Load cell

• US 4,815,547 A
• Filed: 11/30/1987
• Issued: 03/28/1989
• Est. Priority Date: 11/30/1987
• Status: Expired due to Term

• Current Assignee: Mettler-Toledo Incorporated (Mettler-Toledo International Inc.)
• Original Assignee: Toledo Scale Corp. (Mettler-Toledo International Inc.)
• Inventors: Griffen, Neil C., Weihs, Mark E., Dillon, Benny N.
• Primary Examiner(s): MILLER JR, GEORGE
• Application Number:
  US07/126,272
• Time in Patent Office: 484 Days
• Field of Search: 177/211, 177/255, 177/25.14, 310/338, 73/1 B
• US Class Current: 177/25.14
• CPC Class Codes: G01G 3/1406 combined with special measuring circuits
• CPC Class Codes: G01G 3/18 Temperature-compensating arrangements

Abstract

A digital load cell includes a rocker pin, guided beam, torsion ring or other counterforce, a circuit board mounted on the counterforce and an enclosure sealing the circuit board and all but the load bearing surfaces of the counterforce. The circuit board includes an A/D converter and a microcomputer. Digital communication is provided with the circuit board through a connector mounted on the enclosure. Weight data are corrected digitally. The load cell may be calibrated, characterized, controlled and monitored without physically penetrating the enclosure. One or a number of digital load cells may be connected to a computer or controller to form one or more weighing scales.

Claims

1. Weighing apparatus comprising a counterforce, transducer means mounted on said counterforce, circuit means associated with said counterforce, said circuit means being responsive to external control and including means for producing digital representations of loads applied to said counterforce, means for applying at least one correction factor to said digital representations and means for transmitting said digital representations, means providing a sealed enclosure for said transducer means and said circuit means, and means providing a path through said enclosure means for external communication with said circuit means.

2. Weighing apparatus as claimed in claim 1 wherein said counterforce is a rocker pin and said correction factor corrects for nonlinearity of said digital representations with varying loads on said rocker pin.

3. Weighing apparatus as claimed in claim 1 wherein said counterforce is a dual guided beam counterforce.

4. Weighing apparatus as claimed in claim 1 wherein said counterforce is a torsion ring counterforce.

5. Weighing apparatus as claimed in claim 1 wherein said circuit means includes means for producing digital representations of the temperature of said counterforce, means for storing a temperature correction factor, and means for utilizing said temperature representations and said temperature correction factor to correct said digital load representations.

6. A method of making a modular digital load cell including a counterforce and digital circuit means mounted on the counterforce for providing digital representations of loads applied to the counterforce, the method comprising the steps of providing a sealed enclosure for said transducer means and said digital circuit means, providing a path through said enclosure for external communication with said digital circuit means, subjecting said counterforce to a variety of load and operating conditions and obtaining digital load representations under said conditions, utilizing said load representations to determine digital correction factors for said load cell, and storing said correction factors for use in operation of said load cell.

7. Weighing apparatus comprising, in combination, a columnar counterforce having a curved loading surface at each end, the radius of curvature of each loading surface being greater than one-half the height of the column, means associated with said counterforce for providing digital representations of a load on said counterforce, means for storing a mathematical expression for correcting linearity of the output of said counterforce, and means for combining said digital representations with said mathematical expression to provide corrected digital representations.

8. Weighing apparatus as claimed in claim 7 including circuit mounting means fastened to said counterforce for mounting said digital representation means, said storage means and said combining means.

9. Weighing apparatus comprising a plurality of load cells, each load cell including a counterforce, transducer means mounted on said counterforce, circuit means associated with said counterforce, said circuit means including means for producing digital representations of loads applied to said counterforce and means responsive to external interrogations for transmitting said digital representations, means providing a sealed enclosure for said transducer means and said circuit means, and means providing a path through said enclosure means for external communication with said circuit means, load receiving means supported by said load cells, means connecting said load cells in a local area network, means for interrogating said load cells to receive said digital representations, and means for combining said digital representations to produce digital representations of the total weight on said load receiving means.

10. Weighing apparatus as claimed in claim 9 wherein said counterforce is a rocker pin.

11. Weighing apparatus as claimed in claim 9 wherein said circuit means includes means for applying at least one correction factor to said digital representations.