Strain-gauge balance

Parameters such as impeller speed and shaft power (in a stirred bioreactor) and fluid velocity are indicators of the degree of mixing and thus play an important role in the control of mass transfer. Impeller speed is easily monitored with a tachometer (electronic or mechanical) [39], but the measurement of shaft power input is not as straightforward. The most common method utilizes a torsion dynamometer attached to the impeller drive however, this technique includes losses due to friction in the drive shaft. Better data can be obtained from balanced strain gauges mounted on the impeller [37]. On-line measurement of the liquid velocity in a flowing or stirred system can be obtained by a heat-pulse method in which a resistance thermometer is used to measure a brief temperature increase caused by an upstream pair of electrodes [43]. Use of this sensor system has been limited to laboratory applications. 

Impacted force (static and inertial) Load cells, elastic elements, force gauge, balances, strain gauge, bending elements Hooke s law, transforming force to displacement by an elastic element, piezoresistive effect, capacitive effect, direct or inverse magnetostrictive and magnetoelastic effects... 

Force measurement spring balances, strain gauges, piezoelectric transducers. 

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. 

During clamping and when applying pressure on the molds, the tie rods stretch. If everything is in balance, the platens and mold stretch evenly. The distance the rods stretch is directly proportional to the applied load. Sensors, such as electrical strain gauges, can be used to detect the stretch or load applied and if an unbalance situation occurs, an indicator can alert the operator or the process control system. Bar sensing can also be used as a means of signaling the switch from pack to hold pressures, a potential alternate or support to pressure transducer use. 

In this technique, commonly known as TMA, a vertical probe (flat, 0.140" diameter) is placed on the sample and thermal expansion measured as the sample is heated or cooled. The vertical probe is balanced in oil suspension and a certain weight is added to the probe to arrive at a net zero weight on the sample. Additional weight may be placed on the probe to improve the signal/noise ratio, but this affects the results as does spring loading in the horizontal dilatometer. Strain gauge techniques were also examined by us and were found to be less useful.(4)... 

Many of the uncertainties associated with the above tests arise from the model used to calculate the stress or strain transferred between the matrix and fibre. (Laser Raman or Fluorescence Spectroscopy) LRS is a technique for determining directly the strain in the fibre in analogy to an embedded strain gauge. The strain is probed by recording a Raman (or fluorescence) spectrum of the reinforcing fibre at increments of applied strain. The shift in the frequency at which a stress-sensitive peak occurs can be used to estimate the strain profile in fhe reinforcing fibre. The rate of strain development in the fibre can be used to assess the quality of the interface. Quantification still requires an appropriate stress-transfer model although a simple force-balance calculation can be used to estimate the interfacial shear stress. 

Mass and weight Balances, scales Balancing of the gravitation force, Hooke s law, springs deflection, strain gauge, ie, length-sensitive electrical resistance... 

A prototype laboratory balance was built using the deflection of ion-implanted polymer strain gauges to measure the weight of a sample. To eliminate the effects of the large TCR, measurements were made relative to a second, undeformed, reference resistor, which was placed in thermal contact with the strain gauge. 

Balances compare unknown weights with one standard weight, or alternatively with a well-known force. Balances for weight measurement are very reliable and accurate instruments their measuring accuracy is often better than +0.1% [4]. It must be kept in mind that the gravitational attraction on the Earth s surface can vary by as much as 0.5% but this can be compensated by calibration standards [4]. The hydraulic and electrical strain gauge load cells and the electrical strain... 

In electronic balances the force exercised by the load on the base is measured with a force measurement cell (for example, an electrical strain gauge) and transformed into an electrical signal. This signal is processed within the balance in a digital or analog fashion and is then displayed. These systems can be calibrated and used in fully automatic installations. As force measurement cells one can use pressure sensors with lower requirements for accuracy. These are installations in which the weight is transformed into pressure pneumatically or hydraulically one can determine levels in tanks or reaction vessels by this method, which can also be used to meter automatically the main ingredients of a batch process, for example the water and monomer phase in an emulsion or suspension polymerization. 

The use of a common elbow can be expanded to a solids flow measuring device. As the solids traverse an elbow, the elbow surface is bombarded by the solids, creating a considerable stress or force on this section. The flow can be equipped with a strain gauge arrangement and vibrationally isolated from the rest of the piping system (see Fig. 7-11). A force balance on the elbow can then relate the force on the strain gauge to the solids flowing inside the pipe. See Example 7-2 for details. 

More recently, the use of piezoelectric devices has grown dramatically as a consequence of increases in automation and consumer attraction to modern sophisticated gadgets. Piezoelectric devices are used in many of today s applications, including automotive—wheel balances, seat-belt buzzers, tread-wear indicators, keyless door entry, and airbag sensors computer/electronic—microphones, speakers, microactuators for hard disks and notebook transformers commercial/consumer—ink-jet printing heads, strain gauges, ultrasonic welders, and smoke detectors medical—insulin pumps, ultrasonic therapy, and ultrasonic cataract-removal devices. 

The apparatus used was a non-commercial porosimeter which enabled us to make accurate measurements between 0.4 and 2000 bar corresponding to a pore radius between 2 10 and 3.6 nm. The porosimeter consists of a steel cylinder and a piston forced into the cylinder by a ram (ref. 2). The pressure and the volume change were measured accurately by a strain gauge and by the displacement of the piston respectively. Up to a pressure of 5 bar the mercury was forced into the porosimeter by an air pump and the amount of mercury was determined accurately by a balance (ref. 3). Fig. 1 shows schematically the... 

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