Position transducers

Linear position Linear motion is typically driven by the use of lead screws, ball screws, or worm drives with ranges from less than a 25 mm to over 6 m. Linear sensors for position feedback in the lower range include LVDTs, magnetic, and optical encoders. For longer strokes, the linear feedback devices include encoders and magnetostrictive position transducers. Optical encoders are practical up to 2 m. Magnetostrictive position transducers can be used up to 20 m. 

An LVDT is suitable for measuring relatively short travel distances at high accuracy, in the range of microns to several centimeters. It is usually cylindrical in shape and is provided with a core that moves into the center bore of the cylinder. A magnetostrictive position transducer can have as high a resolution as 1 /on and a range from less than 25 mm to over 20 m. Typical error is 0.01% of range. 

If a double pushrod configuration is used, not only the expansion of the reference material must be added, but differences in length between sample and reference must be accounted for.4 If, for example, a one-inch sample and a 1/2-inch reference are used, then the expansion of 1/2-inch of reference and 1/2-inch of pushrod material must be added to the displacement indicated by the position transducer. When the sample and reference lengths are closely matched, the expansion of the pushrod... 

The most suitable type of glass cell for use with gas-liquid mixtures is illustrated in Fig. 5.9. The gas component is dried and degassed in the high-pressure apparatus shown in Fig. 5.8. The gas-liquid mixture is prepared in the autoclave in Fig. 5.9(a). The autoclave is flushed with the gas at atmospheric pressure. Then a defined amount of the degassed liquid is introduced into the autoclave with a syringe fitted with a hypodermic needle. The autoclave is closed immediately, and the gas is forced into the autoclave at the lowest pressure used later in the experiments. During this process the bronze bellows has to be kept in a contracted position which is controlled by linear-position transducers and regulated by the flow of standard-pressure liquid into the bellows. 

Linear position transducers The simplest form is a linear potentiometer, where the position of the slider is proportional to the output voltage. Linear variable differential transformers (LVDls) move a metal core between primary and secondary coils to produce a voltage proportional to core position. 

Linearity, in measurement systems, 1879 Linear models, 2524-2525 Linear optimization, see Linear programming Linear position transducers, 1902 Linear programming (LP), 1725-1726, 2055-2056, 2524-2538 and additivity, 2525-2526 applications of, 2538 computer software for, 2534-2536 discrete optimization, see Discrete optimization... 

LPT Enear position transducer M, Z-average molecular weight... 

The information presented to the operator and the display system is derived from position transducers consisting of an encoder and 4 potentiometers. 

The amplitude and frequency of barrier oscillation and hence wave propagation are variable. Frequencies between 0.005 - 1 Hz can be obtained and amplitudes up to 0.5 cm can be used. The other barrier can be smoothly adjusted to alter the extent of the interfacial area, as in a conventional Langmuir type film balance. The change of interfacial tension produced by the area variation is monitored continuously. Use is made of Wilhelmy plate suspended from one arm of a microforce balance (Beckman microforce balance). The output of this feeds one arm of an X-Y recorder. A position transducer monitors the movement of the oscillating barrier and this feeds the Y axis of the recorder. Lissajou figures are therefore produced on the X-Y recorder. Here 0 is defined as being... 

Lateral movement of the microscope stage, and hence the capillary system, is recorded via a position transducer. By observation of an interface within the capillary, and by maintaining it in the view of the fixed viewing optics, the displacement velocity can be directly determined. The interface can be photographed through the microscope optics, and the dynamic (or static) wetting angle measured (12,18). 

Position is simply a location within a frame of reference thus, any measurement of displacement relative to the frame is a measurement of position, and any displacement transducer whose input is referenced to the frame can be used as a position transducer. 

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... 

Position transducers are also very important in the plastics industry. Both linear and rotary displacement sensors are widely used. In injection molding, screw position for shot size and cushion must be very accurately measured. Mold open and close positions as well as ejector plate travel are also controlled with input from linear position sensors. Generally, it is recommended that linear position sensors provide an accuracy of better than 0.01%, a response time of less than 1 ms, and good vibration resistance [9]. 

The exact shot size delivered to that point wiU have been determined by the shot size. This starting position is accurately controlled by a linear position transducer. The screw will have arrived at that preinjection point by turning the screw at a set RPM and under back pressure which the operator establishes as control set points. 

Figure 2 Kinetics of effect of adding JA to pea leaf sections (as above) attached to a position transducer geared to a growth recorder. Experimental details as in Figure 1.

The position regulation of the proportional amplifier in conjunction with the position transducer see to it that the magnetic armature (pre-tensioned valve spring) goes to and remains in the pre-selected position. 

Position transducer Ball screw Ball nut Driveline Cover Flanges Motor Brake... 

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