Embed Size (px)
Citation preview
ELECTROMAGNETIC PROPAGATION IN
LOW COAL MINES AT
MEDIUM FREQUENCIES
Prepared for
UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF MINES
Collins Communications Switching Systems Division Commercial Telecommunications G r o u ~ Cedar Rapids, Iowa 52406
Rockwell International
FINAL REPORT Contract No. H0377053 12 JUNE 1978
REPORT DOCUMENTATION PAGE,
1 3. Recipient's Accession No. I
I
4. T ~ l t and Subtitle
Electromagnetic Propagation i n Low Coal Mines a t Medium Frequencies
7. Aulhor(9)
Terry S. Cory
Department o f t h e I n t e r i o r Washlngton, D.C. 20241 14.
5. Report Date
12 June 1978 - 6.
8. Performing Orgnniration Report No.
523-07691 30-001 31M
9, Performing Organization Name and Address
Co l l i n s Communications Swi tch ing Systems D i v i s i o n Commercial Tel ecomnunications Group
Rockwell I n t e r n a t i o n a l Cedar Rapids, Iowa 52406
12. Sponsoring Orgmiznrbn Name and Addreu
O f f i c e o f t h e Ass is tan t D l r e c t o r - Mining Bureau o f Mines
- 15. Supplemenlary Notes
P r i o r r e l a t e d work - Propagation o f EM Signals I n Underground Mines USBM Contract H0366028
10. Projrcr/Tark/Work Unit No.
20-1308/93-6527 11. Contract or Grant NO.
H0377053
13. ~ y p , of Report
Final Report
16. Abrrrsct
This r e p o r t covers magnetlc f l e i d s t reng th measurements vs range and frequency i n low-medium coal mines. Both quasi-conductor-free and conductor-proximity areas were inves t iga ted . The program covered 5 mines, 4 seams, 6 measurement sets, and 3 geographic areas. The r e s u l t s have been summarized i n terms o f maximum comnunication range expected per seam and no ise cond i t ion . Sca t te r ga in i s f u r t h e r explored as a simple measure o f energy coupled t o conductors.
17. Orilinatoc'r Key Words 18. Availability Stacemen1
MF w i re less r a d i o propagatlon; maximum communication range; conductor-free areas; conductor-proximity areas; s e t l i m i t e d noise; median mine no ise
1 iccurity Classif. of rhr Report
IJ..~! ~ s i f i e d
21. No. of Pagn
94 20. U.S. Security Classif. of This Page
Unclassified
22. Price
FOREWORD
This r e p o r t was prepared by Ter ry S. Cory, P.E., f o r C o l l i n s Communications Swi tch ing Systems D iv i s ion , Commercial Telecommuni- ca t ions Group, Rockwell I n t e r n a t i o n a l , Cedar Rapids, Iowa, under USBM Contract H0377053 and Ter ry S. Cory, P.E., Subcontract C-651672. The c o n t r a c t was i n i t i a t e d under t h e Coal Mine Heal th and Safe ty Program. It was adminis tered under t h e techn ica l d i r e c - t i o n o f Bruceton Research Center w i t h Mr . Harry Dobroski a c t i n g as the Technical P ro jec t O f f i c e r . The Bu Mines Cont rac t ing O f f i c e r was Alan G. Bol ton, J r .
This r e p o r t i s a summary o f t h e work r e c e n t l y completed as p a r t o f t h i s c o n t r a c t du r ing the pe r iod October 19, 1977 t o May 31, 1978. This r e p o r t was submitted by t h e author on June 12, 1978.
For c l a r i t y , t h i s r e p o r t conta ins equipment brand names as being g e n e r i c a l l y rep resen ta t i ve o f equipments which may be ava i l ab le t o implement medium frequency systems i n coal mines. Reference t o s p e c i f i c brands, equipment, o r t rade names i n t h i s r e p o r t i s made t o f a c i l i t a t e understanding and does n o t imply endorsement by t h e Bureau o f Mines. No patentable techniques o r items o f equipment have been developed o r otherwise used du r ing the course o f t h i s program.
Table o f Contents
Page
Report Documentation Page---------------- Forewor&-------------------------------- 1.0 Introduction------------------------ 1.1 Program Background------------------ 1.2 Program Overview-------------------- 1.3 Report Contents--------------------- 2.0 Execut ive Summary------------------- 2.1 Resul ts Summary--------------------- 2.2 Transmission Characterization------- 2.2.1Computatlon C r i t e r i a 8 Techniques--- 2 .2 .2Ut i l i t y o f t h e Character izat ion-----
Technique 2.3 Recomendations--------------------- 3.0 Technical Approach------------------ 3.1 Empir ica l Technique----------------- 3.2 System Calculations----------------- 3.3 Sca t te r Galn Comparisons------------ 4.0 Ind i v idua l Mine Tes t Descript ions--- 4.1 Margaret # I I Mine------------------- 4.2 Adrian Mine------------------------- 4.3 Nanty Glo Mlne #31------------------ 4.4 Ehrenfe ld #38D Mine----------------- 4.5 St inson #3 Mine--------------------- Append i x A - l Margaret # 1 1 Test Data a t Medium----
Frequency A-2 Adrian Mine Test Data a t Medi urn-----
Frequency A-3 Nanty Glo #3 I Mine Test Data at-----
Med i um Frequency A-4 Ehrenfe ld #38D Mlne Test Data at----
Mad l um Frequency A-5 St inson #3 Mine Test Data at--------
Medium Frequency References------------------------------- Special Technical Report-----------------
I n - S i t u Measurement o f Coal Seam Conduct iv i ty Using a P a r a l l e l Wire Transmission L i n e Method
L l s t o f I l l u s t r a t i o n s
F igure Page
I Maximum Communl c a t i o n Range vs Operat ing Frequency I n Conductor-Free Areas o f Coal Mines - S e t Noise Limit------------------------ 10
2 Maximum Communication Range vs Operat ing Frequency I n Conductor-Free Areas o f Coal Mines - Median Mine Noise ..................... 11
3 Maximum Communication Range vs Operat ing Frequency I n Coal Mines In Prox imi ty t o Conductors - Tx Located Remotely - Median M i ne No 1 se------------------------------------- 12
4 Maximum Communication Range vs Operat ing Frequency i n Coal Mines I n Prox imi ty t o Conductors - Tx Located Remotely - Set ~~i~~ ~imit------------------------------------ 14
5 Required F i e l d Strength S e n s i t i v i t y Levels f o r Mine Wireless Radios Based on t h e C o l l i n s - Developed Mine W I r e less Prototype Radios a t 520 KHZ------------------------------------- 16
1 .0 I NTRODUCT I ON
Th is i s t h e F i n a l Report cover ing work performed by C o l l i n s D iv is ions , Rockwell I n t e r n a t i o n a l Corporat ion under Bureau o f Mines Contract H0377053 e n t i t l e d Electromagnetic Propagation i n Low Coal Mines a t Medium Frequencies.
The techn ica l work was performed by Ter ry S. Cory, P.E. under Subcontract C-651672 w i t h a d m i n i s t r a t i v e d i r e c t i o n and techn ica l support prov ided by C o l l i n s and us lng C o l l i n s ' f a c l l l t l e s .
The pr imary work cons is ted o f per forming measurements o f magnetic f i e l d s t reng th i n f i v e (5 ) mines and f o u r ( 4 ) coal seams coordinated w i t h a concurrent t h e o r e t i c a l study performed by A r thu r D. L i t t l e , Inc. (ADL) under separate cont rac t * t o t h e Bureau. The measurements were taken i n such a manner as t o enable t h e reduced r e s u l t s t o charac ter ize the w i re less r a d i o t ransmiss ion p rope r t i es o f each m i ne/coa l seam; bo th i n areas w i thou t conductors and w i t h conductors.
Th i s program was a techno log ica l extension o f a prev ious program e n t i t l e d Propagation o f EM S lgna ls i n Underground Mlnes ( performed under Bureau o f Mines Contract H0366028 here in r e f e r r e d t o as t h e "EM Signal l i n g Program". Th is c u r r e n t program has appl l ed an es tab l ished technique f o r t ransmiss ion charac ter iza t ion , t o se lected h i g h l y p roduct ive low-coal areas. The t e s t equipment, furn ished GFE, was developed and/or conf igured under t h i s prev ious fy?gram and t h e reader i s r e f e r r e d t o t h e f i n a l r e p o r t f o r t h a t program f o r a de ta l led d e s c r i p t i o n o f t h e technique and t h e measurement system.
The magnetic f i e l d s t reng th measurement data se ts from each mine were separa te ly repor ted i n each o f f i v e (5 ) i n t e r l m Summary Data Reports. The data summaries i n t h e form o f f a m i l i e s o f curves o f magnetic f i e l d s t reng th vs range and frequency and t h e mine map topo log i ca l descr i p t i o n o f t h e measurement t raverses have been compended and are g iven i n t h e Appendix t o t h i s repor t . The f u r t h e r summarizing o f t h i s data i n terms o f maximum communlcatlon range w i t h a technique which can be used t o apply t h e r e s u l t s t o system designs f o r p a r t i c u l a r mines i s t h e sub jec t o f t h i s repo r t .
Secondari ly, a technique was developed under t h e c o n t r a c t funding f o r t h e independent i n - s l t u measurement o f coal seam c o n d u c t i v i t y and pre l i m i nary measurements us ing t h i s technique were performed i n two mines. Th is work was beyond t h e o r i g i n a l scope o f t h i s Ysqgrarn and has been repor ted separate ly i n a Special Technical Report
which i s n o t a p a r t o f t h i s F ina l Report. For convenience, t h i s Special Technical Report i s submitted concur ren t ly as an Attachment t o t h i s F i n a l Report.
A l l program measurements were p e r f o n e d by a team c o n s i s t i n g o f t h e Subcontractor and P r i n c i p a l I nves t i ga to r Te r ry S. Cory, a Bureau o f Mines furn ished technic ian, and a C o l l i n s fu rn lshed techn ic ian .
*Task Order #4, Basic Ordering Agreement H0346045.
5
I. I PROGRAM BACKGROUND
The v i a b i l i t y o f w i re less r a d i o t ransmission i n coal mines has been establ ished; l a rge ly as a r e s u l t o f t h e Bu Mines sponsored EM S i g n a l l i n g Program, the companion ADL program, and p r i o r Bu Mines sponsored research i n t h l s area da t ing back t o 1973. The basel ine s tud les and measurements were performed l a r g e l y i n high-coal i n West V i r g i n i a and I l l i n o i s and i n DC mines, Renewed nat iona l emphasis on coal product ion, l a r g e l y underground, has spurred t h e here-to-fore embryonic and somewhat ant iquated mine e l e c t r o n i c s technology i n t o a major arena o f f e r i n g - subs tan t ia l l y increased c a p a b i l i t i e s f o r product ion e f f i c i e n c y , con t ro l , and f o r enhanced mine safety. A large p o r t i o n o f t h e U.S. coal reserves res ide i n low-coal ( seams nominal ly 36 - 48 Inches t h i c k . Newer AC mines do n o t p rov ide the t r o l l e y w l re t ranspor t mechanism f o r implementation o f t h e c a r r i e r phone comnunication systems preva lent i n o l d e r mines f o r handl ing veh ic le t r a f f i c . Pager phone systems alone, e s p e c i a l l y i n low-coal where physical m b i l i t y i s d i f f i c u l t , are n o t s u f f i c i e n t t o regu la te veh ic le t r a f f i c , personnel movement, and t o e f f i c i e n t l y supervise product ion r e l a t e d a c t i v i t i e s i n la rge working sec t i on panels.
Wi th in t h e l a s t year, sources o f medium frequency po r tab le rad ios have been i d e n t i f i e d and w i t h i n t h e next one t o two years, these rad ios are expected t o have been c e r t i f i e d and t o become a v a i l a b l e i n t h e marketplace. ( RACAL Model TR58 frm South A f r i c a and a U.S. manufactured r a d i o now i n the product lon pro to type stage sponsored by CONSOL v i a Lee Engineering 1.
The Bureau o f Mines c u r r e n t l y has an RbD program underway t o de f ine mine w i re less system con f igu ra t i ons adaptable t o t rack less haulage mines ( H0366056 ) and planned research r e l a t i n g t o po r tab le and veh icu lar antenna development and coupl ing t o e x i s t i n g mine w i r i n g conductor conf igura t ions .
Th is program accomplishes t h e w i re less t ransmission cha rac te r l za t l on o f low-coal mines and provides a data base which may be used f o r p r e l iminary est imates o f w i re less transmission system requirements.
1.2 PROGRAM OVERVIEW
Measurements were performed i n f i v e ( 5 ) mines i n chronological o rder as fo l lows:
( I ) Decsmberl977, H e l v e t i a Coal Co. Margaret #11 Mine I n Armstrong Co., Pennsylvania - Upper Freeport seam
(a) F i e l d s t reng th vs range and frequency i n I -But t Sect ion - quasi -conductor-f ree
(b) F i e l d s t rength vs range a t 900 KHz i n 2-Butt Sect ion - conductor-proximi t y
(2 ) January 1978, Upshur Coal Corp. Adrian Mine i n Upshur Co., West V i r g i n i a - Upper Freeport seam
(a ) F l e l d s t reng th vs range , and frequency i n area paral l e l t o Road 8 X between 1st R ight and 2nd Right - quasi- conductor-f ree
(3 ) February 1978, Bethlehem Steel Coal Mlne #31 ( Nanty Glo ) i n Cambria Co., Pennsylvania - Lower K i t t ann ing seam
(a) F l e l d s t reng th vs range and frequency I n Main-N area - quas I -conductor-f ree conductor-proximi t y
(b ) F i e l d s t reng th vs range and frequency I n 5-Cross area - quas I-conductor-f ree conductor-proximi t y
( 4 ) February 1978, Bethlehem Steel Coal Mine #38D ( Ehrenfe ld i n Cambria Co., Pennsylvania - Lower Freeport seam
(a ) F l e l d s t reng th vs range and frequency i n I-Right Main-B area - quasi-conductor-f ree
conductor-proximi t y
(5 ) May 1978, Nat ional Mine Corp. St lnson #3 Mlne I n Knot t Co., Kentucky - El khorn #3 seam
(a) F i e l d s t reng th vs range and frequency i n C-Section area - quasi-conductor-free conductor-proximity
1.3 REPORT CONTENTS
Sect ion 2.0 presents an Executive Summary cons is t i ng o f an overview o f t h e r e s u l t s i n terms o f maximum communication range vs frequency p lus s p e c i f i c observations, conclusions, and recomnendaTlons.
Sect ion 3.0 presents t h e Technical Approach consisting o f a desc r ip t i on o f t h e new two-turn rece ive antenna used, d e t a i l s o f t h e data reduct ion process inc lud ing c a l i b r a t i o n , and d e t a i l s concerning t h e comparison o f measured and computed s c a t t e r gains and d e r i v a t i o n o f t he simple s c a t t e r gain formulas.
Sect ion 4.0 presents l ndi v idua l Mine Test Descr ip t joss l n c l uding a sumnary o f r e s u l t s f o r each o f t he f i v e (5 ) mines v i s i t e d .
Appendix presents the compended f i e l d s t reng th curves and mine map t raverses f o r each s e t o f measurement r e s u l t s obtained. These have been ext rac ted from t h e ind i v idua l Summary Data Reports.
2.0 EXECUTIVE SUMMARY
The primary goal f o r t h i s program has been t o expand t h e mine/seam wi re less r a d i o t ransmission data base i n t o a d d i t i o n a l low-coal mines/ seams, wh i l e comparing t h e r e s u l t s f o r consistency w i t h the prevlous EM S i g n a l l i n g program resu l t s . The program work exceeded t h e o r i g l n a l expectat ion o f four mines, four seams, and one measurement sample per mine by p rov id ing data from f l v e mines, four seams, and s i x measurement samples. Q u a l i t a t i v e observat ions o f noise were made along t h e way dur ing t h e program, 'sewchlng f o r no ise cond i t ions which had n o t p rev ious ly been experienced i n high-coal. Quan t i t a t i ve noise measures i n opera t ing mines were n o t poss ib le dur ing the program t ime frame as m s t measurements were made dur ing t h e mine s t r i k e . Th is s h i f t o f emphasis away from q u a n t i t a t i v e nolse t e s t s made it poss ib le t o gather add i t i ona l f i e l d s t rength data, espec ia l l y i n c lose p rox im i t y t o conductors, as we1 i as expanding on t h e mine/seam/ measurement s e t format.
A secondary goal f o r t h i s program has been t o de f ine simple-to- implement measures f o r cha rac te r i z ing p a r t i c u l a r mines and t o expand on the technique(s1 f o r using t h e data base resu l t s , conf ident ly , t o ob ta in system performance est imates based on t h e mine/seam charac ter iza t ions . An important p a r t o f ob ta in ing t h i s goal has been t o v a l i d a t e the concept o f s c a t t e r ga in and t o e s t a b l i s h a simple means f o r measuring it. Once va l ida ted, s c a t t e r gain provides an easy-to-use e m p i r i c a l l y based way t o est imate conductor coupl ing t o rad io f i e lds . Also an important p a r t o f ob ta in ing t h i s goal has been t o ob ta in conductor p rox im i t y data usefu l t o ADL i n t h e i r more r igorous ana lys is o f conductor coupl ing and o f t h e t ransmission modes associated w i t h c u r r e n t t r a v e l l n s along mult i -conductor ensembles.
To provide t h e m s t complete " t o t a l sumnary" o f t ransmlsslon e f f e c t s , t h i s r e p o r t includes the use of data from t h e prpy{oy;i,EM Signal l lng Program and conducti v l t y data der ived from AOL's ' modei i ng eva luat ion o f t h e measured f i e l d st rengths.
2.1 RESULTS SUMMARY
From the measured magnetic f i e l d s t reng th vs range and frequency data, maximum comnunication ranges were computed both I n quasi-conductor- f ree mine areas and i n conductor-proximity s i t u a t i o n s f o r each seam under assumptlons o f both s e t - l i m i t e d no lse and median mine noise. S p e c i f i c c r i t e r i a upon which these computatlons were based are summarized i n t h e nex t subsection.
As was c h a r a c t e r i s t i c o f a l l seams except, perhaps, t h e P i t t sbu rgh seam, a l l measurements ( and, thus,ihe expected performance o f actual radios ) were set-noise- l lml ted when t h e rece ive r was removed one o r more e n t r i e s away from an e n t r y conta in ing conductors. Conversely, t h e received no ise l eve ls i n conductor e n t r l e s are expected t o conform approximately t o median mine nolse. The very few est imates o f noise made c lose t o energized conductors ve r l f l e d t h i s ; however, due t o t h e s t r i k e , determinat ion o f t y p i c a l opera t iona l no lse l eve ls was n o t possible.
The maximum comnunication range i n quasi-conductor-free environments f o r t h e t o t a l data base o f seven seams f o r se t - l im i ted noise and f o r median mine no ise are g iven respec t i ve l y i n F igures I and 2. The comnunication ranges obtained were f a i r l y t i g h t l y grouped; being greater i n value than those f o r t he H e r r i n #6 seam and less i n value than those f o r t h e Pocahontas # 3 seam.
I n se t - l im i ted noise, t h e low-coal mines exh ib i ted maximum ranges o f 180-260 meters a t frequencies l y l n g between 200 and 300 KHz.
I n median mine noise, t h e low-coal mines exh ib i ted maximum ranges o f 115-140 meters a t frequencies l y l n g between 400 and 800 KHz w l t h t h e optimum frequency/range cond i t i ons being q u i t e broad.
These range curves c l e a r l y show the P i t t sbu rgh seam t o be the exception r a t h e r than t h e r u l e for range performance w i t h t h e range being approximately t w i c e t h a t f o r t h e o t h e r seams i n the data base.
The maximum comnunication range i n p rox im i t y t o conductors f o r s i x o f t he seven seams ( ADL data f o r t h e Elkhorn #3 seam was n o t ava i l ab le a t t h e t ime o f t h i s w r i t i n g ) f o r median mine noise i s given I n Figure 3. The t r a n s m i t t e r i s assumed t o be located one e n t r y away from conductors and t h e rece ive r i s assumed t o be located i n t h e conductor en t ry . Here, t he re i s considerable d i f f e r e n c e between t h e values o f range f o r t h e t h r e e displayed low-coal seams. The Upper Freeport seam gives t h e best range o f 890 meters a t 900 KHz and t h e Lower K i t t a n n i n g g ives the poorest range o f 570 meters a t 1150 KHz. With the exception o f t he P i t t sbu rgh seam, t h e Upper Freeport seam gives the best performance o f t h e t o t a l seam set; a l l o the r seams are f a i r l y t i g h t l y grouped a t between 570-670 meters a t from 900-1150 KHz. The range shown i s obs tens ib ly t h e range along t h e conductor s t r i n g w i t h t h e conductor a t tenua t ion assuming a s i n g l e t ransmission l i n e mode ( o r s i n g l e dominant m d e ).
- - > 9 0 ?? w W Z 3 - s= E 5 - a 0 E g
WLO a w 0 z - LO I >
-I w a a 0
3 : Z
0
2 2 i- a K 0 4 - Z W 2 w E K I L L 0 1
5 & 7 .c - 0 X Z
2 8
FIG
UR
E
3 M
AX l
MUM
COM
MUN
l C
AT l O
N R
ANG
E VS
O
PER
AT l N
G
FREQ
UEN
CY
I N C
OAL
M l t
JES
IN P
RO
XIM
ITY
TO
CO
tJD
UC
TOR
(S)
- TX
LO
CAT
ED R
EMO
TELY
- M
ED
IAN
MIN
E N
OIS
E
100
FREQ
UEN
CY
- I(H
Z
The maximum communication ranges i n p rox lm l t y t o conductors f o r t he th ree low-coal seams f o r which data was a v a i l a b l e are given i n Figure 4 f o r se t - l im i ted noise. These ranges were n o t p rev ious l y computed i n high-coal as the u t i l i t y o f t h i s s i t u a t i o n was a t t he t ime questionable. Recently, t h e p o s s i b i l i t y o f an e n t r y c a r r y i n g on ly an AC power cable o r t h e cable p lus a phone l i n e w i t h low nolse i n newer AC n ines has a r i sen so as t o make t h i s a reasonable l i m i t i n g case. The data i s shown assuming t h e t r a n s m i t t e r located both one e n t r y and two e n t r i e s removed from t h e e n t r y c a r r y i n g t h e conductor(s). Jus t as the optimum frequency f o r coup l ing when both t h e t r a n s m i t t e r and rece lve r are c lose t o the conductors i s known t o be lower; so t h e optimum frequency f o r lower noise ( i e g rea te r margin t o accmodate conductor a t tenuat ion) i s a l so lower. For one-entry remoting o f t h e t ransmi t te r , t he maximum comnunication ranges are between 2400-5000 meters a t optimum frequencies ranging between 220 and 350 KHz. For two-entry remoting o f t he t ransmi t te r , t he maximum conununicatlon range l i e s between 470-1050 meters a t optimum frequencies ranging between 220 and 700 KHz. In each case, the Lower Freeport seam provides t h e best range performance.
2.2 TRANSMISSION CHARACTERIZATION
2.2.1 COMPUTATiON CRITERIA 8 TECHNIQUES
The summaries o f maximum comnunicatfon range presuppose values o f rece ive r s e n s i t i v i t y and t ransmi t NIA. The f o l l o w i n g c r i t e r i a have been assumed f o r these summaries based on t h e C o l l i n s mine w i re less (51 pro to type fm rad ios developed f o r t h e Bureau and t h e NBS noise study ( Bu Mines Contract ti0133005 1:
NIA = 2.5, t h e t ransmi t magnetic cu r ren t moment o f t h e r a d l o us ing a loop antenna
Receive s e n s i t i v i t y o f 0.02 microamps/meter f o r 12 dB SlNAD f o r 12 KHz no ise bandwidth
Set-nolse-l imited magnetic f i e l d s t reng th l eve l f o r I2 dB SlNAD given by
where, Af i s t h e 12 KHz bandwidth Q i s t he antenna "Q" made as narrow as poss lb le t o be consistent w i t h transmission; Q = 44 f o r t h e C o l l i n s pro to type fm r a d l o
?, A i s the antenna area = 0.217 mL
N i s t h e no lse f i g u r e o f t h e rece iver = 2 dB f o r t h e C o l l i n s Prototype f m rad lo
Median mine no ise magnetic f i e l d s t reng th l eve l f o r 12 dB SlNAD ( 13.51 dB s ignal-noise-rat lo , Hamshur 1 i s g iven b y
FIG
UR
E
4 YA
XlM
UM
CO
MM
UN
ICAT
ION
RA
NGE
VS
OP
ER
ATI
NG
FR
EQU
ENC
Y IN
CO
AL M
INE
S
IN P
:WX
IMIT
Y T
O
CO
ND
UC
TOR
(S)
- TX
LO
CAT
ED R
EMO
TELY
- SE
T LJ
OlS
E LI
I.?I
T
TX
IJIA
=
2.5
RX
SE
NS
ITIV
ITY
0.
02
uAM
P/M
12
DB
SI N
AD,
BW
= 12
KH
Z C
ON
DU
CTO
R Z
o =
50
OHM
S
- TX
30
MET
ERS
FRO
M C
OND
UCTO
RS
TX 6
0
MET
ERS
FRO
Fl C
OND
UCTO
RS
. .
. ~
'0
100
I 3n0
FREQ
UEN
CY - K
Hz
H~~ = 175.8 - 32.5 loglO f ( h z )
dB above one microamp/meter i n a 12 KHz band
The ranges are then der ived by p i c k i n g o f f t h e ranges from t h e measured data corresponding t o t h e receive noise c r i t e r i a given above. The formula r e s u l t s shown above a re given i n convenient form i n Figure 5.
The sumnaries o f maximum c m u n i c a t l o n range i n p rox im i t y t o conductors f u r t h e r presuppose a coup! i n g t o the conductors o f the r a d l o f i e l d s and an a t tenuat ion r a t e o f t h e coupled c a r r i e r c u r r e n t along the conductor s t r i n g s as w e l l as s p e c i f i c distances o f the t ransmi t and receive antennas from the conductors. The a t tenua t ion constants used are those appropr ia te f o r a s i n g l e l i n e source i n c lose p r o ~ & ~ i t ~ ) t o the roof ( a r f l o w ). U s i ~ q t h e ADL der ived c o n d u c t i v i t i e s ' o f the overburden/underburden; the a t tenuat ion constants glven i n Table I were obtained. Other l i n e parameters assumed were:
where, a i s the spacing from the conductor center t o the rock
ai i s t he conductor rad i us
Z = 50 ohms, the surge impedance o f tRe ~ o s s y t ransmission I I ne
The est imate o f conductor coupl ing i s based on the s c a t t e r ga in r a t l o , which i s t h a t o f t h e f i e l d s t rength a t l h e rece iver w i t h the conductor present t o the f i e l d s t rength a t the rece iver i n absence o f t he conductor. Sca t te r gain has been determined dur ing t h i s program t o be a v a l i d way o f s p e c i f y i n g the coupl ing. For each seam, the computation o f s c a t t e r ga in has been reduced t o the simple formulas g iven i n Table 2. These formulas g ive values w i t h i n 3 dB on average of measured s c a t t e r gain samples.
To ob ta in the f i e l d s t rength a t t he receiver , the computation proceeds as f o l lows;
( 1 ) Choose ranges o f the t ransmi t and receive antennas from the conductor(s)
( 2 ) Obtain t h e magnetic f i e l d s t rength a t the c loses t range between t h e t r a n s m i t t e r and the conductor assuming the conductor i s absent from measured f i e l d s t renqth curves ( o r from ADL m d e l c a l c u l a t i o n s ) for a conductor-free environment
MAGNETIC FIELD STRENGTH IN DB GREATERTHAN 1 *A PER METER
& II, 2 < .& b k 0 0 0 0 0 0 0
I I I I 1 I
- A N
0 - 0 0
I I 1 - - - - -
2
0- O
N-
0 -
P -
"7-
m-
-4 - m- (0 - 2
8- 0
- -
SUMMARY OF SHORT FORMULAS FOR CONDUCTOR ATTENUATION VS COAL SEAM ( BASED ON SINGLE CONDLCTOR GEOMETRY 1
SEAM - FORMULA
PI TTSBURGH d = 0.02665 DB/M @ I MHz
POCAHONTAS #3 = 0.02277 DB/M @ I MHz
HERRIN #6 * = 0.02916 DB/M @ I MHz
LOWER FREEPORT = 0.02130 DB/M @ 1 MHz
UPPER FREEFORT = 0.02171 DB/M @ I MHz
LOWER KI TTANN I NG 4 = 0.02171 DB/M @ I MHz
TABLE 2
SUMMARY OF SHORT FORMULAS FOR SCATTER GAIN CALCULATION VS COAL SEAM
SEAM -
PITTSBURGH
POCAHONTAS #3
LOWER FREEPORT
UPPER FREEPORT
LOWER KITTANNING
FORMULA
(3 ) M u l t i p l y the f i e l d s t rength o f (2 ) by the s c a t t e r gain ( o r add dB ) as computed from Table 2
( 4 ) Subtract the r e s u l t o f (3 ) i n dB from t h e s e n s i t i v i t y level obtained from Figure 5 f o r t he appropr iate type o f noise
(5) Div ide t h e dB magln o f ( 4 ) by t h e conductor a t tenuat ion as computed from Table I . This g ives the range along the conductor s t r i n g .
2 .2 .2 LlTlLlTY OF THE CHARACTERIZATION TECHNIQUE
The arrangements o f conductors encountered i n mine environments are h igh l y var iab le . These impact both t h e coup l ing o f t ransmi t ted rad io f i e l d s i n t o the conductors and t h e propagation o f t he induced c a r r i e r cur rents along t h e conductors. Usual ly, the coupl ing can be measured; i e measured s c a t t e r gain, by t r a n s m i t t i n q from a known usefu l locat ion, measuring t h e f i e l d s t reng th a t a desi red d is tance away from the conductor w i t h a receive loop ( b u t along the sho r tes t d ls tance between the t r a n s m i t t e r and t h e conductors ) and then measuring t h e received f i e l d s t rength again a t the same spacing from the conductors b u t a t a considerable d is tance "down" t h e conductor ( ie , beyond the d i r e c t f i e l d range ) where t h e cu r ren t a t tenua t ion r a t e f l a t t e n s out.
During the program, the st rongest f i e l d s t rength was observed along the sho r tes t path from the t r a n s m i t t e r t o t h e conductor even though the t ransmi t loop was o r ien ted p a r a l l e l t o the conductors. The coupl ing t o the conductors was near optimum because of t h e r e l a t i v e l y good agreement between measured and computed s c a t t e r gains. Th is does n o t i n f e r t h a t t he optimum o r i e n t a t i o n o f t he t ransmi t antenna f o r best coupl ing i s known, however. To assure optimum coupi i ng when measuring s c a t t e r ga in one should begin w i t h t h e "d is tant1 ' measurement o r i e n t i n g t h e t ransmi t antenna f o r optimum coupling; then, keeping t h i s t ransmi t antenna o r i e n t a t i o n constant, nave i n c lose and ob ta in t h e " i n - l ine" measurement o r i e n t i n g t h e receive antenna again f o r optimum coupl ing. This simple technique f o r assessing coupl lng w i l l work and provide meaningful r e s u l t s p rov id ing t h e mine w i r i n g topology does not change between receive measurement locat ions.
Conductor a t tenuat ion may be d i f f i c u l t t o determine i f t h e con f igu ra t i on i s complex. Measurement may be required o f t he a t tenuat ion i n !@eciflc mines r a t h e r than computation t o ob ta in accurate resu l rs . ADL has computed t h e complex propagation constant f o r t y p i c a l mult i -conductor conf igura t ions which lend i n s i g h t t o these p a r t i c u l a r s i t ua t i ons . ADL i s c u r r e n t l y formulat ing a conductor coupl ing model from which t o determine optimum antenna o r i e n t a t i o n s f o r conductor coupl ing. A p a r t i c u l a r s e t o f conductor-proximity measurements made I n the St inson #3 Mine showed t h a t t h e VMD o r i e n t a t i o n produced the greates t coupl ing a t low frequencies o f 200-300 Khz o r less, VMD and both p r i n c i p a l HMD o r i e n t a t i o n s produced near ly equal coupl ing a t 400-500
KHz, and a t 800-900 KHz the HMD o r i e n t a t i o n w i t h t h e loop plane perpendicular t o the conductors was predominant.
2.3 RECOMMENDATIONS
From t h e r e s u l t s o f t h i s program and t h e EM S i g n a l l i n g Program, the quasi-conductor-free t ransmission performance o f w i re less rad io i n most seams i s f a i r l y we l l bounded t o a small reg ion o f optimum ranges and frequencies. Whl l e s c a t t e r ga in seems t o work i n def i n l n g rough coupl ing est imates from a remotely located po r tab le t ransmi t te r , more accdrate coupl ing d e f i n i t i o n from p r a c t i c a l mineworthy antenna mountings t o a v a r i e t y o f usefu l mine w i r i n g topo log ies should be made. Th is i s p a r t i c u l a r l y t r u e f o r t ransmi t locat ions i n c lose p rox im i t y t o t h e conductor ensembles. I n add i t ion , measurements o f a t tenuat ion along a v a r i e t y o f useful mine w i r i n g topo log ies should be made and co r re la ted w i t h ADL theory.
The trpggmission along mine w i r i n g conductor s t r i n g s has been shown by ADL t o be aided by t h e presence o f a dedicated wire. A l te rna t i ve l y , a mine w i r e less r a d i o ys tem could operate w i t h the a i d o f a leaky feeder s p e c i a l l y designed t o provide opt imal coupl ing from a t r a n s m i t t e r i n a p a r t i c u l a r worklng area, c a r r y the c u r r e n t from t h i s area a long d is tance and then " rerad ia te" most of t h e energy over another predetermined working area. The local coupl ing from a remote t r a n s m i t t e r I n t o t h i s type o f conductor should be invest igated.
3.0 TECHNICAL APPROACH
3.1 EMPIRICAL TECHNIQUE
The measuring equipment arrangement was Iden t i ca l t o t h a t used dur ing t h e EMp$jgnal l ing program and described i n Sect ion 3.0 o f t h a t f l n a l repo r t . Again, Singer NM-12 and NM-25 f i e l d s t rength me3ers were used f o r reception. The s ing le- tu rn shie lded coaxia l 0.73 m loop antenna was rewound i n t o two-turns on easy-to-assemble wooden frames t o f a c i l i t a t e physical maneuvering i n low-coal. The new design preserved the antenna reactance so t h a t t h e same coarse tun ing networks could be used. The two-turn loop usage resu l ted i n an approximate 6 dB decrease i n System s e n s i t i v i t y . C a l i b r a t i o n data comparlsons between the one-turn and two-turn loops are given i n Table 3. These comparison d l f f e r e n t i a l s were used t o a d j u s t t h e c a l i b r a t l o n data obtained dur ing the EM S i g n a l l i n g Program t o ob ta in new absolute ca l i b ra t i ons . The two-turn loops were used t o o b t a i n most o f t h e measurements dur ing t h i s program.
The NM-12 f i e l d s t reng th meters were c a l i b r a t e d so t h a t a known inc ldent f i e l d s t rength w i l l produce a readlng o f +25 dB on t h e instrument panel meter w i t h the a t tenua to r i n the -20 dB p o s i t i o n . The NM-25 f i e l d s t rength meters were c a l i b r a t e d so t h a t a known inc lden t f l e i d s t rength w i l l produce a reading of + I0 dB on the instrument panel meter w i t h the a t tenuator i n t h e -20 dB pos i t i on . These known f l e l d st rengths are i n terms o f microvol ts/meter ( t h e plane wave equ iva lent e l e c t r i c f i e l d s t rength ) . As the ac tua l c a l i b r a t i o n was p e r f o r m d using loop antennas, t h e t r u e H c a l i b r a t i o n f i e l d s t rength i s obtained by d l v i d l n g the equ iva lent e l e c t r i c f i e l d s t rength by 377 ohms.
I n reducing t h e f i e l d s t reng th data, t he f i e l d s t rength a t each loca t ion i n dB g rea te r than I microamp/meter was found as the sum o f the meter reading as determined i n dB minus t h e f i e l d s t reng th c a l i b r a t i o n p o i n t i n dB ( + I0 f o r t he NM-25, +25 f o r t he NM-12 p lus t h e a t tenuator range s e t t i n g i n dB p lus 20 dB p lus t h e c a l i b r a t i o n f l e l d s t rength i n dB greater than I microamp/meter p l u s t h e NIA n o n a l l z a t l o n factor . I n equation form, t h i s i s expressed as
F i e l d Strength = analog meter readlng - ( 10 o r 25 + a t tenua to r range s e t t i n g +20 + c a l i b r a t i o n f l e l d s t reng th +
2.5 20 l o g l o Tx cu r ren t x NIA
NIA = 2.04 f o r 7-turn loop below IOOOKHz 1.17 f o r 4-turn loop above 1000 KHz
This equation normalizes t h e NIA t o a standard o f 2.5 which i s representa t ive o f t h e C o l l i n s f m pro to type r a d i o and the o l d e r ECAM am radlo.
The absolute calibrations i n terms o f equ iva lent e l e c t r i c f l e l d st rengths used t o eeduce the data taken du r ing t h i s program are g iven i n Table 4.
TABLE 3
COMPARISON OF ONE-TURN AND TWO-TURN LOOP W ANTENNAS
500 500 500 500
1000 I 000 1000 1000 1500 1500 2000 2000 2000 2000 3000 M O O M O O 3000 4000 4000 4000 4000
RX ANTENNA RELATIVE ANT TYPE (TU WS ) BAND SET # FIELD STRENGTH(DB1
TABLE 4
CALI BR4TION F l ELD STRENGTHS USED DURl NG THE PROGRAM
RX ANTENNA BAND SET #
FREQUENCY KHz
98- 100
2 18-220
252-258
420
440
470-486
470
440
880-900
1750
1850- 1860
1890- 1900
3620-37 I 0
3620
3750
4050
F l tLD STRENGTH bII CROVOLTS/M
549.6
144.0
139.0
128.0
123.9
115.7
88.8
82.8
73.3
43.4
41.4
37.5
22.4
13.3
12.8
11.8
3.2 SYSTEM CALCULATIONS
The c r i t e r i a used t o prepare the maximum communication range summaries are presented i n Sect ion 2.0 and w i l l n o t be repeated here. The comparison o f t he c r i t e r i a used w i t h t h a t expected f o r o the r rad ios is , however, o f i n te res t . The C o l l i n s f m r a d i o c r i t e r i a were used i n t h i s r e p o r t f o r consistence w i t h t h e EM S i g n a l l i n g Program r e s u l t s which, when prepared, were representa t ive o f t he r a d l o parameters expected t o be ava i lab le .
The t ransmi t NiA has, i n a l l cases, byen assumed t o be 2.5. Th is corresponds t o 20 wat ts i n t o a 0.22 m antenna o f 7 tu rns w i th an NA o f 1.52 ( t y p l c a l f o r a po r tab le man-carried antenna 1. Newer rad ios are expected t o be i n the 1-5 w a t t range f o r por tab les and probably SSB where the power r a t i n g i s i n PEP. Normally we t h i n k o f SSB having an approximate 9 dB advantage over am and being aporoximately equal t o fm on a PEP bas is under low b u t i n t e l l i g i b l e signal-to-noise condit ions. The receive system s e n s i t i v l t y o f t h e C o l l i n s f m rece ive r and the new RACAL SSB u n i t a re roughly equal us ing t h e Hamshur c r i t e r i a o f 12 dB SlNAO which was t h e bas is f o r t he r e p o r t summary ca lcu la t ions . This I s shown as
S e n s i t i v i t y , dB above I ua/m ( I ) C o l l i n s fm r a d i o f o r 12 dB
SlNAD 8 2 dB noise f i g u r e @ 520 KHz, 12 KHz BW
(a) Hamshur -34.0
(b) Shimbo -37.6
(c) measured -35.5
(2) RACAL SSB r a d i o 0.2 uv f o r 15 dB S/N For 10 dB S/N -34.9
The conclusion i s t h a t t h e PEP SSB power r a t i n g r a t i o e d t o 20 wat ts gives t h e NIA reduct ion f a c t o r and, hence, t h e t o t a l system comparison o f t he C o l l i n s f m system as analysed here in and new SSB r a d i o systems using t h e same antenna.
3.3 SCATTER GAIN COMPARISONS
Measured s c a t t e r gains f o r t he Upper Freeport and Lower K i t t ann ing seams have been given t o t h e Bureau i n m n t h l y progress repor t s under t h i s program. These were based on t h e f l e l d s t rength i n absence o f t h e conductor being t h a t taken d i r e c t l y from t h e quasi-conductor-free curves i n t h e s a w manner as i f t h e s c a t t e r ga ins were being a n a l y t i c a l l y calculated. Analys is has shown these p rev ious l y reported values t o be i n c o r r e c t as t h e actual measured f i e l d s t reng th a t t h e rece ive r v i a the sho r tes t path between t h e t r a n s m i t t e r and the conductor should have been used. Using these ac tua l measured values o f t h e dominant d l r e c t f i e l d s t rength a t t he rece ive r on t h e " i n - l i ne " path, t he re i s good agreement between measured and computed s c a t t e r gains. Th is a l s o shows t h a t t h e " i n - l inel' measured values were near optimum f o r t h e o r i e n t a t i o n o f t h e t ransmi t antenna employed ( loop plane p a r a l l e l t o the conductors 1. For a c t t ~ a l system estimates, t h e f i e l d s t reng th on the f t i n - l i ne " path was assumed t o be t h a t between coplanar loop antennas. Based on t h e St inson # 3 resu l ts , t h i s p o l a r i z a t i o n w i l l probably produce optimum
24
coupl ing from a t leas t 500 KHz upward i n frequency and t h i s i s i n agreement w i t h p e r i o d i c observat ions made over t h e term o f t h i s program and t h e EM Signal l i ng Program f o r e l t h e r t h e transmitter o r the rece ive r located a t l eas t one e n t r y removed from the conductors.
The s c a t t e r ga in computations i n the data summaries used simple "short formula" expressions for s c a t t e r gain. These were der ived v i a co r rec t i ng t h e " f u l l formula" s c a t t e r ga in expression s l l g h t l y t o be cons is tent w i t h t h e measured s c a t t e r ga in frequency dependence.
The " f u l l formula " Scatter gain is given by
The s c a t t e r ga in was ca lcu la ted using coal seam and rock conduc t i v i t y va l ues de r i ved from ADL mode I i ng and comput i ng oc and (3 from
where, K i s the d i e l e c t r i c constant = 6 C
. dr I s t h e rock conduct1 v i t y
4, i s t h e coal seam conduc t i v i t y
h i s the seam he igh t
The simple "shor t formula" s c a t t e r gains were der ived using t h e form
G = Fl F2
where F expresses t h e frequency dependence o f t h e " f u l l formula" and F2 expresses t h e frequency dependence co r rec t i on t o make the o v e r a l l frequency dependence agree w i t h t h e measured data.
Comparisons o f t h e measured and computed s c a t t e r gains f o r t h e Upper Freeport, Lower Freeport, and Lower K i t t a n n i n g seams are g iven respec t i ve l y i n Tables 5, 6, and 7. These comparisons show good agreement between measured and computed r e s u l t s except i n t h e case o f t h e AC power cable i n t h e Upper Freeport seam ( Margaret 811 1 case. Oddly enough, t h e complex phone l i n e and b e l t support c a b l i n g con f i gu ra t i on gave good r e s u l t s whereas t h e simple conductor d i d not . The on ly conclus ion t o be drawn i s t h a t t h e AC power cable must have been open c i r c u i t e d somewhere i n t h e v i c i n i t y o f t h e measurements so as t o c rea te a h igh surge impedance.
TAB
LE
5
CO
MPA
RIS
ON
O
F M
EASU
RED
8
CO
MPU
TED
SC
ATTE
R
GA
INS
M
ARG
ARET
#
I1 M
INE
- U
PPER
FR
EEPO
RT
SEAM
FU
LL F
OR
4 SH
ORT
FO
RM
MEA
SUR
ED
y(M
) R
R(M
) G
S(D
B)
CA
LCU
LATE
D
ME
AS
/CA
LC
GS
( DB
) C
ALC
ULA
TED
M
EAS/
CAL
C
FRE
Q(K
HZ)
-
GS
(DB
) -
A(D
B)
(DB
)
900
4.3
0.25
-2
6.0
-15.
6 10
.4
NO
TE:
AC
POW
ER
CA
BLE
MUS
T H
AVE
AC
POW
ER
14.0
0.
25
-41.
5 -2
0.7
20.8
BE
EN O
PEN
C
lRC
UlT
ED
NEA
R
CAB
LE
,, TH
E M
EASU
REM
ENT
AREA
ONL
Y 10
.4
3.7
-57.
5 -4
2.8
14.7
I1
28
.4
0.25
-1
8.0
-23.
8 5
.8
-18.
5 0.
5
PHO
NE
LIN
P
25.0
3.
0 -3
9.5
-44.
8 5.
3 -3
9.5
0 8
BELT
,,
w
SUPP
ORT
9.
8 0.
25
-22.
0 -1
9.1
2.9
-13.
9 8.
1 .I
NO
TE:
CA
LCU
LATI
ON
ASS
UM
PTIO
NS
Zo
= 5
0 O
HMS,
F
ULL
FO
RM
ULA
2
5 O
HMS,
SH
ORT
FO
RM
ULA
CO
MPA
RIS
ON
OF
MEA
SUR
ED 8
. C
WP
UT
ED
SC
ATTE
R G
AIN
S
EHR
ENFE
LD #
38 M
INE
- LO
WER
F
RE
EW
RT
SEA
M
FU
LL F
OR
4 SH
OR
T FO
RY
MEA
SUR
ED
CA
LCU
LATE
D
ME
AS
/CA
LC
CA
LCU
LATE
D
y(M
) R
R(M
) FR
EQ4K
HZ)
G
S( D
B)
GS
(DB
) A
(DB
) G
~(D
B)
NOTE
: C
ALC
ULA
TIO
N A
SS
LMP
TIO
NS
h =
1.12
M
4c
= 6
.3 x
?4
iO/M
4 r
= 5.
4 x
MH
O/M
Zo =
50
OHM
S
TAB
LE
7
CO
MPA
RIS
ON
OF
MEA
SUR
ED 8
CO
MPU
TED
SC
ATTE
R G
AIN
S
NA
NN
GLO
#3
1 M
INE
- LO
WER
KIT
TA
NN
ING
SEA
M
FLJL
L FO
RM
SHO
RT
FORM
---
-
MEA
SUR
ED
CA
LCU
LATE
D
MEA
S/C
ALC
C
ALC
ULA
TED
R+
M)
RR
(M)
GS
(DB
) G
S(D
B)
GS
(DB
) - -
A (D
B)
NO
TE:
CA
LCU
LATI
ON
ASS
UM
PTIO
NS
h =
1.04
M
-5
dc
=6
.2
x 10
M
HO/M
4 r =
7.2
x W
O/M
Zo
= 5
0 O
HMS
4.0 INDIVIDUAL MlNE TESTS DESCRIPTIONS
4.1 .,MARGARET # I I MlNE
The Margaret #11 Mine i s i n low-medium coal i n t h e Upper Freeport seam. I n t h e area used f o r t es t i ng , t h e seam was approximately 48-54 inches th i ck . In haulage en t r i es , t h e overburden and underburden have been trenched o u t t o g ive e n t r y he ights o f approximately 6 feet .
Th is mlne i s t h e most product ive one Helvetia/R&P Coal Cos. has and i s a "punch mine" w i t h an expected l i fet ime of rough1 y 5-10 years. A t t h i s locat ion, t he Upper Freeport seam i s about 100-120 f e e t beneath the surface. The mine employs on ly two working sec t ions and th ree mining machines. The mine i s AC w i t h b e l t haulage using t racked support vehic les i n t h e mains and rubber t i r e d veh ic les I n t h e sect ions. I n t h i s mine, the AC power cable i s run i n t h e e n t r y adjacent t o t h e haulage en t ry . The AC power i s 7200 VAC. Both the miner(s) and the s h u t t l e cars operate from stepped-down 480 VAC.
The e n t r i e s are nominal ly 18-20 fee t wide and t h e coal p i l l a r s are nominal l y on 60 f o o t centers. There are pager phones on ly a t t h e sec t ion head and t a i l pieces.
Most o f t h e measurements were performed i n t h e c o n d u c t ~ r - f r e e !-Butt and i n t h e conductor-proximity 2-Butt sect ions w i t h supplemental measurements being performed I n t h e #I malns. The mlne t rave rse topology and t h e measured f i e l d s t reng th data p l o t t e d vs range and frequency are g iven i n Appendix A-I.
Selected observat ions based on t h e reduced data include:
(1 ) The f i e l d v a r i a t i o n near t h e phone l ine/bel tway from a t r a n s m i t t e r located 32 f e e t away due t o i n t e r a c t i o n o f t h e d i r e c t and scat te red f i e l d s was about 5 dB and t h e r i p p l e due t o SWR was about 2 2.5 dB.
(2) The coupled cu r ren t i n t h e phone l i n e / b e l t support cab l ing from a t r a n s m i t t e r located 32 f e e t away was about 15 dB greater i n t h e d i r e c t i o n toward the face than i n t h e d i r e c t i o n toward t h e mains.
( 3 ) I n an e n t r y conta in ing t h e phone l i n e and b e l t support cabl ing, t h e VMD and HMD f i e l d components i n t h e oppos i te r i b plane were o f near-equal amplitue. The r i b plane f i e l d s t rengths were about 15 dB less than those a t c lose p rox lm i t y t o the conductors when t h e t r a n s m i t t e r was 32 fee t away and about 25 dB less when the t r a n s m i t t e r was located 88 fee t away.
(4 ) I n an e n t r y con ta in ing o n l y t h e AC power cable, t h e cable " c a r r i e r " cu r ren t was about 12 dB greater when the t r a n s m i t t e r was located 14 fee t away than when it was located 46 fee t away. The r i b plane f i e l d s t reng th was about 15 dB less than the c lose p rox im i t y f i e l d s t reng th when t h e t r a n s m i t t e r was located 46 f e e t away.
4.2 ADRIAN MlNE
The Adrian Mine i s i n h igh coal i n t h e Upper Freeport seam. I n the area used f o r t es t i ng , t h e seam i s approximately 72 inches t h i c k .
Th is mine, es tab l ished i n 1965, i s o f small-to-moderate size, and i s scheduled f o r another 18-20 years o f l i fe. Th is i s one of t he f a r t h e s t south mines i n t h e Upper Freeport seam. Although t h e overburden i n t h e t e s t area was approximately 300 feet, t h e seam outcrops I n the nearby area. The mine employs cont inuous miners and b e l t haulage, working th ree sec t ions w i t h a product ion o f approximately 94 tons per man s h i f t .
The mine uses t h e room and p i l l a r technique w l t h the p i l l a r s being on 70 f o o t centers i n length and on 50 foo t centers i n width. The e n t r y crossect lonal widths are nominal ly 17 feet . The overburden mate r ia l i s me tawhas ized shale w l t h no draw s l a t e adjacent t o t h e seam. No top coal i s l e f t i n mining. The mine employs t r a c k and t r o l l e y f o r serv ice vehic les. The continuous miners are AC operated a t 2480 o r 1575 v o l t s stepped down from t h e 4160 VACl ine. The s h u t t l e cars are DC operated and t h e r o o f b o l t e r I s AC operated.
A l l measurements were performed I n t h e area p a r a l l e l t o Road 83C between 1st-Right and 2nd-Right w i t h the t ransmi t ,antenna o r ien ted HMD w i t h the loop plane coplanar i n t h e e n t r y crossect ion. The mine measurement t rave rse topology and t h e measured f i e l d s t reng th data p l o t t e d vs range and frequency are given i n Appendix A-2. Only frequencies o f 90 and 220 KHz were used i n t h i s mine.
The data taken I n t h e two e n t r i e s compared w i t h i n 2 dB a t 90 KHz and w i t h i n 5 dB a t 220 KHz a t t h e same range w i t h t h e t r a n s m i t t e r e n t r y having t h e advantage over t h e en t ry two e n t r i e s remved from t h e t r a n s m i t t e r en t ry .
4.3 NANTY GLO MlNE #31
The Nanty Glo #31 Mine i s i n low-medium coal i n t h e Lower K i t t ann ing ( "B" ) seam. I n t h e area used f o r t es t i ng , t h e seam was approximately 39-43 inches t h i c k .
Th is i s a la rge o l d mine ( approximately 50 years ); t h e Main-N and 5-Cross areas o f t h e mine being approximately 16 mi les apar t underground. This s h a f t e n t r y mine maintains 600-900 fee t o f overburden w i t h a substant ia l v a r i a t i o n i n the seam e levat ion . The Leidy Por ta l , i n a va l ley , marks the low p o i n t o f t h e seam and t h e Maln-N area i s r e l a t i v e l y near t h i s p o r t a l . The 5-Cross area i s approximately 900 fee t h igher i n e l e v a t i o n than Main-N and i s near where the seam outcrops on a mountain top.
The mine uses e n t r i e s d r i ven on 60-foot centers ( crosscuts every 120 f e e t i n t h e o l d area ) i n Main-N and on 70-foot centers ( crosscuts every 100 f e e t ) i n 5-Cross. The e n t r y widths are 18 feet. The roof i s hard rock and i s f l a t ; t h e best roo f t h e author has ever experienced. No top coal i s l e f t i n mining.
This mine provided t h e equ iva lent o f two mines worth o f data due t o t h e wide separat ion o f measuring locat ions. Although both quasi-conductor-free and conductor-proximity data were taken i n t h e Main-N area, on l y t h e quasi-conductor-free data was conclusive. This data was "dearly won" for t h e f l o o r had heaved and the data was gathered w i t h o n l y 2-3 f e e t o f head clearance. Both quasl- conductor-free and conductor-proximity data were oathered i n t h e 5-Cross area. The t e s t t rave rse and reduced data are g iven i n Appendix A-3.
Selected observat ions based on t h e reduced data include:
( I ) The l i m i t e d conductor p rox im i t y data taken i n t h e Main-N area show comparable coupled f i e l d s t reng th l eve ls along e n t r y centers a t 218 KHz i n both power cable and b e l t en t r i es . I n the power cab le entry, t h e coup led f i e l d s t reng th i s about 5 dB more a t 480KHz than a t 218 KHz and about 22 dB more than a t 3620 KHz.
(2 ) I n t h e 5-Cross area very c lose t o t h e power cable, t h e optimum coupled f i e l d s t reng th appears t o be i n the 1860-4050 KHz range (approximately 10 dB greater than a t 890 KHz ) wh i l e I n the r l b plane, t h e f i e l d st rengths seem t o be much lower w i t h the pu re l y coupled f i e l d s t reng th condition n o t being obtained.
( 3 ) Pursuant t o (2), t he re appears t o be an e f f e c t a t h igher frequencies which produces a p e r i o d i c v a r i a t i o n I n f i e l d s t reng th w i t h d is tance along t h e power cable e n t r y r i b plane.
4.4 EHRENFELD #38D MINE
The Ehrenfe ld #38D Mine i s i n low-medium coal I n the Lower Freeport ( "D" ) seam. I n t h e area used f o r t es t i ng , t h e seam was approximately 42-46 inches th i ck .
Th is d r i f t mine, es tab l ished i n t h e l a t e 1950ts, i s o f m d e r a t e s i z e w i t h several seams being mined. Current ly , most o f t h e product ion comes from t h e "D" seam; an operat ion t o mine t h e Upper Freeport ( "E"
seam i s j u s t beginning. Th is mine employs conventional mining sec t ions w i t h b e l t haulage. I n the t e s t area, t h e overburden level was approximately 250 feet.
The mine uses t h e r o o m and p l l l a r technique w i t h t h e p i l l a r s being on 100 f o o t centers I n length and on 70 f o o t centers I n width. The e n t r y crossect ional widths are nominal ly 18 feet . The power cable e n t r y used f o r t h e conductor-proximity t e s t i n g contained on ly t h e 4160 VAC cable suspended beneath a 3/8 " stranded s t e e l messenger cable.
A l l measurements were performed i n the I-Right Main-B area w l t h the t r a n s m i t t e r i n a f i x e d locat ion. Quasi-conductor-free measurements were made i n t h e en t ry conta in ing t h e t ransmi t te r . Conductor-proximity measurements were made i n t h e adjacent power cab le entry. The t e s t t rave rse topology and t h e measured f i e l d s t reng th data p l o t t e d vs range and frequency are g iven i n Appendix A-4.
Selected observat ions based on the reduced data l n c l ude:
( I ) The optimum coup1 lng frequency observed i n t h e r i b plane was about 470 KHz.
(2 ) Optimum coupl ing immediately adjacent t o t h e AC power cable appears t o be between 470 and 880 KHz.
(3 ) A t 200 KHz, the coupled f i e l d s t reng th i s 10-15 dB below t h e optimum coup led resu l t s .
4.5 STINSON #3 MINE
The Stinson # 3 Mine i s i n low-medlum coal i n t h e Elkhorn # 3 seam. I n the area used f o r t es t i ng , t h e seam was approximately 50-56 inches t h i c k .
This i s a small d r i f t mine and i s one o f a connected s e t o f mines i n the i m e d i a t e area; serv iced v i a separate power systems and separate p o r t a l s t o f a c i l i t a t e operation us In@ b a t t e w operated serv ice veh i c les , accomodate t h e mountainous ' to~ography, and minimize b e l t - t o - t i p p l e runs. This seam i s one o f seven Elkhcrn seams ( numbered from the bottom up ) and stacked approximately 60 fee t apart. E x i s t i n g leases I n t h e area w i l l permi t Nat ional Mine Corp. t o cont inue opera t ion I n t h e h i g h l y product ive #3 seam alone f o r 20-30 years. Th is mine employs conventional mining sect ions w( th b e l t haulage. I n the t e s t area, the overburden was approximately 500 fee t t h i c k and about 100 f e e t t h i c k a t t he C Sect ion face ( outcropped Just before our t r i p ) ,
The mlne uses t h e room and p i l l a r technique w i t h t h e p i l l a r s being on 60 f o o t centers ( nominal ly 38 f o o t p i l l a r widths and are roughly square. The mine i s n o t p l l l a r e d I n r e t r e a t mlning due t o the intended mining o f t he o the r seams. The p i l l a r s i n these f u t u r e mines w i l l be made t o co inc ide v e r t i c a l l y w i t h the p i l l a r s i n t h e c u r r e n t l y mined areas.
The overburden/underburden cons is ts o f approximately l i f e e t o f shale on t h e r o o f / f l o o r fo l lowed by sandstone.
This mine runs a l l conductors i n the b e l t en t ry : t he 4160 VAC power cable l i e s on t h e f l o o r . A l l se rv i ce vehic les are b a t t e r y operated and a re o f t he a r t i c u l a t e d var ie ty .
A l l measurements were performed i n C-Section o f t h i s mlne. The quasi-conductor-free measurements were made i n an e n t r y t h r e e e n t r i e s removed from t h e conductor en t ry . Conductor-proxlmlty measurements were made both from a remote t r a n s m l t t e r ( same locat ion as f o r t h e quasi-conductor-free t e s t s ) and from a t i g h t l y coupled t r a n s m i t t e r f o r t h e coupled f i e l d p o l a r i z a t i o n measurements. The t e s t t rave rse topology and the measured f i e l d s t rength data p l o t t e d against range and frequency are g iven i n Appendix A-5.
Selected observat ions based on t h e reduced data include:
( I ) Conductor-proximity measurements show:
VMD p o l a r i z a t i o n t o be predominant a t low frequencies
HMD p o l a r i z a t i o n w i t h t h e loop plane perpendicular t o t h e conductors t o be predomi nant a t h igher frequencies
A l l p o l a r i z a t i o n s produce nea r l y equal f i e l d s t rengths a t 486 KHz
A pronounced n u l l , j u s t o f f t h e loop-plane-paral lel d i r e c t i o n i n t h e HMO p o l a r i z a t i o n
The best coup l ing frequency t o b e . t h e h ighes t used; 890 KHz.
APPEND l X
MINE TEST DATA - - -
This Appendix g ives t h e mine maps and summary f i e l d s t rength reduced data se ts from each o f t h e f i v e Sumnary Data Reports prepared dur ing t h i s program. For add i t i ona l in format ion regarding a p a r t i c u l a r mlne, t h e reader i s r e f e r r e d t o the p a r t i c u l a r Summary Data Report f o r t h a t mlne.
The in format ion i n t h i s Appendix i s organized as:
A- 1 Margaret "I I Mine A-2 Adrian Mine A- 3 Nanty Glo #31 Mine A-4 Ehrenfe ld #38D Mine A- 5 St inson #3 Mine
The p a r t i c u l a r references f o r t h e f i v e Summary Data Reports a re given as References ( 10) th'rough ( 14).
A- l
MARGARET # I I TEST DATA AT MEDIUM FREQUENCY
W z W W Z K - 5 ZE ul a -
4 F Z G 0
0 - I- Zt- W
W a 0 K LL w a S 2" - O t - a LL -t- z + 3
a m - 0 1 0 0 - 0 2 z --I
L L - a W O t-a 0
k 2 a z o - 2 L a > LL -I t- W
I . > a 0 J 0 a 0 t-
TRAN
SMLT
TER
L0
CAT
I:ON
TN
C
RO
SSC
UT
BETW
EEN
B
ELT
AND
PO
WER
CAB
LE.
EN
TRIE
S
TRAN
SMLT
TER
LO
CAT
[,ON
AT
BA
RR
IER
AD
JAC
ENT
TO
POHE
R C
AB
LE E
NTR
Y
OWER
C
AB
LE E
NTR
Y
FlG
UR
E
A3
MI~
NE
!IAF
SHO
WLN
G
TOPO
LOG
Y,
TRAN
SMI.T
TER
LO
CAT
ION
S,
AND
MEA
SUR
EMEN
T S
TATI
ON
S A
LWc
BE
LT E
F_?IT
PY
FOR
CO
ND
UC
TOR
-PR
OXI
MIT
Y M
EASU
REM
.ENT
S IN
2-B
UTT
S
EC
TIO
N A
ND
#I.
MAI
.NS
- TO
WAR
D PO
RTA
L
HE
LVE
TI'A
C
OAL
CO
. M
ARG
ARET
#I1
MIN
E
FIG
UR
E
A4
MA
GN
ETI
C
FIE
LD
STR
ENG
TH V
S RA
NGE
IN
CO
FID
UC
TOR
-FR
EE
I-B
UTT
S
EC
TIO
N O
F
HE
LVE
TIA
CO
AL C
O.
MAR
GAR
ET #
I I
MIN
E
NIA
= 2
.5
DAT
A TA
KEN
IN
EN
TRY
CO
NTA
ININ
G T
RA
NS
MIT
TER
CO
FLAN
AR H
MD
OR
IEN
TATI
ON
OF
ANTE
NN
AS
0
20
40
60
80
100
120
I40
RANG
E FR
OM
TR
AN
SM
ITTE
R -
MET
ERS
FIG
UR
E
~5
MA
GN
ETI
C F
IEL
D S
TREN
GTH
VS
RANG
E IN
CO
ND
UC
TOR
-FR
EE
I-B
UTT
S
EC
TIO
N O
F
HE
LVE
TIA
CO
AL
CO.
MAR
GAR
ET
#I
I M
INE
NIA
=
2.5
DA
TA T
AK
EN
ON
E P
AR
ALL
EL
ENTR
Y R
EMO
VED
FRO
M E
NTR
Y C
ON
TAIN
ING
TR
AN
SM
ITTE
R
CO
PLAN
AR H
MD
OR
1 EN
TAT
I ON
OF
ANTE
NN
AS
0 2
0
40
60
80
10
0 12
0 1 4
0
RAN
GE
FRO
M T
RA
NS
MIT
TER
- M
ETER
S
FIG
UR
E
A6
MA
GN
ETI
C F
IELD
STR
ENG
TH Y
$ R
ANG
E AL
ONG
B
ELT
EN
TRY
IN 2
4T
T S
EC
TIO
N O
F H
ELV
ET
IA C
OAL
CO
. M
ARG
ARET
#
II
MIN
E @
90
0 KH
z W
ITH
TR
AN
SM
IT
LOO
P LO
CAT
ED
It
EN
TRIE
S
AWAY
N
IA =
2.
5
DAT
A TA
KE
N A
LONG
PH
ON
E LI
NE
/BE
LT
SUPP
OR
T C
AB
LIN
G
IS
FOR
MAX
IMU
M
FIE
LD S
TREN
GTH
AD
JAC
ENT
TO
LIN
E/C
AB
LIN
G
TX
ANTE
NN
A LO
OP
PLA
NE
OR
IEN
TED
PA
RA
LLE
L TO
EN
TRY
CA
BLE
CR
OSS
ES
RY @
W
WER
C
ENTE
R
0 10
0 20
0 ;O
O 40
0 5
00
DIS
TAN
CE
ALO
NG
BE
LT E
NTR
Y -.
MET
ERS
PP
MAGNETIC FLELD STRENGTH IN 08 GREATER THAN 1 MICROAMP PER METER
I - + - + + + + + o N w e cn (3, CI 0 0 0 0 0 0
? 0 0 0 0 in M N - 0
7 + + + 0 +
t1313W t13d dWVOtl31W I NVHl t131V3t13 Ba NI H13N3HlS 01314 3113N3VW
46
A-2
ADRIAN MINE TEST DATA AT MEDIUV FREQUENCY
MAG
NET
IC
FIE
LD
STR
ENG
TH V
S RA
NGE
IN C
ON
DU
CTO
R-F
REE
AR
EA
PA
RA
LLE
L TO
R
OAD
83C
BETW
EEN
IS
T-R
IGH
T AN
D 2
ND
-RIG
HT
63 90
KHZ
FOR
NIA
= 2
.5
....
....
....
....
....
....
....
....
....
...
UPS
HU
R C
OAL
S CO
RP.
AD
RIA
N
MIN
E
----
----
---
----
- R
EC
EIV
E A
NTE
NN
AS O
RIE
NTE
D H
MD
WIT
H
LOO
P P
LAN
E O
F TR
AN
SM
IT 8
R
EC
EIV
E A
NTE
NN
AS
PA
RA
LLE
L
RAN
GE
FRO
M T
RA
NS
MIT
TER
- M
ETER
S
A- 3
NANTY GLO #31 MINE TEST DATA AT MEDIUM FREQUENCY
0 5: 3 $I 0 0 - 0 - 0
I p N 0 N + + + + + I I
$: I
t1313W t13d dWVOt131W I NVHl t131V3t13 €la NI H13N3HlS a131d 3113N3WW
54
FIG
UR
E
A16
MAG
NET
IC F
IEL
D S
TREN
GTH
VS
RANG
E AL
ON
G C
ENTE
R O
F PO
WER
CA
BLE
OR
BE
LT E
NTR
IES
,
AS
NOTE
D,
TRA
NS
MIT
TER
LO
CAT
ED O
NE
ENTR
Y RE
MO
VED
FRO
M P
OW
ER C
AB
LE E
NTR
Y AN
D
TWO
EN
TRIE
S R
EMO
VED
FRO
M B
ELT
EN
TRY,
TR
AN
SM
IT A
NTE
NN
A LO
OP
PLA
NE
PA
RA
LLE
L TO
E
NTR
IES
..
....
....
....
....
..
BETH
LEH
EM S
TEE
L C
OAL
MIN
E N
ANTY
GLO
#3
1 M
AIN
-N
AREA
..
....
....
....
....
..
RE
CE
IVE
AN
TEN
NA
OR
IEN
TED
WIT
H L
OO
P P
LAN
E H
MD
AND
PA
RA
LLE
L 7 ;O
EN
TRY
Dl H
ECT
ION
DIS
TAN
CE
ALO
NG
PO
WER
CA
BLE
OR
BE
LT E
NTR
IES
- M
ETER
S
2 4 " I
- 9 4
G Z
I W 1 Z
W 0 W W O > + Z I- Z a > I Z I r a w a
a I Z I
> W a 1 w 1 %
2 x E 2 l Z l ? 5 = I - - < - 1 5 1 -
J I-
z II a V W x " Y 1 4 1
a V) I- a z
I- a $ 1 8 1 - w In V 0 Z -
I I J I LT o w n w -1 W I W I
0
W a - I- n - L a "Y I LL I W I I x
ZZ U O I - W - CL
I- - 4
L S 5 5 z z n z I W Z
4 3 L a
a 0 Z U I - ul E?
W Z a Z W 0 01 y 1 a ;a#", [ L a V) t- 0 1 s Z W 0 1 0
W t- I
2 2 I m
m W I - a 2 0 - 1 I K I
J* (L Z l 0 W 4 3 a 1 2 0 a W I
w Z >
LL a l l - O & l Z W Z Z ~ I
5 8 W
C" a - 1 ' 5
a m 4 1 Z - 2 1 2
W w z a
W I O
5 9 5 i l 0 - 3 ' , i L a b W
w E ' 5 W V ) I Z Z I U ~ I W = ( L I V)
c l y ' I W I W + t - m 9 E 1 W Z I 01 V) t - Z I V) a
(L I 0 C
A-4
EHRENFELD #38D MINE TEST DATA AT MEDIUM FREQUENCY
FIG
UR
E
A21
MAG
NET
IC
FIE
LD
STR
ENG
TH V
S RA
NGE
IN Q
UAS
CO
ND
UC
TOR
-FR
EE
I-R
IGH
T M
AIN
B
FRES
H A
IR
ENTR
Y C
ON
TAIN
ING
TR
AN
SM
ITTE
R
- --
----
----
BE
THLE
HEM
STE
EL
CO
AL M
INE
EH
REN
FELD
#3
8(
----
----
----
N
IA =
2.5
CO
PLAN
AR H
MD
OR
IEN
TATI
ON
OF
ANTE
NN
AS
0 20
40
6
0
80
100
RANG
E FR
OM T
RA
NS
MIT
TER
- M
ETER
S
m LT
L L 1 ? Z O N , W > I1 0 x 4 I-- W - I I r z 2 * rr (L 1 I - - w - z J u r n -
a 0 W U - Z m 0 0 CI
k 9 W J - I 1 0 1 m w -I a A I W I 0 1 LL a 1 2 1
' U L T L L W N W 4 IIrI 4 3 a I
& w I W I
W Z I W I L T w 4 Z 3 Z J I - l - 9 n l = , L e a J
0 1 4 1 w o 0 a J 1 0 1 Z
a 1 -11 Li!z w Z I W I
( O W I-- > t- I ( O 1
Z I 4 1 x 1 t- W a I - - 1 x 1 2 - W
t3 I-- W '. - LT LL W
U E - - kt 5 Z Z
I-
FIG
UR
E
A23
MA
GN
ETI
C F
IEL
D S
TREN
GTH
VS
RAN
GE
ALO
NG
R
IB P
LAN
E O
F PO
WER
C
AB
LE
ENTR
Y,
ONE
EN
TRY
REM
OVE
D FR
OM
TR
AN
SM
ITTE
R;
TRA
NS
MIT
AN
TEN
NA
LOO
P P
LAN
E
PA
RA
LLE
L TO
C
AB
LE
NIA
= 2
.5
----
----
----
----
B
ETH
LEH
EM
STE
EL
CO
AL
MIN
E
EH
RE
NFE
LD #
38
(D)
I-R
IGH
T
MA
IN B
0 20
4
0
60
8
0
100
120
140
160
I 80
DIS
TA
NC
E A
LON
G
POW
ER
CA
BLE
EN
TRY
- MET
ERS
A-5
STINSON # 3 MINE TEST DATA AT MEDIUM FREQUENCY
Z - a 5" 3 k - mu)
W
PI- I- 5 z ,= [La 4 N W - Z [L
4 W J ZO -a r > ml- *- I
8 z " Z & -a
-J t;& N 0 4 Zi- 2 2 2 3 i-0 u $ 2
Z " 8
- 2 - n 4
a 0 lI L - M - m 3 Z
CO V) 0 I -
I 4-
x + - 0
p' @ 5
V) V) Z Z I
" -9 0 0 --- kn",
W W I -
5 2" 1 I- V)
I- +o k L p W7m-l 4 z - -- LL V) >
z I- V) w u -
V) + z n z + V) V) - k- - V ) + W z X w m I - i- w
I- 2 M9@ * a a
J 0 I
sY f= ,= Z W L L
L - a 0 Z 0
I Z N g 2 n - - O X ( L n -+I N + a n 5 a 'ooz
3 a o 0 0 n I L E 5-l" z LL 3 - 2 0
8 P Z L E Z % z - W7<w m a - I- w 5 0'2 0 V)
0 u L L LLod l .. a o n LL n W O
zV)+ ZI P o n u
- W 3
z 2 + > a 0 0 - % S 5 5 a I- y 2 u -I- - " n Z Z V)
9 c - W 4 x z x n O W 0
I n p' V) 3 E , - a Ln 4
a W 5 - z I
2 s u W I 2 +
F 2 - - z 3
I - In I . Y Z S a 2 2 0 " Z s ;* z W
W o z I- a m w o 5 z a 3 > m v ) 4 W (3 - Z N +
s o - L + L I- + 11 0-
(3 l v ) r Z a zv) w a . - 0 Z
F&!S - a I n 4 0 u
!? E I-
0 W Z W - I W W W I WKZ - L - L I Z
2'- 0 (3
z a - 0g-I u z i k g Z-
z n - G Z t -
4," C = 0 0 9 8 5 o u
0 20
40
60
80
100
120
140
160
180
200
220
RANG
E - M
ETER
S
MA
aJE
TlC
FIE
LD S
TREN
GTH
VS
RANG
E AW
AY
FRO
M C
OND
UCTO
RS
( R
EFER
ENC
ED T
O V
IRT
UA
L TR
ANSM
IT
ANTE
NN
A LO
CA
TIO
N
) O
N TR
AVER
SE
PE
RP
EN
DIC
ULA
R T
O C
OND
UCTO
R EN
TRY
- 8
25
8 K
Hz
FOR
THR
EE O
RTH
OG
ON
AL
RE
CE
IVE
AN
TEN
NA
PO
LAR
IZA
TIO
NS
N
IA =
2.
5
10
20
3
0
RANG
E - M
ETER
S
MAG
NET
IC F
IEL
D S
TREN
GTH
VS
RANG
E AW
AY
FRO
M C
ON
DU
CTO
RS
( R
EFER
ENC
ED T
O
VIR
TU
AL
TRAN
SMIT
AN
TEN
NA
LOC
ATI
ON
O
N TR
AVER
SE
PE
RP
EN
DIC
ULA
R T
O C
OND
UCTO
R EN
TRY
@ 48
6 KH
Z FO
R T
HR
EE O
RTH
OG
ON
AL
RE
CE
IVE
AN
TEN
NA
PO
LAR
IZA
TIO
NS
N
IA =
2.
5
20
30
RANG
E - M
ETER
S
MAG
NET
lC F
l ELD
STR
ENG
TH V
S R
AN
E A
WAY
FR
OM
CO
ND
UC
TOR
S (
REF
EREN
CED
TO
V
l RTU
AL
TRA
NS
MIT
AN
TEN
NA
LOC
ATI
ON
)
ON
TRAV
ERSE
P
ER
PE
ND
ICU
LAR
TO
CO
ND
UC
TOR
EN
TRY
@ 89
0 K
Hz
FOR
THR
EE O
RTH
OG
ON
AL R
EC
EIV
E A
NTE
NN
A P
OLA
RIZ
ATI
ON
S
NIA
= 2
.5
20
30
RANG
E - M
ETER
S
REFERENCES
( I ) T.S. Cory, " Propagation o f EM Signals i n Underground Mines", C o l l i n s Radio Group, Rockwell I n te rna t iona l Corporation, F ina l Report, Bureau o f Mines Contract H0366028, September 1977.
(2 ) T.S. Cory, " In -S i tu Measurement o f Coal Seam Conduct iv i ty Using a Paral l e l W i r e Transm1.ssion Line Method", Col l i n s Groups, Rockwell I n te rna t iona l Corporation, Special Technical Report, Bureau o f Mines Contract H0377053, 18 May 1978.
(3 ) R.L. Lagace, A.G. Emslie, M.A. Grossman, "Vode l l ing and Data Analysis o f In-Mlne Electromagnetic Wave Propagation", Ar thur D. L i t t l e , Inc., I n t e r i m Report, Task Order #4, Bureau o f Mlnes Contract H0346045, May 1978.
(4 ) R.L. Lagace, A.G. Emsl ie, "Analysis o f MF Propagation Data from Margaret # I I, Nanty Glo, Ehrenfeld, And Adrian Coal Mines", Ar thur D. L i t t l e , Inc., Working Memorandum, Task Order 64, Bureau o f Mines Contract H0346035, May 1978.
(5) R.P. Decker, "Research and Development Contract f o r Coal Mlne Communication System, Vol. 3 Theore t ica l Data Base", C o l l i n s Radio Co., F ina l Report, Bureau o f Mines Contract H0232056, Sect ion 6 pp 6-1 t o 6-30, 15 November, 1974.
Summarizing:
( A ) W. Bensema, M. Kanda, J.W. Adams, "Electromagnetic Noise i n Robena #4 Coal Mine, NBS Technical Note 654, A p r i l 1974, ( work performed under Bureau o f Mlnes Contract H0133005 ).
(0 ) J.W. Adams, W.D. Bensema, M. Kanda, Electromagnetic Nolse i n Grace Mlne", NBSlR 74-388, June 1974, Bureau o f Mines Contract H0133005.
(C) M. Kanda, J.W. Adams, W.D. Benserna, "Electromagnetic Noise i n McElroy Mine", NBSlR 74-389, June 1974, Bureau o f Mlnes Contract H0 133005.
(D) W.D. Bensema, M. Kanda, J.W. Adams, "Electromagnetic Noise i n ltmann Mine", NBSlR 74-390, June 1974, Bureau o f Mines Contract H0 133005.
(E l W.W. Scott, J.W. Adams, W.D. Bensema, H. Dobroski, "Electromagnetic Noise i n Lucky Fr iday Mine", NBSlR 74-391, October 1974, Bureau o f Mlnes Contract H0133005.
(6 ) Loc. Ci t. R.L. Lagace, A.G. Ems l le, M.A. Grossman.
(7 ) Loc. C i t . R.L. Lagace, A.G. Emslie.
(8) A.G. Emslie, R.L. Lagace, R.H. Spencer, P.F. Strong, "Theory o f t h e Dedicated Wire as a Means o f A ld ing Propagation on a T r o l l e y Wire", Ar thur D. L i t t l e , Inc., Working Memorandum 1-8, Bureau o f Mlnes Cont rac t H0346045.
( 9 ) Loc. C i t . A.G. Emslie, et .a l .
( I0)T.S. Cory, "Electromagnetic Noise 8 Propagation I n Low-Coal Mlnes, Sumnary Data Report - I, H e l v e t i a Coal Co. Margaret # ! I Mine", C o l l i n s Groups, Rockwell l n te rna t l ona l Corporat ion, Bureau o f M i nes Contract H0377053.
(1I)T.S. Cory, "Electromagnetic Noise & Propagation I n Low-Coal Mines, Sumnary Data Report - 2, Upshur Coals Corporat ion Adrian Mine". C o l l i n s Groups, Rockwell I n t e r n a t i o n a l Corporat ion, Bureau o f Mines Contract Ho377053.
(12)T.S. Cory, "Electromagnetic Noise & Propagation i n Low-Coal Mines, Sumnary Data Report - 3, Bethlehem Stee l Coal Mine #31 Nanty Glo", C o l l i n s Groups, Rockwell I n te rna t i ona l Corporation, Bureau o f Mines Contract H0377053.
(13)T.S. Cory, "Electromagnetic Noise & Propagation i n Low-Coal Mines, Sumnary Data Report - 4,Bethlehem Steel Coal Mine #38D Ehrenfeld", C o l l i n s Groups, Rockwell l n t e r n a t l o n a l Corporat ion, Bureau o f Mines Contract H0377053.
(14)T.S. Cory, "Electromagnetic Noise & Propagation I n Low-Coal Mines, Sumnary Data Report - 5, Nat ional Mine Corp. St lnson # 3 Mine", C o l l i n s Groups, Rockwell l n t e r n a t l o n a l Corporation, Bureau o f Mines Contract H0377053.
PREPARED FOR:
SPECIAL TECHNICAL REPORT . . . . . . . . . . . . . . . . . . . . . . . IN-SITU MEASUREMENT OF COAL SEAM CONDUCTIVITY
USING A PARALLEL WIRE TRANSMISSION LINE METHOD
Technlque Development
Technique App l i ca t i on i n Two Mines
PREPARED BY:
Col l i ns Groups Rockwe I I In te rna t i ona l Corporat ion 400 C o l l i n s Road N.E. Cedar Rapids, Iowa 52406
Under: Bureau o f Mines Contract ~0377053 Ter ry S. Cory, P.E. Subcontract C-651672
Te r ry S. Cory, P.E. 2857 West. Mount Vernon Road S.E.
18 May 1978
1.0 INTRODUCTION
The conduc t i v i t y of coal seams g r e a t l y a f f e c t s t h e a b i l i t y t o t ransml t
r a d i o waves underground t o any s i g n i f i c a n t distance. Recent F ie lds t reng th
measurements and t e s t i n g o f two-way rad ios a t medium frequency i n coal
mines under Bu Mines sponsershi p have demonstrated comnun l c a t l on ranges
as great as 1600 f e e t ( i n t h e P i t t sbu rgh seam ) and as l i t t l e as 400 f e e t
( i n t h e H e r r i n #6 seam and o the rs ) i n areas w i thout conductors. The
d i f f e rence i n range i s due i n p a r t t o d i f f e rences i n coal seam conduc t l v l t y
i n the "para1 l e l p l a t e wavegul de " formed by t h e seam sandw l ched between
t h e overburden/underburden rock.
Two-way rad io t ransmission a t medium frequency i s expected t o have a
s i g n i f i c a n t impact on f u t u r e underground coal mine operat ions I n some
mines. The design o f systems embodying t h i s type o f transmisslon w i l l
r equ i re a knowledge o f coal seam conduc t i v l t y ( as we l l as, f o r t h a t
matter, overburden/underburden c o n d u c t i v i t y and a means t o simply
ob ta in it i n p a r t i c u l a r mines.
Th is repo r t presents the r e s u l t s o f i n - s i t u c o n d u c t i v i t y measurements
i n two seams employing a simple empi r ica l technique which may have wide
appl i cab i l i t y i n the future. The r e s u l t s o f these measurements conf i rm
t h e low conduc t i v i t y values expected based on computer model ing ana lys is
o f extensive f i e l d s t r e n g t h measurements by ADL.
Previous measures o f coa l seam canduc t l v i t y have been made la rge ly on
samples anaiysed i n t h e l l a b o r a t o r y f o l l o w i n g removal frm t h e mine.
These r e s u l t s suggest t h a t t h e conduc t i v i t y i s a s t rong func t ion of
frequency down t o a t leas t I MHz, i s s t rong ly a f fec ted by water and ash
content, and cou ld be i n t h e lo-* t o mho/meter range. The i n - s i t u
est imates o f coal seam conduc t i v i t y der ived from t h e f i e l d s t reng th
measurements suggest t h a t t h e conduc t i v l t y i s a t m s t weakly dependent
on frequency i n t h e medium frequency range. The r e s u i t s reported here in
support t h i s suggestion.
The technique fo r conduct iv i ty determination involves measurement o f
the open and short c i r c u i t impedance magnitudes o f a pa ra l l e l wire
transmission l i n e i n close proximity t o the coal using two pieces o f
simple bat tery operated equipment, a current probe, and the transmission
l ine. This data i s eas i l y reduced t o provide a measure o f the normallzed
phase constant along the l i n e as a function o f frequency. The
conduct iv i ty i s then determined by f i t t i n g the measured data wi th a
computed curve; the algorithm, f o r which, i s a function o f conductivi ty.
The accuracy o f the resu l ts are not s i gn l f l can t l y dependent on the
precise spacing o f the t e s t l i ne from the coal.
The technique has been demonstrated t o be e f f ec t i ve f o r use i n both
conventional and continuous mining sections.
The resu l ts reported herein were obtained i n March, 1978 i n the
Bethlehem Steel Coal Mine( Ehrenfeld)#38D ( Lower Freeport seam ) I n
Cambria County Pennsylvania, and i n May 1978 i n the National Mine Corp.
Stinson #3 Mine ( El khorn 13 seam ).
2.0 SUMMARY
The r e s u l t s o f t h e t e s t i n g reported here in a re s i g n l f l c a n t i n two
areas; namely, t h e technique - i t s applicability and accuracy, and
t h e r e s u l t s themselves - t h e i r values and frequency dependence.
2.1 MEASURED RESULTS
( I ) The c o n d u c t i v i t y i n t h e Lower Freeport seam data sample i s
est imated t o be 1.05 x mho/meter 2 10% and essent la l l y
Independent o f frequency. The coal seam r e l a t i v e d i e l e c t r i c
constant i s est imated t o be about 2.3.
(2) The r e s u l t s o f ( I ) are app l i cab le over t h e frequency range o f
a t l e a s t 100-600 KHz.
( 3 ) The c o n d u c t i v i t y i n t h e Elkhorn #3 seam data sample i s est imated
t o be ).7 x mho/meter - + 10% and essen t ia l l y independent o f
frequency. The coal seam r e l a t i v e d i e l e c t r i c constant I s
est imated t o be about 2.0.
(4 ) The r e s u l t s o f ( 1 ) a re app l i cab le over t h e frequency range o f
a t l eas t 100-800 KHz.
2.2 MEASUREMENT TECHNIQUE
( 1 ) The dynamic frequency range o f measurement i s between some low
frequency ( t y p i c a l l y 80-100 KHz f o r mho/meter conduc t i v i t y
where t h e conduc t i v i t y dependence o f t h e normalized phase
constant becomes weak, and the frequency a t which t h e r e l a t i v e
d i e l e c t r i c constant predominates over the conduc t i v i t y , d/wso ( f o r mho/meter and r e l a t i v e d i e l e c t r l c constant o f 2-2.5,
t he range i s t y p i c a l l y 600-800 KHz ).
(2) The technique I s r e l a t i v e l y independent o f the precise spacing
o f the t e s t l i n e from the coal. For the smoother continuously
mined Lower Freeport data sample, the low frequency normalized
phase constant was about 1.88 f o r an average spacing o f the
wires from the coal o f 9.5 wi re r a d i i ( 0.3 inches ). For the
rougher conventional ly mined Elkhorn # 3 data sample, the low
frequency normal ized phase constant was about 1.55 f o r an average
spacing o f the wires from the coal o f about 22.2 wi re r a d i i
( 0.71 inch ).
(3) The phase constant accuracy based on the low frequency I i m l t
o f impedance measurement i s a funct ion o f l i n e length. To
obta in accurate measurements below 100 KHz, a l i n e length o f
a t least 200 fee t i s required.
( 4 ) The quasi-frequency independence o f the conduct iv i ty was
establ ished by observing the "goodness o f f i t" o f computed
and measured resu l ts curves having the same shape and by
observing the d i f ference i n shape o f curves where the
conducti v i t y i s changing w i th frequency. I f the conductivity
Increased substant ia l l y w i t h frequency, Instead of g l vlng
an abrupt r o l l o f f w i th frequency and a monotonic decrease
i n phase constant, the p l o t o f B/Po wi th frequency would
e i t h e r be near ly l inear ( decade lncrease i n conduct iv i ty
f o r decade frequency Increase ) o r e x h i b i t a region of
increased negative slope between regions o f lesser negative
slope.
FIGURE I
GEOMETRY OF PARALLEL WIRE L INE NEAR COAL FOR CALCULATIONS
3.0 TECHNICAL APPROACH
The technique cons is ts o f measuring s h o r t and open c i r c u i t impedance
magnitudes on a balanced-fed p a r a l l e l w i r e l i n e w i t h frequency us ing
simple inst rumentat ion from which the normalized phase constant w i t h
frequency i s derived, and then f i t t i n g a computed curve t o the measured
data using an a lgo r i t hm where the normalized phase constant i s a
func t i on o f conduct iv i ty .
3.1 COMPUTATION ALGORITHM
The formal de r i va t i on f o r t he phase constant o f t h e p a r a l l e l w i re l i n e
i s beyond the intended scope o f t h i s repor t . The expression was
der ived consider ing the lowest o rder TM mode on a coaxia l l i n e w i t h a
lossy outer conductor. The determinental equation f o r the complex
propagation constant was reduced t o a form conta in ing logari thms by
making small angle approximations t o the Hankle funct ions. Then, us ing
s t a t i c f i e l d mapping, the geometry was successively mapped t o a s i n g l e
conductor over a lossy hal fspace ( assuming t h a t t h e spacing from the
halfspace was much greater than t h e conductor rad ius I and then t o a
balanced l i n e p a i r over the lossy halfspace ( assuming t h a t t h e
conductor spacing was much greater than the w i re r a d i i ). The geometry
o f t he l i n e over t h e lossy halfspace i s i l l u s t r a t e d i n F igure I.
The r e s u l t i n g expression f o r the normalized phase constant i s i m p l i c i t .
The expression was solved on an HP-67 i t e r a t i v e l y assuming a s t a r t l n g
value f o r the phase constant, conputing the r e s u l t e x p l i c i t l y , and
then ad jus t i ng the s t a r t i n g value each t ime u n t i l convergence was
obtained.
The expression for t h e normalized phase constant i s :
where,
4- 2aS
[.-jaee][n ( - ) - I n ( A I]
a t
where,
a i s the spacing o f each conductor from t h e ha i fp lane s
ad i s the spacing o f t h e p a r a l l e l conductors
al i s t h e conductor rad ius
6 , G r are t h e c o n d u c t i v i t y and r e l a t i v e d i e l e c t r i c constant
o f t h e ha1 f ~ l a n e
The expression i s o f t he form
so lv ing i t e r a t i v e l y on an HP-67 w i t h a s t a r t i n g value o f F = f i f o r a60
@/(lo and modi f ied i n each step as
w i t h i n a spec i f i ed degree o f accuracy.
The normal i zed phase constant i s taken t o be t h e magnitude o f t he
complex r e s u l t .
3.2 EMPIRICAL TECHNIQUE
The l i n e parameters were chosen t o conf ine the transverse f r i n g i n g
f i e l d s o f t he l i n e t o the coal seam so t h a t t h e much higher overburden/
underburden conduc t i v i t y would n o t in f luence the resu l ts . A l i n e
spacing o f 6 inches was chosen w i t h t h e l i n e conductors being # I 4
wire. The l i n e was a t tched as c lose as poss ib le t o the rough coal r l b
face using n a i l s o r spads through spacers support ing the i ine . The
l i n e was d r i ven balanced from an HP-204C s igna l generator. The
impedance magnitude data was obtained by separate measurement o f t h e
i npu t l i n e vol tage and the i npu t l i n e c u r r e n t ( and then, of course,
t a k i n g the r a t i o o f vo l tage t o c u r r e n t ). The c u r r e n t was measured
using a Stoddard cu r ren t probe w i t h a p r i o r c a l i b r a t e d re la t i onsh ip
between the l i n e cu r ren t and the probe output voltage. The probe
output vol tage and the balanced l i n e vol tage were both measured using
an HP-4038 voltmeter. The arrangement o f t h e measuring equipment i s
i l l u s t r a t e d i n F igure 2. The c u r r e n t and vol tage were measured f o r
both open c i r c u i t and s h o r t c i r c u i t cond i t ions o f t he transmission
l ine . The c a l i b r a t i o n curves f o r t he Stoddard c u r r e n t probe are
given i n F igure 3.
3.3 REDUCTION OF MEASURED DATA
The normalized phase constant was determined from the measured
impedance data through t h e use o f a Smith Chart. The open c l r c u l t
and sho r t c i r c u i t impedances always l i e on opposi te s ldes o f t h e
cha r t such t h a t they are jo ined by a s t r a i g h t edge through t h e c h a r t
center. For a given data point , and using a normalized Smlth Chart
( u n i t y Zo a t t he center 1, the s t r a i g h t edge i s ro ta ted u n t i l al ignment
i s obtained between a normal ized s h o r t c i r c u i t reactance value ( on
t h e r ight-hand edge o f t h e c h a r t ) and a normalized open c i r c u l t
reactance value equal t o t h e sho r t c i r c u i t value m u l t i p l i e d by the
HP
-204
C
SIG
NA
L G
ENER
ATO
R
NO
MIN
AL
RANG
E 20
-100
0 KHZ
60
0 O
HM
BALA
NC
ED O
UTP
UT
STO
DD
ARD
CU
RR
ENT
PRO
BE
PA
RA
LLE
L W
lRE
TR
AN
SM
ISS
ION
L
lNE
20
0-30
0 FE
ET
#I4
WlR
E
SPAC
ED 6
IN
CH
ES
L lN
E
END
EIT
HE
R S
HO
RT
Cl R
CU l T
O
R O
PEN
CIR
CU
IT
FIG
UR
E 2
MEA
SURE
MEN
T E
WIP
MN
T A
RR
ANG
EMEN
T FO
R D
ETE
IWIN
ING
TH
E M
AGN
ITU
DE
OF
THE
OPE
N AN
D SH
ORT
CIR
CU
IT
LlN
E
IMPE
DAN
CE
OF
PA
RA
LLE
L W
lRE
TE
ST
LlN
E
000 1 008 OOL 009 00s OOP
OOE
r a t i o o f t h e measured open c i r c u i t - t o - s h o r t c i r c u i t Impedance
magnitudes. Once t h i s alignment i s obtained, the l i n e e l e c t r i c a l
length i s given e i t h e r as the wavelengths from t h e c h a r t top ( shor t
c i r c u i t t o the r ight-hand al ignment p o i n t o r as the wavelengths
frm t h e c h a r t bottom ( open c i r c u i t ) t o the left-hand alignment
point . The normalized phase constant i s then t h i s e l e c t r i c a l length
d i v ided by the ca l cu la ted f ree space e l e c t r i c a l length knowing t h e
physical length o f t h e l i n e and the frequency. The Smith Chart
al ignment process i s i l l us t ra ted i n Figure 4.
I t should be noted t h a t on l y the r a t i o o f t h e open c i r c u i t - t o - s h o r t
c i r c u i t impedance magnitudes I s requ i red t o implement the technique.
I f t h e same value o f d r i v i n g c u r r e n t can be maintained f o r both
sho r t and open c i r c u i t condi t ions, then a simplification o f the
empi r ica l and data reduct ion methods resu l t s . Under t h i s condi t ion,
t h i s r a t i o i s j u s t t h e r a t i o o f open c i r c u i t - t o - s h o r t c i r c u i t l i n e
vo I tage.
I n ob ta in ing a computed f i t , a low frequency p lus an a r b i t r a r y
conduc t i v i t y and d i e l e c t r i c constant i n t h e expected range are
taken f i r s t and the r a t i o o f as/ai i s var ied . u n t i I computed and
measured values match. The c o n d u c t i v i t y i s then va r ied u n t i l a f i t
i s obtained over t h e cen t ra l p o r t i o n o f t h e frequency range. The
d i e l e c t r i c constant i s then var ied f o r best f i t over the h igh
frequency por t ion . The f i n a l f i t i s obtained consider ing small
incremental changes i n both a /ai and conduct iv i ty . s
OPEN CIRCUIT
FIGURE 4
ILLUSTRATION OF THE USE OF THE SMITH CHART TO OBTAIN THE TRANSMISSION LINE ELECTRICAL LENGTH FOR A RATIO OF Zoc /ZSC OF 25
4.0 PRESENTATION OF DATA
The raw data f o r each o f t h e two se ts o f measurements are g iven i n
t h e Appendix t o t h i s repo r t .
Summaries o f t h e reduced data i n t a b u l a r form f o r t h e two measurement
se ts a re shown i n Tables I and 2.
The Ehrenfe ld #38D reduced data i s shown o n l y f o r 80-600 KHz al though
data was measured from 20-1200 KHz. Th is i s because t h i s was t h e f i r s t
s e t 03 data reduced and t h e frequency "edges" r e s u l t i n smal l e l e c t r i c a l
lengths on the Smith Chart which are hard t o read accura te ly unless
extreme care i s taken. For t h i s f i r s t set, a very c lose f i t was obta ined
us ing on l y t h e "easy-to-reduce" data. The St lnson #3 data was reduced
from 40-800 KHz e x e r c i s i n g g rea te r carewi th t h e Smith Chart as t h e
measured data sample was more scattered.
The Ehrenfe ld #38D data i s g iven i n F igure 5 showing both t h e nominal
f i t assuming t h e c o n d u c t i v i t y was frequency i n v a r i a n t p lus the f i t w l t h
small excursions i n c o n d u c t i v i t y from nominal. The accuracy o f t h e
nominal f i t was, thus, est imated t o be 2 10%.
The St inson 83 data i s g iven i n F igure 6 showing both t h e nominal f i t
assuming t h e c o n d u c t i v i t y was frequency i n v a r i a n t p lus t h e f i t w i t h
small excursions i n t h e c o n d u c t i v i t y from nominal. The accuracy o f t h e
nominal f i t was, again, est imated t o be + 10%.
To i l l u s t r a t e the e f f e c t o f c o n d u c t i v l t y which increases l l n e a r l y w l t h
frequency, computations were made f o r comparison w i t h t h e Ehrenfe ld #38D
nominal f i t assuming l i n e a r increases o f x 10 and x 5 f o r a decade i n
frequency matched t o t h e geometric mean frequency o f t h e 80-600 KHz
range. This data i s g iven i n F igure 7. By n o t i n g t h e shapes o f t h e x 10
and x 5 curves and t h e f a c t t h a t t h e measured data was very c l o s e l y f i t
w i t h t h e m d e l on a frequency i n v a r i a n t basis, t h e c o n d u c t i v i t y was
judged t o be quasi-frequency independent.
REDU
CED
DAT
A FO
R C
ON
DU
CTI
VIT
Y M
EASU
REM
ENTS
IN
BET
HLE
HEM
S
TEE
L C
OAL
M
INE
#3
8D E
MPL
OYI
NG
ME
PA
RA
LLE
L W
IRE
TRA
NS
MIS
SIO
N L
INE
TE
CH
NIQ
UE
SHO
RT
C I R
CU I T
FR
EQ
( KH
z)
I(M
A)
V(V
0LT
S)
IZI
I(M
A)
-
--
80
8.25
0.
77
93.3
3.
20
100
7.85
0.
99
126.
1 3.
43
20
0
8.60
2.
15
250.
0 5.
65
400
6.75
4.
8 71
1.1
7.20
60
0
0.90
4.
0 44
44
8.50
OPE
N C
IRC
UIT
V
(V0L
TS
) IZ
I I
z~
~/
z~
~I
$
-
$0
@/P
o
4.8
1500
16
.08
0.03
82
0.02
032
1.88
0
4.6
1341
.1
10.6
34
0.04
75
0.02
54
1.87
0
3.4
601.
8 2.
407
0.09
05
0.05
08
1.78
2
1.7
236.
1 0.
332
0.16
70
0.10
16
1.64
4
0.33
38
.8
0.00
87
0.23
50
0.15
24
1.54
2
F R
EQ (K
Hz)
REDU
CED
DAT
A FO
R C
ON
WC
TIV
ITY
MEA
SUR
EMEN
TS
IN N
ATI
ON
AL
MIN
E
CORP
. ST
INSO
N #
3 M
INE
EM
PLO
YIN
G T
HE
PA
RA
LLE
L W
IRE
TRA
NS
MIS
SIO
N
LIN
E T
ECH
NIQ
UE
SHO
RT
CIR
CU
IT
(PEN
CIR
CU
IT
I (M
A)
V(V
0LT
S)
IZ(
I (M
A)
V(V
0LT
S)
IZI
IZO
C/Z
SC
( @
- --
-
Po
@/P
o
F Z W 89 W. W O O O O 5 N N - f -
W
-Z w I m
4 -J z a a u 0 z v n -
W J J N w-iLI W A Y t- < - L? 2 %
Y Z O J W z 1U Z w i 2 z .s ELI m o
3
Z C $ - Lo > 'Z t - - J
m 2 k . Z g - 0 W Lul c W Z C 3 Y W 0 3OCJ - m LL a w i 5
W S J 2 t- :f >- W + Z 3 - - -3' > + - - 3 :; s I- t3 3 m w nz t - Z C 8 5 % C -
t- 2-I- t- c - - J L Lo W i L U
Z Z D - W %
'x 2 LL 5 C> 0 W >- ' 0 - k -
5 0 3 3 0 om^ W M U Y 3 >
W (OW .4 2 n x - a n 1 0 v o w w a 5 N - - - - 15 , _J - a J Ji?? a 0 J 2 z g u a t- 1 n a + z n
LL W 2 0 9 - > a
(OCJ *-a z > m W - I + a w- CLmu 3 2 2 ( O W 0 4 w J w a I W I W
t. t- 3 I- 0 - a - > Z Z - - + + 5 0 4 W
2 E + z(Ou 8235
5L I- 3wt- + a - - LL In w
I Z W 2-2- - z [ L
3 LLmv 0 * > (Ozt- t-0- J (O 0 3 Z O (O-J
2 s 2
FIG
UR
E
7
COM
PUTE
D R
ESU
LTS
BA
SE
D O
N E
HR
EN
FELD
#38
D D
ATA
ILLU
STR
ATI
NG
TH
E SH
APE
OF
THE
NO
RM
ALI
ZED
PH
ASE
VE
LOC
ITY
C
UR
VES
WIT
H
FREQ
UEN
CY
FOR
THE
FREQ
UEN
CY
INV
AR
IAN
T N
CM
INA
L F
IT A
ND
FOR
ASSU
MED
LI
NE
AR
Iii
CR
EA
SE
IN
CO
ND
UC
TIV
ITY
W
ITH
FR
EQU
ENC
Y
RAW DATA FROM COAL SEAM CONDUCTIVITY MEASUREMENTS VIA OPEN 8 SHORT
CIRCUIT IMPEDANCE MEASUREMENTS ON PARALLEL WIRE TRANSMISSION LlNE
A DATA FROM BETHLEHEM STEEL COAL MINE #38D EHRENFELD IN LOWER
FREEPORT SEAM
250.3 FEET OF LlNE DEPLOYED AROUND COAL PILLAR
SHORT CIRCUIT HP-4038 READING CURRENT PROBE L l NE VOLTAGE
0.066 VOLTS 0.7 VOLTS
0.042 1.55
0.0225 2.60
0.0037 4.0
0.0 14 5.0
0.020 4.8
0.019 3.40
0.0135 2.15
0.0068 0.99
0,0054 0.77
0.0040 0.57
0.0028 0.38
0.00044 0.295
OPEN CIRCUIT HP-4030 READING CURRENT PROBE LlNE VOLTAGE
0.03 VOLTS 3.4 VOLTS
0.068 4.62
0.057 1.90
0.037 0.33
0.030 1 ,oo 0.022 1.70
0.013 2.55
0.008 3.40
0.0024 4.60
0.0016 4.80
0.00095 5.0
0.00043 5.2
0.00010 5.3
B DATA FFEDM NATIONAL MINE CORP. STINSON #3 IN ELKHORN #3 SEAM
201 FEET OF LlNE DEPLOYED ALONG RIB
SHORT CIRCUIT HP-4030 READING CURRENT PFEDBE LlNE VOLTAGE
0.020 VOLTS 2.20 VOLTS
0.007 3.15
0.002 2.63
0.009 3.40
0,010 2.55
0.020 3.70
0.020 3.15
0.020 2.85
0.020 2.60
0.010 1.21
0.0060 0.70
0.0050 0.58
0.0031 0.36
0.0020 0.235
0.0010 0.1175
OPEN CIRCUIT HP-4038 READING CURRENT PROBE LlNE VOLTAGE
0.100 VOLTS
0.060
0.050
0.040
0 030
0.020
0.020
0.010
0.010
0.0050
0.0010
0.00090
0.00050
0.00020
0.00015
2.80 VOLTS
0.540
0.205
0.73
1.10
1.25
2.22
2.00
3.6 1
4.40
3.50
4.90
4.90
4.70
5.35
