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BACKGROUND
The transducer is a device which can convert a form of energy into another form, such as pressure and force into the electrical signal, etc. A load cell is such a transducer that can convert the applied force into an electrical signal, and its magnitude is directly proportional to the other one. Hydraulic, Pneumatic, piezoelectric and strain gauge are the various types of the load cell in which the most important is a strain gauge.1 It is widely used in industry to measure the essential parameters like weight, force, displacement, etc. It is even used to determine the acting torque, stress, or strain by indirect methods.
Strain gauge materials show a change in resistance when exposed to mechanical or physical variation in the property. The strain gauge is available in 120 ohm, 130 ohm, and 140-ohm resistance values, and its setup consists of mild steel structured strip which is duly grounded from both the sides that are supported on a massive stable base structure, rigidly mounted on a sturdy solid square bar. The strain gauge can measure a slight change in resistance with a variation of temperature, as it is connected in the form of bridge type structure which processed the generated electronic signal by the instrumentation amplifier. The bridge connection may contain one, two, or four strain gauges as the active element and balance resistances as the passive element.2
Apart from strain gauge, hydraulic load cell uses the conventional cylinder and piston arrangement, whereas a pneumatic load cell uses a diaphragm of a flexible material. Piezoelectric crystals are used in piezoelectric load cells, which is used for dynamic force measurement.
The main objective of this experiment of this experiment is to measure load using the load cells.
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REQUIREMENTS
Materials: Load cell
Mechanical stand and pan with cantilever strip
Electronics exciter with a digital indicator
Weight ranging from 20 kg to 500 kg.
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PROCEDURE
First of all, ensure that all the equipment has proper connections, and electronic display responds gentle pressure at the cantilever. Now, calibrate the reading on the screen to “0.0” with empty pan hooked, and note down the bridge excitation voltage on DMM. After placing the calibration weight in pan, note down the display reading.3 Repeat this process with different weights, and after this, reverse the process by sequentially removing the weights.
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CONCLUSION
The method of finding load measurement using a load cell (strain gauge) is discussed. Strain gauge has a bridge type structure which can record slightly change of resistance due to temperature variation, and show it on the display unit.
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REFERENCES
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J. L. M. J. Moon, “Load cell having reduced sensitivity to non-symmetrical beam loading”. US Patent US5600104A, 20 10 1997.
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D. H. B. R. B. H. L. W. S. Agras, “A Mechanical Strain Gauge For Recording Penile Circumference Change,” Journal of Applied Behaviour Analysis, vol. 3, no. 79-76, 1970.
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Khajure N.S., “Lab Manual,” Shri Ramchandra College of Engineering, Pune.
