TA Instruments AR 2000, Руководство оператора

Страница: 23 / 144

AR 2000 Operator's Manual
2 3
Instrument Components
The instrument consists of a main unit mounted on a
cast metal stand, with the electronic control
circuitry contained within a separate electronics control
box. Figure 2.4 shows the rear of the electronics control
box.
The AR 2000 Rheometer contains an electronically-
controlled induction motor with an air bearing support
for all the rotating parts. The drive motor has a hollow
spindle with a detachable draw rod inserted through it.
The draw rod has a screw-threaded section at the
bottom, which allows the geometry to be securely
attached.
The measurement of angular displacement is done by an
optical encoder device. This can detect very small
movements down to 40 nRad. The encoder consists of a
non-contacting light source and photocell arranged
either side of a transparent disc attached to the drive
shaft. On the edge of this disc are extremely fine, accu-
rate photographically-etched radial lines. Therefore, this
is a diffraction grating. There is also a stationary
segment of a similar disc between the light source and
encoder disc. The interaction of these two discs results
in diffraction patterns that are detected by the photocell.
As the encoder disc moves when the
sample strains under stress, these patterns
change. The associated circuitry interpo-
lates and digitizes the resulting signal to
produce digital data. This data is directly
related to the angular deflection of the
disc, and, therefore, the strain of the
sample.
The main electronics are housed in a
separate control box. (The interplay
between the rheometer/electronics and
controller are explained in more detail in
Chapter 5.)
Temperature control is achieved via
interchangeable temperature options.
These are discussed in more detail in
Chapter 3.
Figure 2.3
The AR 2000 Rheometer (Rear)
Figure 2.4
Electronics Control Box (Rear)