Training Stuff

Self-Creep Compensation Strain Gages

release date:2017-02-07 23:53:21


Introduction:
The creep characteristics exist in spring element because of an elasticity of its materials, which makes the transducer output increasing with the addition of time (positive creep), and depends on several variables such as spring element material, structure, strain field, span, heat treatment and test temperature, etc. The backing of gages and adhesive for bonding have high viscoelasticity, results in the output decreasing with the addition of time; but grid material of gages has an elasticity which makes the output increasing with the addition of time. The result of accumulation is that the strain gages have positive or negative creep under fixed load; its direction and value could be adjusted by modifying the design of grid structure, backing material ratio and key technology parameter. For example, changing the dimension of the end grid and fixing the other parameters, we can get the curve of creep characteristic After selecting materials of spring element, if gage creep is equal to spring element creep in value but the direction is opposite, then we can compensate the creep of spring element. In the same way, during making transducers, the creep error caused by other factors could be adjusted this way, and the combined creep value could be limited in minimum range (as shown in picture 3). ZEMIC offers many models of gages which standard creep grads to be selected by transducer manufacturers. (The N※, T※ in strain gages designation refer to creep code, different codes represent different creep value. The rule is: creep difference between any two-neighbor codes is 0.01-0.015%FS/ 30min)


Picture 3:Sketch map of the creep

Notes for using self-Creep Compensation strain gages:

(1)For the first time using, please select one or two models of gages which have great different creep values (different creep codes) and bond them onto the spring element. The matched creep codes will be determined according to actual test value of comprehensive creep and direction.
(2) For transducers with the same spring materials and structure, the smaller the capacity is, the more positive creep it would be, therefore a more negative creep code should be selected.
(3) Different element material exhibits different creep characteristics. Therefore, different creep code should be selected for steel and aluminum transducers with the same capacity and structure.
(4) Transducer creep depends on many variables such as spring elements, strain gages, adhesive as well as the sealing form, protective coating, technique parameters, etc. The direction and magnitude of such error can be predicted, and shall be considered when selecting creep code.