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SURVEY OF PATENTS 24 April-20 June 1968
Miscellaneous
Information r e c o r d t ~ system
Kiirleer, K. Methods of g a s - p r e s s u r e testing hollow v e s s e l s British Patent 1,112,881 (8 May 1968) (Applied for 14 May 1965) (Applied for in Japan 19 March 1964) This hollow vessel leak detection agent and method, comp r i s e s , using a carbohydrate, protein or water-soluble synthetic resin coagulable material and a surface-active agent. Specifically the resin is a UF or urea-phenol resin, and an acid hardener, e.g. chromic or phosphoric acids, may be added. An antiseptic additive may also be used. The hardening of the resin causes any leaking bubbles to he fixed in the surface of the vessel for inspection. (Non-Destructive
Testing Patent Survey August 1968)
Apparatus for the inspection and fault rectification of coiled metal
British Patent 1,115, 924 (6 June 1968) (Applied for 11 May 1966) The occurrence of, for example, different faults in the production of cigarettes is r e g i s t e r e d on corresponding counters. A photoelectric device is used to detect the passage of each cigarette. (Non-Destructive Testing Patent Survey
August 1968) Photoelectric position measurement
United Aircraft Corporation British Patent 1,116,851 (12 June 1988) (Applied for 15 September 1965) A work-piece is scanned by an electron beam which is bent onto It by an electromagnet. To control the electromagnet, an i n f r a - r e d image of the beam impingement point is sensed by two photocells which are compared. (Non-Destructive
Testing Patent Survey August 1968)
Pressed Steel Fisher Ltd British Patent 1,113,536 (15 May 1968) (Applied for 26 October. 1966)
Radiation detectors
An apparatus is described which enables mild steel strip to be inspected and marked to eliminate defective sections.
British Patent 1,116,877 (12 June 1968) (Applied for 14 October 1966)
(Non-Destructive Testing Patent Survey August 1968)
Graviner (Colnbrook) Ltd
Thickness measuring instruments
A number of gas-discharge photocells which are sensitive to ultraviolet radiation are used to detect flames, f i r e s or explosions. They ar e directed at an area and their outputs compared, the result being used to activate an alarm, ff necessary. (Non-Destructive Testing Patent Survey August
Dunlop Co Ltd
1968)
British Patent 1,113,882 (15 May 1968) (Applied for 27 September 1965) A knife edge is placed adjacent to the top surface of the layer and the f i rs t reading is taken from a dial. The second reading is obtained when the knife edge coincides with the bottom surface of the layer. (Non-Destructive Testing
"Patent Survey August 1968)
Measuring system Industrial Nucleonics corporation British Patent 1, 114,459 (22 May 1968) (Applied for 17 December 1965) (Applied for in USA 24 December 1964) This compound system measures the moisture in paper from a dryer. It has a capacitative moisture probe and an infrared temperature r e c o r d e r to give a temperaturecompensated humidity signal. An optional beta radiation detector can measure the weight of the paper. The infrared detector has a thermistor mounted on its m i r r o r to detect and allow for variations in the ambient temperature of its housing. (Non-Destructive Testing Patent Survey August
1968)
Ultrasonics. Inspection devices
Automation Industries British Patent 1,113,311 (15 May 1968) (Applied for 30 July 1965) (Applied for in USA 24 August 1965) This patent describes a spring nest which holds the probes of an ultrasonic flaw detector in position as the unit is rotated about three mutually perpendicular arcs. (Non-
Destructive Testing Patent Survey August 2968) Inspection by So--d~,~_ Of products by means of an ultrasonic beam
[nstitut de Recherches De La Sid6rurgie Franpaise British Patent I, 114,284 (22 May 1968) (Applied for 3 September 1965) (Applied for in France 17 September 1964) The effective a r e a of the active face and the ultrasonic beam width of an ultrasonic pulse-echo inspection device ar e varied with the dimensions of the inspected material. This enables flaws to be detected and located more accurately. (Non-Destructive Testing Patent Survey August
1968)
Method and apparatus for testing the filling Of the ends of tobacco a r t i c l e s
Kiirleer, K. British Patent 1,115,923 (6 June 1968) (Applied for 11 May 1966)
Apparatus for automatic registration of material defects determlned by ultrasonic appliances
Zavody V. I. Lenina Plzen, Naroahi Podnik British Patent 1,114, 835 (22 May 1968) (Applied for 2 June 1965) (Applied for in Czechoslovakia 3 June 1964)
Four feeler devices prod the ends Of cigarettes and their movement is r e s i s t e d b y unacceptable cigarettes, which fall to obstruct a photoelectric device. A rejection pulse passes to a magnet which operates a nozzle to a storage device which counts the number of cigarettes with faults in a particular segment. (Non-Destructive Testing Patent Survey
Conformal maps of defects in sheet material are obtained by the scanning of an ultrasonic probe which moves over the surface in two orthngonal ways: a discontinuous and a reciprocating step. The maps are derived either from a pen r e c o r d e r on a rotating drum or from a photographic record of a synchronized B-scan. In these ways both the depth and position of the defect are given. (Non-Destructive
August 1968)
Testing Patent Survey August 1968)
324
non-destructive testing August 1968
Radiometry
M e t h o d of and a p p a r a t u s f o r m e a s u r i n g the t h i c k n e s s of a workpiece
M e a s u r i n g the s u r f a c e d e n s i t y and t h i c k n e s s of s h e e t a n d film materials
Ceskoslovenske Zavody Gumarenske A Plastikarske, Obarove Reditestvi Gottwaldov
Rizhskiy Filial Vsesionznogo N auchno-lssledovatelskogo Instituta Radiatsionnoy Tekhniki
B r i t i s h P a t e n t 1 , 1 1 1 , 1 0 3 (6 J u n e 1968) (Applied f o r 15 F e b r u a r y 1966) (Applied f o r i n C z e c h o s l o v a k i a 19 J u n e 1965)
B r i t i s h P a t e n t 1 , 1 1 2 , 1 2 3 (1 May 1968) (Applied f o r 25 J u n e 1965) R a d i a t i o n s h e e t and film t h i c k n e s s and s u r f a c e d e n s i t y t e s t e r m e a s u r e s the E - r a d i a t i o n b a c k - s c a t t e r e d f r o m the m a t e r i a l ; it c o m p r i s e s a s o u r c e and d e t e c t o r . No d i r e c t l y r e f l e c t e d r a d i a t i o n can e n t e r the d e t e c t o r . T h e p r e d o m i nant b a c k - s c a l t e r i n g of l o w - e n e r g y / e l e c t r o n s p r o d u c e s high s e n s i t i v i t y at s m a l l film t h i c k n e s s e s . Specifically, the s o u r c e of soft E - r a d i a t i o n i s the isotope P m 147.
(Non-Destructive Testing Patent Survey August 1968)
Continuous r a d i a t i o n t h i c k n e s s and e c c e n t r i c i t y t e s t e r , p a r t i c u l a r l y f o r e x t r u d e d p l a s t i c tubing, which u s e s a c o m b i n a t i o n of B r e m s s t r a l f l u n g and 13-radiation. A d r u m , r o t a t a b l e t h r o u g h 360 °, c o n t a i n s a s o u r c e and d e t e c t o r and a b u s h i n g guide c o l l i m a t o r a c c o m m o d a t i n g the workpiece. Good r e s u l t s a r e obtained on 1 - 2 0 m m tubing with a/3: B r e m s s t r a h l u n g r a d i a t i o n r a t i o of 2:1 to give an o v e r a l l : e r r o r of O. 9-1.8%. (Non-Destructive Testing Patent Sur-
vey August 1968)
D e t e c t i o n of f l a w s i n d e n s e m a t e r i a l s
Plessey- UK Ltd B r i t i s h P a t e n t 1 , 1 1 3 , 5 9 4 (15 May 1968) (Applied f o r 16 July 1965) A d i r e c t i o n a l n e u t r o n d e t e c t o r i s u s e d to e x a m i n e d e n s e m a t e r i a l s for f l a w s and i m p u r i t i e s . The d e t e c t o r h a s a n u m b e r of s c i n t i l l a t o r e l e m e n t s which r e s p o n d to n e u t r o n b o m b a r d m e n t by the e m i s s i o n of l i g h t p u l s e s . The I n t e n sity of the light p u l s e s i s g r e a t e s t when the n e u t r o n s a r e not i n t e r r u p t e d b y f l a w s or i m p u r i t i e s . The flaw p a t t e r n ~ a y b e shown on a cathode r a y tube. (Non-Destructive
Testing Patent Survey August 1968) Medical radiation detecting probe
NASA
Eddy current Method and a p p a r a t u s f o r m a g n e t i c r e a c t i o n t e s t i n g
F. W. Bell Inc B r i t i s h P a t e n t 1 , 1 1 3 , 0 0 6 (8 May 1968) (Applied for 22 M a r c h 1967) (Applied for in USA 6 A p r i l 1966) T h i s p a t e n t d e s c r i b e s an e d d y - c u r r e n t c r a c k d e t e c t o r f o r t e s t i n g in situ without d i s m a n t l i n g the c o m p o n e n t s of the s t r u c t u r e b e i n g i n v e s t i g a t e d . The d e v i c e u s e s a m a g n e t i c f i e l d i n d u c t o r g e n e r a t o r and a s e m i c o n d u c t o r s e n s i n g d e v i c e . Specifically the l a t t e r i s a Hall effect d e v i c e and the i n d u c t o r and s e n s e r a r e i n a r a d i a l l y - o u t w a r d s p a c e d r e l a t i o n s h i p . (Non-Destructive Testing Patent Survey
B r i t i s h P a t e n t 1 , 1 1 4 , 2 3 7 (22 May 1968) (Applied f o r 19 D e c e m b e r 1966) (Applied f o r i n USA 23 D e c e m b e r 1965)
August 1968)
A pn j u n c t i o n s i l i c o n n u c l e a r r a d i a t i o n d e t e c t o r i s i n s e r t e d into a v e i n or a r t e r y , o r next to the b r a i n . The e n e r g y of r a d i a t i o n at v a r i o u s points in the body i s found by the d e t e c t o r , which r e s i s t s a t t a c k by body a c i d s , etc. (Non-
Magnetic
Destructive Testing Patent Survey August 1968) Linear dimension measuring device Dosimeters
National Research Development Corporation
Electrospace Corporation
B r i t i s h P a t e n t 1 , 1 1 2 , 8 5 5 (8 May 1968) (Applied for 27 A p r i l 1967)
B r i t i s h P a t e n t 1,115, 809 (29 May 1968) (Applied f o r 11 May 1966) (Applied for in USA 16 July 1965) I n t e n s i f i e s of n e u t r o n and g a m m a r a y s a r e m e a s u r e d b y a s o l i d - s t a t e s i l i c o n diode and a r a d i o p h o t o l u m l n e s c e n t g l a s s c o m p o n e n t ( s i l v e r a c t i v a t e d phosphate). T h e g a m m a r a y i n t e n s i t y i s g i v e n by l u m i n e s c e n c e f r o m the g l a s s when UV light i s applied. The n e u t r o n flux i s m e a s u r e d in a n e l e c t r i c c i r c u i t . (Non-Destructive Testing Patent Survey
T h i s i s a m a g n e t i c t h i c k n e s s gauge which m e a s u r e s n o n m a g n e t i c c o a t i n g s on a m a g n e t i c s u b s t r a t e and can a c t u a t e a s i g n a l if t h e r e a r e d e v i a t i o n s f r o m the s e t t h i c k n e s s . A s p r i n g d e v i c e i s u s e d to stop the m a g n e t i c i n d i c a t o r device f r o m a t t r a c t i n g the s u b s t r a t e a s it a p p r o a c h e s it. A bellows i n d i cating a r r a n g e m e n t m a y b e used. (Non-Destructive Testing
Patent Survey August 1968)
August 1968) Method of t e s t i n g c e l l u l o s i c s h e e t m a t e r i a l
Reed Paper Group B r i t i s h P a t e n t 1,115, 904 (6 J u n e 1968) (Applied f o r 8 S e p t e m b e r 1965) Soft x - r a y s a r e t r a n s m i t t e d t h r o u g h c e l l u l o s e s h e e t and, f r o m t h e i r i n t e n s i t y , the c o n c e n t r a t i o n of any c o m p o n e n t of the s h e e t m a y b e found. If only one m a t e r i a l ' s c o n c e n t r a tion v a r i e s and if the m a s s p e r unit a r e a i s c o n s t a n t , one m e a s u r e m e n t i s enough. F o r m o r e than one v a r i a n t , two w a v e l e n g t h s a r e used, c l o s e to and on e i t h e r side of a n a b s o r p t i o n edge of the e l e m e n t to b e m e a s u r e d . The d e v i c e can b e adapted to m e a s u r e m o i s t u r e content of p a p e r .
(Non-Destructive Testing Patent Survey August 1968) Apparatus for measuring radiation intensity
Electrical A r r a n g e m e n t s f o r d e t e r m i n i n g the m o i s t u r e c o n t e n t o f g r a n u l a r m a t e r i a l s , m o r e partlc-la~-ly moulding s a n d for f o u n d r i e s
Musaeriparikutato lntezet B r i t i s h P a t e n t 1 , 1 1 1 , 6 9 5 (1 May 1968) (Applied for 29 A p r i l 1965) (Applied for in Hungary 14 May 1964) This dielectric constant moisture tester, particularly for foundry moulding sand, m e a s u r e s the content in 1rain. T h e v a r i a t i o n in t h e dc intake of a HF LC o s c i l l a t o r c i r c u i t is a m e a s u r e of the m o i s t u r e content. An additional s e r i e s connected c a p a c i t o r d i m i n i s h e s the l o s s r e s i s t a n c e . P r e s s u r e c a n b e applied to t h e m a t e r i a l u n d e r t e s t . (Non-Destructive
Testing Patent Survey August 1968)
Telefunken Patentverwertungs-GmbH B r i t i s h P a t e n t 1,116, 170 (6 J u n e 1968) (Applied for 16 N o v e m b e r 1966) (Applied f o r in G e r m a n y 30 D e c e m b e r 1965) The e q u i p m e n t h a s a n u m b e r of s e m i c o n d u c t o r Gunn effect o s c i l l a t o r s (of d i f f e r e n t f r e q u e n c i e s ) and the s a m p l e of e a c h i s b i a s e d to give a field b e l o w the c r i t i c a l v a l u e a t which Gunn effect o s c i l l a t i o n s o c c u r . On the i n c i d e n c e of tight, r a d i o waves, o r heat, a t l e a s t one of the s a m p l e s a t t a i n s the c r i t i c a l value. T h e f r e q u e n c y i s a m e a s u r e of the i n t e n s i t y of the r a d i a t i o n . (Non-Destructive Testing
Patent Survey August 1968)
Sensing probes
Johnson, E. E. , Steele, M. S. B r i t i s h P a t e n t 1, 115, 276 (29 May 1968) (Applied for 27 F e b r u a r y 1967) T h e t h i c k n e s s of two touching l a y e r s of m a t e r i a l s which have d i f f e r e n t p r o p e r t i e s i s m e a s u r e d by a m e t a l tape and a n e l e c t r i c a l c i r c u i t w h i c h i s c o m p l e t e d by the m a t e r i a l b e t w e e n two t e r m i n a l s . (Non-Destructive Testing Patent Survey
August 1968)
n o n - d e s t r u c t i v e t e s t i n g August 1968
325
P i p e joint locator
C W Fuelling Inc B r i t i s h P a t e n t 1,116, 784 (12 J u n e 1968) (Applied for 14 July 1966) A pair of Iron-coved inductors in a frame (with ferromagnetic wheels on the ends of the cores so that the circuit is completed through the pipe) a r e used to locate joints in pipelines. The device can be towed through the pipeline beneath joint sealing apparatus (see US Specification 2,896, 155). (Non-
Destructive Testing Patent Survey August 1968~
A p p a r a t u s for i n s p e c t i n g a m o v i n g web of m a t e r i a l to d e t e c t defects therein
Columbia Ribbon & Carbon Mfg Co Inc B r i t i s h P a t e n t 1,115, 982 (6 J u n e 1968) (Applied for 8 July 1965) (Applied for in USA 23 July 1964) An a r r a y of p h o t o c e l l s s c a n s a n a r e a w h i c h is a n u m b e r of s e g m e n t s on the web; d e f e c t s a r e i n d i c a t e d by a d e p a r t u r e f r o m the fixed n o r m a l r e f l e c t e d intensity. A c o n t r o l s i g n a l m a y a c t to cut out d e f e c t s or to count t h e m . T h e e q u i p m e n t d e t e c t s s m a l l d e f e c t s and s u r f a c e r o u g h n e s s . (Non-Destructive Test-
ing Patent Survey August 1968) D e t e c t i o n of double t e x t i l e t h r e a d s
Optical A p p a r a t u s f o r t h e v i s u a l c h e c k i n g of i m p u r i t i e s c o n t a i n e d in t h e c o n t e n t s of pht~l~ o r like t u b u l a r c o n t a i n e r s
Ditta Brevetti C.E.A.-S.p.A. B r i t i s h P a t e n t 1, 111,345 (24 A p r i l 1968) (Applied for 14 F e b r u a r y 1966) (Applied for in Italy 9 M a r e h 1965) P h i a l i n s p e c t i o n device, which c o m p r i s e s m e a n s for b r i n g i n g the p h i a l s into the i n s p e c t i o n position, i l l u m i n a t i o n and l e n s e s for v i s u a l i n s p e c t i o n , m e a n s for d i s c h a r g i n g r e j e c t e d c o n t a i n e r s and, optionally, m e a n s f o r s c o r i n g the neck of the t u b u l a r c o n t a i n e r to f a c i l i t a t e s u b s e q u e n t opening. (Non-Destruc-
Zellweger Ltd, Uster Factories for Apparatus and Machines B r i t i s h P a t e n t 1,116, 009 (6 J u n e 1966) (Applied for 23 M a r c h 1966) (Applied for in S w i t z e r l a n d 24 July 1964) The p r e s e n c e of double t h r e a d i s i n d i c a t e d by d e t e r m i n i n g t h r e a d t h i c k n e s s in m o r e than one d i r e c t i o n : the a m p l i t u d e of an ac signal I m p o s e d on a de b a c k g r o u n d c o r r e s p o n d s to the t h i c k n e s s . T h e light s o u r c e and d e t e c t o r m a y b e r o t a t e d on a p l a t f o r m a r o u n d the t h r e a d , or e l s e the t h r e a d itseff m a y b e r o t a t e d . (Non-Destructive Testing Patent Survey August
1968) Photoelectric scanning system for ultracentrifuges
Beckman Instruments
tive Testing August 1968)
B r i t i s h P a t e n t 1,116, 782 (12 J u n e 1968) (Applied for 27 A p r i l 1966) (Applied for in USA 3 May 1965)
A r r a n g e m e n t s f o r t e s t i n g b l o c k s of c i g a r e t t e s
The d i s t r i b u t i o n of m a t e r i a l s in a c e n t r i f u g e i s d e t e r m i n e d b y - s c a n n i n g the c e n t r i f u g e cell with a p h o t o - r e s p o n s i v e d e v i c e , which p r o v i d e s a n e l e c t r i c a l s i g n a l which depends on the a b s o r p t i o n of light by the m a t e r i a l in the cell. A c a l i b r a tion s i g n a l i s g e n e r a t e d and is c o m p a r e d with the m e a s u r i n g signal. ~Non-Destructive Testing Patent Survey August 1968)
Alfred Schmermund B r i t i s h P a t e n t 1,112, 687 (8 May 1968) (Applied for 9 M a r c h 1966) T h i s p h o t o e l e c t r i c c i g a r e t t e pack t e s t i n g d e v i c e s e n s e s the a b s e n c e f r o m or faulty c i g a r e t t e s in a pack, including iaulty i n s c r i p t i o n s on the p a p e r , by c r e a t i n g a n e l e c t r i c w a r n i n g c u r r e n t or voltage. UV or IR r a d i a t i o n m a y be u s e d to i l l u m i n a t e the c i g a r e t t e s ; t h e r e f l e c t e d light s t r i k e s p h o t o c e l l s f o r m i n g a b r i d g e c i r c u i t . Any faults c a u s e a flow of c u r r e n t t h r o u g h a r e l a y o r s i m i l a r device. (Non-Destructive Testing
Patent Survey August 1968) T e s t i n g of g l a s s w a r e
Steinkoplenbergruerke Matthias Stinnes AG B r i t i s h P a t e n t I, I15, 542 (~.9 May 1968) (Applied for 23 August 1965) (Applied f o r in G e r m a n y 6 June 1964) G l a s s w a r e is t e s t e d p h o t o e l e c t r i c a l l y by equipment which i n c l u d e s a light s o u r c e , a n u m b e r ooncave m i r r o r s and a n u m b e r of l i g h t - s e n s i t i v e e l e m e n t s (silicon p h o t o - v o l t a i c cells). T h e light s o u r c e is on the a r c of t h e g l a s s w a r e a n d the m i r r o r s ane e l e m e n t s r o t a t e and m o v e v e r t i c a l l y to s c a n the whole s u r f a c e . The r e a d i n g s m a y b e u s e d to r e j e c t d e f e c t s . (Non-Destructive Testing Patent Survey August 1968) O p t i c a l fibre s c a n n i n g d e v i c e
Schneider Feinwerklechnik B r i t i s h P a t e n t 1,115, 681 t29 May 1968) (Applied for 9 J a n u a r y 1967) (Applied foi" in G e r m a n y 17 F e b r u a r y 1966) T h e d i m e n s i o n s of an object a r e d e t e r m i n e d when i t s i m a g e is s c a n n e d b y one o r m o r e o s c i l l a t i n g light f i b r e s . With a p h o t o e l e c t r i c d e t e c t o r , t h e light f i b r e s p r o d u c e p u l s e s which m a y b e counted. (Non-Destructive Testing Patent Survey
August 1968)
D e t e c t i n g flaws in f a b r i c s
Corah-Matic Ltd (12 J u n e 1968) (Applied for 30 May 1967) Holes in moving t u b u l a r knitted m a t e r i a l a r e d e t e c t e d by the r e f l e c t i o n of light f r o m a l i g h t - r e f l e c t i v e r i n g o v e r which the m a t e r i a l p a s s e s . When a hole is p r e s e n t , the r e f l e c t e d light i m p i n g e s on a p h o t o c e l l which a c t i v a t e s a b r a k e and a m a r k e r of the m a t e r i a l . (Non-Destructive Testing Patent Survey
August 2968)
Microwaves M i c r o w a v e a p p o x a t u s f o r m e a s u r i n g m o i s t u r e content
Microwave Instruments Ltd B r i t i s h P a t e n t 1, 111, 384 (24 A p r i l 1968) (AppLied for 4 D e c e m b e r 1964) T h i s continuous m i c r o w a v e m o i s t u r e t e s t e r can d e t e c t v e r y small amounts of moisture accurately. It comprises a microwave source, a resonance waveguide cavity containing holes for the sample, a detector and power coupling means between the source and detector. Specifically,the source is swept in frequency by means of a sawtooth wave derived from or s y n c h r o n i z e d with an o s c i l l o g r a p h , t h e l a t t e r showing a m p l i t u d e a g a i n s t f r e q u e n c y at the d e t e c t o r . (Non-Destruc-
tive Testing Patent Survey August 1968) D e t e r m i n a t i o n of moisture content
AEI L i m i t e d B r i t i s h P a t e n t 1,114, 157 (15 May 1968) (Applied f o r $0th S e p t e m b e r 1965)
Electro-optical measuring apparatus
Licentia-Palentverwaltungs-GmbH B r i t i s h P a t e n t 1, 115, 950 (6 J u n e 1968) (Applied f o r 9 D e c e m b e r 1966) If m a t e r i a l i s i n c a n d e s c e n t or e m l t s d n f r a r e d r a d i a t i o n , a t r a n s d u c e r u s e s t h e r a d i a t i o n to a c t i v a t e a d e v i c e w h i c h ' s i g n a l s optically w h e n t h e edge of the m a t e r i a l h a s p a s s e d . A n o t h e r d e v i c e is u s e d when the m a t e r i a l is not hot enough to g e n e r a t e light. (Non-Destructive Testing Patent Survey
August 1968
T h e m o i s t u r e in a m a t e r i a l is m e a s u r e d b y finding the a t t e n uation of a b e a m of m i c r o w a v e s t h r o u g h the m a t e r i a l . M i c r o w a v e s at 10GHz a r e m o d u l a t e d at 3.2kHz. C o m p e n s a t i o n i s made for t e m p e r a t u r e v a r i a t i o n s by u s i n g the f o r m u l a W = W o + k 1 + (1 + k2I(T))(A-A o) w h e r e W i s t h e w e t n e s s of t h e s p e c i m e n , f(T) is a function of t e m p e r a t u r e , A is the a t t e n u a tion and W o, k t , k 2 a n d A o a r e c o n s t a n t s . A l t e r n a t i v e l y , a r e l a t i v e w e t n e s s m a y b e obtained by c o m p a r i n g the output a f t e r p a s s a g e t h r o u g h the m a t e r i a l with a r e f e r e n c e output.
(Non-Destructive Testing Patent Survey August 1968)
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