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Multiplexing, Demultiplexing and Data Acquisition Systems
Multiplexing, Demultiplexing and DataAcquisition Systems
Data acquisition systems (DAS) interface between the real world of physical parameters, which are analog, and the artificial world of digital computation and control (digital systems are used widely because complex circuits are low cost, accurate, and relatively simple to implement. In addition, there is rapid growth in the use of microcomputers to perform difficult digital control and measurement functions).
The devices that perform the interfacing function between analog and digital worlds are known as data converters ( ADC &DAC).
Besides the converters, data acquisition and distribution systems may employ one or more of the following circuit functions:
Transducers, Amplifiers, Filters, Nonlinear analog functions, Analog multiplexers, Sample-holds.
Data Acquisition Systems Basics
Digital Data Acquisition System
The input to the system is a physical parameter such as temperature, pressure, flow, acceleration, and position, which are analog quantities is first converted into an electrical signal by means of a transducer; once in electrical form, all further processing is done by electronic circuits.
An amplifier boosts the amplitude of the transducer output signal to a useful level for further processing. Transducer outputs may be microvolt or millivolt level signals, which are then amplified to 1 to 10V levels.
The amplifier is frequently followed by a low-pass active filter that reduces high-frequency signal components, unwanted electrical interference noise, or electronic noise from the signal.
Data Acquisition System Functioning
The processed analog signal next goes to an analog multiplexer, which switches sequentially between a number of different analog input channels.
Each input is in turn connected to the output of the multiplexer for a specified period of time by the multiplexer switch. During this connection time, a sample-hold circuit acquires the signal voltage and then holds its value while an A/D converter converts the value into digital form. The resultant digital word goes to a computer data bus or to the input of a digital circuit
Data Acquisition System Functioning
Data Distribution System
The data distribution portion of a feedback control system, illustrated in the previous slide is the reverse of the data acquisition system.
The computer, based on the inputs of the data acquisition system, must close the loop on a process and control it by means of output control functions.
These control outputs are in digital form and must, therefore, be converted into analog form in order to drive the process.
The conversion is accomplished by a series of D/A converters.
Data Distribution System Functioning
Each D/A converter is coupled to the computer data bus by means of a register, which stores the digital word until the next update.
The registers are activated sequentially by a decoder and control circuit, which is under computer control.
The D/A converter outputs then drive actuators that directly control the various process parameters such as temperature, pressure, and flow.
Thus, the loop is closed on the process and the result is a complete automatic process control system under computer control.
Data Distribution System Functioning
Multiplexing and Demultiplexing
• Multiplexing (and demultiplexing) allows for sending multiple signals through a single medium as well as for bidirectional use of that medium.
Multiplexing and Demultiplexing
• A MUX is a digital switch that has multiple inputs (sources) and a single output (destination).
• The select lines determine which input is connected to the output.
• MUX Types 2-to-1 (1 select line) 4-to-1 (2 select lines) 8-to-1 (3 select lines) 16-to-1 (4 select lines)
Multiplexer Block Diagram
SelectLines
Inputs(sources)
Output(destination)
12N
N
MU
X
Multiplexing and Demultiplexing
MP3 PlayerDocking Station
Laptop Sound Card
DigitalSatellite
DigitalCable TV
Surround Sound System
MU
X
D0
D1
D2
D3
Y
B A Selected Source
0 0 MP3
0 1 Laptop
1 0 Satellite
1 1 Cable TV
Multiple Sources Single DestinationSelector
Practical Example for Multiplexer
Multiplexing and Demultiplexing• A DEMUX is a digital switch
with a single input (source) and a multiple outputs (destinations).
• The select lines determine which output the input is connected to.
• DEMUX Types 1-to-2 (1 select line) 1-to-4 (2 select lines) 1-to-8 (3 select lines) 1-to-16 (4 select lines)
DemultiplexerBlock Diagram
SelectLines
Input(source)
Outputs(destinations)
2N1
N
DE
MU
X
Multiplexing and Demultiplexing
Single Source Multiple DestinationsSelector
D0
D1
D2
D3
X
DE
MU
X
B A Selected Destination
0 0 B/W Laser Printer
0 1 Fax Machine
1 0 Color Inkjet Printer
1 1 Pen Plotter
B/W LaserPrinter
Color InkjetPrinter
PenPlotter
FaxMachine
Practical Example for Demultiplexer
Multiplexing and DemultiplexingMultiplexer Demultiplexer
Computer Controlled Instrumentation
Transducer PC Based Controller Transducer
Output Controlling
Unit
MONITOR
KEYBOARD
PRINTER
To Process
Physical Variable
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Grounding Techniques
Why Ground ?• There are a number of good reasons to ground but
primary among them is to ensure personnel safety.• Good grounding is not only for the safety of personnel
but to provide for the protection of plants and equipment.
• A good ground system will improve the reliability of equipment and reduce the likelihood of damage as a result of lightning or fault currents.
• The purpose of a ground besides the protection of people and equipment is to provide a safe path for the dissipation of Fault Currents, Lightning Strikes, Static Discharges, Electromagnetic Interference.
What is a ground and what does it do ?
• The NEC, National Electrical Code defines a ground as: "a conducting connection, whether intentional or accidental between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth.“
• When talking about grounding it is actually two different subjects, earth grounding and equipment grounding.
• Earth grounding is an intentional connection from a circuit conductor usually the neutral to a ground electrode placed in the earth.
• Equipment grounding is to ensure that operating equipment within a structure is properly grounded.
Ground resistance values• There is a good deal of confusion as to what constitutes a
good ground and what the ground resistance value needs to be. Ideally a ground should be of zero ohms resistance.
• Telecommunica ons industry has o en used 5 ohms or less as their value for grounding and bonding.
• The goal in ground resistance values is to achieve the lowest ground resistance value possible that makes sense economically and physically.
Ground conductor
Connection between the ground conductor and ground electrode
Ground electrode
Components of a ground electrode
Spheres of Influence
There must be proper spacing between ground electrodes and earthstakes to reduce or eliminate their spheres of influence
Ground Resistance• The resistance of a ground electrode has 3 basic
components:A. The resistance of the ground electrode itself and the
connections to the electrode.B. The contact resistance of the surrounding earth to
the electrode.C. The resistance of the surrounding body of earth
around the ground electrode.
• The NEC specifies that the ground electrode shall be installed so that it is at least 2,4 m in length and in contact with the soil.
Ground Resistance• There are 3 variables that affect the resistance of
a ground electrode:1. The ground Itself2. The length/depth of the ground electrode3. Diameter of the ground electrode.
• Increasing the diameter of the ground electrode has very little effect in lowering the resistance. For example you could double the diameter of aground electrode and your resistance would only decrease by as much as 10%.
• One very effective way of lowering resistance is to drive ground electrodes deeper..
Ground Resistance Values• Soil resistivity depends on soil composition, moisture and temperature. It stands to reason that soil resistivity will vary through out the year in those areas of the country where seasonal changes bring about a change in the moisture and temperature content of the soil. For a grounding system to be effective it should be designed to withstand the worst possible conditions.
• Since soil and water are generally more stable at deeper strata, it is recommended that the ground rods be placed as deep as possible into the earth.• Ground rods should also be installed where there is a stable temperature.
Types of Ground Systems
Single Ground Rod Multiple Ground Electrodes
Ground MeshGround Plate
Types of Ground Systems
• There are two types of grounding systems, simple and complex. • Simple consist of a single ground electrode driven into the ground. • The use of a single ground electrode is the most common form of grounding and can be found outside your home or place of business. • Complex grounding systems consist of multiple ground rods connected, mesh or grid networks, ground plates and ground loops. • The complex grounding systems are typically installed at power generating substations, central offices and cell sites.
