Strain Gauge: Principle, Types, Features and Applications

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Strain Gauges are an important geotechnical tools that measure strain in underground cavities, tunnels, buildings, concrete, masonry dams, bridges, embedment in soil/concrete. etc. The main purpose of a strain gauge is to indirectly determine stress and its variation with time, quantitatively. Change in stress is determined by multiplying the measured strain by the modulus of elasticity.

Well, if you are confused regarding strain gauges, here’s everything that you need to know about it. We have covered its working principles, characteristics, features, as well as, application areas.

What Is A Strain Gauge?

Strain Gauge or Strain Gage measures the strain (amount of contraction as well as expansion caused by external forces) on any object. The strain gauge was invented in 1938 by Edward E. Simmons and Arthur C. Ruge.

Any basic strain gauge consists of an insulating flexible backing that supports a metallic foil pattern. The gauge is attached to the object under stress using an adhesive. The deformation in the object causes the foil to get distorted as well which ultimately changes the electrical resistivity of the foil.

This change in resistivity is measured by a Wheatstone bridge which is related to strain by a quantity called, Gauge Factor.

Types of Strain Gauges

There are several types of strain gauges based on the principle of their working viz. mechanical, optical, acoustical, pneumatic or electrical. Considering the mounting, strain gauges can be either bonded or unbonded and based on the construction, we can have foil, semiconductor, and photoelectric strain gauges.

Encardio-rite primarily deals with five different types of strain gauges:

Model EDS-11V/Hermetically Sealed Vibrating Wire Strain Gage

The model EDS-11V strain meter is suitable for embedment in soil or concrete or for surface mounting by welding on steel structures. It provides significant quantitative data on the magnitude and distribution of compressive and tensile strain and its variations with time.

The Encardio-rite strain meter incorporates the latest vibrating wire technology to provide the remote digital readout of compressive and tensile strain in dams, bridges, underground cavities, tunnels, mines, steel structures and other areas of application where strain measurement is required.

Long term stability is achieved by thermal and load cycling, the unique method of wire clamping by generating a vacuum of 1/1000 Torr inside the sensor by electron beam welding. This results in the effect of oxidation, moisture, environmental conditions and any ingress of water being completely eliminated.

Working Principle of Hermetically Sealed Vibrating Wire Strain Gage

The Encardio-rite vibrating wire strain meter basically consists of a magnetic, high tensile strength stretched wire, one end of which is anchored and the other end is displaced proportionally to the variation in strain. Any change in the strain directly affects the tension of the wire, resulting in a corresponding change in the frequency of vibration of the wire. The resonant frequency, with which the wire vibrates, is read by the readout unit. The strain is proportional to the square of the frequency and the readout unit is able to display this directly in strains.

Characteristics of Hermetically Sealed Vibrating Wire Strain Gage

1. The strain gauge is accurate, robust and low cost
2. It ensures long term stability with high reliability
3. It’s hermetically sealed under a vacuum of 0.001 Torr
4. The strain gauge is made up of stainless steel construction
5. It doesn’t require any special installation and maintenance
6. A wide range of accessories are available along with this strain gauge
7. A thermistor is available for temperature correction
8. Remote digital readout for strain measurement
9. Ease in data logging

Applications of Hermetically Sealed Vibrating Wire Strain Gage

1. Measurement and monitoring of strain in concrete, rock and ..[Continue Reading]