Apparatus for extracting a variable from two quadrature signals being functions of the variable

Apparatus for providing from two quadrature input signals, which each is a function of a variable, an output proportional to the variable, the apparatus comprising:

• trigonometric transformation means for receiving two quadrature input signals;
• dynamic control means for acting on an output of the trigonometric transformation means to generate a dynamic control means output, the trigonometric transformation means and dynamic control means, in use, co-operating to linearize the two quadrature input signals;
• feedback means provided between said dynamic control means and said trigonometric transformation means;
• and
• reset means having input means and output means provided in the feedback means, the input means, in use, receiving said output generated by said dynamic control means and said output means of said reset means being connectable to at least one trigonometric function generator in the trigonometric transformation means, the function generator being adapted to generate a periodic trigonometric function with a fixed period, the reset circuit being operative to reset said output generated by the dynamic control means by subtracting values representative of multiples of said fixed period from said output generated by said dynamic control means, thereby to map said output generated by said dynamic control means within a predetermined limited range of values.

An open-loop fiber optic gyroscope system comprising a light source connected to one port of a first optical fiber coupler, a fiber polarizer connected to a second port of said first optical fiber coupler, one output of said polarizer being connected to a first port of a second optical fiber coupler, a second port of said second fiber optical coupler being connected to a first end of a fiber coil, a second end of said fiber coil being connected via a fiber phase modulator to a third port of said second optical fiber coupler;

• a photodetector connected to a third port of said first optical fiber coupler;
• synchronous detection means connected to said photodetector to provide two quadrature signals, which each is a function of a so-called Sagnac phase shift caused by rotation of said fiber coil;
• trigonometric transformation means for receiving said two quadrature signals;
• dynamic control means for acting on an output generated by the trigonometric transformation means, the trigonometric transformation means and dynamic control means, in use, co-operating to linearize said two quadrature signals;
• feedback means provided between said dynamic control means and said trigonometric transformation means;
• adder means;
• and feedforward means provided between said trigonometric transformation means and said adder means;
• the adder means, in use, adding an output generated by the dynamic control means and an output of said feedforward means to provide a system output which is proportional to said Sagnac phase shift.