TA Instruments AR 2000, Руководство оператора, Страница: 21 / 144

AR 2000 Operator's Manual
2 1
Chapter 2
Description of the AR 2000
Overview
This chapter describes the main components of the rheometer and provides technical information on perfor-
mance and design. Please read this chapter thoroughly to become familiar with the nomenclature used
throughout this manual.
A Brief History of
Controlled-Stress Rheometers
Sir Isaac Newton (c.1700) was the first to formulate a mathematical description of a fluid's resistance to deform
or flow when a stress was applied to it. He described this resistance as the
viscosity . It is mathematically
described as the shear stress divided by the shear rate or strain. Until Couette developed the first rotational
viscometer (c.1890), viscosity was measured using stress driven (gravity) flow. Many of today's techniques still
use this principle, such as flow cups, U-tubes, capillaries, etc.
The development of an electromechanical instrument, using synchronous motors, and the electronic versions,
using controlled speed servomotors, made controlled rate the widely used technique for versatile rheological
instruments for many years.
The first controlled-stress instrument, capable of continuous rotation, was developed by Davis, Deer, and
Warburton (1968
J.Sci. Instr . 2, I, 933-6) at the London School of Pharmacy. This instrument used an air turbine
and an air bearing. In the early 1970's, a second generation of instruments was developed, using an induction
motor drive to avoid the problems associated with the air turbine. These, however, were restricted to a maxi-
mum torque of 5000 µNm.