1505. Interchangeability and Improved Weighing Techniques

Paper

Abstract

Accurate and reliable weight/mass measurements with load cells require reliable procedures as well as
accurate/reliable measurement instrumentation. This paper describes a procedure, utilizing currently
available instrumentation, which simplifies recertification logistics, improves utilization of existing
hardware, eliminates disastrous effects on program schedule of instrument failure, while maintaining or
improving overall weighing accuracy.
Today’s ‘typical’ weighing system consists of two parts, a digital display instrument and load cells.
Once certified as a system, these parts are ‘married’ forever. If one part of the system fails, or is
damaged, the complete system must be returned for recertification. Obviously no weighing can take place
while the system is being re-certified.
The weighing system discussed in this paper adds a third component to the above described system (a
Standardizer) and modifies the instrument specifications so that the instrument calibration is independent
of load cell and cable characteristics. (Interchangeability) In an Interchangeable system the load cell
and Standardizer are independently certified and then the instrument is certified by the Standardizer.
Thus the load cell and instrument are no longer married.
The Gage and Standards Center, Naval Weapons Station, Seal Beach, Pomona Annex has been using the
Interchangeability concept for about 18 years. The recertification cycles which they use for the various
weighing system components are shown and, recertification data taken on two load cells over a five year
period are included in Appendix 1. Appendix 11 shows typical resolution, accuracy, Interchangeability
etc. specifications that are obtainable with present day instrumentation.