649 



HISTORICAL NOTE ON THE COPPER DIAPHRAGM GAUGE 



J. H. Powell 



Naval Construction Research Establishment 

 Rosyth 



March 1950 



Original c'csifn. 



The 1 2' Gauge. 



One of the earliest devices for the mcasurenGnt of the explosive efficiency of underwater 

 txplosions vas the Copper Oiaphragn Gauge. Its first r?corded use was in Mining School, 

 Portsnouth (now Admiralty Mining EstaDl i shmrnt, Havant) in 19 20 where it was originally designed 

 to indicate if r\ sorics of nominally eqjil charges did in fact develop the sane power as estimated 

 By the size of the indentation at any given distance. Experincnt, however, showed that the 

 di.iphragns were cr-.paDle of giving approximate -^.bsoluti? measures of Cjrtain physical quantities 

 connected with tht explosion. 



Under static pressure the diaphragm distorts to a spherical fonn as nearly as can be 

 measured, an'j a static ciiliDration was m"idc so that the work done in distorting the diaphragm could 

 Oe oxprossed as a function either of the volume change, the surface area change or the central 

 depression. Under the influonc; of explosion pressure the diaphragm distorts to a ranarkably 

 STiooth form which, howr^var, is not a sphere, but a compromise between a cone and a paraboloid. 

 It was assumed that the vmrk dore by the explosion wave in producing a given volumetric distortion 

 is the sane as that done by a uniform static pressure in producing an equal volumetric distortion, 

 though it was admittod that this supposition was not strictly correct. 



The diaphragms originally consisted of Cdrc-fuUy anne:ilcd copper plates, 0.04' in 

 thickness. They w.- rs d'snpcd within f1 angis =it the end of ; circular steel cylindrical drum, 

 so that the exposed area of each diaphragm was a circular plate 6" in radius. 



Actual experiment soon demonstrated that the relationship 



w = consf.nl x Ed^ 



held approximately for ch irges totwjen U5 lb. and 300 lb. T.N.T, where w = weight of charge; 

 E = energy absorbed by giuge and d = distance of the gauge from the charge. The quantity E 

 was determined by static calibration and it was found that the value based on the volume estimate 

 was more consistent than that determined on an increase in area basis. The volume estim_." >;.■'.? 

 therefore, adopted as the basis of measurement. Since the energy is roughly proportional to 

 the square of the depression (A), the approximate relation 



A = constant X if 16 



is al so appl i cabl e. 



The original suggestion for this type of gauge was due mainly to Mr, F. B. Shaw 

 {Chief Technical Adviser) and to Mr. F. Pickford of H.M. Mining School, nfiile the elementary 

 mathematical analysis was due to Dr. G.W. Walker (Chief Scientist), from whose reports the 

 foregoing paragraphs are largely quoted. 



Standard design. 



The 6" Gauge. 



Following the death of Dr. Walker in 1921, no further attempt was made to develop the 

 diaphragm giugc as an absolute meter of any particular parameter of the pressure pulse, but it 



