Strain Gauges or Strain Gages are the geotechnical instruments used to measure strain or pressure applied on an object. This object can be as small as a machine or even as large as a TBM. Invented in 1938 by Edward E. Simmons and Arthur C. Ruge, strain gauges have been extensively used in geotechnical engineering since then.
While there are numerous types of strain gauges that are used to determine strain, here are the Encardio’s Models of the strain gauges along with their working principle, features, and applications.
Different Types Of Strain Gauges
Encardio mainly deals with four different types of strain gauges. We have the following Models:
Model EDS-11V Hermetically Sealed Vibrating Wire Strain Gage
Model EDS-12V Vibrating Wire Sister Bar Strain Meter
Model EDS-20V-V Series Vibrating Wire Strain Gage
Model EDS-30V Shortcrete Strain Gage
Let’s understand each one of them in detail with their working principle, specifications, and features.
Model EDS-11V Hermetically Sealed Vibrating Wire Strain Gauge
The Model EDS-11V hermetically sealed vibrating wire strain gauge finds its application mainly in soil, concrete structures, or on steel structures. It gives precise readings for the distribution of both the compressive, as well as, tensile strain varying with time.
Operating Principle Of Model EDS-11V Hermetically Sealed Vibrating Wire Strain Gauge
The Model EDS-11V has a magnetic wire with high tensile strength. One of the ends of the wire is anchored while the other one displaces proportionally with respect to the strain.
Even a minor deflection in the strain directly affects the tensile strength of the wire thereby, changing its corresponding vibrating frequency. The strain is proportional to the resonant frequency of the wire and is directly displayed through a readout unit.
Strain Meter & Its Components
EDS-11 Strain meter
In an EDS-11 strain gage meter, the coil magnet assembly is enclosed in a stainless steel ‘magnet enclosure’ which is an electron beam welded to two stainless steel tubes with integral stainless steel bellows which are rubberized for protection.
The purpose of the bellows is to reduce the modulus of elasticity of the strain meter such that it truly reflects the expansion and contraction of the concrete in which it’s embedded or the steel structure to which it is welded.
The bellows are a special feature of Encardio-rite strain meters. The ends of the stainless tubes are electron beams welded to two cylindrical end blocks, one of which has a ‘V’ groove around its circumference. The vibrating wire assembly is permanently anchored to the end blocks.
The leads from the coil magnet are terminated on the glass to metal seal which is integrally electron beam welded to the stainless steel body of the strain meter. The two pins marked red and black on the glass to metal seal are connected to the coil magnet.
The other two pins are used with a thermistor for measurement of temperature. A cable joint housing and cable gland are provided for the cable connection. Standard cable gland is NG 16 MS which is suitable for a cable size of 6-8 mm.
EDS-12/13 Spider For Strain Rosettes
Encardio-rite manufactures spiders for five and thirteen position strain rosettes. A strain rosette is used to measure strains along different directions of the component that is being monitored.
The spider is precisely machined to the specified angles. The strain gage meters are screwed on to the 200 mm rods attached to the spider at the correct angular positions.
The Encardio-rite Model EDS-12 five position spider permits precise and accurate installation in a concrete dam or structure of four strain meters at angles of 0°, 45°, 90°, and 135° in one plane and one strain meter at right angles to this plane.
The Encardio-rite Model EDS-13 thirteen position spider has eight rods in the vertical plane at 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°; four rods in a plane at 45o to the above plane at angular positions of 22.5°, 112.5°, 202.5°, 292.5° and one rod placed ...[Continue reading]
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