0 ASSIGNMENT APPLIED INSTRUMENTATION RE - 501 Submitted byMORADIYA PIYUSH B ROLL NO – 14 J4-1003-2012M. TECH. INPROCESSING & FOOD ENGINEERINGSubmitted to DR. R. A. GUPTADEPARTMENT OF EXTENSION EDUCATION COLLEGE OF AGRICULTUR AL ENGINEERING & TECHNOLOGYJUNAGADH AGRICULTURAL UNIVERSITYJUNAGADH
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Elastic deformation of a flexible membrane that separates two different pressures. The
deformation of the diaphragm is dependent on the difference in pressure between the
two faces. It can be used to measure gauge, differential, vacuum or absolute.
It uses the deflection of a flexible membrane that separates regions of different
pressure. The amount of deflection is repeatable for known pressures so the pressurecan be determined by using calibration. The deformation of a thin diaphragm is
dependent on the difference in pressure between its two faces. The reference face can
be open to atmosphere to measure gauge pressure, open to a second port to measure
differential pressure, or can be sealed against a vacuum or other fixed reference
pressure to measure absolute pressure. The deformation can be measured using
mechanical, optical or capacitive techniques. Ceramic and metallic diaphragms are
used.
Applications
A diaphragm is a more mechanically stable element than a bourdon tube and can stand
mechanical shock with less damage. Diaphragm Pressure Gauges can be used toindicate pressures below those practical for bourdon tube pressure gauges.
2 - Testing Pump3 - Pressure Gauge to be calibrated
4 - Calibration Weight
5 - Weight Support
6 - Piston7 - Cylinder
8 - Filling Connection
Dead weight testers are a piston-cylinder type measuring device. As primary
standards, they are the most accurate instruments for the calibration of electronic or
mechanical pressure measuring instruments.
They work in accordance with the basic principle that P= F/A, where the pressure (P)
acts on a known area of a sealed piston (A), generating a force (F). The force of thispiston is then compared with the force applied by calibrated weights. The use of high
quality materials result in small uncertainties of measurement and excellent long term
stability.
Dead weight testers can measure pressures of up to 10,000 bar, attaining accuracies of
between 0.005% and 0.1% although most applications lie within 1 - 2500 bar. The
pistons are partly made of tungsten carbide (used for its small temperature
coefficient), and the cylinders must fit together with a clearance of no more than a
couple of micrometers in order to create a minimum friction thus limiting the
measuring error.
The testing pump (2) is connected to the instrument to be tested (3), to the actual
measuring component and to the filling socket. A special hydraulic oil or gas such as
compressed air or nitrogen is used as the pressure transfer medium. The measuring
piston is then loaded with calibrated weights (4). The pressure is applied via an
integrated pump (1) or, if an external pressure supply is available, via control valves in
order to generate a pressure until the loaded measuring piston (6) rises and 'floats' on
the fluid. This is the point where there is a balance between pressure and the mass
load. The piston is rotated to reduce friction as far as possible. Since the piston isspinning, it exerts a pressure that can be calculated by application of a derivative of the
Describe the working principle of following electrical members used
for force measurement :
1. Spring
A spring is an elastic object used to store mechanical energy. Springs are usually made
out of spring steel. Small springs can be wound from pre-hardened stock, while larger
ones are made from annealed steel and hardened after fabrication. When a spring is
compressed or stretched, the force it exerts is proportional to its change in length. The
rate or spring constant of a spring is the change in the force it exerts, divided by the
change in deflection of the spring. That is, it is the gradient of the force versus
deflection curve.
An extension or compression spring has units of force divided by distance, for
example lbf/in or N/m.
Torsion springs have units of force multiplied by distance divided by angle,
such as N·m/rad or ft·lbf/degree.
Spring is widely used in the spring balance instrument.
Working principle of spring balance:
- A spring balance is used for measuring the weight of an object. It has a spring, one
end of which is fixed. The other end of the spring is attached to a hook to hold an
object. The steel spring is enclosed in a metallic case. There is a pointer, which is
attached to the spring. The pointer moves over a scale marked on the metallic case.
- One should always check that the pointer points at the zero mark of the scale under
no-load condition.
- When a load is attached to the hook, the spring gets elongated because of the weight of the body. Along with the spring, the pointer also moves over the scale. The final
position of the pointer gives the weight of the body.
A structural frame system is a combination of primarily vertical and horizontal
members that are designed to transmit applied loads to the ground.
The major components of the frame system are horizontal members, vertical members,
and some sort of foundation. These members work together to resist both verticallyand horizontally applied loads. Vertical loads are typically the result of the applied
live loads that the building is designed to contain as well as climactic loads such as
wind, snow, and seismic activity. Horizontal loads are most commonly applied by
wind and seismic activity.
Vertical Loads – Vertical loads are generally applied to either a roofing system or a
flooring system. These systems can consist of a variety of elements such as metal deck,
concrete slabs, wood sheathing, etc. These elements are usually fastened to or rest
upon horizontal members called beams. Beams are designed to resist these loads. In
certain instances, the flooring system can aid the beams in supporting the loads by
adding rigidity to the beams. These systems are called composite flooringsystems. Typically, the loads applied to the beams are then transferred through the
beams’ end connections to either another horizontal member, called a girder, which is
in turn connected to a vertical member, or directly to the vertical member. These
vertical members are called columns. The columns in turn transmit the loads axially to
their bases, which usually rest upon a foundation. The most common foundation type
for a column is called a spread footing. A spread footing is a mass of reinforced
concrete that distributes the load over a larger area to the earth. If the soil is not
capable of supporting these loads, the column may rest upon a pile cap, which, in turn,
rests upon piles. A pile cap is similar to a spread footing in that it is a mass of
reinforced concrete. Piles are vertical structural members that are usually driven into
the ground to a depth where the soil is capable of supporting the loads.
Below is an axially loaded diagram and a problem sketch to explain the meaning
Cantilevers are widely found in construction, notably in cantilever bridges and
balconies.
In cantilever bridges the cantilevers are usually built as pairs, with each cantilever
used to support one end of a central section. The Forth Bridge in Scotland is an
example of a cantilever truss bridge.
Temporary cantilevers are often used in construction. The partially constructed
structure creates a cantilever, but the completed structure does not act as a cantilever.
This is very helpful when temporary supports, or falsework, cannot be used to support
the structure while it is being built (e.g., over a busy roadway or river, or in a deep
valley). So some truss arch bridges (see Navajo Bridge) are built from each side as
cantilevers until the spans reach each other and are then jacked apart to stress them in
compression before final joining. Nearly all cable-stayed bridges are built using
cantilevers as this is one of their chief advantages. Many box girder bridges are built segmentally, or in short pieces. This type of construction lends itself well to balanced
cantilever construction where the bridge is built in both directions from a single
support.
These structures are highly based on torque and rotational equilibrium.
A schematic images of three types of cantilevers:
The example of first figure has a full moment connection
(like a horizontal flag pole bolted to the side of a building).
The example of second figure is created by an extension of a simple supported beam
(such as the way a diving-board is anchored and extends over the edge of a swimmingpool).
The example of third figure is created by adding a Robin boundary condition to the
beam element, which essentially adds an elastic spring to the end board.
The middle and bottom example may be considered structurally equivalent, depending
on the effective stiffness of the spring and beam element.
The micrometer screw and the vibrating reed are attached to the internal bosses of the
ring. In modern rings, the upper and lower internal and external bosses are machined
as an integral part of the ring to avoid mechanical interferences during the application
of the force.
To read the diameter of the ring, the vibrating reed is set in motion by gently tapping it
with a pencil. As the reed is vibrating, the micrometer screw on the spindle is adjusteduntil the button on the spindle just contacts the vibrating reed, dampening out its
vibrations. When this occurs a characteristic buzzing sound is produced. At this point a
reading of the micrometer dial indicates the diameter of the ring.
The number of divisions on the micrometer dial and the graduation of the vernier
index vary by type of proving ring. Typically, proving rings are designed to have a
deflection of about 0.84 mm (0.033 in) to 4.24 mm (0.167 in). The relative
measurement uncertainty can vary from 0.075 % to about 0.0125 %.
5. Load cell
A load cell is a transducer that is used to convert a force into electrical signal. This
conversion is indirect and happens in two stages. Through a mechanical arrangement,
the force being sensed deforms a strain gauge. The strain gauge measures the
deformation (strain) as an electrical signal, because the strain changes the effective
electrical resistance of the wire. A load cell usually consists of four strain gauges in a
Wheatstone bridge configuration. Load cells of one strain gauge (Quarter Bridge) or
two strain gauges (half bridge) are also available.
The electrical signal output is typically in the order of a few millivolts and requires
amplification by an instrumentation amplifier before it can be used. The output of the
transducer can be scaled to calculate the force applied to the transducer.
Although strain gauge load cells are the most common, there are other types of load
cells as well. In industrial applications, hydraulic (or hydrostatic) is probably the
second most common, and these are utilized to eliminate some problems with strain
gauge load cell devices. As an example, a hydraulic load cell is immune to transient
voltages (lightning) so might be a more effective device in outdoor environments.