Strain gage,

A Procedurefor the Specijication, Calibration and Testing of Strain Gage Eoad Cells for Industrial Process Weighing and Force Measurement, Institute of Measurement and Control, London. 

Spannungs-messer, m. strain gage tensiometer Elec.) voltmeter, -optik, /. photoelasticity. 

Strain gages may be applied to the test unit at all points where high stresses are anticipated, provided that the configuration of the units permits such techniques. The use of finite element analysis, models, brittle lacquer, etc., is recommended to confirm the proper location of strain gages. Three-element strain gages are recommended in critical areas to permit determination of the shear stresses and to eliminate the need for exact orientation of the gages. 

The unit shall be loaded to the maximum test load carefully, reading strain gage values and observing for yielding. The test unit may be loaded as many times as necessary to obtain adequate test data. 

If the acceleration is variable, as in sinusoidal movement, piezoelectric systems are ideal. In case of a constant acceleration, and hence a force that is also constant, strain gages may be employed. For petroleum applications in boreholes, however, it is better to use servo-controlled accelerometers. Reverse pendular accelerometers and single-axis accelerometers are available. 

Strain gages are usually used for the first four measurements. 

Strain Gages. Strain gages are used to measure the strain or elongation caused by the stress on a material. They are usually made of a thin foil grid laid on a plastic support as shown in Figure 4-259. They are the size of a small postal stamp and are glued to the structure to be stressed. 

Welght-on-BIt. Weight -on-bit is usually measured with strain gages attached to a sub subjected to axial load. The axial load is composed of three parts ... 

Figure 4-259. Sketch of principle of glued foil strain gage transducers.

Torque. The torque is measured by placing two strain gages at 45° on the sub as shown in Figure 4-260. Stress at 45° due to torque is... 

Figure 4-260. Sketch of theoretical strain gage position in a sub to read WOB, torque, and bending moment.

Mud Pressure. Internal and external mud pressures are usually measured with strain gages mounted on a steel diaphragm. Figure 4-262 shows a sketch of principle. 

Figure 4-268. Sketch showing the theoretical position of strain gages for torque measurement.

Urethane Liquid Exceptional abrasion, cut, and tear resistance. Poor moisture and heat resistance. Variety of formulations leading to different properties including range of durometers without plasticizers. Antistatic rollers and tires, hose for transfer of flammables, strain gages, pressure transducers. 

In order to investigate the friction properties of lubricant film in TFL, an apparatus with a floating device was developed by Shen et al. as shown in Fig. 17 [48]. The steel ball is fixed so that it does not roll in the experiment and a pure sliding has been kept. The measuring system of micro-friction force is composed of a straining force sensor with a resolution of 5 yu,N, a dynamic electric resistance strain gage, an AD data-collecting card, and a computer. 

Fig. 17—Floating device for friction measurement [48]. 1—Carrier of strain gage 2—Strain gage 3—Beam 4—Plank 5—Steel ball 6—Oil cup 7—Mandril.

Suk, M. and GUIs, D. R., Comparison of Friction Measurement Between Load/Unload Ramps and Suspension Lift Tabs Using Strain Gage and Actuator Current, IEEE Trans. Magn., Vol. 36,2000, pp. 2721-2723. 

This method of welding may also be used for the permanent attachment of nonstructural items, such as strain gages or thermocouples, provided that... 

Compression Test. Compression tests similar to that described in (5) were conducted for yield stress C and modulus E measurement. Rectangular neat resin specimens (1.27 cm x 1.27 cm x 2.54 cm) cut from the cast resin plates were tested under compression, as shown in Figure 1, in an universal testing machine at a loading rate of 0.05 cm/min. For each resin system studied, tests were conducted at several temperature levels between -60 and 60 degree C. All specimens were instrumented with strain gages for... 

The gage used to record the strain pulse produced in the rock was a radial strain gage consisting of a resistance-wire sensing element shielded with. Cu and bonded to a short... 

FIG G2 Construction of a typical size of SR-4 bonded strain gage... 

FIG G4 Simple form of unbonded strain gage developed by Statham Laboratories... 

Elementary strain gage circuits are shown in Fig G5. The first circuit [Fig G5(A)] is probably the most simple that may be used with a strain gage. For this circuit the signal voltage may be represented byi... 

Vs - battery voltage, volt Rj = ballast resistor, ohm R = Strain gage resistance when relaxed, ohm... 

The two teems in the parentheses of this equation represent the potential in the unstrained condition (the right term) and in the strained condition (the left term). By setting the value of the ballast resistor Rj equal to the strain gage resistance R, a process that is often used in practice, the equation for the signal voltage becomes ... 

Besides strain measurement, strain gages are used in measurement andcontrol, Load cells are prefabricated transducers and are increasingly used because the strain gages are already mounted. One application of a load cell is the rapid weighing of heavy equipment withinfinitesimalmotion... 

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