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What are strain gauges made of and how to select the right thermal expansion coefficient?

ZEMIC is one of the leading manufacturers of strain gauges. With over 50 years of experience in the development and production of strain gauges, ZEMIC produces a high quality and wide variation of strain gauges. With professional and reliable technology ZEMIC is able to produce an annual output of over 50 million stable, reliable and first-class quality strain gauges which are divided in more than a dozen series and over a thousand different combinations. There are several characteristics which can be specified for every strain gauge which make these combinations. A few of these characteristics will be shown and explained in the blog.

 

Grid and backing material

The Zemic series have different combinations of backing material and grid material:

BF Series
Fully encapsulated Constantan foil strain gauges with modified Phenolic backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has high accuracy and excellent stability but only at room temperature. Especially suitable for accuracy class 3 transducers. Easy to use and available in a resistance range of 60 up to 1000Ω.

ZF Series

Fully encapsulated Karma foil strain gauges with modified Phenolic backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has high accuracy and excellent stability over a wide temperature range. Especially suitable for accuracy class 0.02 transducers. Especially suitable for usage with DC/AC electronic weighing instruments. 

BA Series
Fully encapsulated Constantan foil strain gauges with a polyimide backing. Offers Self-Temperature compensation. Has a high elongation rate and excellent heat resistance on a wide temperature range. Primarily intended for both stress analysis and normal accuracy transducers with usage of temperatures up to 150℃. 

BAM Series
Fully encapsulated Constantan foil strain gauges with thin polyimide film backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has a high elongation rate and excellent heat resistance on a wide temperature range and low hydroscopicity. Shows good specifications for creep and zero-return. The strain gauges are primarily intended for high accuracytransducers at class 3 or better. 

BHB Series
Fully encapsulated Constantan foil strain gauges with glass fibre reinforced epoxy backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has high accuracy and excellent stability over a wide temperature range and high moisture resistant capability. Has a low hydroscopicity and shows good specifications for creep and zero return. The strain gauges are primarily intended for high accuracy transducers at class 3 or better. 

ZAM Series
Fully encapsulated Karma foil strain gauges with thin polyimide film backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has high accuracy and excellent stability over a wide temperature range and high moisture resistant capability. Has a low hydroscopicity and shows good specifications for creep and zero return. The strain gauges are primarily intended for high accuracy transducers at class 3 or better.

BB (BAB) 250°C Series
Karma foil strain gauges with Glass Fibre Reinforced Polyimide Backing. Offers an excellent heat resistance, good insulation and high stability. The strain gauges are primarily used for both high precision stress analysis and accurate transducers with a usage temperature up to 250℃. 

BYM Series
Fully encapsulated Constantan foil strain gauges with a special thin polyimide film backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has a high elongation rate and excellent heat resistance on a wide temperature range and low hydroscopicity. Shows good specifications for creep and zero-return. The strain gauges are primarily intended for high accuracy transducers at class 3 or better.

ZYM Series

Fully encapsulated Karma foil strain gauges with a special thin polyimide film backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has high accuracy and excellent stability over a wide temperature range and high moisture resistant capability. Has a low hydroscopicity and shows good specifications for creep and zero return. In addition it can realise high resistances with small size strain gauges which makes it excellent for usage in low power devices. The strain gauges are primarily intended for high accuracy transducers at class 3 or better.

BKM Series
Fully encapsulation Constantan foil strain gauge with a special PEEK film backing. Offers both Self-Temperature (or elastic modulus) and creep compensation simultaneously. Has high accuracy, excellent stability and high moisture resistant capability. Shows good specifications for creep and zero return. The special PEEK film backing has an exceptional high toughness. The strain gauges are primarily intended for high accuracy transducers at class 3 or better.

BEB Series
Fully encapsulation Constantan foil strain gauge with a Glass fibre reinforced epoxy backing. Offers both Self-Temperature and creep compensation simultaneously. Has an elastic modulus compensated backing. Has an excellent creep and zero return, responds quickly to applied load and recovers directly to zero. In addition it has a high thermal stability and is used for high precision transducers and high precision aluminium scales. 

Strain gauges

Self-Temperature Compensation

Every material reacts when it heats up or when it cools down. This will cause strain gauges to register a deformation in the material which will make it change signal. To prevent this from happening strain gauges are made so they will compensate this change due to temperature. Dependent on the material of the surface where the strain gauge is assembled on, a different expansion can be measured. There are some common used materials for which a standard STC-code is used. 

Zemic Europe currently offers STC-compensation for the following different surfaces / materials. The code in brackets indicates for which type of material the strain gauge is best suitable:
(9): Titanium test surfaces with a typical expansion coefficient of 8.8 x 10⁻⁶ / ℃
(11): Martensitic, Age hardenable-stainless and alloy steel test surfaces with a typical expansion coefficient of 11.3 x 10⁻⁶ / ℃
(16): Copper-based and austenitic stainless steel test surfaces with a typical expansion coefficient of 16 x 10⁻⁶ / ℃
(23): Aluminium-alloy test surfaces with a typical expansion coefficient of
23.2 x 10⁻⁶ / ℃
(27): Magnesium-alloy test surfaces with a typical expansion coefficient of
26.1 x 10⁻⁶ / ℃

Creep

When a material is pushed out of it’s natural shape by an external force, this material will always try to get back into its original, natural shape. When this happens, this so called negative creep will be registered by the strain gauges. When a product is loaded with a force, it always takes some time to reach the final deformation caused by this applied force. This creep is called positive creep. For these reasons, several different creep codes are available to best suit the creep which the customer experiences. This however is an empirical process and can’t be calculated up front. 

Zemic Europe currently offers Creep-compensation in the following possibilities. The codes are positioned from the most positive creep compensation code to most negative creep compensation code. Zemic Europe strain gauges the rule is as follows: the creep difference between two neighbouring codes is approximately
0.01-0.015%FS/30min.

Creep

 

In case you need more information or advice:  Contact us

We are looking forward to help you!

With over 50 years of experience in the development and production of strain gauges, ZEMIC gives advice on which strain gauges are the most suitable for your application.

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