PLATINUM-TUNGSTEN STRAIN GAGES: THE PLATINUM STANDARD

Since 2002 , Micro-Measurements has been producing foil strain gages using our advanced foil technology. Our strain gages are highly sensitive resistive sensors used to determine surface strain on an object caused by applied force. These sensors are used to measure stress in the aviation, military, oil & gas, and medical industries. Engineers throughout the world trust our strain gages to capture stress analysis data from automobiles, aircrafts, bridges, medical scales, and more.

In today’s blog, we discuss the high sensitivity available using our Platinum - Tungsten (Pt-W) strain gages (strain gages made using 92% platinum, 8% tungsten foil) and why these sensors are the platinum standard in high-sensitivity strain measurement.

First, how is strain sensitivity of a strain gage determined? 

After bonding to an object that will subsequently be mechanically loaded, strain gages have an initial resistance (could be anything from 50 ohms to 5000 ohms). When subjected to the object’s surface deformation caused by the applied load, the sensors change resistance. It is the change in resistance relative to the applied strains that determines strain sensitivity. To achieve this relationship, a calibration is performed on batches of strain gages, whereby the test gage is subjected to a known applied strain and the resulting change in gage resistance measured. The transfer coefficient value relating resistance change to strain is recorded with that batch of gages and is termed “gage factor”.

How sensitive are Micro-Measurements’ Pt-W strain gages? 

The unique Micro-Measurements strain gages made with 92% platinum & 8% tungsten sensing foil are highly sensitive. In fact, this strain gage series offers a strain sensitivity (or gage factor, as described above) more than double all other foil strain gage types. This feature is particularly useful in fatigue-rated load cells since strain levels can be reduced while still providing a standard 2 mv/V output. It is also helpful in dynamic (impact) transducers since normal transducer deflections can be reduced and dynamic response improved, while maintaining standard signal levels. These Pt-W  gages are supplied with flexible polyimide backings, full encapsulation, and preformed solder dots.

What are the limitations of the Pt-W strain gage?

While Pt-W strain gages might sound ideal for transducers, they do have a couple of limitations. Most notably the following:

• Pt-W strain gages have high thermal sensitivity. This makes static measurements extremely difficult, even in full-bridge circuits.

• Pt-W strain gages have a limited linear strain range and cannot be used for high strain measurements.

However, even with these limitations there are many applications for which no other strain gage type will suffice.

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