9 intelligent instruments

7/27/2019 9 Intelligent Instruments

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Electronic InstrumentationLecturer Touseef Yaqoob 1

Intelligent InstrumentsAn intelligent Instrument comprise all

the usual elements of a measurement

system and is only distinguished fromdumb (non-intelligent instrument)measurement system by the inclusion

of a microprocessor to fulfill the signalprocessing task.


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Processing with a microprocessorA microprocessor can readily perform

correction of the instrument output for

biased caused by environmentalvariations (e.g. Temperature changes)

Microprocessor can do conversion to

produce a linear output from atransducer whose characteristic isfundamentally non-linear.


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The advent of the microprocessor has had anequally significant impact on the field of

instrumentation. It is therefore necessary todescribes the principles of operation ofmicroprocessors and explaining how they areincluded and programmed as a

microcomputer within a measuringinstrument, Thereby what has come to beknown as an intelligent instrument.


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Microprocessor and MicrocomputerThe key element of a microcomputer is the LSImicroprocessor chip, whose circuitry can

acquire, interpret, and execute a sequence oflogical and arithmetic instructions. Althoughmost computer programming is done in a highlevel language, the processor itself deals onlywith binary numbers that represent operation

codes (move data, add, subtract, compare,jump, etc.) and addresses (routing informationfor the data flow) of registers, memorylocations or input/output data ports


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Beside the microprocessor, a completecomputer requires a power supply,

memory, interface circuits to provideportsto external devices, andinput/output devices such as a

keyboard, display, DACs and ADCs, andmagnetic or other (optical) datastorage.


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Functional Elements of the Computer

The functional elements of a computer

are the

central processing unit (CPU),

random access storage (memory), and input/output to external devices (I/O).


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The sub-units of the CPU are instruction decode and CPU control,

control of addressing for memory andI/O ports,

data transfer control,

data and address registers and

arithmetic logic unit.


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To keep track of the CPU steps, the processormaintains a special register, known as theprogram counter. The program counter points

to (contains the address of) the nextinstruction to be executed. The instructionitself specifies

the operation to be performed,

the processor registers to be used and possibly data (or a pointer to data in

memory).


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Execution cycle of CPUThe CPU will typically perform the followingexecution cycle:

use the program counter to fetch the nextinstruction. decode the instruction and fetch data from

memory into internal registers as required, perform the instruction and put the result in

another internal register and set status bits in the status register as

required.


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A typical computer design showing two

multi-wire buses


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Mechanical Arrangement Machines with the lowest cost and

highest reliability are generally those

with the fewest mechanical connectorsand socketed components, while thosewith more connectors and sockets are

more easily expanded and maintained.


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One design is to have all circuits onmechanically equivalent boards that plug intoa common bus, this is the most modulararrangement and is easily maintained. Analternative design is the single-boardcomputer which places the CPU and asubstantial portion of the memory and I/Ointerface circuits onto a single circuit board.This design is more compact and lessexpensive


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Addressing Devices on the Bus The address determines the destination or

source of information. Since the wires of a

bus are common to all functional units,each unit will see all the data placed on thebus lines. The address lines are used withina receiving unit to determine if available

information should be processed orignored. Each data repository on a commonbus will have a unique address.


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When the CPU needs to transfer databetween itself and a particular location, itimplements a sequence of signals as specifiedby the read or write operation protocol forthe bus. The range of numbers that can berepresented by the available address lines(wires) on a bus is known as the addressspace. A range of numbers is used mostly toaccess information from memory and is thusknown as the memory address space.


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Control of the Bus The information flow on the computer bus is

time-multiplexed to allow different functional

units to use the same bus lines at differenttimes. We will assume that only one devicetries to write (drive) a given bus line at anytime. A special unit, known as a bus master,

has the responsibility for controlling the otherunits, which are correspondingly known asthe bus slaves.


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Often a direct memory access (DMA)unit is allowed to communicate with a

slave memory without going throughthe CPU bus master. This allowsmemory access at a higher speed than

having to go through the intermediateCPU bus master.


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Clock Lines

The changes of state of all busedsignals are synchronized to one or more

clock signals, which are distributed toall functional units on the bus.


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Read and write operations between the CPUand memory units are the most common.

One approach is for the CPU to set theaddress lines and data lines and then blindlyissue the control pulses, assuming that theslave unit will respond as needed within theallowed time. A more elegant but slightlyslower technique uses a handshakewhichrequires an acknowledgment response fromthe slave before proceeding.


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Random Access Memory

The random-access memory (RAM) supportsboth read and write operations. Integratedcircuit RAM comes in two main types: static RAMin which a single bit of memory is

simply a digital flip-flop and requires onlycontinuous power to maintain its state.

dynamic RAMin which a bit of memory is a

storage capacitor in either the charged ordischarged condition. The term dynamic refers tothe need to periodically renew or refresh theslowly discharging capacitor.


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Compared to dynamic memory, staticmemory has the following advantages.

It is simpler to use, about ten timesfaster and more reliable. On the otherhand, it is more expensive, consumes

more power and requires more physicalspace.


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Both types of RAM are volatile, meaningthat stored information is lost when

power is removed from the chip. Somecomputer designs provide a limitedamount of non-volatile read/write RAM

storage by using special low-power(and slower) dynamic memoriespowered by re-chargeable batteries.


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Read-Only Memory

Another form of non-volatile random accessstorage is the read-only memory (ROM). Herea single memory bit is nothing more than aconnection that is either open or closed. Themost common ROM types are known as field-programmable (as opposed to factoryprogrammable). This programming process

consists of stepping through all the bits andsetting the necessary ones by burning openthe fuse-like material associated with that bit.


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There are many varieties of field-programmable ROM units:

PROM - programmable read-only memory, EPROM - erasable PROM (using ultraviolet light),

and

EEPROM (E PROM) - electrically erasable PROMs.

The most common uses of ROM memory in acomputer are to provide initialization such asmemory tests and disk bootstrapping.


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I/O Ports

Input and output ports are thepathways by which the CPU

communicates with the world outsidethe computer. The pathway may beeither

1-bit wide (bit-serial),

8-bit wide (byte-serial), or

16- to 32-bit wide (word-serial).


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Interrupts

Real-time applications require thecomputer to respond immediately to an

external stimulus. The hardwareinterrupt can be used to suspend thecurrent sequence of instructions,

perform a specific and usually short I/Otask, then return to the originalsequence of instructions.


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Computers and DATA


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Number Systems


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Binary Numbers


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Binary to decimal conversion


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Decimal to binary conversion


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Octal number system


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Converting decimal to Octal


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Electronic Instrumentation

Lecturer Touseef Yaqoob 35

Hexadecimal System


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Converting Decimal to Hexadecimal


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Programming and Program execution

In most mode of usage, including useas a part of intelligent instruments,

computers are involved in manipulatingdata. This requires data values to beinput, processed and output according

to a sequence of operations defined bythe computer program.


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A/D and D/A converter


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D/A converter


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4 Bit D/A converter


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A/D converters


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Counter based A/D converter


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Intelligent Instrument in use

A typical intelligent flow rate measuringinstrument is a good example. The flow rateis proportional to the square root of the

difference in pressure across orifice plate. Fora given flow rate this relationship is affectedboth by the temperature and pressure in thepipe. Intelligent instrument contains threetransducers a primary one measuring the

pressure difference and secondary onesmeasuring absolute pressure andtemperature.

9 intelligent instruments

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