Jon R. Pratt, David B. Newell, John A. Kramar
A FLEXURE BALANCE WITH ADJUSTABLE RESTORING TORQUE FOR NANONEWTON FORCE MEASUREMENT

The NIST electrostatic force balance compares mechanical probe forces to an SI realization of force derived from measurements of the capacitance gradient and voltage in an electronic null balance. As we approach the nanonewton regime, the finite stiffness of the guiding flexure in the balance becomes a limiting factor. Here, we consider an equal arm balance mechanism constructed using flexure pivots as an alternative to the compound rectilinear spring of the present design. We review how the sensitivity of such mechanisms can be adjusted either by manipulating the center of gravity, or by applying a negative restoring torque using a spring. We examine tradeoffs associated with tuning the stiffness of these mechanisms with regards to tilt sensitivity and various nonideal flexure behaviors. Results obtained with a prototype mechanism are presented.

Douglas T. Smith, Shane Woody, Jon R. Pratt
COMPACT FORCE SENSORS FOR LOW-FORCE MECHANICAL PROBE CALIBRATION

The loading mechanisms of instrumented indentation machines are often calibrated using deadweights. In many cases, due to the geometry of the loading frame, the applied deadweight is tensile, while the indentation loads to be measured are compressive. In this paper, we report preliminary efforts to develop a compressive load cell for use on a typical instrumented indentation machine. Two devices were evaluated, one a compact capacitance-based device (fabricated at the National Institute of Standards and Technology), the other a piezoresistive force sensor. We will describe the calibration sensitivity, stability and drift of each, and discuss the potential use of each as a force transfer artifact for the calibration of instrumented indenters.

Thomas Allgeier, Helmut Gassmann, Ulrich Kolwinski, Peter Giesecke
MULTI-COMPONENT MEASUREMENT TECHNOLOGY FOR FORCES AND MOMENTS

This paper introduces the requirements and possibilities of simultaneous force and moment measurements in industrial testing. Apart from describing the principal mechanics of force and moment vectors, important implications of ignoring disturbing components are mentioned. This is followed by an overview of practical applications of multicomponent measurements. The main part of the paper describes a new measurement tool for the data acquisition, evaluation and vector analysis. This comprises issues of transducer selection and applicability, details of the electronics used and also addresses the software design. Examples of typical applications of the entire system are given with an emphasis on outlining the mode of operation and ease of adaptation to new problems. Finally, the principles of system calibrations are described.

Udo Milz
DYNAMIC WEIGHING AND DOSING WITH FAST INTELLIGENT TRANSDUCERS FIT

We present new, weighing sensors with integrated electronics, specially optimized for dynamic weighing and dosing. There is already extensive signal processing in the transducer, with all the necessary functions for fast weight value acquisition and for full, local dosing control.

Oliver Mack
INVESTIGATION OF THE INFLUENCE OF DISTURBING COMPONENTS ON A PIEZOELECTRIC FORCE TRANSDUCER

For the measurement of the physical quantity force with conventional transducers it is assumed that the preferred direction of the force transducer is the same as that of the vector of the force. In practice this case is rarely being observed. Due to insufficient alignment of the transducer or of the measurement facility mechanically disturbing components such as bending moments, shear forces or additional axial forces occur which may influence the measurement result significantly. This paper deals with the investigation of the influence of static mechanical disturbing components on a piezoelectric force transducer. To determine a disturbing sensitivity of a piezoelectric force transducer different kinds of experimental setups are discussed. The measurement results show a characteristic direction depending disturbing sensitivity of piezoelectric force transducers, which is well known of piezoelectric accelerometers. The investigations point out that the influence of mechanical disturbing components on piezoelectric force transducers cannot be neglected for precision measurements.