Tank level gauge and sensor head therefor

A linear distance gauge comprising:

• an elongated and longitudinally movable code-bearing surface,
• a fixed code sensor including two optical detectors disposed relative to the code-bearing surface for detecting the code thereon and generating corresponding electrical signals indicating the direction of movement of the code-bearing surface,
• at least one magnet disposed adjacent to an end of the code-bearing surface,
• a fixed magnetic sensor including a magnet detector disposed for sensing proximity of the magnet and generating a corresponding electrical signal to establish a reference position of the code-bearing surface, and
• a processor coupled to the code sensor and to the magnetic sensor and operating under stored program control for interpreting the electrical signals and generating corresponding output signals indicating the position of the code-bearing surface relative to said sensors.

A float gauge for measuring liquid level in a vessel comprising:

• a float element floating in the liquid for rising and falling with the level thereof,
• an elongated code-bearing surface coupled to the float element for rising and falling therewith,
• a code sensor fixed relative to the vessel and including two optical detectors disposed relative to the code-bearing surface for detecting the code thereon and generating corresponding electrical signals indicating the direction of movement of the code-bearing surface,
• a magnet at an end of the code-bearing surface,
• a magnetic sensor including a magnet detector fixed relative to the vessel and disposed for sensing proximity of the magnet and generating a corresponding electrical signal to establish a reference position of the code-bearing surface, and
• a processor coupled to the code sensor and the magnetic sensor and operating under stored program control for interpreting the electrical signals and generating corresponding output signals indicating the position of the code-bearing surface relative to its reference position for indicating the liquid level.