Improvements relating to pressure gauges

TLDR: In this article, a pressure gauge includes a transducer support 25 carrying a semi-conductor body 10 having a plurality of piezo-resistive strain sensing elements 13 formed therein, mounted in an enclosure 32, 22 containing a fluid at a predetermined pressure, a bore 28 extending through the enclosure part 22 to allow fluid whose pressure is to be measured to communicate with a cavity 26 defined by the support 25 and semi conductor body 10 and thereby flex the sensing part of body 10.

Abstract: 1,248,087. Semiconductor devices. FERRANTI Ltd. 27 Feb., 1970 [28 Feb., 1969], No. 10732/69. Heading H1K. [Also in Division G1] A pressure gauge includes a transducer support 25 carrying a semi-conductor body 10 having a plurality of piezo-resistive strain sensing elements 13 formed therein, mounted in an enclosure 32, 22 containing a fluid at a predetermined pressure, a bore 28 extending through the enclosure part 22 to allow fluid whose pressure is to be measured to communicate with a cavity 26 defined by the support 25 and semi-conductor body 10 and thereby flex the sensing part of body 10. The transducer 10, Fig. 1, comprises superimposed P-type substrate 11 and N-type epitaxial layer 12 having formed in its central region 14 diffused P-type sensing resistive elements 13, P-type layer 11 being removed from region 14 to allow layer 12 to flex. Four resistors 13 are provided at the centre of 14 and two pairs os U-shaped resistors 13 at its periphery which resistors are connected by aluminium strips 17 to terminals 18. In operation two of the central resistors 13 and two of the U-shaped resistors are connected to form a Wheatstone Bridge the output from which varies in response to changes in pressure on region 14. Others of the resistors 13 may be employed as balancing or calibrating resistors, or pairs may be connected in series and used as temperature sensors together with thin film trimming resistors to provide a temperature independent output. The silicon support 25 is bonded to a metal tube 23 having a matching coefficient of expansion and which extends through header 22 forming part of the hermetically sealed enclosure. The pressure in the enclosure may be a vacuum or can be preselected by a valve connected to tube 33 communicating with metal can 32. Instead of mounting the pressure gauge to anchorage 42 by means of screwthreaded part 38 of header 22 the metal can 32 may be provided with a screw-threaded block to which is attached tube 33, Fig. 3 (not shown).