NBSIR 74-389

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

June 1974

Prepared for

U. S. Bureau of Mines

United States Department of the Interior

Pittsburgh, Pennsylvania 15222

Working Fund Agreement HO 133005

NBSIR 74-389

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 Interior

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

June 1974

Prepared for

U. S. Bureau of Mines

United States Department of the Interior

Pittsburgh, Pennsylvania 15222

Working Fund Agreement HO 133005

u s DEPARTMENT OF COMMERCE, Frederick B Dent, Secretary

NATIONAL BUREAU OF STANDARDS Richaid W Roberts Director
FOREWORD

This report was prepared by the National Bureau of Standards,

Boulder, Colorado, under USBM Contract No. HO 133005. The

contract was initiated under the Coal Mine Health and Safety

Research Program. It was administered under the technical

direction of the Pittsburgh Mining and Safety Research Center

with Mr. Howard Parkinson and Mr. Harry Dobroski acting as the technical project officers.

This report is a summary of the work completed as part of

this contract during the period January 1973 to June 1974.

This report was submitted by the authors in October 1974.

iii
CONTENTS

Page

1. INTRODUCTION 1

1.1 Background 2

1.2 Mine Description 3

2. MEASUREMENT INSTRUMENTATION 5

3. SPECTRUM MEASUREMENT RESULTS 10

3.1 Introduction 10

3.2 Antenna Sites 10

3.3 Electromagnetic Noise Spectrum Results 10

3.3.1 Interpretation 10

3.3.2 Uncertainties 11

3.3.3 Section Measurements 11

3.3.4 Haulageway Measurements 14

3.3.5 Arc Welder Measurement 15

3.3.6 Surface Measurements 16

3.4 Miscellaneous Measurements 17

3.4.1 Measurement o£ Voltage Between Roof

Bolts 17

3.4.2 Shuttle-Car Current Spectrum 17

3.5 Intercomparison of Magnetic -Field Noise in

Different Mines 18

3.5.1 Summary of 1 kHz to 3 kHz Data 18

3.5.2 Summary of 3 kHz to 180 kHz Data 19

1 iv
CONTENTS (continued)

Page

4. AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS 67

4.1 Introduction and Uncertainties 67

4.2 Results 68

4.2.1 Introduction 68

4.2.2 Measurement Results 69

4.2.3 RMS and Average Values 70

4.2.4 Summary Curves 71

5. CONCLUSIONS 151

6. RECOMMENDATIONS 153

7. ACKNOWLEDGMENTS 153

8. REFERENCES 154

9. APPENDIX 155

V
Figure 2-1.

Figure 2-2.

Figure 2-3.

Figure 3-1.

Figure 3 - 2

.

Figure 3-3.

Figure 3-4.

Figure 3-5.

Figure 3 - 6

.

Figure 3-7.

Figure 3-8.

Figure 3-9,

Figure 3-10.

Figure 3-11.

LIST OF FIGURES

Page

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 ^

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 23

Spectrum at location D near operating

miner. Spectral resolution is 78.1 Hz 24

Spectrum at location E in crosscut.

Spectral resolution is 78.1 Hz 25

Expanded spectrum at location E in crosscut. Spectral resolution is 3.91 Hz 26

Spectrum at location F in middle of angle

cut. Spectral resolution is 78.1 Hz 27

Spectrum at location B with no equipment

operating. Spectral resolution is 78.1 Hz- 28

Expanded spectrum at location B with no

equipment operating. Spectral resolution

is 3.91 Hz 29

Spectrum at location B near operating miner

and loader. Spectral resolution is 78.1 Hz ^0

vi
LIST OF FIGURES (continued)

Page

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

is 3.91 Hz 31

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 33

Figure 3-15. Spectrum at location A near operating

machinery. Spectral resolution is 156 Hz-- 34

Figure 3-16. Spectrum at location A near operating

machinery. Spectral resolution is 19.5 Hz- 35

Figure 3-17. Spectrum at location A near operating

machinery. Spectral resolution is 156 Hz-- 35

Figure 3-18. Spectrum at location A near operating

machinery. Spectral resolution is 156 Hz-- 37

Figure 3-19. Spectrum at location A near operating

machinery. Spectral resolution is 19.5 Hz- 38

Figure 3-20. Spectrum at location A near operating

machinery. Spectral resolution is 156 Hz-- 39

Figure 3-21. Spectrum at location A near operating

machinery. Spectral resolution is 156 Hz-- 40

Figure 3-22. Spectrum at location A near operating

machinery. Spectral resolution is 19.5 Hz- 41

Figure 3-23. Spectrum at location A of an impulse.

Spectral resolution is 156 Hz 42

Figure 3-24. 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. Spectrum at location B near train passing

by. Spectral resolution is 78.1 Hz 45

Figure 3-27. Expanded spectrum at location B near train

passing by. Spectral resolution is 3.91 Hz 46

Figure 3-28. Expanded spectrum at location B near empty

train going by. Spectral resolution is

3.91 Hz 47

Figure 3-29. Spectrum at location C at head piece with

conveyor and car-pull operating. Spectral

resolution is 78.1 Hz 48

Figure 3-30. Expanded spectrum at location C at head

piece with conveyor and car-pull operating.

Spectral resolution is 3.91 Hz 49

Figure 3-31. Spectrum at location A of haulageway.

Spectral resolution is 156 Hz 50

Figure 3-32. Expanded spectrum at location A of haulageway. Spectral resolution is 19.5 Hz 51

Figure 3-33. Spectrum at location A which was the highest

measured on April 12, 1973. Spectral resolution is 78.1 Hz 52

Figure 3-34. Spectrum of operating arc welder 15 meters

away. Spectral resolution is 78.1 Hz 53

Figure 3-35. Spectrum of noise near powerline on surface

above McElroy Mine. Spectral resolution is

78.1 Hz 54

Figure 3-36. Expanded spectrum of noise near powerline

on surface above McElroy Mine. Spectral

resolution is 3.91 Hz 55

Figure 3-37. Spectrum of noise at surface above McElroy

Mine. Spectral resolution is 156 Hz 56

Figure 3-38. Spectrum of noise at surface above McElroy

Mine. Spectral resolution is 156 Hz 57

viii
LIST OF FIGURES (continued)

Page

Figure 3-39. Expanded spectrum of noise at surface above

McElroy Mine. Spectral resolution is 19.5

Hz 58

Figure 3-40. Voltage spectrum from roof bolts separated

21.7 meters. Spectral resolution is 78.1

Hz 59

Figure 3-41. Expanded voltage spectrum from roof bolts

separated 21.7 meters. Spectral resolution is 3.91 Hz 60

Figure 3-42. Expanded voltage spectrum from roof bolts

separated 11.2 meters. Spectral resolution

is 3.91 Hz 61

Figure 3-43. Expanded spectrum of noise from currentcarrying conductor. Spectral resolution is

3.91 Hz 62

Figure 3-44. Logarithmic average magnetic field strength

in McElroy Coal Mine in the frequency range

1080 Hz to 2880 Hz, produced usually by

power line harmonics 3 through 8 of 360 Hz.

Antenna sensitive axis orientation is

vertical (up-down) 63

Figure 3-45. Comparison of magnetic field strengths of

Grace and Robena Mines as a function of

distance from noise source 64

Figure 3-46.

Figure 3-47

Figure 4-1.

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

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 levels

65

66

APD , 10 kHz, vertical component, location B

on figure 3-1 ^-^

ix
LIST OF FIGURES (continued)

Page

Figure 4-2. APD , 30 kHz, vertical component, location B

on figure 3-1 74

Figure 4-3. APD, 70 kHz, vertical component, location B

on figure 3-1 75

Figure 4-4. APD, 130 kHz, vertical component, location B

on figure 3-1 76

Figure 4-5. APD, 160 kHz, vertical component, location B

on figure 3-1 77

Figure 4-6. APD, 250 kHz, vertical component, location B

on figure 3-1 78

Figure 4-7. APD, 500 kHz, vertical component, location B

on figure 3-1 79

Figure 4-8. APD, 1 MHz, vertical component, location B on figure 3-1 80

Figure 4-9. APD, 2 MHz, vertical component, location B

on figure 3-1 81

Figure 4-10. APD, 6 MHz, vertical component, location B

on figure 3-1 82

Figure 4-11. APD, 14 MHz, vertical component, location B

on figure 3-1 83

Figure 4-12. APD, 10 kHz, horizontal component, (NE-SW),

location B on figure 3-1 84

Figure 4-13. APD, 30 kHz, horizontal component, (NE-SW),

location B on figure 3-1 85

Figure 4-14. APD, 70 kHz, horizontal component, (NE-SW),

location B on figure 3-1 86

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

location B on figure 3-1 87

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

location B on figure 3-1 88

Figure 4-17. APD, 250 kHz, horizontal component, (NE-SW),

location B on figure 3-1 89

X
LIST OF FIGURES Ccontinued)

. -.. Page

Figure 4-18. APD, 500 kHz, horizontal component (NE-SW)

,

location B on figure 3-1 90

Figure 4-19. APD, 1 MHz, horizontal component, (NE-SW),

location B on figure 3-1 91

Figure 4-20. APD, 2 MHz, horizontal component, (NE-SW),

location B on figure 3-1 92

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

location B on figure 3-1 93

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

location B on figure 3-1 94

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

location B on figure 3-1 95

Figure 4-24. APD, 10 kHz, vertical component, quiet

time, location B on figure 3-1 96

Figure 4-25. APD, 30 kHz, vertical component, quiet

time, location B on figure 3-1 97

Figure 4-26. APD, 70 kHz, vertical component, quiet

time, location B on figure 3-1 98

Figure 4-27. APD, 130 kHz, vertical component, quiet

time, location B on figure 3-1 99

Figure 4-28. APD, 10 kHz, vertical component, location A

on figure 3-1 100

Figure 4-29. APD, 30 kHz, vertical component, location A

on figure 3-1 101

Figure 4-30. APD, 70 kHz, vertical component, location A

on figure 3-1 102

Figure 4-31. APD, 130 kHz, vertical component, location

A on figure 3-1 103

Figure 4-32. APD, 160 kHz, vertical component, location

A on figure 3-1

xi
LIST OF FIGURES (continued)

Page

Figure 4-33. APD, 250 kHz, vertical component, location

A on figure 3-1 105

Figure 4-34. APD, 500 kHz, vertical component, location

A on figure 3-1 106

Figure 4-35. APD, 1 MHz, vertical component, location A

on figure 3-1 107

Figure 4-36. APD, 2 MHz, vertical component, location A

on figure 3-1 108

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

,

location A on figure 3-1 109

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

location A on figure 3-1 110

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

location A on figure 3-1 111

Figure 4-40. APD, 130 kHz, horizontal component (N-S),

location A on figure 3-1 112

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

location A on figure 3-1 113

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

location A on figure 3-1 114

Figure 4-43. APD, 1 MHz, horizontal component (N-S),

location A on figure 3-1 115

Figure 4-44. APD, 10 kHz, vertical component, quiet

time, location A on figure 3-1 116

Figure 4-45. APD, 30 kHz, vertical component, quiet

time, location A on figure 3-1

Figure 4-46. APD, 70 kHz, vertical component, quiet

time, location A on figure 3-1 118

Figure 4-47. APD, 130 kHz, vertical component, quiet

time, location A on figure 3-1 119

xii
LIST OF FIGURES (continued)

Page

Figure 4-48. APD, 1 MHz, vertical component, quiet

time, location A on figure 3-1 120

Figure 4-49. APD, 10 kHz, vertical component, location B

on figure 3-2 121

Figure 4-50. APD, 30 kHz, vertical component, location B

on figure 3-2 122

Figure 4-51. APD, 70 kHz, vertical component, location B

on figure 3-2 123

Figure 4-52. APD, 130 kHz, vertical component, location

B on figure 3-2 124

Figure 4-53. APD, 160 kHz, vertical component, location

B on figure 3-2 125

Figure 4-54. APD, 500 kHz, vertical component, location

B on figure 3-2 126

Figure 4-55. APD, 1 MHz, vertical component, location B

on figure 3-2 • 127

Figure 4-56. APD, 2 MHz, vertical component, location B

on figure 3-2 128

Figure 4-57. APD, 6 MHz, vertical component, location B

on figure 3-2 129

Figure 4-58. APD, 14 MHz, vertical component, location B

on figure 3-2 1-^0

Figure 4-59. APD, 10 kHz, vertical component, location A

on figure 3-2 1^1

Figure 4-60. APD, 30 kHz, vertical component, location A

on figure 3-2 '^^^

Figure 4-61. APD, 70 kHz, vertical component, location A

on figure 3-2

Figure 4-62. APD, 130 kHz, vertical component, location

A on figure 3-2---

xiii
LIST OF FIGURES (continued)

Page

Figure 4-63. APD, 160 kHz, vertical component, location

A on figure 3-2 135

Figure 4-64. APD, 250 kHz, vertical component, location

A on figure 3-2 136

Figure 4-65. APD, 500 kHz, vertical component, location

A on figure 3-2 137

Figure 4-66. APD, 1 MHz, vertical component, location A

on figure 3-2 138

Figure 4-67. APD, 2 MHz, vertical component, location A

on figure 3-2 139

Figure 4-68. APD, 6 MHz, vertical component, location A

on figure 3-2 140

Figure 4-69. APD, 10 kHz, roof bolt measurements 141

Figure 4-70. APD, 150 kHz, roof bolt measurements 142

Figure 4-71. 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

Figure 4-72. 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

Figure 4-73. 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

Figure 4-74. 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

xiv
LIST OF FIGURES (continued)

Page

Field strength excursions between 0.001 and

99% o£ the time as a function of frequency,

horizontal component, location A on figure

3-1 147

Field strength excursions between 0.001 and

99% of the time as a function of frequency,

vertical component, quiet time, location A

on figure 3-1 148

Field strength excursions between 0.001 and

99% of the time as a function of frequency,

vertical component, location B on figure

3_2 149

Field strength excursions between 0.001 and

99% of the time as a function of frequency,

vertical component, location A on figure

3_2 150

XV
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, West 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: 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

spectral density.

1. 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.
Only representative samples of the total data measured

are given in this report, and only a limited set of datapresentation formats have been used. Additional data, or

data presentation in other formats may be obtained from

the authors with the specific permission of the Bureau of

Mines. A more complete description of the measurement systems

used is given in previous publications [1,4].

1.1 Background

The need for reliable communication systems in mines is

a long-standing problem. For emergency use, when all power

in a mine is off, the residual electromagnetic noise is no

problem. However, if a communication system were designed only

for emergency use, it would have two serious drawbacks. First,

it would not be ready for immediate use in an emergency; second,

it would not be of any value during normal operations. Therefore, the Bureau of Mines decided to design a communication

system that could be used for both emergency and normal operational conditions.

During operation, the electrical machinery used in mines

creates a wide range of many types of intense electromagnetic

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

the design of a communication system.

The work reported here gives the results of comprehensive

measurements of this EMI in critical communication locations

where miners extract coal, as well as along haulageways.

There are several EMI 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

2
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

.

3
Mining is accomplished using a continuous miner, headloader, shuttle-cars (buggies), conveyor belt, and electrictrolley haulage. The electric trolley and the shuttle-cars

were powered by 300 volts dc. All other equipments, including

fans and rock dusting machines, were ac powered. The continuous miner had a telescoping feature to allow roof

bolting simultaneous with mining. No one had to work under

roofing that had not been bolted.

4
2. MEASUREMENT INSTRUMENTATION

Two measurement techniques were used. In the first technique used, a large portion of the spectrum is covered as a "snapshot" at one relatively short period of time. In threedimensional form, several such "snapshots" can show how drastically 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, dust-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-s trength parameters are

required, H and H^. 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], , versus frequency for

broadband noise in the spectral plots. In the amplitude

probability distributions, results are given as the rms value

5
of one component of the instantaneous magnetic field strength

versus percent of time this value is exceeded. The APD gives

the distribution of the actual instantaneous value only as far as the measurement -system detector bandwidth will allow

the detector to follow the time variations of the actual

magnetic field. (In this context, noise envelope is sometimes used.) Thus, the results are applicable for a communication receiver whose bandwidth is similar to the

measurement -system detector bandwidth.

Three measurement systems were used to make measurements

underground. The three systems are described in the block

diagrams shown in figures 2-1, 2-2, and 2-3. Figures are

located at the end of each section in this report. For a detailed description of these systems, see previous publications [1,4]. The systems used in McElroy are the same as

those used in Grace

.

In the first system, data is measured for spectral plots

and is fully mine permissible and portable. In the second

system, data is measured for statistical descriptions of time

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.

6
SIGNAL MONITORS

LOUD

SPEAKER

SYSTEM

#1

LOOP

ANTENNA BROADBAND

AMPLIFIER

OSCILLOSCOPE

IMPEDANCE^

TRANSFORMER

10 METERS

OF CABLE

lOO-kHz

LOW PASS

FILTER

SYSTEM

#2

SYSTEM

#3

200^^Hz CRYSTAL

OSCILLATOR

SHORT

r

MICROPHONE

PORTABLE

TAPE RECORDER

(30 ips, record)

TRACK I (FM)

TRACK 2 (DIR)

TRACK 3 (FM)

TRACK 4 (DIR)

TRACK 5 (FM)

TRACK 6 (DIR)

TRACK 7 (FM)

EDGE TRACK

(VOICE)

Figure 2-1 Block diagram of portable instrumentation. FM

used to record from 100 Hz to 100 kHz

are used from 3 kHz to 320 kHz.

3 are identical to system 1. When

,,xacks are used, the lOO-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.

tracks are

direct tracks

Systems 2 and

the direct tra

7

\U'T> -29151
COLLAPSIBLE

ANTENNA

LOOP

ANTENNA

f =1 0kH 2-250kH z

455kHz

FIELD

STRENGTH

METER A

BW=1 .4kHz

MIXER

40kHz

FIELD

STRENGTH

METER

BW=3 .3kHz

25kHz

OSC

455kH2^ MIXER

40kHz

f =1 50kHz-32MHz

CHANNEL 1

CHANNEL 2

CHANNEL 3

PORTABLE

TAPE

RECORDER

DIRECT

RECORDING

15 IPS

f =100Hz-50kHz

SCOPE

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

probability distributions.

8
COLLAPSIBLE

LOOP

ANTENNA

BALUN

FIELD

STRENGTH

METER

IOkHz-250kHd

455 KHz MIXER 40 kHz

10 kHz

HIGH PASS

FILTER

BALUN

LOOP

ANTENNA

(SENSITIVE AXIS VERTICAL)

COLLAPSIBLE

LOOP

ANTENNA

25 kHz

OSCILLATOR

EQUIPMENT

SIMILAR TO 3, O—

BUT WITH HORIZONTAL

ANTENNA ORIENTATION

FIELD

STRENGTH

METER

l50kHz-32MHz|

455 kHz MIXER 40 kHz

20 kHz

LOW PASS

FILTER

RECORDER

CHANNEL I (FM)

CHANNEL 2 (DIR)

CHANNEL 3 (DIR)

CHANNEL 4 (DIR)

CHANNEL 5 (DIR)

CHANNEL 6 (DIR)

LOOP

ANTENNA

(SENSITIVE AXIS VERTICAL)

CHANNEL 7 (FM)

30ips

Figure 2-3 Block diagram of laboratory recording system modified

for field use.

9
3. SPECTRUM MEASUREMENT RESULTS

3.1 Introduction

In this section o£ the report, spectrum plots are

presented and discussed. Most of these plots present magnetic

field strength up to 100 kHz. Measurements were made at many

different locations and results can be used to characterize

electromagnetic noise levels generated by most fixed and

mobile equipment used in this mine.

3.2 Antenna Sites

Figure 3-1 is a map of section 1-left 1-north as it was

on April 10, 1973 when the first day of measurements were

made. In the mining operation, four entries are driven forward

and are identified on figure 3-1, from right to left: power

entry, rail entry (trolley tracks), belt entry, and return

air entry. Noise spectrum measurements were taken in 7 locations the first day and are designated by letters A through

G on figure 3-1. Results are reported from measurements

taken at five locations on the second day, four of which are

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

3 . 3 Electromagnetic 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 microamperes per meter (yA/m) , as these are cw signals.

10
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 [ (yA/m) //x Hz] , where x is the

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

1-to-lOO-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

(yA/m) /i/Hz". For spectra with a resolution bandwidth of 78.1

Hz, subtract 10 log^^ (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 ± 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 ± 1 dB uncertainty from 100 Hz to 3 kHz. The 20 kHz

spectra have an uncertainty of ± 1 dB from 750 Hz to 20 kHz.

The spectra shown to 180 kHz have an uncertainty of ± 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

11
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.

12
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.

13
3.3.4 Haulageway Measurements

On April 12, 1973, the second day in the mine, measurements were made at three locations along the mine haulageway.

Figures 3-24 and 3-25 show the vert ical -antenna-axis

noise spectrum measured at the point in the haulageway where

men board man-trips for transportation to the working sections.

No trains were in the vicinity when the measurement was made.

This point is near the bottom o£ an elevator shaft and is

several kilometers from the locations measured in section

1-left, 1-north. Between 5 and 60 kHz the noise received

with the antenna sensitive axis vertical was stronger by 10

to 20 dB than the noise received for horizontal antenna axis

orientation. Here, as in most other locations, the noise is

primarily powerline-related multiples of 360 Hz. The spectrum

shape was slightly different. For example, the relative minimum was at 25 kHz instead of 22 kHz. Below 2 kHz, the noise

received on the antenna with the sensitive axis horizontal

was 8 to 15 dB stronger than the noise shown on figure 3-25.

At this location, the 100 kHz unmodulated carrier signal

strength from a mine phone on a portal -bus 210 meters away

was measured as 47 dB yA/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

14
moving slowly. From this it can be seen that a transient has

briefly raised the background level o£ 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-around" 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 hel ium- 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

15
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 section 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.

16
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 .

17
3 . 5 Intercompar ison of Magnet ic -Field

Noise in Different Mines

3.5.1 Summary of 1 kHz to 3 kHz Data

Figure 3-44 is a summary of magnetic field strength at

power-line harmonic frequencies observed within McElroy.

Plotted are the logarithmic averages (arithmetic average dB

value) of the six highest powerline harmonics. The logarithmic

average masks the highest single value. Average fields at

nine locations in the mine and one on the surface are plotted

as a function of distance from the nearest current -carrying

cable or wire. The six frequencies chosen are between 1020 Hz

and 2940 Hz and are either the third through eighth harmonic

of 360 Hz, or the highest adjacent powerline harmonic.

Figure 3-45 is a summary of magnetic field strength over

the same frequency region as measured in the Robena Coal Mine

(all 600 V dc) and the Grace Iron Mine (diesel -powered

haulage)

.

A comparison of the magnetic noise from 1 kHz to 3 kHz

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 yA/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.

18
b. The quietest location in McElroy 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

McElroy 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 dB uncertainty is valid only from 3 to 180 kHz.

The Robena curves are shown to 100 kHz.

19
Face, for figures

3-3 thru 3-7

Conveyor belt end

II. ., . II tail piece

Main haulage

(trolley)

"run around"

Return air

entry

Face, for figures

3-11 and 3-12

>p© Power center

Rail end

Power entry

Rail entry

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

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

20
Face on

April 12

Conveyor belt end

tail piece

Main haulage

(trolley) ^

Conveyor belt end

II , , . II head piece

II .11 run around

Return air

entry

Conveyor belt

entry

1 \

ii J) 11 r

r

^' r 1

^1

1

1 —//—

]

\—

D

Figure 3-2 Map of McElroy Coal Mine, section 1-left, 1-north

for April 12, 1973, the second day of measurements..

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66
4. AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS

4 . 1 Introduction and Uncertainties

Statistical representations are required since the variations o£ 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 telecommunications system 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 ± 1-dB quantization error limit.

One -decibel step attenuators are used to achieve the

± one decibel.

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

data processing, has a calibration uncertainty of

± 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.

67
4. The gain instability during measurements, gain

changes between measurements and calibration, and the

non-linearity o£ electromagnetic interference and field

strength (EIFS) meters and mixers, all combined, contribute ± 0.5 dB uncertainty.

5. The gain instability and non-linearity of the digital

level counter, the tuned frequency converter, the amplifier, and attenuators, all combined, contribute ± 0.5 dB

uncertainty

.

6. Connector losses and BNC cable losses, particularly

at higher frequencies above 100 kHz, contribute ± 2.0 dB

uncertainty.

Some additional uncertainty beyond the stated measurement

system uncertainty is caused by the in-mine environment. Care

was taken to provide at least one meter separation from

metallic objects wherever possible. However, coal, rock, or

earth was sometimes immediately adjacent to a loop antenna.

In all observed cases, this had no effect at frequencies up

to 1 MHz. Above 1 NlHz, earth and other reflections did in

some cases cause ± 1 dB variations, even with a shielded,

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 Introduct ion

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

during operation in the McElroy 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 horizontal 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 APD ' s of vertical

components of magnetic field noise and figures 4-12 through

4-23 show the APD ' s of horizontal components (NE-SW) of

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

on April 10, 1973. APD ' s 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 APD ' s of the vertical

component of magnetic field noise and figures 4-37 through

4-43 show APD's of the horizontal component of magnetic

field noise measured at location A in figure 3-1 on April 10,

69
1973. APD measurements made at a quiet time at location A in

figure 3-1 are also shown in figu res 4-44 through 4-48. Again,

only the vertical component o£ magnetic noise was measured at

five frequencies ranging from 10 kHz to 160 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 4-49 through 4-58 show the APD's of magnetic

field noise measured at location B in figure 3-2. Figures

4-59 through 4-68 show the APD's of magnetic field noise

measured at location A in figure 3-2 on April 12, 1973.

Only the vertical component of the magnetic field was measured at ten frequencies ranging from 10 kHz to 32 kHz.

Figures 4-69 through 4-70 show results of the roofsupport bolt measurements made at location B in figure 3-1

on April 10, 1973. The separation between the two roofsupport bolts was 3 meters. The APD's were measured using

non-shielded copper wire clipped to the roof -support bolts.

It is not easy to analyze what was measured using non-shielded

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 RMS and Average Values

The APD's are integrated to give rms and average values

of the field strength, according to the equations

00/ H dp(H)

o H

avg

70
and

U

H

rms

-/ dp(H)

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.

71
Figures 4-59 through 4-68 (near operating continuous miner)

are summarized on figure 4-78. Magnetic 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 considered further.

72
V)

01E

Q.

Eo

o

u

E

o

k. COTJI

c

0;

k.

0;cO

80

70

60

SO

40

Lineor by -y logi^l-lnp)

Z 30

20

r-r- 4

j

-- -

-f I

i

—

1 in m r * d N oi 4ne e sc 1

j --

1 k

1

i 4 -4^ 1 RMS

4

-- -i

--1 1 -1- V G

1 --j

1

-1-

--ft

-.

1

--) j.

-4— t ~

-[

< itenn N cli 9 C

1

-

1

-I

!

-

-20

jOOOI.OOI.OI j .5 I 5 10 20 30 40 50 60 70 80 85 90 95

Percent of Time Ordinate is Exceeded

99

Fieure 4-1 APD, 10 kHz, vertical component. 1.0 kHz predetection

bandwidth, April 10, 1973. 11:40 a.m., McElroy Mine.

73
Linear by - j log|p(-lnp)

-40' " " ' I ' " Ill " '

I I I I I I I I I I I I I— I —^ 1—^ "

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

74
Lineor by log,g{-lnp) 60. II II I I n il I I iiii M ii I I

I I I , —,1111,1111111 I I It

1 1

t 1

50

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.

75
Lineor by - y logi^t-lnp)

.0001.001.01 .1 .5 I 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 kHz predetection

bandwidth, April 10, 1973, 3:25 p.m., McElroy Mine.

76
jOOOI.OOI.OI .1 .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99

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.

77
Lineor by - y log (-In p)

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.

78
Lineor by -j log|Q(-lnp)

1 r 1

llj .

1 —

T"

-

1— i —|-- 1—

-l- f

1

> ^- - i

-ji[|- n——

\r -f1 ^'

—t t HH

- 4

-

4—

4f

-^ line Sen erat€ d

i

! 1

; [

1 1

1

-i— -tt1 - -

1 - 1 i — —

— -

-t -j- 4+ —

-

-t—

1 — —.RMS

-J

1 L AVG \ -+ --

— 1

H

— 4+

r

^- -H

-t- o itfn1 N u 1 :>( ^-—

—

u

—

1

- —1--

1 -t

i

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

Percent of Time Ordinate is Exceeded

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

bandwidth, April 10, 1973, 11:40 a.m., McElroy Mine.

79
Linear by -y log J-lnp)

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

Percent of Time Ordinate is Exceeded

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

bandvd.dth, April 10, 1973, 1:10 p.m., McElroy Mine.

80
Linear by - y log J-lnp)

20

10

20

30

40

60

70

—

[

V\

A

Get

+4-

r 3 re d N0 s e

1

'

-|-

i 4

ti fi 1- |t

L j1

. RMJ

(

T

I'T

< stern fMc)i 9 —Hi

T

'

I'—

T

J000l.00l.0l .1 .5 I 5 K) 20 30 40 50 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 predetectlon

bandwidth, April 10, 1973, 2:20 p.m., McElroy Mine.

81
Lineor by - j logi^l-lnp) 40

30

20

10

10

30

40

50

1

1

4— 4

1 j— 4-

-4- j

! 1

1 -H

\\

1 -4

1

M

j

1 —f- -i

i

-i

-j-. ii. I— fi

-4 4. Min 9 G,e ns r ted tH—

M J

h1

1 4+

1

i 1 1 j H

4-

-U L

1

t

; i-H1

1

;

s| -U-- rH-^

h1 III -

1 4

+-t —

'

i RMS

—

1

_)_...

"T+^ L AVG

1 1— [—] oi sc . 5 f—1

;

•

I i—

1

: 1

1 V—1

1

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

Percent of Time Ordinate is Exceeded

Figure 4-10 APD, 6 MHz, vertical component, 1.2 kHz predetecti

bandwidth, April 10, 1973, 3:25 p.m., McElroy Mine.

82
Percent of Time Ordinate is Exceeded

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

bandwidth, April 10, 1973, 5:30 p.m., McElroy Mine.

83
Linear by log|Q(-lnp)

.0001.001.01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99 Percent of Time Ordinate is Exceeded

Figure 4-12 APD, 10 kHz, horizontal component (NE-SW), 1.0 kHz

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

McElroy Mine.

84
Linear by - j log (-In p)

.0001.001.01 .1 .5 I 5 10 20 30 40 SO 60 70 80 85 90 95 96 99

Percent of Time Ordinate is Exceeded

Figure 4-13 APD, 30 kHz, horizontal conponent, (NE-SW), 1.0 kHz

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

McElroy Mine.

85
Linear by - y log|p(-lnp) 30

20

10

-10

20

40

60

70

-

1 -+- ——rr

1

1 —

1

III

1 1

j - -4- T

-1— - U1

"

i

--

1 i! 414+ — —"H" j

1

1

! --t-4- —

,

j

i

1

i

; j T'

(- -|- 4-

4

4--4-

---j—1-- — 1

! +X- i

i

I —tf"

-1—

t4- —J-- i -i—

_4

-i1 A /line Generat ed N0 s e —

F

[ j 4 —— i

' ii - k44- +-4---U

1

! 'j

i

: h \ -A— -t--

"f'l" -4U- —ij--- — 1 \

f- —Ttt- —^-

u . i +-

—

I

rH—

t\--

H—

1

+-

It RMS —1 II

i

'"T H~ill'. —

'\ 1

'—

m

^4i- -

r- —i

!

' H— H— wAVG 1

: 1 —!

IT-*- -

1

1

-41--^ —

rill! -H 4^

-f

-H--

-d €-1+4 —

r1

'

1 i

'

j

-i-rl— —

1

-i-

-i—i- ^ T

-A —1- c>ysItem Nois

1 -4-

H

1 4|- i

i

1 r""—

-+1—

1 -4t— i4l- ' F

I T

-[[-

1 ji

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

Percent of Time Ordinate is Exceeded

Figure 4-14 APD, 70 kHz, horizontal component (NE-SW) , 1=0 kHz

predetection bandwidth, April 10, 1973, 2; 50 p.m.,

McElroy Mine,

86
Linear by - j log^jt-lnp) 20

10

20

30

40

50

60

1 H —

r

-\I'ii

1

-jj

^-

1 - H 1

1

' - V 4- \^ -ft}-—

1 — n —t" 1-

--i-i

-- -H--

t -4---

1 rr '~h~r h

1 jf- 4

h1

1

i -li—

I

1 —

h

-f

-\- ^- —

r

—t1 --^

1 1

1

—r -

-1 \

Mine

i --t1 -i

1

- +li 1

1

i ^- -rr

1 "t \ !

i

1

1

--t- ''1

i -4 a: RMS —

1

1,

1

i !

1 —r4-- —

f1 ii'A

-4-

'i'l

-fi-.i

I. AVG

r

-r 4f—

--^

-T—

-4-

i -H—-L

1 it +

B 1 VIII 1 ^ois e

i

-\t-

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

Percent of Time Ordinate is Exceeded

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

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

McElroy Mine.

87
-70

-80

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

Percent of Time Ordinate is Exceeded

99

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

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

McElroy Mine.

88
Linear by - j \oi}^J,-inp)

(0

OfE

a

0)Q.

0*>

m

c

01

0)

Ofc

O

.0001.001.01 .1 .5 I 5 K) 20 30 40 50 60 70 80 85 90 95

Percent of Time Ordinate is Exceeded

99

Figure 4-17 APD, 250 kHz, horizontal component (NE-SW), 1.0 kHz,

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

McElroy Mine.

89
-70

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

Percent of Time Ordinate is Exceeded

99

Figure 4-18 APD, 500kHz, horizontal component CNE-SW), 1.2kHz

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

McElroy Mine.

90
Linear by -y log J-lnp)

20

10

-10

-30

-40

-50

-60

r 1 — 1 I -\

I -1 1 — - i 1

[ - fl —f-

-jj —

i + — T" ! -1 1

—

-t

1 —

f

4-|- —

+4 — T

1

1 \

-f -- --t*t

-4- H1 K1

1 1

"ft —

i r 1 -

1 -I-

-|.

1 —

1 -1-Hi— -4

1 \ t

j 4 —

-

-i —

1

-

1 1 -j

— — - -

1

-4

1 t 1

'

1 --V

1 —1

— u —

f

!—»n 1—

1

IV —rt inc ciener

1 \ a »c No ilIf —(-

1 — -

!

1 -+

— 1 ^

1 —

1

— — - T~

1

' \\

'

i — h

— —

uL

r- -

i -f 1 hl-

— — 1

1 —f1 1 -ll""[^

1 h+f-l —

^ —

>

—

L

j ---i i1 n 4 h -H

1 Th[*- -A

4' —

. AVG —

t

I + —

1 'r

-A

—

-r

. 1 r —

1

+ — — —H- —

F

1 te m f s t

r

j

1)001.001.01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

Figure 4-19 APD, 1 MHz, horizontal component (NE-SW), 1.2 kHz

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

McElroy Mine.

91
.0001,001.01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

Figure 4-20 APD, 2 MHz, horizontal component (NE-SW), 1,2 kHz

predetection bandwidth, April 10, 1973, 2:50 p.m.,

McElroy Mine.

92
Linear by --j- log.J-lnp)

Percent of Time Ordinate it Exceeded

Figure 4-2! APD, 6 MHz, horizontal component (NE-SW), 1.2 kHz

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

McElroy Mine.

93
-80

-90

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

Percent of Time Ordinate is Exceeded

99

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

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

McElroy Mine,

94
Lineor by --j- loguj(-lnp)

10

-10

-20

-40

-50

-60

-70

-80

-90

rr

1 4-

n

—r—

1 "I— -r1 -t —

i + —

1 —

1 ...

j

--

-H 4+ — I -1 ! -

—]

4- -H

1 —

j —

__.

"i

'

1

-i

i

-1— I

i — 1

,

-i— — -

>- —

,

— —

i -it

1 -4-

-I h —

1

i

1

1—

1

1

!

.

-i- —

-

- —1

I —

r

i i_

- h-J

I ] -

! ..I.. "t

r

-1 T 1' r 1 -4

Gen(if c te(j

1

f VI s

1 t' A' —

-4-4 -4—

t1 —j—i- -i

i;

i

1

1 -t1 5ys n r 0 ISC i

i +

-

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

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.,

ffcElroy Mine.

95
-20

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

Percent of Time Ordinate is Exceeded

99

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

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

measurements, McElroy Mine.

96
Linear by - j

log|Q(-lnp)

V)

cc

9>a

a

E

oo

m

T3

C

(b

L

o

c

o

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

Percent of Time Ordinate is Exceeded

99

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

bandwidth, April 10, 1973, 4:10 p.m., quiet time measure- ments, McElroy Mine.

97
Lineor by - Y log,Q(-lnp)

50

30

20

10

10

20

30

i—

I T'

1 i 1^

1— —

1 |- —

-j-

!

1 1 "I

-4

j-

-i-f--- 1-

1

1 t

-

--f

_| M 4 -4

|i- ^-

1 \ , 4^

li H \- r

-i—

4- -J —

1

,

\]

i —

1

—

1

r' r

I-+

H -J line Gene ra1red Noi s

-1 B

-U- +"t—t- —

1

- M

i

1 1

1

1 "^"T — 7T

1 LL_ ^

i -1- -4

j—

{- AVG

r

- 1-

|. - -i- hi1

1 r — 1

i

-

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

Percent of Time Ordinate is Exceeded

Figure 4-25 APD, 70 kHz, vertical component, 1.0 kHz predetection

bandwidth, April 10, 1973, quiet time measurements,

McElroy Mine.

>93
-50

-60

jOOOI.OOI.OI .1 .5 1 5 10 20 30 40 50 60 70 80 85 90 95

Percent of Time Ordinate is Exceeded

99

Figure 4-27 APD, 130 kHz, vertical component, 1.0 kHz predetectlon

bandwidth, April 10, 1973, 4:30 p.m., quiet time measurement, McElroy Mine.

99
Linear by - y log J-lnp)

50

40

10

10

20

30

—

T

— - 4

1 4-- -4

1

! -.1

4- --ii 4

1

1 —

h

1 --i

Hi"~ —

f1—

i 4

i 1

j— 4 1. _

Vli n Gene

-+ u

1 X -ii+1- — —i

1

1 t- ^- L -

-H -t

4-

1 - --J.

-+

1

1

! V RMS ^ 4 -A

:

1 + H

i—

, AVG

! r

^

1

1

i 1

1 - -H

j 4—

! — - L

.

System Noite

-

.0001,001.01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

Figure 4-28 APD, 10 kHz, vertical component, 1,0 kBte predetectlon

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

100
-40

1)001.001.01 .1 .5 I 5 10 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.

101
.0001.001.01 .1 .5 I 5 K) 20 30 40 50 60 70 80 85 90 95 98 99

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.

102
Linear by - j log (-Inp)

1)001 .001 .01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

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.

103
-70

.0001,001.01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

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., McElroy Mine.

104
Linear by -

-j- log^jC-lnp)

-90' II " III' " ! ' " I " ' " I I I I M I I II I II I I M M 1 1 \ 1

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

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.

105
Linear by - y log|p{-lnp)

-90' 'III I I I'll I II II I M M I I I I IMM II M \ 1 1 1

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

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.

106
Lineor by -j log (-In p)

-70

-80' " 'I 11""' I I "" ' " I I I I I 1 1 11 —I 1

\ 1

.0001.001.01 .1 .5 I 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.

107
Lineor by - j log (-Inp)

Percent of Time Ordinate is Exceeded

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

bandwidth, April 10, 1973, 5:15 p.m., McElroy Mine.

10 8
Lineor by - j log,g(-lnp)

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

Percent of Time Ordinate is Exceeded

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

bandwidth, April 10, 1973, 1:30 p.m., McElroy Mine.

109
Linear by -

-j- log|Q(-lnp)

Percent of Time Ordinate is Exceeded

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

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

110
Linear by - j log|Q(-ln p)

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

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.

Ill
Linear by - -j- log|Q(-ln p)

.0001.001.01 .1 .5 I 5 10 20 30 40 50 60 ?0 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

Figure 4-40 APD, 130 kHz, horizontal component (N-S), 1.0 kHz predetection

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

112
30

20

1 10

%

E

Q. 0

01

a>Q.E

o

o

o -10 Eo

-20 o

a>

CDO

Linear by - y logi^t-ln p)

30

C

co

-50

-60

-70

"

'

1

1

'

_ L.' J

- H

1--- i

I

_^

-+ ;

^

-J

i

i —1

1 —1

-H

>

—[

1

lerU I cr ri r^ ui se —i

iviine

1

1

, , ,

1

I

'

—*—j—

i —1

1

^ . -_ Si— 1

T • -f - 1—

1

1

j

! AVG I 1 -- — i

'—

. 1

1

——i-i1

1 1 i i

'

1

:

1 j

1 t—^-1 1

-ill.

1 1

' '

1 -i

! I — i

j

'

i

i

i

i

1

i

—i-

'

1

: M '

1—i

]

i

1

-J- ! i

1

1

' 1

' —r-

— —\——1

A- vi—Lr^-

"t'

. ..,

;

. 1 fr

1 ! 1 U -

1

,01 J .5 I 5 10 20 30 40 50 60 TO 80 85 90 95

Percent of Time Ordinate Is Exceeded

98 99

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

bandwidth, April 10, 1973, 6:00 p.m., McElroy Mine.

113
Linear by - y log|p(-lnp)

jo MrTr^Mi! ITIflllill i M M I . M I I I I HIHIII I M M M I 1 \ I \— .0001.00101 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

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.

114
20

Linear by - j

log|Q(-lnp)

It-

+ 4-

Tttt I

I

! I

n- 5

-10

-20

-30

-40

-50

-60

-70

Mine Generated Noise

RMS'

J-4 AVG

System Noise

.0001.001.01 .1 .5 I 5 10 2 0 30 40 50 60 TO 80 85 90 95

Percent of Time Ordinate is Exceeded

98 99

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

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

115
Linear by - j log|g(-lnp)

Percent of Time Ordinate is Exceeded

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

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

116
.0001.001.01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

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

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

117
-70

-80

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

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 measure- ments, McElroy Mine.

118
Linear by - j log|Q(-lnp)

Percent of Time Ordinate is Exceeded

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

bandvd.dth, April 10, 1973, 4:20 p.m., quiet time measurements, McElroy Mine.

119
-90

-100

.0001.001.01 .5 1 5 10 20 30 40 50 60 70 80 85 90 95 Percent of Time Ordinate is Exceeded

99

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

bandwidth, April 10, 1973, 4:05 p.m., quiet time measure- ments, IfcElroy Mine.

120
Linear by -j loguj(-lnp)

.0001.001.01 .1 .5 I 5 10 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,

121
Linear by -y log|Q(-lnp)

SO

30

20

10

20

•30

40

—

t

T 4

T

1

n

II -4+ - -1

1 4-

1 -4- —r — 4—

r

.. 1 i—

'

- 1 —tj-

\ -4- -i-\

1 -i1 4- —1— r

1

--_ - 4

\- 4

t— u

---

i -

j -r

I — 1 1 —4-h4

j 1

i r

\

i 4 u j. 4

4

r1 i -4-- ;: ! -4

--1

H

1 u

—

i

-t-^ -4

'—-H 4- in

71"

! —

1

[it'

4 —

'

4-

\4l 4

-jH

\

"tt" j—

-j- 4-

—i-

! H -4

1

' — -4- —l-^ -4

1 f

1 l-H

1

hff

d4 i

1

j

: i

. 1

1 4r1

'-^ - Mine Generated Noise 1

1

4 1 1 -H

1 -V+4-H 4

1

1 -t r-4— -i- -^- —

1

- 4

J4

— U

r

4

i —I-

--1

i: — 4-

1

-j — -1- —i— + 4H

4

"1

-A 4

4+

V

c S

-

4 — 4

i L

-I 4

H

—

r AVG

4 —^ 1

1—

[ -^

p -i —

4-^

1 4 -i--

1 —

t

—1-

1 V

+-t —

'

! —

1

1 1

-r —

r

1 4 i -\

4

1 -4 4—

1

-r rt4-^

-- 4- —

j

1

1—-H

4 t

1 S err1 N()i!MI —t

1

1 n- 4 -+-|- —

1

1 i4

1

-|

t -- [r 4 —

r

-

"4~

4

-H

1 M 4— 1

1 , 1

0001 .001 .01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

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

bandwidth, April 12, 1973, 12:25 p.m., McElroy Mine.

122
31.001.01 .1 ,5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

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

bandwidth, April 12, 1973, 12:50 p.m., McElroy Mine.

123
.0001.001.01 .1 .5 I 5 10 20 30 40 50 60 TO 80 85 90 95 98 99

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.

124
-60

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

Percent of Time Ordinate is Exceeded

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

bandwidth, April 12, 1973, 2:10 p.m., McElroy Mine.

125
-70

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

Percent of Time Ordinate is Exceeded

98 99

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

bandwidth, April 12, 1973, 11:50 a.m., McElroy Mine.

126
20

Linear by -y log|J-lnp)

.0001.001.01 .1 .5 I 5 10 20 }0 40 50 60 TO 80 85 90 95

Percent of Time Ordinate is Exceeded

99

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

bandwidth, April 12, 1973, 12:25 p.m., McElroy Mine.

127
Linear by - j log j-lnp)

-70' I I II ' ' '

I I M I M M I I I I I III I I M I I I \ 1 \ 1

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

Percent of Time 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.

128
Lineor by - y loQigl-lnp)

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.

129
Linear by -y log|Q(-lnp) 30

1

I

I

I

I 1 1 n il I I | || | Mj| I r 1 1 1 1 1 1 1 I I I iiiiiiii 1 1 M

1

1 1 I I—\—I\—

I

20

-60

-70' 'I I I'll'^ ' ' ^ ' ' "i ii ' ii '

I I M I I I I

\ \ \ 1

.0001.001.01 .1 ,5 I 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 predetectlon

bandwidth, April 12, 1973, 2:10 p.m., McElroy Mine.

130
Linear by - y

log|g(-lnp)

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

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.

131
Lineor by - j log J-lnp)

70

60

50

40

50

20

10

10

20

30

1 _j JT —

1

h -

— --- fH— — —

vr

i ll r

H ~H

i T

h 4

j +H- _i

j

"1

-4--

1

1 -V--- — —

\

i

1 —

1

—

i —

'

t

-- + 4—

i -4 —

r

1 -i-H—

1 —

ft

-H —

1

- —

1

,- —

> tf-

-tf — j

-4 —

— -

1 ~*~rT

-4 — - —j— — 1— —

1

-H

ul

—

1

i

! 1

1

- -t1

1 -t k Mi en ei e — --L-f— a 1

1

! —

i

! tl— —f- \

—1—

1

—i

—

1

- 4 —

L

r- —

1

-L i

i ^

-4 :| RMS

1 -Ht—

-i X tr

ii —

1

1 4 , AVG

4--I— —f

-4 ;! 1

—l

1 4- rr tr I

\

I —

+

—I i

1

. -I

! — 1

h

1 — i . kf

— -t —

i —

f

— —1- -

1

1 fftii- —Ir- —

'

-

1- T

'

4-.

+-

i -i

I

1

1 -t- -

t' \-

4-- —

1

1

H —t1

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

Percent of Time Ordinate is Exceeded

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

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

132
Linear by - y log|Q(-lnp)

Percent of Time Ordinate is Exceeded

Figure 4-61 APD, 70 kHz, vertical component, 1.0 kHz predetection

bandwidth, April 12, 1973, 1:00 p.m., McElroy Mine.

133
Linear by log.(-lnp)

50

40

30

20

10

20

30

50

T

1

1

1 ,

I

1

1

1

1

1 T""'

!

j —1

r1

i i

1

>

j

"tl" —

{

1

j

i 1

i

i

1 -4I — 1 —

1

^ i —1

, — —

1 '1 ' M !

1

1(- i

\' —i

—H- tr —

—

-1r "i

1 —h-- N

1

1

' —

1

—1

1 + - j —

fj \ i; nt-r

ni-f-

"It' — 1 'r

1 i ^+

-1 -1r- T 1

"

1

\' -ii

! i -H

+++ —1

rf -

—

1

1 'TV— —T —1—

i

1 ;

1

i

1 !

1 : 1 i

1 —i"

1 AS ne CSenen

-

Moi

! -t- -H--

i M u K -j—

+t+

- —1— H

! —f' —

!

—\

!

1

1 -

-\—

—

I

—|-

1

1 -

--

[

i —

1

—|l -[ —1

1

1 :^ 1 1 -4- ^\

i 1

1

-

\\\ RM

- —

"t

j — 0 —

1

"Hi""

i,

-

1 —

1

\"

— -

1 — \

\ i —fi1 i 1 —1

H-i AVG

1 —

i — —

H

1

'

i "T

—I

t trr-

\ 1

i Xi 1 -

—

1

—+--w 1

;

I

i

-i h- -

! -+- —4+

-|-4+i

i

— if —

s S t€ nr1 1 9C

1

1 -- —— -

- ii

.0001.001.01 ,1 .5 I 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.

134
Linear by - y log|Q(-ln p)

.0001.001.01 .1 .5 I 5 10 20 30 40 50 60 70 80 85 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., McElroy Mine.

135
Linear by - y log (-In p) 40

30

10

10

20

40

50

rn 1 -

I I

! — -1- - -+-ui- —

1

— — r

u

1

j 1

L

1 h 1 1 -j -U

-A - 4- --+- f4-

1 -h —

- -1-

! 1 4-1-- J + 4j

r- —

+

1

1

-i —

1 -i- — -

i ;|

il--

1

i -1- —— 1 —

t

1

! i 1

--ft- — - -1—

-1 -

—

—H

1 - - —

t

t--

<^ —

1

-4- —I

-[ f-1

1

1 -1

\ Vlin e Gen€TO fed N 0 s e

\

-r- 4--f- —

1

jS ft-11—

--^ r -

1

1t1 T ! ^ —i—

1

1 -11-

1 —j-

||4-

1 4- L -H1—j— —1— —i—

t-iL- —

1

1 4-\\-

-ji

. —\—

1 —

i

— - 4- + — i..

1

1

1

1 -4 avg] —

1

H -H -t- K — 1

' --

1 -4

-U—

1

r- —

1

+

1

i

--+- -I —1-

1 4

1 --^ + i

1 L -4-

-ti tf

tl- - -r -U

1

1 — t^ — -

-f

-\ —-A 4- —

tr

! —

,

-I— 4--ij- —

.... "T

--|

' i T

-- —i

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

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.

136
.0001.001.01 ,1 .5 I 5 10 20 30 40 50 60 70 80 85 90 95 98 99

Percent of Time Ordinate is Exceeded

Figure 4-65 APD, 500 kHz, vertical component, 1.2 kHz predetection

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

137
Linear by - 7 logigl-lnp)

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.

138
Linear by - j log -l-lnp)

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

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.

139
Linear by -j log (-In p)

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-40

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70

80

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bandwidth, April 12, 1973, 2:15 p.m., McElroy Mine.

140
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-60' " 11 ' I I I "I M M M I I I I m illll I I I M I I I I \ 1 \ 1

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Percent of Time Ordinate 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.

141
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30

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

McElroy Mine.

142
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5. CONCLUSIONS

The range of magnet ic -field noise levels in McElroy is

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

1 yV/m at 180 kHz. This compares with the 12 5 dB range in

Robena, except that the Robena levels were higher, from.

+105 dB to -20 dB with respect to 1 yA/m. Grace Mine had a range of 158 dB , from +122 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. However, from 3 kHz

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

McElroy were both relatively high, 10 to 80 dB above 1 yA/m,

near operating equipment, compared to levels in Grace and

Itmann mines of -10 to 50 dB above 1 yA/m. From 100 kHz to

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

+15 dB above 1 yA/m. Data from Robena is not available in

this frequency range, but levels may well be comparable to

those in McElroy 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 yA/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 yA/m. The carriers come

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

harmonics were the dominant source of noise. The range covers

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

APD measurements were taken during quiet times as well

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

but 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 yA/m

151
at 30 kHz, and near haulageways, were 10 dB above 1 yA/m at

30 kHz. The range o£ these measurements is consistent with

the wide range of levels that have been measured in some

other mines

.

152
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 systems

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 systems,

avoiding use of powerline harmonic frequencies is of

primary concern.

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 Matheson, 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

Consolidation Coal Company.

7. ACKNOWLEDGMENTS

153
8 . REFERENCES

Bensema, W.D., Kanda , M. , Adams, J.W., Electromagnetic

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

April 1974.

The Institute o£ Electrical and Electronic Engineers, Inc.,

IEEE Dictionary of Electrical and Electronic Terms,

Std. 100, 1972.

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.

Adams, J.W., Bensema, W.D., Kanda, M. , Electromagnetic

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

Crichlow, W.Q., et al . , Amplitude-probability distributions

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

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

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.

154
9. APPENDIX

Decoding of Spectrum Captions

Spectrum captions are generally organized into the following format:

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

where

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

2^^ 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, 2 048

NPO = Number of spectra averaged between output calls,

example, 2 0

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.

155
Third line: RUN, SESSION, DAY, MONTH, YEAR Gain corr., rec . = tot. constr. =, where

Run and Session = the title of the portrayed frame identifying

the digitizing session and run number,

example, 21 8 3

Month, Day, Year = date data were recorded in the mine,

example, 8 2 5 73

Gain corr. rec. = receiver gain correction, example, -6

tot. const. = constant gain correction of entire system,

example ,-46.4

Fourth line: C =, RG =, DG =, FG =, AG =, where

C = correction curve used with data, example, 25

RG = receiver gain and accompanying correction in dB added to

the data, example, 200 (-6 dB)

DG = digitizer gain, example, 0

FG = filter gain in dB, often rounded to nearest single digit,

example, 0

AG = absolute gain correction added to data, example, 52

Fifth line: Top of Scale, Standard Error, Spectral Peak, where

Top of Scale = largest scale marking for computer drawn

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 10^)

156
NBS-n4A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 74-389

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Electromagnetic Noise in McElroy Mine

5. Publication Date June 1974

6. Performing Organization Code

7. AUTHOR(S) 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, Boulder Labs

DEPARTMENT OF COMMERCE

Washington, D. C. 20234

10. Project/Task/Work Unit No.

^76-840^2

11. Contract /Grant No.

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

S. Bureau of Mines

4800 Forbes Avenue

Pittsburgh, Pa. 15213

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention 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 re- corded using broadband analog magnetic tape and the noise data is later transformed tci give spectral plots. The other technique records noise amplitudes at several discrete frequencies for a sufficient amount of time to provide amplitude probability

distributions.

The specific, measured results are given in a number of spectral plots and amplitudt

probability distribution plots.

17. KEY VCORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first kev word unless a ornner 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 spectral density

18. AVAILABILITY [x2 Unlimited

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