TOPIC- Load cell A load cell is a transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured .

Thing to be considered before buying load cell Magnitude of force/load/weight being measured-This is important .If you apply loads – even temporarily – beyond this maximum load – you can seriously damage your load cell and might need to recalibrate it to ensure accurate readings. Accuracy needed for application-Accuracies of load cells are generally rated as a percentage of full scale. So you need to pick the right capacity load cell for your application

Operating Temperature Conditions-Although most load cells offer certain degree of temperature compensation, you need to consider the operating conditions before you pick a load cell. Direction of loading -Load cells generally are designed for measurement in one direction - either in Tension or in Compression. Mounting Options - Pay special attention to the mounting options offered by load cells on the top as well as bottom of the load cell. Total cost of Ownership-You need to consider the total cost of solution before making a decision about which load cell to purchase

Types of load cell 1. BASED ON WORKING PRINCIPLE- 2. Based on design Cantilever/Bending beam Compression Tensile Shear 2. Based on design Bending beam Binocular Beam Shear beam (Single ended/Double ended) S-type

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HOW DOES A LOAD CELL WORKS? A strain gauge based load cell is made of a specially engineered mechanical component called as an element. Four strain gauges are positioned precisely and bonded on to the element using a special adhesive. (strain gauge is a device that changes resistance when it is deformed or stressed).

The force-electrical signal conversion happens in two stages- force applied deforms the element which in turn deforms the strain gauges. strain gauges converts the deformation to electrical signals The strain gauges are wired in Wheatstone bridge configuration. The bridge is connected to a power supply unit and a signal conditioner through a 4-core cable. When an input voltage (10VDC) is applied to the bridge, the output is a voltage in the range of few millivolts.

EXCITATIONAND RATED OUTPUT The bridge is excited with stabilized voltage usually 10V ,but can be 20V, 5V or less for battery powered instrumentation. The output will be in the form of voltage.

Basic specifications of a load cell- 1. Capacity (kg) 2 Basic specifications of a load cell- 1.Capacity (kg) 2.Full scale Output (mV) 3.Sensitivity (mV/V) 4.Excitation Voltage (VDC) 5.Input resistance (ohms) 6.Output resistance (ohms) Below are the commonly used standard values- 1.Excitation voltage: 10V or 12V DC 2.Full scale output: 10mV, 20mV and 30mV 3.Load cell sensitivity: 1mV/V, 2mV/V and 3mV/V 4.Input resistance: 350Ω and 700Ω 5.Output resistance: 350Ω and 700Ω Sensitivity = full scale output/excitation voltage .

NUMERICAL PROBLEM 1. A strain gauge load cell is given a excitation voltage of 10 V , it was seen that the full scale output voltage was 20 mV. What is its sensitivity? Solution- Sensitivity = full scale output/excitation voltage therefore,20mV/10V = 2mV/V

COMMON ISSUES 1.Mechanical mounting – The cells have to be properly mounted. Wrong mounting may result in the cell reporting forces along undesired axis,which still may somewhat correlate to the sense load, confusing the technician. 2.Overload- Within its rating , the load cell deforms elastically and returns to its shape after being unloaded.

3. Wiring issue – The wires to the cell may develop high resistance due to corossion . 4.Electrical damage –The load cell can be damaged by induced or conducted current.

Thank you BY-GOURI ANDHARE ROLL NO -06