Load Cells Types, How It Works, and Applications

1. Load Cells Types, How It Works, Applications, & Advantages

2. 1 5 INTRODUCTION LOAD CELL CIRCUIT 2 6 WHAT IS A LOAD CELL? TYPES OF LOAD CELLS TABLE OF CONTENT 3 7 WHAT IS A LOAD CELL USED FOR? ADVANTAGES OF LOAD CELL 4 8 WHAT IS THE WORKING PRINCIPLE OF A LOAD CELL? APPLICATIONS OF LOAD CELL

3. 1 INTRODUCTION Load cells are geotechnical instrument that are commonly used to measure weight. They can measure things as small as a needle to as heavy as big drilling machines.

4. 2 WHAT IS A LOAD CELL? A load cell is a transducer that converts the mechanical force into readable electrical units, similar to our regular weighing scales. The load cell sensors are always bonded along with elastic material, known as strain gauges.

5. 3 WHAT IS A LOAD CELL USED FOR? Load cells find their application in the geotechnical field and, they are commonly used to monitor: • • • • Deep foundations: excavation bracing like struts, soldier pile; tiebacks or anchors; retaining walls Tunnels and shafts: Steel liner plate, cast-in-place concrete, segmented precast concrete, shotcrete Dams: Concrete Dams, Underground Power House Piles: Pile load test

6. 4 WHAT IS THE WORKING PRINCIPLE OF A LOAD CELL? Strain Gauges are thin elastic material made up of stainless steel and are fixed inside the load cells using proprietary adhesives. When a force is applied on the load cell, it bends or stretches causing the strain gauge to move with it and when the length and cross-section of the strain gauge changes, its electrical resistivity also gets altered, thereby changing the output volt- age. A load cell works only when the strain gauge has some change in its resistance and, we use the Wheatstone Bridge to measure this change.

7. 5 LOAD CELL CIRCUIT The input voltage supplied by a signal conditioner or digital display is attached to the two opposite corners of the bridge i.e. C and D whereas, the output voltage is measured by joining the A and B resistors to the signal side of the digital display.

8. 5 LOAD CELL CIRCUIT When no load is applied to the load cell (Load=0), the circuit is said to be balanced. As soon as the load is applied to it, the strain gauge resistors will witness a change in its resistance, thereby, altering the voltage flowing through the circuit. Hence, the voltage across A and B will change which will be displayed as the weight on the readout unit or the digital display. The output of the Wheatstone bridge or a load cell is an analogue data which is con- verted to readable units using an interpreter.

9. 6 TYPES OF LOAD CELLS Model ELC-150S-H High Capacity Compression Load Cell The Encardio-rite Model ELC-150S-H high capacity compression load cell is exten- sively used for compressive load measurement during testing of piles. It is a resistive strain gage type precision engineered, high capacity load cell sensor designed to measure large compressive load or axial forces.

10. 6 TYPES OF LOAD CELLS The load applied to the cell can be measured by using any standard digital read-out unit suitable for resistance strain gauge applications. The load cell has great resistance to extraneous forces and is protected against dust, moisture and adverse environmental conditions.

11. 6 TYPES OF LOAD CELLS Model ELC-210S Resistive Strain Gauge Type Compression Load Cell The Encardio-rite Model ELC-210S resistive strain gauge type compression load cell is a heavy duty precision load cell specially designed to meet the increasing demand in load measurement with a high degree of accuracy and reliability. The load cell sensor is ideally suited for measurement of compressive load or forces in struts application. It is available in capacities ranging from 1000 kN to 3500 kN.

12. 6 TYPES OF LOAD CELLS Model ELC-30S Resistive Strain Gauge Type Center Hole/Anchor Bolt Load Cell Encardio-rite Model ELC-30S resistive strain gauge type centre hole load cell is ex- tensively used to determine the load in rock bolts, tiebacks, foundation anchors, cables or struts depending on the application. It is also used for compressive load measurement between structural members i.e. tunnel supports or at the junction between a beam and the top of a pile strut. It is specially designed for civil engineering applications and is available in capaci- ties ranging from 200 kN to 2000 kN.

13. 6 TYPES OF LOAD CELLS Model ELC-30S-H Resistive Strain Gauge Type Center Hole/Anchor Bolt Load Cell Encardio-rite Model ELC-30SH is used for compressive load measurement between structural members i.e. tunnel supports or at the junction between a beam and the top of a pile strut. To minimize the effect of uneven and eccentric loading, the strain gauges are equal- ly spaced along the circumference. The load applied to the cell can be measured by using any standard digital read-out unit suitable for resistance strain gage applications.

14. 6 TYPES OF LOAD CELLS Model ELC-31V Vibrating Wire Hydraulic Center Hole-Anchor Bolt Load Cell The Encardio-rite Model ELC-31V is a precision engineered vibrating wire hydraulic centre hole load cell, specially designed for civil engineering applications. The model ELC-31V vibrating wire hole load cell is made of a sensitive pressure pad which is formed by joining together two very stiff steel discs at their periphery.

15. 6 TYPES OF LOAD CELLS The space inside the cell is filled with de-aired fluid. When the load is applied to the cell, the pressure on the fluid changes. This change in fluid pressure is used to record the variation in the load being applied to the cell.

16. 6 TYPES OF LOAD CELLS Model ELC-32V Vibrating Wire Center Hole-Anchor Bolt Load Cell The Encardio-rite Model ELC-32V is a precision engineered load cell sensor with a central cylindrical hole. It is specially designed for civil engineering applications. The load applied to the cell is measured individually by the vibrating wire strain gauges using Encardio-rite model EDI-51V digital read-out unit for vibrating wire sensors

17. 6 TYPES OF LOAD CELLS Pneumatic Load Cell Pneumatic Load cells are designed as such that the balancing pressure is automati- cally adjusted by them. When air pressure is applied to one end of the diaphragm, it releases through the other end/nozzle, at the bottom of it. A pressure gauge attached to the load cell measures the pressure inside the cell.

18. 6 TYPES OF LOAD CELLS Piezoelectric Load Cell Piezoelectric load cells work on the same principle as that of the strain gauge load cells but, the voltage output is generated by piezoelectric material which is propor- tional to the deformation of the load cell. The Piezoelectric load cells find their application in the areas of dynamic loading where strain gauge load cells often fail with high dynamic loading cycles.

19. 7 ADVANTAGES OF A LOAD CELL • • • • • • • Load Cells have rugged & robust construction along with outstanding reliability and long term stability They are specially designed to suit the harsh & severe industrial environment. Load Cells are temperature compensated. They have a stable system with no moving parts and linkages. A few of them have multiple strain gages incorporated to reduce positioning effect. Any standard strain gage bridge measuring read-out device can be used with the load cells. The load cells have negligible side and eccentric load effect

20. 8 APPLICATIONS OF LOAD CELLS • • • • • • • • • To determine the load in rock bolts, tiebacks, foundation anchors, cables or struts. Proof testing and long term performance monitoring of different kind of anchor systems. Compressive load measurement between structural members i.e. tunnel supports or at the junction between a beam and the top of a pile strut. Used extensively for correlating data obtained from borehole extensometers. To determine the load in experimental research, pile testing and measurement of the thrust of rocks. Compressive load measurement between structural members. Measurement of compressive load and axial forces in struts. Load testing in piles. Determination of roof convergence in underground mines.

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