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BCM SENSOR TECHNOLOGIES BVBA
Brechtsebaan 2
B-2900 Schoten - Antwerpen, BELGIUM
Industriepark Zone 4,
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website: www.bcmsensor.com
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Creep Code of BCM Strain Gauges
All the class-A strain gauges are manufactured of multiple creep compensation choices. The last
letter of gauge part number (P/N) is the creep code of the concerned P/N strain gauges. Here we
discuss some more on the creep compensation.
1. Creep Phenomenon and Creep Level
Creep is mechanical characteristics of materials. For instance, due to elastic-after-effect, the output
signal of strain gauges or load cells under loading increases with time though the strain sustains
constant. This phenomenon is called creep (positive creep). On the other hand, it is found that both
the backing material of strain gauges and the adhesive that is used to bond the gauges onto the
substrate, cause a decrease in the output signal of strain gauges or load cells. This is called negative
creep and is due to so-called viscoelasticity effect of the polymers used.
Thus, due to both the elastic-after-effect and the viscoelasticity effect, strain gauges may exhibit
either negative creep or positive creep and the creep could be set at different levels (values) by
changing gauge design, foil and backing materials.
For given foil and backing material, the creep variation of stain gauges is achieved by varying the
width-ratio of the end loop to strand of the gauge grid: a larger ratio results in a more positive creep
while a smaller ratio leads to a more negative creep. The length of gauge grid can also influence the
creep level. Therefore, a delicate designing and manufacturing of grid pattern, and careful
preparation of backing material, can result in a desired creep for the concerned strain gauge over a
certain range of creep levels. The strain gauges possessing such creep characteristic are known as
creep-compensated strain gauges.
The creep-compensated strain gauges are especially important for load cell manufacturing because
the creep error of load cells under loading can be corrected by using a proper type of creep-
compensated strain gauges.
2. Considerations in Choosing Strain Gauges of a Proper Creep Code
Though spring element materials under load exhibit positive creep, the total creep error of a particular
type of load cells depends on several variables, such as spring element material, heat treatment,
distribution of strain field, the type and thickness of the adhesive used to bond strain gauges, and
operating temperatures. Therefore, without testing it is hard to choose in advance a proper creep-
compensated strain gauge that is necessary to achieve the best creep result of the transducer.
To determine which creep code is the proper creep, a practical way is to do the test by bonding the
gauges onto the load cell spring element. In practice, it is smart to start this creep test with the
gauges of at least two different creep codes. According to the test results of those two creep gauges,
a strain gauge of most proper creep will be selected for achieving a better creep result.
It is very necessary to do such creep tests before going to high volume production of transducers.
3. Creep Code of BCM Class-A Strain Gauges
BCM class-A strain gauges are creep-compensated gauges, and manufactured of multiple creep
codes (N7 through P7). For a certain type of load cell of given capacity and made from given
material, its initial creep may appear either positive or negative. With the creep-compensated strain
gauges one can obtain a desired creep result for the load cell as long as a proper creep code of the
strain gauges is selected in application.