle is two to four 

minutes, 20 minutes may not be sufficient in other locations 

where longer cycles may exist. Perhaps this should be cons idered further. 
Percent of Time Ordinate is Exceeded 

Figure 4- 1 APD, 10 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 11:40 a.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-2 APD, 30 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 1:10 p.m., McElroy Mine. 
Linear by - 3 log,&- In p) 

11001.001.01 .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-3 APD, 70 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 2: 20 p .m., McElroy Mine. 
D001.001.01 .I .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-4 APn, 130 kHz, vertical component, 1.0 k~z predetection 

bandwidth, April 10, 1973, 3: 25 p.m., McElroy Mine. 
Linear by - j loglo(-ln p) 

Percent of Time Ordinate is Exceeded 

Figure 4-5 APD, 160 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 5:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-6 APD 250 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 6:35 p.m., McElroy Mine. 
.0001 .MI .01 .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-7 APD, 500kHz, vertical component, 1.2 kHz predetection 

bandwidth, April 10, 1973, 11:40 a.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-8 APD, 1 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 10, 1973, 1:10 p.m., McElroy Mine. 
- 50 

-60 

-70 

- 80 

D001.001.01 .I 5 1 5 HI 20 30 40 51) 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-9 APD, 2 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 10, 1973, 2: 20 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-10 APD, 6 MHz, vertical componen3 1.2 kHz predetection 

bandwidth, April 10, 1973, 3:25 p.m., McElroy Mine. 
Linear by - 3 loglo(-~n p) 

Percent of Time Ordinate is Exceeded 

Figure 4-1 1 APD, 14 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 10, 1973, 5: 30 p .me, McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-1 2 APD, 10 kHz, horizontal component (NE-SW), 1.0 kHz 

predetection bandwidth, April 10, 1973, 12: 20 p.m., 

McElroy Mine. 
. . . . .. 

.0001.001 Dl .I .5 1 5 HI 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-1 3 APD, 30 kHz, horizontal conponent, (NE-SW), 1.0 kHz 

predetection bandwidth, April 10, 1973, 1: 50 p.m., 

McElroy Mine. 
Magnetic Fie
Percent of Time Ordinate is Exceeded 

Figure 4- 15 APD, 130 kHz, horizontal component (NE-SW) , 1.0 kHz 

predetection bandwidth, April 10, 1973, 5: 00 p.m., 

FkElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4- 16 APD, 160 kHz, horizontal component(NE-SW) , 1.0 kHz 

predetection bandwidth, April 10, 1973, 6:00 p.m., 

McElroy Mine. 
10'100'1000' 1' IS' S 01 01 OE 0) OS 09 01 08 $8 06 S6 86 66 

09- 

01- 

- 09 

- 0s 
Percent of Time Ordinate is Exceeded 

Figure 4-1 8 AW, 500 kHz, horizontal component (NDSW), 1.2 kHz 

predetection bandwidth, April 10, 1973, 12:20 p.m., 

McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-1 9 APD, 1 MHz, horizontal component (NE-SW), 1.2 kHz 

predetec tion bandwidth, April 10, 1973, 1: 50 p .m., 

McElroy Mine. 
IO'K1~1000' I' IS S 01 02 O$ Ob OS 09 01 08 $8 06 S6 86 66 

OB01- 

- 09 
.0001.001.01 .I .5 1 5 K) 20 30 40 50 60 70 bO 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-21 APD, 6 MHz, horizontal component (NE-SW), 1.2 kHz 

predetection bandwidth, April 10, 1973, 5:00 p.m., 

McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-22 APD, 14 MHz, horizontal component (NE-SW) , 1.2 kHz 

predetection bandwidth, April 10, 1973, 6:00 p.m., 

McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-23 APD, 32 MHz, horizontal component (NE-SW), 1.2 kHz 

predetection bandwidth, April 10, 1973, 7: 00 p.m., 

McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-24 APD, 10 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 4:00 p.m., quiet time 

measurements, MElroy Mine. 
Linear by - log,o( - In p) 

Percent of Time Ordinate is Exceeded 

Figure 4-25 APD, 30 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 4:10 p.m., quiet time measurements, McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-26 APD, 70 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, quiet time meaeuremente, 

&Elroy Mine. 
Percent of Time Ordinate io Exceeded 

Figure 4-27 APD, 130 kHz, vertical component, 1.0 kHz 'predetection 

bandwidth, April 10, 1973, 4:30 p.m., quiet time measurement, McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-28 APD, 10 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 1:00 p.m., McElroy Mine. 
- 10 

-20 

- 30 

0001 ROl Dl .I 5 1 5 K) 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-29 APD, 30 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 2:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-30 APD, 70 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 5:15 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-31 APD, 130 kHz, vertical component, 1.0 kHz predetection bandwidth, April 10, 1973, 7:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-32 APD, 160 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 6:45 p.m., HcElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-33 APD, 250 kHz, vertical component, 1.2 kHz predetection 

bandwidth, April 10, 1973, 7:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-34 APD, 500 kHz, vertical component, 1.2 kHz predetection 

bandwidth, April 10, 1973, 1:00 p.m., McElroy Mine. 
Linear by - i lop,,(- In p) 

.0001.001 .01 .I .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-35 APD, 1 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 10, 1973, 2:30 p.m., McElroy Mine. 
.0001.00191 .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-36 APD, 2 MHz, vertical component, 1.2 kHz predetcction 

bandwidth, April 10, 1973, 5:15 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-37 APD, 10 kHz, horizontal component (N-S), 1.0 kHz predetection 

bandwidth, April 10, 1973, 1: 30 p.m., McElroy Mine. 
i001 DM Dl .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-38 APD, 30 kHz, horizontal component (N-S), 1.0 kHz predetect 

bandwidth, April 10, 1973, 2:00 p.m., McElroy Mine. 

ion 
Percent of Time Ordinate is Exceeded 

Figure 4-39 APD, 70 kHz, horizontal component (N-S), 1.0 kHz predetection 

bandwidth, April 10, 1973, 6: 00 p.m., McElroy Mine. 
DOO1.OO1.O1 .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

ig~~re 4-40 APD, 130 kHz, horizontal component (N-s), 1.0 kHz predetect 

bandwidth, April 10, 1973, 6:45 P.m., McElroy Mine* 

112 
.0001.001 .01 .I .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-41 APD, 160 kHz, horizontal component (N-S) , 1.0 kHz, predetection 

bandwidth, April 10, 1973, 6:00 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-42 APD, 500 kHz, horizontal component(N-S), 1.2 kHz predetection 

bandwidth, April 10, 1973, 1:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-43 APD, 1 MHz, horizontal component (N-S) , 1.2 kIIz predetection 

bandwidth, April 10, 1973, 2:00 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-44 APD, 10 kHz, vertical component, 1.0 WIz predetection 

bandwidth, April 10, 1973, 4:00 p.m., quiet time measurements, McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-45 APD, 30 kHz, vertical component, 1.0 WIz predetection 

bandwidth, April 10, 1973, 4:05 p.m., quiet time meaaurements, McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-46 APD, 70 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 4:15 p.m., quiet time measurements, McElroy Mine. 
Linear by - i log,o( -In p) 

.0001.001.01 .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordi note is Exceeded 

Figure 4-47 APD, 130 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 10, 1973, 4:20 p.m., quiet time measurements, McElroy Mine. 
0 -70 

0, 

i 

0 .- 

C 

0, 

c 

o -80 

r" 

-90 

-100 

D001.001.01 .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-48 APD, 1 MHz, vertical component, 1.2 kHz prede tection 

bandwidth, April 10, 1973, 4:05 p.m., quiet time measurements, McElroy Mine. 
0 

- 10 

-20 

-30 

0001 .OM dl .I 5 1 5 I0 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-49 APD, 10 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 11: 50 a.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-50 APD, 30 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 12:25 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-51 APD, 70 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 12:50 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-52 APD, 130 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 1:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-53 APD, 160 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April12, 1973, 2:10 p.m., NcElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-54 APD, 500 kHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 11:50 a.m., McEtroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-55 APD, 1 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 12:25 p.m., McElroy Mine. 
Percent of Ti me Ordinate is Exceeded 

Figure 4-56 APD, 2 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 12:50 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-57 APD, 6 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 1:30 p.m., McElroy Mine. 
~001.001.01 .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-58 APD, 14 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 2:10 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-59 APD, 10 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 11:30 a.m., McElroy Mine. 
Percent of Time Ordinate it Exceeded 

Figure 4-60 APD, 30 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 12:15 p.m., McElroy Mine. 
0 

rl 

E 

G 

8 5 

v 

tl 

h 

e o t4 t4 arc 

W 

2 3 

LJ Ia. 4 

*- 

N 

d 4 

L4 

u 

4 

e 

k 

rl 

-4 

0 

35 

N 

v 

r. 

3 

-4 

E .v !i 

<a 
al .- 

LL 

0 

.- 

C 

B 

C -30 

P 

- 40 

-50 

DO01 .OM .OI .I 5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-62 APD, 130 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 1:30 p.m., McElroy Mine. 
-40 

- 50 

-60 

-70 

.0001.001.01 .I .S I s 10 20 30 40 50 60 70 80 8s 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-63 APD, 160 kHz, vertical component, 1.0 kHz predetection 

bandwidth, April 12, 1973, 2:15 p.m., IlcElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-64 APD, 250 kHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 11:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-65 APD, 500 kHz, vert ice1 component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 12:15 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-66 APD, 1 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 1: 00 p.m., McElroy Mine. 
Linear by - 10g,~(-ln p) 

40 

Percent of Time Ordinate is Exceeded 

Figure 4-67 APD, 2 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 1:30 p.m., McElroy Mine. 
Percent of Time Ordinate is Exceeded 

Figure 4-68 APD, 6 MHz, vertical component, 1.2 kHz predetection 

bandwidth, April 12, 1973, 2:15 p.m., McElroy Mne. 
Percent of Time Ordi note is Exceeded 

Figure 4-69 APD, 10 kHz, roof bolt measurements, 1.0 kHz 

predetection bandwidth, April 12, 1973, 2:45 p.m., 

McElroy Mine. 
Percent of Ti me Ordi note is Exceeded 

Figure 4-70 APD, 150 kHz, roof bolt measurements, 1.2 kHz 

predetection bandwidth, April. 12, 1973, 2:45 p.m., 

Mc El roy Mine. 

N 

P-. 

1 * 
10 kHz 100 l MHz 10 

X 

X 

- 40 - 

cn 

2 0 

[X A 

L 

Frequency 

Q] 

+ 20 I@ 

. E c L 

6 a rn a C 

ze 

60) 

V) a. 

E 

mu - 

0, ,O . - 

LL .O " E -20 . - 

C - 

Q, 

c 9 

g = ' -40 u - 

Q] 

L 

m 

TJ 

V 

-60 

- 80 

Figure 4-73 Field strength excursions between 0.001% and 99

function of frequency, vertical component loca

1 kHz predetection bandwidth, April 10, 1973, q

ments, McElroy 

oLA 

- 

- 

- 

I I I I 111 I 
Frequency 

60 I I1 

I IIlI

X X 

40 

Figure 4-74 Field strength excursions between 0.001% and 

function of frequency, vertical component loc

1 kHz predetection bandwidth, April 10, 1973, 

0 

A 

- 

20 - 

0 

;lo - 

-204- 

X 

X X 

-40 

-60 

-80 

10 kHz I00 I MHz 1

- 

- A a 

n 

A 

1 I IIjl I I I 1111 11


tn Q) 

cdk 

3 Q) bn E .d 

.d W a, 4J c 

c -74 

Q) OC 

G 4Jm 3\ 

5. CONCLTJSIONS 

The range of magnetic-field noise levels in McElroy is 

130 dB, from 90 dB above 1 pV/m at 60 Hz to 40 dB below 

1 pV/m at 180 kHz. This compares with the 125 dB range in 

Robena, except that the Robena levels were higher, from 

+lo5 dB to -20 dB with respect to 1 pA/m. Grace Mine had a 

range of 158 dB, from +I22 dB to -36 dB. In the lower portion of the spectrum, below 3 kHz, McElroy was approximately 

20 dB quieter than Robena in most cases. Iiowever, from 3 kHz 

to 100 kHz the magnetic-field noise levels in Robena and 

ElcElroy were both relatively high, 10 to 80 dB above 1 pA/m, 

near operating equipment, compared to levels in Grace and 

Itmann mines of -10 to SO dB above 1 pA/m. From 100 kHz to 

200 kHz, McElroy and Itmann had the highest levels, -20 to 

+15 dB above 1 pA/m, Data from Robena is not available in 

this frequency range, but levels may well be comparable to 

those in FlcElroy and Itmann. 

Along haulageways, McElroy was the quietest (by a small 

margin) of the mines visited. From 30 kHz to 180 kHz, this 

level was equal to or less than -30 dB above 1 pA/m. 

Surface measurements over the underground working 

section show a number of man-made, cw carriers. If these 

carriers are omitted, the background, broadband noise is 

-30 to -40 dB with respect to 1 pA/m. The carriers come 

up to 0 dB with respect to 1 pA/m. Below 20 kHz, powerline 

harmonics were the dominant source of noise. The ranpe covers 

-20 to +60 dB above 1 pA/m. 

APD measurements were taken during quiet times as well 

as during normal operation. The measurements show quiettime levels at some frequencies at least 60 dB below 1 pA/m, 

hut at most frequencies below 1 MHz, the peak and rms levels 

did not change significantly from quiet to operating condition. Levels near operating equipment were 30 dB above 1 uA/m 
at 30 kHz, and near haulageways, were 10 dB above 1 pA/m at 

30 kHz. The range of these measurements is consistent with 

the wide range of levels that have been measured in some 

other mines. 
6. RECOMMENDATIONS 

Particularly in mines similar to McElroy, but also 

in most other coal mines as well, the wide ranges of magneticfield noise levels due to spatial variations should be used 

to maximum advantage. For example, keep receivers away from 

noise sources whenever possible . This applies to frequencies 

below 200 kHz, where interference levels near machinery are 

extremely severe. Shorter-range , higher -frequency sys tems 

could be designed for use near machinery. 

Surface noise measurements at McElroy show the need for 

only one design criterion : avoid powerline harmonics. There 

are other criteria which show up at other mines, but for 

low- frequency, through - the -earth communication sys tems , 

avoiding use of powerline harmonic frequencies is of 

primary concern. 

7. ACKNOWLEDGMENTS 

Those making significant contributions to this program 

are as follows: laboratory development and field use of measurement equipment, Ed Neisen, Doug Schulze , and Tom Bremer ; 

data processing , Anne Rumfelt, Nancy Tomoeda, Winston Scott, 

Frank Cowley, and David Stearns. Those making valuable but 

less time -.consuming contributions are Gerry Reeve, Bob 

Matheson, Don Spaulding , John Chukoski , Lorne Vatheson, Dave 

Lewis, and Sharon Foote. 

Winston Scott provided much assistance in proofreading, 

while Sharon Foote and Janet Becker typed tirelessly through 

many versions. Jocelyn Spencer and Barbara Bolton provided 

drafting assistance. 

Finally, none of this would have been possible without the 

excellent cooperation of John Burr of Lee Engineering Company 

and of Dick Rouse, John Stock, Randy Fizer, and others of 

C o n s o l i d a t i o n Coal Company. 
8. REFERENCES 

[I] Bensema, W.D., Kanda, M., Adams, J.W., Electromagnetic 

Noise in Robena No. 4 Coal Mine, NBS Tech. Note 654, 

April 1974. 

[2] The Institute of Electrical and Electronic Engineers, Inc., 

IEEE Dictionary of Electrical and Electronic Terms, 

Std. 100, 1972. 

[3] Taggart, H.E. and Workman, J.L., Calibration Principles 

and Procedures for Field Strength Meters (30 Hz to 1 GHz), 

NBS Tech. Note 370, March 1969. 

[4] Adams, J.W., Bensema, W.D., Kanda, M., Electromagnetic 

Noise in Grace Hardrock Mine, NBSIR 74-388, June 1974. 

[5] Crichlow, W.Q., et al., Amplitude-probability distributions 

for atmospheric radio noise, NBS Monograph 23 (1960b). 

[6] Thompson, W.I., 111, Bibliography of ground vehicle communications and control. AKWIC index, Report No. DOTTSC-UMTA-71-3, July 1971. 

[7] Spaulding, A.D. and Disney R.T., Man-Made Radio Noise: 

Part 1: Estimates for Business, Residential, and Rural 

Areas, Office of Telecommunications OT Report 74-38, 

June 1974. 
9, APPENDIX 

Decoding of Spectrum Captions 

Spectrum captions are generally organized into the following format : 

First line: MP NDT NZS NDA NPO RC DF date, time, frame, serial, 

where 

MP = Two's power of length of Fourier transform, example, 

zMP where MP = 12 

NDT = Detrending option, example, 0 (dc removed) 

NZS = Restart spectral average after output, example, 0 

(restarted) 

NDA = Data segment advance increment, example, 2048 

NPO = Number of spectra averaged between output calls, 

example, 20 

RC = Integration time in seconds per spectra, example, 0.168 

DF = Resolution bandwidth, spectral estimate spacing in 

hertz, example, 62-5 

Date = Date of computer processing, example, 03/21/73 

Time = Time of computer processing, example, 15:06:34 

Frame= Frame set number, example, 10 

Serial = Film frame serial number, example, 42. 

Second line: DTA DA(1) DA(2) DA(3) NSA NRP NPP, where 

DTA = Detrending filter parameter a, example, 0.00195 

DA(1) = Detrending filter average, K=l, example, 59.4 

DA(2) = Detrending filter average, K=2, example, 0 

DA(3) = Detrending filter average, K=3, example, 0 

NSA = Number of periodograms averaged, example, 20 

NRP = Number of data points processed since spectrum 

initialization, example, 43008 

NPP = Number of data points processed since data initialization, example, 43008. 
Top of Scale = largest scale marking for computer drawn 

4 graph, example, 1.000+004 (1.0 x 10 ) 

Standard Error = standard error of curve, example, 0.3162 

Spectral Peak = largest spectral peak observed, example, 

4.108+003. (4.108 x lo3) 
16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant 

bibliography or literature survey, men lion it here.) 

Two different techniques were used to make measurements of the absolute value of 

electromagnetic noise in and above an operating coal mine, McElroy Mine, located near 

Moundsville, West Virginia. 300-volt-dc and 480-volt-ac machinery was measured to 

see the electromagnetic environment it created. One technique measures noise over 

the entire electromagnetic spectrum of interest for brief time periods, It is recorded using broadband analog magnetic tape and the noise data is later transformed tc~ 

give spectral plots. The other technique records noise amplitudes at several discrete frequencies for a sufficient amount of time to provide amplitude probability 

distributions. 

NBS-l14A (REV. 7-73) 

17. KEY WORLIS (six to twelve entries; alphabet~ral order; cap~talize only the first letter of the first kev word unless a oronpr 1 

name; separated by semicolons) Amplitude probability distribution; coal mine noise; digital 

data; electromagnetic communications; electromagnetic interference; electromagnetic 

noise; Fast Fourier Transform; Gaussian distribution; impulsive noise; magnetic field 

- 

strength; measurement instrumentation; spectral density; time-dependent sl - 

18. AVAILABILITY k- Unlimited 19.-SECURITY CLASS 

3. Recipicntqs Accession No. 

5. Publication Dare 

June 1974 

6. Performing Organization Code 

8. Performing Organ. Report No. 

10. Project/Task/Work Unit No. 

46- 

1 1. Co!cract~Grant No. 

13. Type of Report & Period 

Covered 

14. Sponsor~ng Agency Code 

1 [I- For Official Distribution. Do Not Release to NTIS 

2. (;nvst Accession 

No. 

U.S. DEPT. OF COMM. 

BIBLIOGRAPHIC DATA 

SHEET 1 

I UNCL ASSIFIED 

1. l'UIjLI('AT1ON OK RI<l'OKl' NO. 

NBSIR 74-38? 

E-2 Order From Sup. of Doc., U.S. Government Printing Office 

Washington, D.C. 20402, SD Cat. No. C13 

* 

El Order From National Technical Information Servlce (NTIS) 

Springfield, Virginia 22 151 

4. 1'11'1.1.; AN11 SIJRl'IT1,H 

Electromagnetic Noise in McElroy Mine 

- 7. AUTttOK(S) 

Motohisa Kanda, John W. Adams, and William D. Bensema 

9. PEKFORMING ORGANIZATION NAME AND ADDRESS 

NATIONAL BUREAU OF STANDARDS, Boulder Labs 

DEPARTMENT OF COMMERCE 

Washington, D.C. 20234 

- - 

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP) 

U.S. Bureau of Mines 

4800 Forbes Avenue 

Pittsburgh, Pa. 15213 

15. SUPPLEMENTARY NOTES 

20. SECURITY CLASS [ (THIS PAGE) 

I UNCLASSIFIED 

-- ectral density. 

21. NO. OF PAGES 

U SCOMM-DC 29042-P74 

UXOMM . EnL