Page 83 - Mechanical Engineers' Handbook (Volume 2)

72 Bridge Transducers

Figure 2 Micro-Measurements’ ‘‘JB’’ pattern strain gage for circular diaphragm pressure transducers.
(Courtesy of Measurements Group, Inc., Raleigh, NC.)

2.4 Error Contributions from the Flexure Properties
When flexures are designed for bridge transducers, the final transducer may have to possess
an accuracy over its operating temperature range of from a few to a fractional percent.
Knowledge of the inelasticities and metallurgical behaviors of flexural elements must be
considered in transducer design. Metals under a constant load experience a minute defor-
mation with time, called creep. Differences between the loading and unloading curve of a
flexure, due to energy absorbed by the material as internal friction, introduce another effect,
known as hysteresis. The modulus of elasticity of materials changes with temperature. Cor-
rosion resistance, machinability, magnetics, fatigue effects, thermal conductivity, and thermal
expansion are other properties of flexural materials to consider in design application. The
300 series stainless steels are useful flexural materials due to their corrosion resistance,
desirable low-temperature properties, and good creep properties at elevated temperatures.