Lebow? Torque Sensors and Load Cells consist of specially designed structures which perform in a predictable and repeatable manner when a force is applied. This force is translated into a signal voltage by the resistance change of strain gages which are applied to the transducer structure. The change in resistance indicates the degree of deformation, and in turn, the load on the structure.

The strain gages are connected in a 4 arm (Wheatstone Bridge) configuration, which acts as an adding and subtracting electrical network and allows compensation for temperature effects as well as cancellation of signals caused by extraneous loading.

A fixed excitation voltage is applied between A and D of the bridge. A force applied to the structure unbalances the Wheatstone Bridge, causing an output voltage to appear between B and C. This voltage is proportional to the applied load. When the shaft of a torque sensor is rotating, means must be provided to transfer the signal voltage from the rotational element to a stationary surface. This can be accomplished through the use of slip rings and rotary transformers.

Lebow? products follow, where possible, the transducer wiring standard of Western Regional Strain Gage committee as revised May

1960. That code, for most Lebow load cells and torque sensors is:

Axis Definition

Lebow? products comply with the Axis and Sense Definitions of NAS-938 (National Aerospace Standard-Machine Axis and Motion) nomenclature and recommendations of the Western Regional Strain Gage committee. For wheel sensors, ASTM specification F-376-73 has been adopted.

These axes are defined in terms of a ?Right Handed? orthogonal coordinate system as shown below:

A + sign indicates force or torque direction which produces a + signal voltage and generally defines a tensile force direction or clockwise (CW) torque.

The principal axis of a transducer will normally be the Z axis. The Z axis will also normally be an axis of radial symmetry or axis of rotation. In the event there is no clearly defined axis, the following preference system will be used: Z, X, Y.

The following illustrations show the recommended axis and sense nomenclature for various transducers supplied by Lebow:

In-Line

Torque Table^?

Load Cell

                           Wheel Sensor