Resonance frequency liquid level sensor

An apparatus for measuring level of liquid medium comprising in combination:

• a) an elongated tubular member with one end open to a liquid medium and a second end opposite to said one end open to ambient surrounding above the free surface of the liquid medium including a first section completely filled with the liquid medium and a second section partially filled with the liquid medium to a level generally identical to the free surface of the liquid medium;
• b) a rigid container vessel enclosing said first and second sections of the elongated tubular member and isolating outer cylindrical surfaces of said first and second sections of the elongated tubular member from the liquid medium wherein said one end of the elongated tubular member open to the liquid medium extends through an end wall of the rigid container vessel in a leak-proof manner and is exposed to the liquid medium, wherein said first section of the elongated tubular member is secured to the rigid container vessel at both extremities thereof, said second section of the elongated tubular member is secured to the rigid container vessel at least one extremity thereof, and the rigid container vessel is secured to a supporting structure;
• c) means for generating flexural vibrations of said first and second sections of the elongated tubular member, and means for measuring natural frequencies of the flexural vibrations of said first and second sections of the elongated tubular member;
• and
• d) means for determining the level of liquid medium as a function of said natural frequencies of the flexural vibrations.

An apparatus for measuring level of liquid medium comprising in combination:

• a) an elongated tubular member with one end open to a liquid medium and a second end opposite to said one end open to ambient surrounding above the free surface of the liquid medium including a first section adjacent to said one end and completely filled with the liquid medium, a second section partially filled with the liquid medium to a level generally identical to the free surface of the liquid medium, and a third section adjacent to said second end and void of the liquid medium;
• b) a rigid container vessel enclosing at least said first and second sections of the elongated tubular member and isolating outer cylindrical surfaces of at least said first and second sections of the elongated tubular member from the liquid medium wherein said one end of the elongated tubular member open to the liquid medium extends through an end wall of the rigid container vessel in a leak-proof manner and is exposed to the liquid medium, wherein said first section of the elongated tubular member is secured to the rigid container vessel at both extremities thereof, said second section of the elongated tubular member is secured to the rigid container vessel at both extremities thereof, said third section of the elongated tubular member is secured to the rigid container vessel at least one extremity thereof, and the rigid container vessel is secured to a supporting structure;
• c) means for generating flexural vibrations of said first, second, and third sections of the elongated tubular member, and means for measuring natural frequencies of the flexural vibrations of said first, second, and third sections of the elongated tubular member;
• and
• d) means for determining the level of liquid medium as a function of said natural frequencies of the flexural vibrations.