Pressure sensing device

A pressure sensing device comprises a housing 6 having a pressure port 7 to which hydraulic fluid at pressure is applied, and a further port 9 which is e.g. open to the atmosphere. A sensing diaphragm 5 is mounted by its edges within a chamber in the housing 6 so that its opposite sides face the pressure port 7 and the further port 9 respectively. A fluid-tight seal is provided by an O-ring 11. The diaphragm 5 incorporates a layer 8 of electrically conductive resistive material on one surface of an electrically insulating glass or ceramic substrate 10, the layer 8 being etched or cut away to produce a resistive bridge 12 shaped as shown in Figure 3. In operation the deflection of the diaphragm 5 is sensed by applying a supply voltage to the resistive bridge 12 of the diaphragm 5, and by then detecting the resultant voltage across the resistive bridge 12 in order to provide an electrical signal indicative of the pressure P.