Patent GB-501872-A (GB)
Title: Instrument for measuring electrical pressures
IPC: G01L23/10
Filed: 1938-04-14
Abstract: 501,872. Compression resistances; condensers; piezo - electric crystals &c. NAAMLOOZE VENNOOTSCHAP DE BATAAFSCHE PETROLEUM MAATSCHAPPIJ. April 14, 1938, Nos. 11506 and 11507. Convention dates, April 20, 1937 and May 5, 1937.. [Class 37] [Also in Group XL] An electrical instrument for measuring mechanical pressure comprises a casing, a diaphragm forming one wall of the casing and subjected to the pressure to be measured and an electrical element within the casing adapted to convert mechanical pressure or variation in dimensions into electrical effects, the diaphragm being provided on the inner side of the casing with a central thickened or extended portion which operates on the electrical element. The electrical element may be a compression resistance, a condenser, or one or more piezo-electric crystals. Fig. 1 shows one construction for measuring the pressure in an internal-combustion engine by means of a cathode-ray oscillograph. The diaphragm 32 carries a table 32A with a flat machined upper face. The table is secured to the diaphragm through a constricted or undercut portion 32B, so that the table follows the motion of the diaphragm without deformation due, to bending thereof. The electrical element may be a quartz crystal cylinder 34, or the table 32A may form the movable plate of a condenser, the fixed plate of which is supported within the casing. A modified casing is shown in Figure 2 in which the diaphragm 42 is formed integral with the casing 41 and has a thickened central portion 42A corresponding to the table 32A, Fig. 1. In the construction shown in Fig. 3, two hollow piezo-electric crystals 54, 54A of opposite polarity are centred by means of a tube 55 and projections on each side of a metal contact member 55A, the thickness of which may be adjusted to obtain the desired compression on the cylinders 54, 64A. In a modification, Fig. 4, the faces of the cylinders 64, 64A are metallized and brazed to the contact member 65A and plug 65 before insertion into the casing 61, the lower edge 61A of the casing then being bent over the thickened edge 62C of the diaphragm, or these parts may be welded or brazed together. The crystal cylinders 54, 54A, 64, 64A may be replaced by condenser plates separated by air or other dielectric. The Specification as open to inspection under Sect. 91 comprises also the construction shown in Fig. 1 (Cancelled). A casing 11 is screwthreaded at 10 to screw into an orifice in the cylinder wall, and has an elastic diaphragm 12 secured pressure-tight by a nut 13. The pressure is taken up partly by the casing and partly by an element 14 by which variations in pressure or lengths are converted into electrical effects, and which is held between the diaphragm 12 and an insulating plug 15. The member 14 is earthed at one end and connected at the other to a wire 16 by which it is connected to amplifying and registering apparatus. The initial tension of the diaphragm 12 on the element 14 is obtained by making this element of correct axial length with respect to the depth of the chamber formed within the casing 11, which may be adjusted by washers 17; 18. The diaphragm 12 and plug 15 may be tightened with a pressure of 1000 to 5000 kgs., whereas the pressure between the diaphragm and the element 14 may be about 50 to 100 kgs. The diaphragm 12 may be integral with the casing 10. The screw-threaded connections may be replaced by riveting, shrinking, welding, brazing, or flanging. If piezo-electric crystals are used as the electrical elements, the contact faces may be metallized. This subject-matter does not appear in the Specification as accepted.