Non-destructive evaluation of ropes by using transverse impulse vibrational wave method

A non-destructive method for evaluating ropes, cables, and strands for flaws and tension is shown. The method permits detecting flaws by recognizing certain vibrational wave amplitude and distribution patterns resulting from striking a test subject with a transverse force. Tension on a test subject is calculated by measuring propagation velocity of the vibrational waves through the test subject. An apparatus is provided which produces vibrational waves in a test subject, measures the amplitude and time distribution of the waves, and displays the measurements for analysis.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to non-destructive testing of ropes, cables, 
and metal strands for flaws and tension. 
2. Description of the Prior Art 
Non-destructive evaluation (NDE) of ropes is known in the art. Some NDE 
methods are in practice, while other methods have been proposed, but are 
not yet perfected. As will be shown hereinafter, no NDE method combines 
the advantageous features of the transverse impulse vibrational wave 
method disclosed in this application. 
In an article by James H. Williams, Jr., John Hainsworth, and Samson S. Lee 
entitled "Acoustic-Ultrasonic Nondestructive Evaluation of Double Braided 
Nylon Ropes Using the Stress Wave Factor" which appeared in Fibre Science 
and Technology, 21 (1984), pp. 169-180, experimentation is performed on 
synthetic ropes with the object of constructing an analytical model 
wherein ultrasonic wave conductivity (Stress Wave Factor) of a rope is a 
function of the condition of the rope and the tension on the rope. It is 
proposed that such a model would enable accurate testing of ropes for 
flaws by measuring Stress Wave Factors. To data, no Stress Wave Factor 
model has been proposed having reliable utility for rope testing. The 
variation in the relationship between Stress Wave Factor, tension, and 
rope condition among different rope compositions and structures is not yet 
fully understood. 
Even if an adequate model for interpreting Stress Wave Factor test results 
were found, the utility of Stress Wave Factor testing would not compare 
favorably with the transverse impulse vibrational method. While the 
transverse impulse vibrational wave method permits testing the entire 
length of a rope from a single test site near one of its ends, Stress Wave 
Factor method tests only a short length of a synthetic rope because 
synthetic ropes quickly dissipate the energy of the vibrations used in 
Stress Wave Factor testing. 
Electromagnetic NDE are presently the only type of non-visual method which 
is in current, widespread practice. Electromagnetic NDE methods are 
discussed in an article by Herbert R. Weischedel entitled "The Inspection 
of Wire Ropes in Service: A Critical Review" appearing in Materials 
Evaluation, 43, December 1986, pp 1592-1605. 
Electromagnetic NDE methods are used for: (1) localized fault detection 
(L.F.) and (2) loss of metallic cross-sectional area testing (L.M.A.) 
Electromagnetic NDE methods are limited to use on ferromagnetic materials, 
unlike transverse impulse vibrational wave method which may be performed 
on ferromagnetic or non-ferromagnetic materials as well as synthetic 
materials. 
L.F. testing is based on the principal that broken wires in a wire rope 
made of ferromagnetic steels distort a magnetic flux passing the point of 
breakage causing magnetic flux leakage which is detectable in the area 
surrounding the rope. L.F. testing is conducted by positioning a strong 
permanent or electromagnet in close proximity to a wire rope to be tested. 
As the rope passes the magnet, or the magnet is moved along the length of 
the rope, a magnetic flux is initiated in the length of rope adjacent to 
the pole interspace of the magnet. Differential sensing coils are 
positioned around the rope to detect magnetic flux leakage. 
Only major flaws, such as broken wires and severe corrosion pitting, are 
detected by L.F. testing, because only substantial changes in the magnetic 
flux leakage are detected by the differential sensors. Small flaws, or 
widely dispersed flaws, do not produce substantial and rapid magnetic flux 
leakage changes and are often missed using L.F. testing. 
L.M.A. testing involves direct measurement of magnetic flux through a 
length of a wire rope. Variation in the magnetic flux through different 
portions of a single rope indicate a change in the cross-sectional area of 
the rope, which, in turn, indicates possible deterioration of the rope at 
areas of decreased cross-sectional area. 
The electromagnetic methods require passing the entire length of a metallic 
rope to be tested through the testing apparatus or the testing apparatus 
be moved along the entire length of the rope. As with Stress Wave Factor 
testing, the necessity for access to the entire length of a rope reduces 
the utility of electromagnetic NDE methods. 
Methods based on measuring vibrational frequencies of ropes and cables for 
determining tension are also known in the art. U.S. Pat. No. 4,565,099 
issued to Arnold, U.S. Pat. No. 4,376,368 issued to Wilson, and U.S. Pat. 
No. 4,158,962 issued to Conoval each related to calculating the tension on 
a rope or cable as a function of its fundamental frequency of vibration. 
The equipment and methods shown in these patents and otherwise known in 
the art are not, however, suitable for practicing the non-tension related 
aspects of the transverse impulse vibrational wave method as described 
herein. 
It would, therefore, be advantageous to develop an NDE method having 
utility for testing ferromagnetic and non-ferromagnetic ropes alike, which 
would require access to only a limited portion of the rope to be tested, 
which would detect minor as well as major rope flaws, and which would 
permit calculating tension on ropes without additional equipment. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an apparatus and 
non-destructive evaluation method which apprises a user of flaws in, and 
tension on, a cable, rope, or metal strand. 
It is another object of the present invention to provide an apparatus and 
non-destructive evaluation method which apprises a user of the relative 
amplitudes and arrival time of pulsed, transverse, vibrational waves 
passing through cable, rope, and metal strand. 
It is another object of the present invention to provide an apparatus and 
non-destructive evaluation method by which the location of a flaw in a 
cable, rope, or metal strand is determined. 
It is another object of the present invention to provide an apparatus and 
non-destructive evaluation method by which the overall flaw population of 
a tested cable, rope, or metal strand may be determined. 
It is another object of the present invention to provide an apparatus and 
non-destructive evaluation method by which the tension on cable, rope, or 
metal strand may be measured. 
Accordingly, the present invention provides an apparatus and method 
utilizing pulsed, transverse, vibrational waves for non-destructive 
evaluation of cables, ropes, and metal strands for flaws and for tension. 
The method is referred to as transverse impulse vibrational wave method. 
The apparatus for transverse impulse vibrational wave method is designed 
for initiating a transverse vibrational wave motion in a rope, and for 
measuring the amplitude of and time intervals between the resulting waves 
as they travel though the rope. The apparatus comprises an exciting 
mechanism which applies a transverse impulsive force to the tested rope, a 
sensor which detects individual waves as they pass a particular point on 
the rope, a signal amplifier which raises the amplitude of the electrical 
signals form the sensor, a signal conditioner which filters unwanted 
signals from the sensor, and an oscilloscope which displays the 
measurements of the sensor in time versus amplitude units. 
The apparatus optionally includes a computer and recorder or graphics 
printer. The computer is for automating the measurements and calculations 
involved in detecting and locating flaws in a tested rope, as well as in 
determining the tension on a tested rope. The recorder and graphics 
printer are for recording and producing a permanent record of the 
time/amplitude relationships of the vibrational waves as detected by the 
sensor. 
The transverse impulse vibrational method for NDE of ropes is based on the 
fact that flaws in a rope partially reflect vibrational wave energy 
because of the acoustic impedance mismatches at the flaw locations. The 
wave is also reflected at the ends (or terminations) of the rope. The 
sensor of the above-described testing apparatus produces corresponding 
electrical signals. 
Calculations based on measurements of the time between the flaw signals and 
the end-reflected signals and on measurements of the relative amplitudes 
of the signals detected by the testing apparatus allow the user to locate 
rope flaws, to determine tension on the tested rope, and to measure the 
relative population of flaws in the tested rope as compared to a control 
rope sample.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention comprises a method and apparatus for non-destructive 
evaluation (NDE) of cables, synthetic ropes, and wire ropes for tension 
and flaws. The method will be referred to as "transverse impulse 
vibrational wave method" herein. For the purposes of this discussion, 
cable, synthetic rope, or wire rope will be referred to collectively as 
"rope" in most instances. 
Referring to FIG. 1, the testing apparatus is depicted schematically and is 
referred to generally by the reference numeral 10. For reasons to be 
discussed hereinafter, the testing apparatus 10 is for detecting 
individual vibrational waves in a rope 12 and apprising a user of the 
presence, the relative amplitudes, and the sequential arrangement of the 
waves. 
A rope 12 is shown in FIGS. 1, 2 and 3 to show the relationship of the 
components of the testing apparatus 10 to a rope 12 which is to be tested. 
Transverse Impulse Vibrational (TIV) wave method involves striking a rope 
12 to propagate vibrational waves through the rope 12. Consistency in the 
force used to strike the rope 12 is desirable from one test to another. 
Consistency of striking force permits direct analytical comparisons to be 
made between data derived from tests of the same rope at different points 
in service life of the rope 12 service life or from tests of different 
ropes. Therefore, the testing apparatus 10 includes a striking mechanism 
14 which consistently strikes the rope 12 with a predetermined force. The 
striking mechanism 14 of the preferred embodiment is a solenoid 16 with 
its plunger 18 in a position for striking the rope 12 when the solenoid 16 
is activated (see FIG. 3). Other designs for striking mechanism 14, such 
as pneumatic devices or spring biased devices (not shown), would be 
equally acceptable. 
It is noted that although any manner of striking the rope 12 is acceptable 
for any given test; a device providing consistent striking force is merely 
desirable for the above-stated reasons. One could, for instance, 
successfully conduct a TIV wave method test by striking the rope 12 with a 
hammer (not shown). 
Referring again to FIG. 1, a sensor 20 is included in the testing apparatus 
10 for detecting individual vibrational waves in the rope 12 resulting 
from the impact from the striking mechanism 14. To permit testing of a 
wide range of sizes and compositions of ropes, cables, and strands, the 
sensor 20 should be capable of discerning individual vibrational waves 
ranging in frequency up to approximately 1 KHz. 
The particular method of detection for the sensor 20 is not important so 
long as the relative amplitudes and sequential arrangement of vibrational 
waves in the rope 12 may be derived from the output of the sensor 20. The 
sensor 20 may measure the actual displacement of the rope 12, velocity of 
displacement, or acceleration of displacement. 
Referring to FIG. 2, one type of sensor 20 which has been used for a TIV 
wave method comprises a coil 22 and permanent magnet 24 combination. Coil 
22 is attached to the rope 12, and is placed between the positive pole 26 
and the negative pole 28 of the magnet 24. The leads 30 of the coil 22 are 
attached to the components of the testing apparatus 10 which process the 
output of the sensor 20. As the rope 12 vibrates, it causes the attached 
coil 22 to move relative to the field of the magnet 24. The relative 
motion of the coil 22 within the magnetic field created by magnet 24, 
induces a current to flow within the coil 22. This current flow is in 
direct proportion to the magnitude of the relative motion of coil 22 
within the magnetic field which is in turn directly related to the 
magnitude of the vibrational wave within the rope 12. The induced current 
flow within coil 22 thereby provides the necessary electrical signal to be 
processed and analyzed by the remaining components of the testing 
apparatus 10. Any other available electromagnetic displacement sensor such 
as the Electro-Mike Displacement Transducer manufactured by the Electro 
Corp. of Sarasota, Fla., would likewise be appropriate. 
Other designs for the sensor 20 are equally acceptable. Devices which 
physically contact the rope 12 or which detect vibrations by optical 
methods are examples. An optical sensor 20 such as a laser vibration 
sensor is shown in FIG. 3. An optical sensor 20 has the advantage of not 
requiring any direct attachment to rope 12. Light may be directed at the 
vibrating rope 12 from a distance and may likewise be detected at a 
distance as shown in FIG. 3. Any available optical device capable of 
quantitatively detecting the vibrations of the rope 12, such as the Laser 
Through Beam Photoelectric Sensor, LX Series, manufactured by the Keyence 
Company, Ltd. of North America, would likewise be appropriate. 
Referring to FIG. 1, the testing apparatus 10 includes a signal amplifier 
32 which is connected to the sensor 20. The signal amplifier 32 receives 
the electrical signals from the sensor 20 and amplifies the signals to a 
level capable of being detected and processed by the other components of 
the testing apparatus 10. The amplitudes of the signals produced by the 
signal amplifier 32 are higher, but directly proportional to the 
amplitudes of the electrical signals from the sensor 20. The outputs of 
the signal amplifier 32 are, therefore, proportional to the amplitudes of 
the actual vibrational waves in the rope 12. The relative amplitudes of 
the vibrational waves in the rope 12 are important to TIV wave method 
analysis. The frequency response of the signal amplifier 32 should be at 
least coextensive with the sensor 20. 
The testing apparatus 10 further includes a signal conditioner 34 which is 
connected to the signal amplifier 32 for receiving the amplified signals. 
The signal conditioner 34 is a variable filter which filters signal 
frequencies from the signal amplifier 32 falling within a user-defined 
range. This allows a user to filter signals which are not useful for the 
test being conducted. 
Referring in combination to FIGS. 1 and 4, a digitizing oscilloscope 36 is 
believed to be the preferred recording/display device for the testing 
apparatus 10. The oscilloscope 36 is connected to the signal conditioner 
34 for receiving the signals from the signal conditioner 34. The display 
38 of the oscilloscope 36 has a y-axis scale 40 measured in amplitude 
units, and an x-axis scale 42 measured in time units. The oscilloscope 36 
has calibration controls 43 for adjusting the display 38 to units 
appropriate to the particular rope 12 being tested. 
The digitizing oscilloscope 36 not only gives a graphical representation of 
the relative amplitudes and sequential arrangement of the signals from the 
signal conditioner 34, and consequently those of the actual vibrational 
waves in the rope 12, but also records the signals for later re-display or 
computer analysis. 
Referring again to FIG. 1, a trigger switch 44 activates the striking 
mechanism 14 and provides a synchronization signal to start the digitizing 
oscilloscope 36. Therefore, a user may simply throw the switch 44, and the 
striking mechanism 14 will strike the rope and the electronic components 
of the testing apparatus 10 will then process and record the resulting 
vibrational waves. If a computer 58 is used (to be discussed hereinafter), 
the computer 58 may be interfaced with the switch 44, and it may activate 
the components of the testing apparatus 10. 
Transverse impulse vibrational wave method may be conducted through 
analysis of data which may be derived by the testing apparatus 10 as just 
described. Transverse impulse vibrational wave method is made possible 
because of the measurable effect that flaws and tension have on the 
vibrational wave propagation properties of cables, ropes, and strands. 
It is important to note that TIV wave methods may be performed on 
ferromagnetic and non-ferromagnetic metallic materials, as well as 
non-metallic materials alike. This gives TIV wave method a considerable 
utilitarian advantage over presently used NDE methods. It is of further 
importance that a TIV wave method alone permits testing an entire length 
of a cable, rope, or strand from a single access point at one end. As 
previously mentioned, other NDE methods require passing the testing 
apparatus over the entire length of a test subject. 
Referring to FIG. 3, a TIV wave method will normally be performed on 
cables, ropes, or metal strands which are in service as elevator cables, 
guy wires, or in similar highstress and/or safety intensive applications. 
To perform a TIV wave method test, the striking mechanism 14 is placed 
within a specified distance of the rope 12 which is to be tested. Because 
analysis of the test results are simplified by having the sensor 20 in 
close proximity to the striking mechanism 14, the striking mechanism 14 
and the sensor 20 are mounted on a single support stand 46. The remaining 
components of the testing apparatus 10 are connected as discussed above. A 
portable power supply 40 is shown in FIG. 3 for use in areas where 
electricity for the testing apparatus 10 is not readily available. 
The striking mechanism 14 and the sensor 20 should be placed near one end 
50 of the rope 12. This simplifies analysis of test results because a wave 
approaches and then is reflected by the end 50 of the rope 12 closest to 
the sensor 20. These waves will pass the sensor 20 a very short time 
apart. Therefore, the two passages appear, and can be treated as a single 
wave for purposes of a TIV wave method. 
For simplicity's sake, the vibrational waves created by the impact of the 
striking mechanism 14 will be referred to as a single wave in the 
following discussion. 
Referring in combination to FIGS. 1, 3, and 4, when a test is conducted 
with the testing apparatus 10, the rope 12 is struck by the striking 
mechanism 14, and a vibrational wave is propagated from the point of 
impact. As the incident wave reaches an end 50 of the rope 12, it is 
reflected and travels towards the opposite end 50 where it is again 
reflected. This cycle continues until the energy in the rope 12 is 
completely dissipated. A flaw 52 in the rope 12 also reflects vibrational 
waves, but to a lesser extent than the ends 50 of the rope 12. Therefore, 
waves reflected by the flaw 52 will have a lesser amplitude than waves 
reflected by the rope's ends 50. Flaw-reflected waves appear, in time, 
between end-reflected waves because flaw-reflected waves travel a shorter 
distance than end-reflected waves. 
As discussed above, the sensor 20 will produce an electrical signal in 
response to each vibrational wave of detectable amplitude which passes it. 
Each electrical signal will have an amplitude proportional to the 
amplitude of its respective vibrational wave. Signals from an 
end-reflected wave will, like the wave itself, have a larger amplitude 
than signals reflecting flaw-reflected waves. Flaws which are large enough 
to provide reflected waves of measurable amplitude are referred to as 
"discrete flaws." 
Flaws which are too small to reflect such waves are referred to as 
"non-discrete flaws" (not shown). While not individually detectable, the 
presence of non-discrete flaws may be recognized by methods which will be 
discussed hereinafter. 
Referring to FIG. 4, a discrete flaw is indicated in the oscilloscope 
display 38 as a low amplitude flaw signal 54 intervening higher amplitude 
end signals 56. When a flaw signal 54 does appear, calculations may be 
conducted to locate the discrete flaw 52 (shown in FIG. 3) which it 
represents. 
Referring again to FIG. 4, the pulse signal 55 is the wave directly 
resulting from the impact from the striking mechanism 14, and may be 
treated as an end signal 56. 
The position of each discrete flaw 52, the tension on the rope, and the 
presence of non-discrete flaws (not shown) are determined by formulae, one 
or more of which require the following variables which may be derived from 
the oscilloscope display 38: 
t.sub.r =the time interval between adjacent end signals 56. 
t.sub.f =the time interval between an end signal 56 and the next subsequent 
flaw signal 54. 
P.sub.i =the amplitude of an end signal 56 at point i. 
P.sub.j =the amplitude of an end signal 56 at point j. 
L.sub.ij =the traveling distance of the wave between the two end signals 
shown by amplitudes P.sub.i and P.sub.j. 
t.sub.r and t.sub.f are determined simply by measuring the number of time 
units between two adjacent end signals 56 as indicated by the x axis scale 
42 in the oscilloscope display 38. 
P.sub.i and P.sub.j are determined by respectively measuring end signals 56 
at points i and j on the display 38 of the oscilloscope 36 by reference to 
the y-axis 40. The attenuation coefficient formula (to be discusses 
hereinafter) in which these variables are used requires that P.sub.i 
&gt;P.sub.j. 
L.sub.ij may be derived by multiplying the length (L) of the rope 12 by 
twice the number of intervals between successive end signals 56 shown 
between points P.sub.i and P.sub.j on the display 38. 
The following two variables which are required by one or more of the 
transverse impulse vibrational wave method formulae must be independently 
determined: 
L=the length of the rope being tested. 
C=the mass per unit length of the rope being tested. 
If the entire length of a rope 12 may be viewed, as in FIG. 3 wherein the 
rope 12 is used as a guy wire, the length (L) may be determined by 
triangulation. If triangulation is not possible, the length (L) of the 
rope 12 must be determined by other means--either by direct measurement, 
or by reference to blueprints, etc. 
The mass per unit length (C) of the rope 12 may be acquired from the 
manufacturer of the rope 12, or may be determined by analysis of a rope 
sample (not shown) like the particular rope 12 which is to be tested. 
Variables which are derived by the method formulae are as follows: 
D=the distance of a flaw from the end 50 of the rope 12 closest to the 
sensor 20. 
v=propagation velocity of vibrational waves through the rope 12. 
T=the tensile load on the rope 12. 
alpha=the attenuation coefficient of vibrational wave in the rope 12. 
The distance (D) of a discrete flaw 52 from the end 50 of the rope 12 
nearest the sensor 20 may be nearly approximated according to the 
following formula: 
EQU D=L(t.sub.f /t.sub.r) 
The flaw location aspect of the method permits substantial time savings in 
locating a known discrete flaw 52 for determining the need for replacement 
of the rope 12. This is a substantial improvement over existing rope 
testing methods which require passing the testing apparatus over the 
entirety of the rope 12 to detect and to locate a flaw 52. 
During the time between two successive end signals 56, and consequently 
between two successive passages of an end reflected vibrational waves, the 
wave will have travelled the length (L) of the rope 12 twice. Therefore, 
the propagation velocity (v) of vibrational waves in the rope 12 is 
determined by the following formula: 
EQU v=2L/t.sub.r 
Propagation velocity (v) is a function of the tension (T) on the rope 12 
according to the following formula: 
EQU v=(T/C).sup.1/2 
The formula for calculating tensile load (T) when propagation velocity (v) 
is known becomes: 
EQU T=Cv.sup.2 
Since the testing apparatus 10 permits calculating the propagation velocity 
(v) knowing only the rope's 12 length (L) and the constant "C," this 
formula of the method permits the very simple determination of the tensile 
load on a rope 12. Such ease of calculation has obvious practical safety 
implications. 
As briefly alluded to above, transverse impulse vibrational wave method 
includes steps which, in some instances, provide an indicia of 
non-discrete flaws (not shown) in the rope 12. This aspect of the method 
is based upon the fact that the rate at which energy in a vibrating rope 
12 is dissipated is directly proportional to the population of flaws in a 
rope 12. 
Flaws, whether discrete or non-discrete, interrupt the propagation of 
vibrational waves through the rope 12, and energy is thereby dissipated 
more rapidly than in a rope having fewer or no flaws. The rate of energy 
dissipation in the rope 12 is shown by an attenuation coefficient (alpha). 
The attenuation coefficient is calculated by the following formula: 
##EQU1## 
If the tested rope 12 shows a higher attenuation coefficient (alpha) than 
a control rope (not shown) known to be flawless, flaws in the rope 12 are 
indicated. 
As indicated above, the variables necessary for calculating the attenuation 
coefficient are easily derived from the display 38 of the oscilloscope 36. 
While there is no way to distinguish between discrete flaws 52 and 
non-discrete flaws (not shown) by calculating the attenuation coefficient, 
there is considerable value in making the calculation. This is 
particularly so when no discrete flaws 52 are detected. A high variance in 
the attenuation coefficient of the rope 12 from that of a control rope 
(not shown) would, in such a case, indicate a high non-discrete flaw (not 
shown) population. Such a rope should be investigated further. 
Even when discrete flaws 52 are detected, an experienced user may be able 
to recognize that the attenuation coefficient for the rope 12 is not in 
line with the expected value, in light of the severity, or lack thereof of 
the known discrete flaws 52. Such a disparity would be an indication of a 
significant non-discrete flaw population in addition to the known discrete 
flaws 52. 
Referring again to FIGS. 1 and 4, as is apparent from the above discussion, 
proper analysis of the signals from the sensor 20 requires precise 
measurements of time intervals between end signals 56 and flaw signals 54 
and of the relative amplitudes of adjacent end signals 56. Calculations 
based upon the measured amplitudes and intervals are also required. 
Therefore, while not necessary to practice transverse impulse vibrational 
wave method, a computer 58 for automating measurements and calculations is 
desirable. 
The computer 58 should be programed and equipped for the following tasks: 
(1) To receive and store data from the digitizing oscilloscope 36 
representing the amplitude of and time intervals between the signals 
initially produced by the sensor 20; 
(2) To derive comparative amplitudes of the signals; 
(3) To measure time between adjacent end signals 56, as well as between a 
flaw signal 54 and an adjacent end signal 56; 
(4) To receive input of the length of the rope 12 from the user of the 
testing apparatus 10; 
(5) To receive input of the constant C for the particular rope 12 being 
tested, which constant, when multiplied by the propagation velocity 
squared, yields the tension on the rope 12, and to make the calculation; 
(6) To divide the time between the flaw signal 54 and the adjacent end 
signal 56 by the time between adjacent end signals 56 and to multiply the 
quotient by the length of the rope 12 to calculate the discrete flaw's 52 
position on the rope; 
(7) To measure a difference in amplitude between two adjacent end signals 
56 and calculate the attenuation coefficient for the rope 12; and 
(8) Most importantly, to provide the derived information in a useful 
format. 
For producing permanent test records, and particularly for preparing 
graphical depictions of the measurements of the testing apparatus 10 as 
shown in FIG. 4, a recorder or graphics printer 60 should be attached to 
the computer 58. 
The testing apparatus 10 and formulae just discussed provide a method of 
testing cable, synthetic rope, and metal strand which has not been 
previously known. No presently known testing apparatus or method is 
applicable to ferromagnetic and non-ferromagnetic materials, while at the 
same time permitting full-length testing from a single location on a 
cable, rope, or strand. 
The ability to test synthetic ropes made of such materials as nylon and 
KEVLAR.RTM. will enable the use of these ropes for applications previously 
reserved to metallic cables because of inadequate testing procedures. The 
ability to test the full length of a cable, rope, or strand will greatly 
reduce the time and expense involved in testing such things as elevator 
cables, antenna guy wires, crane support cables, and the like.