Data-acquisition and control system for a Rheometrics Mechanical Spectrometer

Abstract

The Rheometrics Mechanical Spectrometer is an instrument that is capable of measuring both the dynamic and steady shear rheological properties of a material over a broad time scale and temperature range. The instrument uses a rotational geometry to apply a constant or periodic strain and then measures the response of the stress in three orthogonal directions FX, FY, and FZ as well as the torque about the x axis. The stresses detected are then recorded on a chart recorder as a function of rotational steady shear measurements or displayed numerically as ‘‘in-phase’’ and ‘‘out-of-phase’’ components of the applied oscillatory strain for dynamic measurements. To fully characterize the mechanical response of a material, several hundred points of data at various temperatures are required. Each point of ‘‘raw data’’ must first be normalized and then used in calculations to obtain discrete rheological parameters. To eliminate this labor-intensive process, a microcomputer has been successfully interfaced to the Rheometrics Mechanical Spectrometer to control the operation of the instrument during all modes of operation, acquire the intermediate raw data, perform calculations and numerical transformations, and present a hard-copy plot and table of rheological parameters. The microcomputer-based data-acquisition and control system not only removes the tedious process of manual operation, collection, and presentation of data, but forms an essential part of a closed feedback loop for substantially improving the speed and accuracy of experimental data. A detailed review of the microprocessor-based data-acquisition and control system is presented.