Inductive pressure sensor using two oscillators

A pressure sensing system, in combination with the induction pipe of an automotive internal combustion engine (I.C.E.), comprising

• at least two substantially identical, thermally coupled but otherwise independent oscillator circuits (15,22), each including an inductance coil (13,20), and each producing an output signal (f.sub.1,f.sub.2);
• a mixer (23) connected to said oscillator circuits for producing a frequency difference signal which is a predetermined function of the output signals of said oscillator circuits;
• wherein, in accordance with the invention, said coils (13,20), forming a part of said oscillator circuits (15,22), are formed as flat films, and
• at least one (13) of said inductance coils is a variable inductance, said compact pressure sensor including
• a diaphragm (12) disposed at a variable distance (d.sub.1) from said one coil (13),
• said diaphragm (12) being deflectable in accordance with the pressure (p.sub.1) to be sensed and having a layer of material (12) thereon which affects the inductance of the coil (13), and whose deflection thereby affects the frequency of the output signal (f.sub.1) of the oscillator circuit (15) of which it forms a part.

A compact, temperature-compensated inductive pressure sensor having

• a least first and second substantially identical, thermally coupled but otherwise independent oscillator circuits (15,22), each including an inductance coil (13,20), and each producing an output signal (f.sub.1,f.sub.2);
• a mixer (23) connected to said oscillator circuits for producing a frequency difference signal which is a predetermined function of the output signals of said oscillator circuits;
• wherein, in accordance with the invention,
• said coils (13,20), forming a part of said oscillator circuits (15,22), are formed as flat films, and are variable inductances, each electromagnetically responsive to the position of a respective diaphragm (12,19),
• each of said diaphragms (12,19) being respectively disposed at a variable distance (d.sub.1,d.sub.2) from its respective coil (13,20),
• a first one (12) of said diaphragm forming a part of a pressure measurement chamber (11), being deflectable in accordance with the pressure (p.sub.1) to be sensed and having a layer of material (12) thereon which affects the inductance of its coil (13), and whose deflection thereby affects the frequency of the output signal (f.sub.1) of said first oscillator circuit (15) of which it forms a part, and
• a second one (19) of said diaphragm forming a part of a reference pressure chamber (18), being deflectable in accordance with the reference pressure (p.sub.2) therein and having a layer of material (19) on said diaphragm which affects the inductance of its coil (20), and whose deflection thereby affects the frequency of the output signal (f.sub.2) of said second oscillator circuit (22) of which it forms a part.