Method and apparatus for monitoring the level of the contents in a container

A monitor of the contents in a container for detecting when the contents are below a predetermined level, said monitor comprising:

• (a) a multivibrator for providing at an output terminal thereof alternating ON and OFF signals;
• (b) a light source electronically coupled to said output terminal of said multivibrator for emitting light responsive to said ON signal, said light source being located on a first side of the space within the container and being oriented such that light emitted thereby is directed into the container;
• (c) a light sensor located on a second side of the space within the container opposite the first side thereof for generating an electronic signal proportional to illumination incident on said light sensor, said optical metering signal being incident to said light sensor only when the contents of the container are below the predetermined level;
• (d) a detector electronically coupled to said light sensor and said multivibrator for producing as an output signal a verification signal when said electronic signal is synchronous with said ON signal, said verification signal being negative and indicating that the level of the contents in the container is below the predetermined level.

A monitor of the contents in a clear-walled container for detecting when the contents are below a predetermined level, said monitor comprising:

• (a) a light source on a first side of the container;
• (b) switching means for activating said light source;
• (c) a light sensor on a second side of the container opposite the first side thereof for generating an electronic signal responsive to illumination incident on said light sensor, light from said light source being incident on said light sensor only when the level of the contents of the container is below the predetermined level;
• (d) a timing comparator electrically coupled to said switching means and to said light sensor for generating an output signal when said light source is activated simultaneously with the receipt of said electronic signal from said light sensor;
• (e) normative means for establishing a reference signal;
• and
• (f) comparator means electronically coupled to said timing comparator and to said normative means for indicating according to a predetermined relationship between an output signal from said timing comparator and said reference signal that light from said light source is incident on said light sensor.

A monitor of the contents in a transparent-walled container for detecting when the contents are below a predetermined level, said monitor comprising:

• (a) a multivibrator for providing alternating ON and OFF signals;
• (b) a light source electronically coupled to said multivibrator and located on a first side of the container for emitting light on the predetermined level in the direction of the container responsive to said ON signals;
• (c) a light-sensitive semiconductor device at the predetermined level on a second side of the container opposite the first side thereof, said semiconductor device generating an electronic signal proportional to illumination incident on said semiconductor device and being positioned so light from said light source is incident on said semiconductor device only when the level of the contents in the container is below the predetermined level;
• (d) a first filter means for removing low-frequency components from the electronic signal generated by said semiconductor device;
• (e) a unity gain amplifier of variable sign coupled electronically to said multivibrator and to said semiconductor device for generating a negative output signal when said electronic signal is synchronized with ON signals from said multivibrator;
• (f) second filter means for removing low-frequency components from said output signal of said unity gain amplifier;
• (g) a voltage divider for establishing a reference signal;
• and
• (h) comparator means electronically coupled to said unity gain amplifier and to said normative means for indicating according to a predetermined relationship between said output signal of said unity gain amplifier and said reference signal that light from said light source is incident on said semiconductor device.

A method for determining when the contents in a container are below a predetermined level, the method comprising:

• (a) generating an intermittent beam of light;
• (b) directing said intermittent beam of light at the predetermined level across the space within the container from a first side thereof;
• (c) detecting incident illumination at a second side of the space within the container opposite the first side, said intermittent beam being incident illumination at said second side only when the level of the contents of the container is below the predetermined level;
• (d) verifying that light detected at said second side corresponds to the intermittent beam of light by generating a verification signal wherein said verification signal is generated when the generation of said intermittent beam of light at said first side is synchronous with the detection thereof at said second side;
• (e) generating a reference signal;
• (f) comparing said verification signal with said reference signal;
• and
• (g) generating a status signal when said verification signal has a predetermined value relative said reference signal.