Abstract: A catheter tip pressure transducer is employed for purposes of measuring fluid pressure within a living body. This includes a tubular housing having a pressure inlet aperture therein. A semiconductor block is carried within the housing and has first and second oppositely facing surfaces, one of which faces the inlet aperture and the other faces in the opposite direction. One of the surfaces has a recess formed therein of such a depth to define an elongated rectangular shaped membrane. A pair of elongated grooves are formed in the nonrecessed surface of the semiconductor block. These grooves are in registry with and straddle the longitudinal side edges of the membrane and define therebetween a raised longitudinally extending central portion in the form of a membrane beam which acts as a free beam supported at its opposite ends by the semiconductor block.

Abstract: The measuring device (10) comprises an ISFET (12) used as a chemically selective ion sensor, a reference electrode (20) positioned adjacent the ISFET (12), an amplifier (22) coupled to the ISFET and control/correction circuitry (30) coupled to the ISFET (12), to the reference electrode (20) and to the amplifier (22). The control/correction circuitry (30) is operable to maintain the drain-source current I.sub.DS of the ISFET (12) at a constant value and to correct drift effects of the ISFET (12) on the basis of the logarithmic equation:.DELTA.V.sub.p =A 1n(t/t.sub.o +1 )where:.DELTA.V.sub.p =potential driftA=scale factor for drift and amplitudet.sub.o =time constant defining the dependence on timet=time during which the sensor is operative in the event of continuous operation.

Abstract: The apparatus (14) is constructed and arranged to measure ions in a liquid (30) and comprises a measuring circuit (10) including an ISFET (16), a reference electrode (32), an amplifier (22) and a protection system (12)/guard circuit (40) connected to the measuring circuit (10). The protection system 12/guard circuit 40 comprises at least one electrode (46 or 47) connected via a low-impedance contact (or ring 62/46 or ring electrode 42) to the liquid (30) and coupled to the ISFET (16) by a protective element (64; 65, 66; or 68 and/or 50; 51, 52; 54; 56; or 58) having a low-impedance for high voltages and a high resistance to low voltages.In one preferred embodiment, the ISFET (16) is provided on a chip (90) and has an electrode (46/62) in as closely spaced relationship as possible to the gate region (34) of the ISFET (16).