Electrical strain gauge

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. 

Figure 16.22 Simultaneous measurement of static strain and strain waves in a cross ply composite using FBG sensors and dual-demodulator system, (a) spedmoi instrumented with FBG saisor, PZT sensor, and electrical strain gauge (ESG) (b) experimental setup schematics [47].

In this case, two types of sensors were applied in order to reconstruct the strain distribution along the backface of aluminum substrate of the joint. Both electrical strain gauges (SG) and FBG sensors were used on different specimens. Strain gauge arr s were used for two specimens, one without any defect and another with an artificial of 5.7 mm. FBG arrays were used for other two specimens, one without any crack and the other with a pre-crack of 10 mm. 

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 measurement of strain is commonly performed through the use of electrical strain gauges. This discussion is limited to such gauges and excludes all purely mechanical methods for determining strain in materials and structures. 

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. 

Strictly, the strain gauges referred to above come into this category, since in such cases the change in the measured quantity causes a corresponding change in the resistance of the element. However, the principle has a much wider application, using changes in either the inductive or capacitive reactance of electrical circuit elements. 

There are different techniques to evaluate the quantitative stress level in prototype and production products. They can predict potential problems. Included is the use of electrical resistance strain gauges bonded on the surface of the product. This popular method identifies external and internal stresses. Their various configurations are made to identify stresses in different directions. This technique has been extensively used for over a half century on very small to very large products such as toys to airplanes. There is the optical strain measurement system that is based on the principles of optical interference. It uses Moire, laser, or holographic interferometry (2,3,20). 

Electric sensing devices (strain gauges, piezoresistive transducers, and piezoelectric transducers)... 

Small pressure transducers with flush-mounted diaphragms are commercially available for the measurement of either steady or fluctuating pressures up to 100 MPa (about 15,000 Ibftin ). The metallic diaphragms are as small as 4.8 mm (%6 in) in diameter. The transducer is mounted on the apparatus containing the fluid whose pressure is to be measured so that the diaphragm is flush with the inner surface of the apparatus. Deflection of the diaphragm is measured by unbonded strain gauges and recorded electrically. 

In this chapter we take a careful look at the phenomenon of electrical conductivity of materials, particularly electrolytic solutions. In the first section, the nature of electrical conductivity and its relation to the electrolyte composition and temperature is developed. The first section and the second (which deals with the direct-current contact methods for measuring conductance) introduce the basic considerations and techniques of conductance measurement. This introduction to conductance measurements is useful to the scientist, not only for electrolytic conductance, but also for understanding the applications of common resistive indicator devices such as thermistors for temperature, photoconductors for light, and strain gauges for mechanical distortion. The third section of this chapter describes the special techniques that are used to minimize the effects of electrode phenomena on the measurement of electrolytic conductance. In that section you will encounter the most recent solutions to the problems of conductometric measurements, the solutions that have sparked the resurgent interest in analytical conductometry. 

Electrical output transducers exist in many forms and consist simply of elastic elements coupled with suitable displacement transducers such as capacitance, inductance and reluctance pick-ups, certain types of strain gauge, piezoelectric elements, potentiometers and eddy current probes. A selection of these is described in the following paragraphs. 

The principle of the resistance strain gauge 2 0 is that the electrical resistance of a conductor will change when it is stretched or compressed due to the consequent variation in its physical dimensions. There is an additional effect called the piezoresistance which is the relation between the resistivity p of the material and the mechanical strain. The resistance R of a conductor of area of cross-section A and length x is given by ... 

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