STRAIN GAUGE

Extremely careful calibration of the strain gauges is required. Known torques must be applied to the shaft and the response measured. Note that no bending loads should be applied during calibration. If a single strain gauge is to be mounted on the shaft, it should be placed toward the top of the shaft where it will not be submerged and above where any impellers are to be mounted. Where 

The gauges are usually placed in turned-down sections of the shaft (which also increases sensitivity), and the connecting wires are best run along a keyway in the shaft or down the centre of a hollow shaft. If very small torques are to be measured, the gauges can be fitted to a special hollow plastic section of the shaft, which will deform more than a steel section, giving greater sensitivity. Gauges of this type are extremely delicate and must be handled and calibrated with extreme care. 

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Correlation between the body forces and the stress state in the head was investigated both by the strain gauge method and the optical coat work stress examination method, and the magnetic measurements were performed at the same time. 

During the optical coat work stress examination method the upper plate of the head of some of the bolts was covered with an optical coat work (Fig. 4). On the head of some other bolts strain gauges were stuck which measured the plain biaxial stress state in the middle of the top surface of the head of the bolt (3.5 x 3 mm). The magnetic probe detected average stresses up to 0.1 mm depth in an area of 14 mm diameter in the middle of the head of the bolt. 

Fig.l shows the layout of the SPATE 9000 system. It basically consists of a scan unit connected to a signal amplifier. The signals are then correlated with a reference signal derived from a load transducer (e.g. strain gauge, load cell, accelerometer, or function generator). 

Very shortly, the first one is based on the stress measurement performed using a rosetta strain gauge located in an area of sufficiently uniform stress distribution. In this case, the calibration factor Cr can be easily obtained by the following equation ... 

The experimental activity was carried out on a cylindrical pressure vessel whose capacity is 50 litres and made from steel 3 mm thick. Fig. 2 shows the layout of the pressure vessel considered. The pressure vessel was connected to an oil hydraulics apparatus providing a cyclical pressure change of arbitrary amplitude and frequency (fig.3). Furthermore the vessel was equipped with a pressure transducer and some rosetta strain gauges to measure the stresses on the shell and heads. A layout of the rosetta strain gauges locations is shown in fig.4. 

Some preliminary tests were performed to set up the experimental apparatus, to check the sensors (pressure and strain gauges) and the SPATE system operation. 

In particular, the known stress calibration method was chosen, therefore 6 rosetta strain gauges (R1-R6) on the shell and 7 (R7-R13) on the the head were applied. Their distances measured from the head centre are listed in table 1. R3 and R4 were applied only to check a uniform stress level on the shell surface. 

The calibration curve of each rosetta strain gauge was so obtained and ftg.5 shows the sum of the principal stresses at the measuring points versus pressure inside the vessel. Further tests were carried out to obtain the calibration factor and to check that it remained constant on the whole scan area of the test surface. This was achieved through additional measurements using the SPATE system on fixed points on the surface located very close to the applied rosetta strain gauges. This procedure gave the following results ... 

Anyway, it can be significant to compare the thermographic results at 5Hz (amplitude of pressure periodic change equal to about 5 bar shown in fig. 11b, 12b and 13 b) to the ones achieved with the rosetta strain gauges shown in fig. 17 at the same pressure inside the vessel. 

Rosetta Strain Gauge Distance from the head centre fmm ... 

A comparison of the results achieved with the FEM Analysis and the rosetta strain gauge measurements is shown in fig. 19. Differences can be noted in areas labeled B and C. The former can be explained as an effect of the discrepancy between the actual shape of the vessel and the ideal one used in the F.E.M. model. The latter can be ascribed to the presence of a muff, located in the centre of the head of the actual vessel, which has not been taken into account in the model. 

Fig 17 Rosetta strain gauges measurements along a generatrix. 

Fig. 19 Comparison of the calculation achieved with FEM Analysis and the rosetta strain gauges measurements..

To measure friction and shear response, one has to laterally drive one surface and simultaneously measure the response of a lateral spring mount. A variety of versions have been devised. Lateral drives are often based on piezoelectric or bimorph deflection [13, 71] or DC motor drives, whereas the response can be measured via strain gauges, bimorphs, capacitive or optical detection. 

Straight-run asphalts Straight run naphthas Strain gauges Strainmaster S. strain NRRL 15496 Stratosphere Stratospheric ozone... 

The principal weighing technologies in use currently are mechanical, hydraulic, strain-gauge, electromagnetic force compensation, and nuclear. 

Strain-Gauge Load Cells. The majority of industrial scales today use strain-gauge load cells as the weighing element. The strain-gauge load cell is a device which, when a force is appHed to it, gives an electrical output proportional to the appHed load. 

Figure 5 shows a typical metallic foil strain gauge. It consists of an etched grid of very thin foil attached to a thin insulating backing material. The... 

The advantages of scales based on strain gauge load cells are as follows ... 

The electronics for a balance based on EMFC technology is very similar to that shown in Figure 8 for a strain-gauge-based scale, with the exception that the weighing element consists of the EMFC cell described herein, together with the circuitry to control the current flow to the compensation cod. 

Strain-gauge load cells are sensitive to temperature gradients induced by, for example, radiant heat from the sun or resulting from high temperature wash down. Load cells should be shielded from such effects or given time to stabilize before use. 

Industrial and Retail Scales. Scales using strain-gauge load ceUs predominate in this market segment, although mechanical and hydrauHc... 

Glass-transition temperatures are commonly determined by differential scanning calorimetry or dynamic mechanical analysis. Many reported values have been measured by dilatometric methods however, methods based on the torsional pendulum, strain gauge, and refractivity also give results which are ia good agreement. Vicat temperature and britde poiat yield only approximate transition temperature values but are useful because of the simplicity of measurement. The reported T values for a large number of polymers may be found ia References 5, 6, 12, and 13. 

Some presses are equipped with strain gauges at key points in the overall feed—compress—eject cycle. Thus, these measure compression and ejection forces. Tight specifications for punch lengths and weU-designed and prepared granulations have led to better control of variations in tablet weight. In fiiUy automated presses, weight variations are adjusted by computer. 

Absolute pressure is pressure measured relative to a perfect vacuum, an absolute 2ero of pressure (2). Like the absolute 2ero of temperature, perfect vacuum is never reali2ed in a real world system but provides a convenient reference for pressure measurement. The acceptance of strain gauge technology in the fabrication of pressure sensors is resulting in the increased use of absolute pressure measurement in the CPI (see Sensors). The pressure reference... 

Piezoresistive Sensors. The distinction between strain-gauge sensors and pie2oresistive (integrated-circuit) sensors is minor. Both function by measuring the strain on an elastic element as it is subjected to pressure. A pie2oresistive transducer is a variation of the strain gauge that uses bonded... 

Pressure. Most pressure measurements are based on the concept of translating the process pressure into a physical movement of a diaphragm, bellows, or a Bourdon element. For electronic transmission, these basic elements are coupled with an electronic device for transforming a physical movement associated with the element into an electronic signal proportional to the process pressure, eg, a strain gauge or a linear differential variable transformer (LDVT). 

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