MINIATURE ELECTRONIC PRESSURE GAUGE

Abstract: A miniature electronic pressure gauge is described comprising a case (10) having an aperture leading to a transducer (1) connected to an amplifier (3), the transducer (1) and amplifier (3) being powered from a power source (2) in the form of a storage battery such as a Nicad battery. A pressure signal from the amplifier (3) is fed to a linearisation circuit (4) and to an analogue/digital converter (6) clocked with pulses from clock generator (5). The output of converter (6) is fed to a decoder/driver (7) for a seven segment L.C.D. (8). In a preferred construction the pressure gauge is releasably retained in a fluid-tight engagement in a bore in the wall of a pressure chamber of a paint spray gun.

Description: MINIATURE ELECTRONIC PRESSURE GAUGE This invention relates to a miniature preferably digital electronic pressure gauge- More particularly, the invention provides pressure transducer means in a sealed enclosure having its own power source, said enclosure being retained by releasable retaining means in fluid-tight engagement in a cavity in a wall of a pressure chamber, said cavity leading to the interior of the chamber. The transducer as aforesaid may be fitted to a paint spray gun, and is removably fastened by means of a screw or bayonet fitting. Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of a miniature digital electronic pressure gauge according to the invention providing for display of the measured pressure; Fig. 2 is a block diagram of a second form of the pressure gauge providing an output signal for further processing; Figs. 3 to 5 are respectively a fragmentary perspective view of a spray gun having a pressure gauge according to the invention fitted thereto, a sectional view of the gun showing the path taken therethrough by compressed air, and a detail section showing how the gauge is retained in the gun body; and Fig. 6 is a side view of a second form of a spray gun. In Fig. 1 a miniature digital electronic pressure gauge comprises a case 10 having an aperture leading to a transducer 1 connected to an amplifier 3, the transducer 1 and amplifier 3 being powered from a power source 2 in the form of a small storage battery. A pressure signal from the amplifier 3 is fed (if necessary) to a linearisation circuit 4 and thence to an analogue/digital converter 6 clocked with pulses from clock generator 5. The output of converter 6 is fed to decoder/driver 7 for a seven-segment display 8 of the liquid crystal type. The casing 10 is made of high grade stainless steel and is sealed against the ingress of liquid or gaseous fluids under pressure. By this means the unit is intrinsically safe for use in hazardous areas. The power source 2 is a nicad battery such as is now common in calculators and watches. On the exhaustion of the cell 2, the unit may be discarded to be replaced with a new sealed unit. The unit is desirably accurate to within 2% and can read from 0 to 400 PSI; it is important that it should always read 0 under nil applied pressure. The unit of Fig. 2 is similar to that of Fig. 1 except that an output signal 15 is taken from the linearisation circuit 4. In Figs. 3 to 5 the unit of Fig. 1 is shown fitted to a manually operated paint spray gun. A threaded aperture in a casing 20 of the gun accepts a retaining bush 22 in which the pressure gauge unit is fitted. The bush 22 seats on an O-ring 24 in the body 20, and a bore 26 leads from a region of the air path downstream of the trigger 28 and adjacent the spreader control valve 30 to the aperture in the casing 10. In Fig. 6 there is shown a paint spraygun for automatic operation having a body 31 fitted with pressure transducers 33, 35 in the fluid and air supply paths. It will be appreciated that transducers of similar structure may be fitted to compressors, air regulators, fluid regulators, tyre pressure gauges and control panels.

Claims: CLAIMS: 1. A pressure transducer means comprising a sealed enclosure for said pressure transducer means, a power source for supplying power to said transducer means, a releasable retaining means, a walled pressure chamber defining a bore in said wall wherein said sealed enclosure is retained by said releasable retaining means in fluid- tight engagement in said bore and said bore leads to the interior of said pressure chamber. 2. A pressure transducer as claimed in Claim 1, wherein said transducer releasably fits into said bore by a screw- threaded retaining means. 3. A pressure transducer as claimed in Claim 1, wherein said transducer releasably fits into said bore by a bayonet retaining means. 4. A paint spray gun having a body defining an interior space through which air under pressure can be passed, a bore defined in said body leading from said interior space, wherein said bore leads to a pressure transducer as claimed in Claim 1.

Inventors: SMITH ROWLAND CHARLES, SMITH, ROWLAND, CHARLES
Applicants: ITW LTD, ITW LIMITED
Application year: 1991
Main classification: G01L19
IPC codes: B05B12, B05B15, G01L19