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Force Measurement

Force Measurement.

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Force Measurement

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  1. Force Measurement • Force is a quantity capable of changing the size, shape, or motion of an object. It is a vector quantity and, as such, it has both direction and magnitude. In the SI system, the magnitude of a force is measured in units called Newton, and in pounds in the British/American system.

  2. Force Measurement • If a body is in motion, the energy of that motion can be quantified as the momentum of the object, the product of its mass and its velocity. If a body is free to move, the action of a force will change the velocity of the body.

  3. Force Measurement There are four basic forces in nature: • gravitational, • magnetic, • strong nuclear, and • weak nuclear forces. The weakest of the four is the gravitational force. It is also the easiest to observe, because it acts on all matter and it is always attractive, while having an infinite range. Its attraction decreases with distance, but is always measurable. Therefore, positional "equilibrium" of a body can only be achieved when gravitational pull is balanced by another force, such as the upward force exerted on our feet by the earth's surface.

  4. Force Measurement Link-Type Load Cell The diagram above represents what might happen if a strip of metal were fitted with four gauges.An downward bend stretches the gauges on the top and compresses those on the bottom.A load cell may contain several similar strain gauges elements. 3 4 1 2

  5. Shear Force Measurement Beam-Type Load Cell The strain gauges are bonded on the flat upper and lower sectionsof the load cell at points of maximum strain. This load cell type is used for low capacities and performs with good linearity. Its disadvantage is that it must be loaded correctly to obtainconsistent results http://www.rdpelectronics.com/ex/hiw-sglc.htm

  6. Force Calculation Where: A is the cross-sectional area E is the modulus of elasticity v is Poissin’s ratio of the material Sg is a gauge factor VO VS

  7. Force Measurement VO VO= k PVS Therefore Force P is measured in terms of Voltage out put as VO VS

  8. Force Measurement Ring-Type Load Cell • This Load incorporates ring as the elastic element. The ring element can be designed to cover wide range loads by: • radius, • The thickness, t, • The depth w. • Strain Gauge or LVDT could be employed to measure displacement related to Force applied. In case of LVDT compression of the ring ,the relationship betweendisplacement  and Load F and is given by: •  = 1.79 FR3/(Ewt3) = K .F Where E is modulus of Elasticity of material; K for given ring is constant = 1.79 R3/(Ewt3) Out put Volts = Vo = S  Vs and S is sensitivity of LVDT F R LVDT t w

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