Strain gauge transducer

Laboratory rotors have been used to evaluate the drag resistance of immersed surfaces as well. The rotational frequency of the innermost cylinder is adjusted to the relevant speed (monitored by a tachometer) and after about 30 minutes of flow stabilisation a 50 Nm strain gauge transducer picks up the torque, M,. All measurements are based on the average of three replicate tests. A sketch of the set-up is shown in Figure 13 details on the set-up and calculations are described in Weinell et al. (2003). 

Further devices use strain-gauge transducers as so-called dead-end instruments or sensors mounted on a pipe with internal flow. The principle of this arrangement is the elastic deformation of a metallic cylinder, measured with the strain gauges. Pressures up to approx. 15 kbar can be measured [11]. 

Experimental measurements of pressure profiles in calenders were conducted by Bergen and Scott (34). A strain gauge transducer was embedded in the surface of one of the 10-in-diameter rolls, and traces were recorded at various conditions corresponding to both calendering and roll milling. 

Consideration should be given to alternative methods of pressure measurement that may provide greato safety than the direct use of pressure gauges. Such methods include the use of seals or other isolating devices in pressure tap hues, indirect obsa-vation devices, and remote measurement by strain-gauge transducers with digital readouts. 

Piezo-resistive pressure transducers offer a number of advantages [82]. The transducer is quite robust because of the relatively thick diaphragm. There is no liquid fill inside the transducer as a result, there is no concern about leakage of mercury. The natural frequency of piezo-resistive transducers is about three orders of magnitude better than strain gauge type transducers. As a result, the dynamic response of piezo-resistive transducers is very good compared to that of strain gauge transducers. 

Typically strain and stress are measured by unbonded strain-gauge transducers, the signals from which are then fed to a phase meter, which provides a direct reading of the relative amplitudes and the phase difference, hence giving values of the modulus and tan <5 [9]. 

A.pparatus for torsion of bars with direct measurements of torque (by strain gauge transducers) and angle (by deflection of a light beam) has been described by Heydemann.2 By interfacing to a computer, the relative amplitudes and phase of torque and deflection can be obtained by a cross-correlation analysis which rejects noise and distortion.22... 

Figure 5.5 shows a schematic view of the Jupiter Recording Membrane Osmometer model 230 and 231 (initially commercialised by Wescan Instrument Co.) [5]. Here, the upper solution cell is separated from the lower solution cell by the semi-permeable membrane. Transfer of solvent from the solvent cell to the solution cell generates a negative pressure in the former, which can be detected and measured by a stainless-steel diaphragm attached to a strain gauge transducer. The precision of measurement is said to be 0.5% and the stability is better than 0.02 cm H2O over a temperature range of 5-130°C. 

The forced oscillation technique can be used over a wider frequency range than the torsion pendulum ranging from 10 to 10 Hz. Uniaxial extension (Fig. 10.8(b)), bending, torsion and shear are used in different commercial instruments. A sinusoidal strain is applied to the specimen and the stress (force) is accurately measured using a strain gauge transducer as a function of time. Knowing both the strain and stress as functions of time enables the complex modulus ( or G ) to be determined. 

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