Strain Gages and Accessories - HBM - #10

Geometry of the SG (depending on the measurement task to be solved)

Typical application:

- strain measurement in one direction

arranged in parallel Typical application:

- measurement on bending beams

For more detailed information see 1) and 2)

T rosettes with two measuring grids (e.g XY11), offset by 90 relative to each other Typical applications:

- analyss of the biaxial stress state with known principal directions

- measurements on tenson/compresson bars For more detailed information see 1) and 2)

0/45/90 or 0/60/120 arrangement Typical application:

- analyss of the biaxial stress state with unknown principal stress directions The three measuring grids are connected each in a so-called quarter bridge circuit. The absolute value and the direction of the rst and second principal stress are computed as described on page 18.

For more detailed information see 2)

V-shaped strain gages (e.g XY21), 2 measuring grids, arranged at 45 relative to the SG axis

Typical applications:

- measurements on torsion bars

- determination of shear stresses occurring in shear beams around the neutral ber

For more detailed information see 1) and 2)

Full bridge strain gages (e.g. VY41), 4 measuring grids, offset by 90 relative to each other Typical applications

- measurements on tension/compression bars

- measurements on torsion bars

- determination of shear stresses occurring in shear beams around the neutral ber

For more detailed information see 1) and 2)

Diaphragm rosettes (e.g. MY11), 4 measuring grids Typical applications

- manufacture of diaphragm pressure transducers

Strain gage chains (e.g. KY11), 10 or 15 very small measuring grids, arranged equidistantly on one common carrier, plus one compensating strain gage Typical application:

- determination of strain gradients

HBM also supplies strain gage chains complete with several rosettes and alternating measuring grid directions so that it is even possble to determine the gradient of a biaxial stress state.

For more detailed information see 2)

1) Using the Wieatstone Bridge Circuit (free brochure)

2) An Introduction to Measurements Using Strain Gages (book)

The strain gage measuring grid length is dependent on the aim of measure­ment because the result of a measurement using strain gages will be the mean value of the strains underneath the measuring grid. In general, measuring grid lengths of 3 or 6 mm represent a good solution.

Long measuring grids are recommended where there is an inhomogeneous material such as e.g. concrete or wood. A long strain gage will bridge the inho-mogeneities of the workpiece and, as a measurement result, will supply the mean strain underneath the measuring grid.

Short measuring gridsare suitable for detecting a local strain state. Therefore, they are to be recommended for deter­mining strain gradients (see strain gage chains), as well as for detecting the maximum point of notch stresses and similar stresses.

Length

The temperatures given in the Speci cations should not be exceeded, nether should the actual temperature fall below the values stated. (see 5<planationson speci cations.

The HBM standard product range comprises 5 different type series for the follo­wing typical applications

Y strain gages: universal strain gage for stress analyss and smple transdu­cers; easy to handle, robust, exible, many geometries and nominal (rated) res-stances available.

Measuring grid: constantan; measuring grid carrier: polyimide

C strain gages: for measurements at extreme temperatures; operating tempe­rature range from -269... up to +250 C temperature response with matching in the range of -200... +250 C.

Measuring grid: Cr-Ni alloy; measuring grid carrier: polyimide Strain gage resistance

HBM strain gages are offered in 120, 350, 700, and 1000 ohm versons The selection of the resstance depends on the constraints of the measurement task. More resistances on request.

+ their insenstivity to variations in insulation resstance, such as may be cau­sed by the effects of humidity.

G strain gages: for the manufacture of transducers nominal (rated) resstances of 120 Q and 350 Q available. Measuring grid: constantan; measuring grid carrier: phenolic resin, glass ber reinforced.

K strain gages: for the manufacture of transducers different creep adjust­ments available, also as a stick on verson complete with touch-dry adhesve coating for optimum measurement results. Measuring grid: constantan; measu­ring grid carrier: phenolic resin, glass ber reinforced.

V strain gages: encapsulated strain gages for experimental stress analyss Measuring grid: constantan; measuring grid carrier: polyimide with a potting made of special plastic material and 3 m stranded wire.

+ less speci c heat because of their lower measurement current + less senstive to ohmic resstances in the connection lines to the measure­ment ampli er

- better antennae for noise pulses.

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Strain Gages and Accessories