Transducers rotational motion

Another type of rotational viscometer is the hehcal-screw rheometer (176). This iastmment is basically a screw-type metering pump that does not pump. The measure of force is the pressure difference resulting from the rotational motion. It is possible to use a bank of pressure transducers of different sensitivities to measure viscosity over a wide range. The iastmment can be used for high temperature rheometry and to foUow polymerkation, shear and heat degradation, and other developments. 

ATP synthase. This enzyme is a molecular assembly that transduces the free energy associated with a proton gradient to the chemical energy associated with ATP. The proton gradient drives the rotation of one component of the assembly within the other. This rotational motion in turn drives the synthesis and release of ATP. 

Dynamic mechanical analysis is used to determine the response of a polyethylene sample to an oscillating force. In its most general form a sample is attached to a pair of movable probes, one of which applies a sinusoidal oscillatory motion while the other measures the force transmitted by the sample. The temperature of the sample and the frequency of oscillation (to) can be varied independently. The sample may be in either its solid or molten state. In the case of molten polyethylene, the sample typically takes the form of a disk sandwiched between a metal drive plate and a torque transducer. Rotation of the drive plate induces shear deformation within the sample, which is measured by the transducer. The basic configuration of the apparatus is similar to that of the cone-and-plate rotational viscometer shown in Figure 9. With appropriate modifications the same equipment can be used for both types of analysis. 

The resolution of potentiometric transducers is dependent upon the construction of the resistance element. In the case of a wire-wound resistance, in order to obtain a high resistance in a small space, the resistance wire is wound on to a mandrel or card which is straight or formed into a circle or helix depending upon the motion of the contact. This limits the resolution of the transducer as the wiper moves from one wire to the next on the mandrel. The best resolution that can be obtained is about 0.01 per cent (see Section 6.10.1). Typical wire-wound potentiometers have strokes of between 0.0025 m and 0.5 m and rotational versions from about 10° of arc to 50 turns. An alternative often employed is the conductive plastic film element. This provides a continuous resistance element and thus, a zero resolution, but such elements suffer from a higher temperature coefficient of resistance. A more recent development is a combination of earlier types in which a conductive plastic coating is sprayed on to a wire-wound resistor. 

The principle of operation of transducers is based on the conservation of either linear (i.e., Coriolis effect) or angular momentum, making a transducer well suited for micromachined rate-sensing gyros. One or more linearly or rotationally vibrating probe masses are required, for which the input motion stimulus and the output signal can be accomplished by various physical effects (electrostatic, electromagnetic, piezoresistive, etc.). Usually the drive motion is resonant, so the detection motion can also be resonant or the two natural frequencies are separated by a certain frequency shift. Drive and detection motion can be excited by inplane motions or by a mixture of in-plane and out-of-plane motions. 

This section discusses those transducers used in systems that control motion (i.e., displacement, velocity, and acceleration). Force is closely associated with motion, because motion is the result of unbalanced forces, and so force transducers are discussed concurrently. The discussion is limited to those transducers that measure rectilinear motion (straight-line motion within a stationary frame of reference) or angular motion (circular motion about a fixed axis). Rectilinear motion is sometimes called linear motion, but this leads to confusion in situations where the motion, though along a straight line, really represents a mathematically nonUnear response to input forces. Angular motion is also called rotation or rotary motion without ambiguity. 

As stated previously, signal conditioning techniques make it possible to derive all motion measurements— displacement, velocity, or acceleration—from a measurement of any one of the three. Nevertheless, it is sometimes advantageous to measure velocity directly, particularly in the cases of short-stroke rectilinear motion or high-speed shaft rotation. The analog transducers frequently used to meet these two requirements are... 

Plastic moves from the hopper onto the feeding portion of the reciprocating extruder screw. The flights of the rotating screw cause the material to move through a heated extruder barrel where it softens (is made fluid) so that it can be fed into the shot chamber (front of screw). This motion generates pressure (usually 50-300 psi [0.35-2.07 MPa]), which causes the screw to retract. When the preset limit switch (or a position transducer, on newer machines), is reached the shot size is met and the screw stops rotating. At a preset time the screw acts as a ram to push the melt into the mold. Injection takes place... 

The mass motion has to be measured and recorded by some device. In early accelerometers, a light beam was reflected in a mirror which rotated with the mass motion. Presently, almost all seismic accelerometers use a capacitive transducer, which gives a voltage output proportional to the mass displacement. This type of transducer is very sensitive - it can resolve displacements of the order of pm (10 mm). 

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