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Measurement of Thermal Expansion

IP.com Disclosure Number: IPCOM000081526D
Original Publication Date: 1974-Jun-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Milburn, LH: AUTHOR

Abstract

Fig. 1 shows material 1 having a coefficient of thermal expansion of a value X. Two strain gages are mounted to material 1 for the purpose of determining the expansion of material 1, as a result of thermal variations. Strain gage 2 has the same thermal coefficient of expansion as does material 1. Strain gage 3 has a thermal coefficient of expansion equal to zero. Fig. 2 shows the Wheatstone bridge connection for connecting strain gages 2 and 3, so as to determine the elongation of member 1 due only to thermal effects.

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Measurement of Thermal Expansion

Fig. 1 shows material 1 having a coefficient of thermal expansion of a value
X. Two strain gages are mounted to material 1 for the purpose of determining the expansion of material 1, as a result of thermal variations. Strain gage 2 has the same thermal coefficient of expansion as does material 1. Strain gage 3 has a thermal coefficient of expansion equal to zero. Fig. 2 shows the Wheatstone bridge connection for connecting strain gages 2 and 3, so as to determine the elongation of member 1 due only to thermal effects.

When a material is exposed to a temperature variation, there will occur an elongation of material, however, some bending of the material may also be present due to some forces within the system. This bending of the material causes a stress to be formed in the material which is sensed by the strain gage. A single strain gage will indicate the stress in the material, not only due to the elongation due to temperature variation but also to the bending of the material. Therefore, the measurement that is obtained from the strain gage is not an accurate indication of the elongation of the material. By using a strain gage having the same coefficient of expansion as does the material and a strain gage having zero coefficient of expansion, the effect of bending the material can be isolated and accounted for.

The Wheatstone bridge of Fig. 2 will be unbalanced only in proportion to the difference of resistance changes in any two...