February 26, 2020

Strain Gauge Type Load Cell- Introduction & How it Works?

Engineered precisely for civil engineering application, Encardio Rite Model ELC-30S Centre Hole Load Cell includes a high strength martensitic stainless steel cylinder. Eight strain gauges are positioned at 45 degrees to each other, thus depreciating the impact of uneven and eccentric loading. The strain gauges are then connected in a Wheatstone bridge circuit.

Engineered precisely for civil engineering application, Encardio Rite Model ELC-30S Centre Hole Load Cell includes a high strength martensitic stainless steel cylinder. Eight strain gauges are positioned at 45 degrees to each other, thus depreciating the impact of uneven and eccentric loading. The strain gauges are then connected in a Wheatstone bridge circuit.

Strain Gauge Type Load Cells can be obtained in standard capacities ranging from 200-2000 kN. Load cells having an internal diameter different from our standard range are available on request.

Strain Gauge Type Load Cell: Application Areas

Strain Gauge Type Load Cells can be used to determine the tensile force in a ground anchor, rock bolt, cable or tie back. It also finds its application in the measurement of compressive load between structural members, i.e. at the junction between a beam and the top of a pile strut or tunnel supports.

One of the greatest concern of geologists, design engineers, and construction companies is the breakdown of the roof or falling of sidewall in underground cavities. As one of the most severe natural disaster, slope failures and landslides are susceptible to happen anywhere in the world without making any distinctions.>

No matter what it is, from the collapse of the roof of a mine or buckling of the sidewall of an underground powerhouse cavity to a landslide or a slope failure, the natural disaster costs an enormous amount of loss of life, property, wealth, and time.

This leads to taking preventive and corrective action to reduce the uncertainty of the doom. One such action is called anchoring where pre-stressed grouted anchors provide an active support system to the structure.

Advantage of Resistive Strain Gauge Type Load Cells

Encardio Rite Model ELC-30S Load Cell is sturdily designed to be used in a stressful environment like the one during construction activity. The main advantage of Strain Gauge Type Load Cell when comparing to a vibrating wire load cell is the ease with which the reading takes place.

The ELC-30S Load Cell can be directly read on a suitable indicator.

On the other hand, the reading for three (or six) elements of the vibrating wire load cell has to be taken separately and then finalized with the average to get the correct data. Likewise, in the case of data logging, the vibrating wire load cells require three (or six) channels.

Another advantage is that the Strain gauge type load cell is hermetically sealed by electron beam welding with a vacuum of 1/1000 Torr inside it, making it immune to ingress of water and most corrosive environments.

Handling of Strain Gauge Type Load Cell

The load cell is a sensitive instrument which works well in a robust environment but needs to be taken care to function accurately. It should be dealt with the utmost care during transportation and installation. Special attention should be paid to avoid dropping the instrument in any circumstances.

The impact generated on being dropped results in a shift of the zero reading. On the other hand, it can also lead to permanent damage rendering the instrument useless.

Strain Gauge Type Load Cell – Construction

Strain-Gauge-Load-Cell
Precision and experience go into making of a perfect load cell that can measure the load with accuracy.

At the base of the stainless steel columnar element stands the strain gauges which are installed in a groove. The stainless steel diaphragm is electron beam welded to the element to cover the groove resulting in a vacuum of around 1/1000 Torr inside the sensor.

The construction ensures that the sensor becomes immune to atmospheric corrosion and the effect of ingress of water. To provide approximately the same mV/V output for a variety of zero to full load, the sectional area of the columnar element and the depth of the groove in it is varied in different capacity load cells.

The instruments include 1 Cable joint housing and 1 Cable Gland- PG 9 along with the Load Cell.

Also Read: Load Cells: Types, How It Works, Applications, & Advantages

Bearing and Load Distribution Plates

It should be kept in mind that the Centre Hole Load Cells are very sensitive and responsive to eccentric loading. The susceptibility is maintained by providing a load distribution plate of proper dimensions at the top. For some application, a load-bearing plate may also be used at the bottom of the load cell.
Standard plates stocked by Encardio Rite have the following dimensions:

CapacityBearing PlateLoad Distribution Plate
kNT mmOD mmID mmWt. kgOD mmID mmWt. kg
20023155116275401
500351551162.598521.5
1000452001505135783.5
10004522517261551054
1500552251658150855.5
1500552602009.51801305.5
200065260195121801059
20006526022672101558.5

Cable Connection

Cable connection circuit board
The leads from the Wheatstone bridge circuit terminate on a six-pin glass to metal seal (2 pins blank) which is integrally electron beam welded to the stainless steel body of the centre hole load cell. A cable joint housing and cable gland are provided for cable connection.

Strain Gauge Type Load Cell: Installation Requirement

Load Cell Installation
The following tools/accessories are required for proper cable jointing and installation of the load cell:

  1. Soldering iron 25 watts, temperature-controlled
  2. Rosin 63/37 solder wire RF-3C, 30 swg.
  3. Thread sealant (Loctite 577 or equivalent)
  4. Cable jointing compound
  5. Accessories for cable jointing compound i.e. rotary tin cutter, stainless steel rod 2 mm φ, 150 mm length for stirring, spatula & pouring funnel
  6. Acetone (commercial)
  7. Toothbrush
  8. Cloth for cleaning (lintless)
  9. Wire stripper and cable cutter
  10. Pliers 160 mm
  11. Spanner 18/19
  12. Fixture for jointing up to five load cells
  13. Digital multi-meter
  14. Encardio Rite model EDI-53L digital indicator/logger

This was all about Encardio Rite Model ELC-30S Strain Gauge Type Load Cell. We will be discussing the installation procedure in the next blog.

If you have any doubts or queries, feel free to drop it in the comment section below.

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