mahalakshmi 4.pdf · brief the principle of digital phase meter. (nov’ 2005 ece) a digital phase...

EC2351–Measurement and Instrumentation VI Sem ECE – R.Vanitha,AP/ECE

MAHALAKSHMI

ENGINEERING COLLEGE TIRUCHIRAPALLI – 621213

QUESTION BANK

DEPARTMENT: ECE SEMESTER: IV

Subject code / Name: EC2351/ Measurement and Instrumentation

UNIT IV

DIGITAL INSTRUMENTS

PART A

1. What is magnetic recorder? (Nov’ 2003 ECE).

A magnetic recorder records a voltage, store it for any time and then reproduce it in

electrical form essentially identical to its original occurrence.

2. What are the essential parts of a ramp-type Digital voltmeter? (Nov’ 2004

ECE).

The essential parts of a ramp-type Digital voltmeter are

a. Attenuator.

b.Ramp generator

c. Comparator

d.Logic control

e. Local oscillator

f. Counter and digital readout.

3. What are the additional features found on individual digital multimeters?

(Nov’ 2004 ECE).

Additional features found on individual digital multimeters are

a. They are having high input impedence.so there is no loading effect.]

b. They are having higher accuracy .

c. The output can interfaced with external equipment.

4. Brief the principle of digital phase meter. (Nov’ 2005 ECE)

A digital phase meter is described which operates on the basis of direct phase

measurement without intermediate amplitude measurement and subsequent

mathematical transformations. Such a phase meter can be optimized on the basis of the

cross correlation function for two harmonic input signals of the same frequency.

5. What is phase-sensitive detector? (Nov’ 2005 ECE).


An electronic circuit that consists essentially of a multiplier and a low-pass

circuit and that produces a direct-current output signal that is proportional to the

product of the amplitudes of two alternating-current input signals of the same

frequency and to the cosine of the phase between them.

6. Discuss the advantages and disadvantages of PDM recording.

(May’ 2005 ECE).

Advantage:

(i) The signal to noise ratio is high, so inaccuracies is very less.

(ii) Signal may be recorded at one speed and played back at any of the others without

change in magnitude , but with compression or an expansion of the time scale,

7. A 3 ½ digit voltmeter is used to measuring voltage (a) Find the resolution of

the instrument (b) How would a reading of 14.3V be displayed of 100V scale.

(May’ 2005 ECE).

(a) R= 1/10n

R- resolution

n = 3 for 3 ½ digit voltmeter

R= 1/103

R= 0.001

(b) In 3 ½ digit voltmeter, there are three full digit and half digit hence 14.3 V

will be displayed as

8. What are the sources of error in D.C voltage measurement? (May’

2005 ECE).

Error in any digital meter is due to quantization i.e rounding off, because of this

some deviation of measurement is there from the actual reading.

9. What is the principle of ramp type digital voltmeter? (May’ 2005 ECE).

The basic principle of the instrument is based on the measurement of time taken by

the linear ramp to rise from 0v to the level of the input voltage or to decrease from the

level of input voltage to zero. This time is measured with the help of electronic time

interval counter and the count is displayed in the numeric form with the help of a digital

display.

10. What are the disadvantages of digital instruments? (May’ 2006 ECE)

The main drawback of digital instrument is they are costly and some of the

instruments are complex. So,in spite of these advantages the digital instrument are not

completely replaced by analog instrument due to the fact that analog instruments are

cheap and simple.

11. Give the various types of digital voltmeter. (May’ 2006 ECE)

The digital voltmeter types are

(i) Ramp type digital voltmeter

(ii) Dual ramp digital voltmeter

(iii) Integrated type digital voltmeter


(iv) Analog to Digital converter voltmeter.

12. Enumerate the advantage of digital meter over the analog meter. (Nov’ 2006

ECE)

The advantage of digital meter over analog meter are

(i) output is in digital form. so easy for processing.

(ii) Less power consumption than analog instruments.

(iii) Reading are clearly indicated in decimal number.

(iv) The resolution of digital instrument is more.

13. Why is period mode preferred for measurement of very low frequency in a

frequency counter?

(Nov’ 2006 ECE)

The signals with a frequency lower than fo(crystal frequency of instrument)

should be measured in period mode and signal with frequency greater than fo should be

measured with frequency mode in order to minimize the effect of ±1 count gating error.

14. For a 10 MHz clock frequency counter of 1 sec sampling period what is the

frequency above which frequency measurements should be made?

(May’ 2006 ECE)

15. What is importance of gate time in frequency counter? (May 2007)

The opening and closing of the count gate ,on the other hand, this gate time

in frequency counter determines the accuracy of the frequency counter.

16. How is trigger time error reduced? (May 2007)

Trigger time errors are reduced with large signal amplitudes and fast rise

times.

17. What is known as persistence? (May 2007-R01)

The length of time during which phosphorescence, or afterglow, occurs

is called the persistence of the phosphor. Persistence is usually measured in terms of the

time required for the CRT image to decay to a certain percentage of the original light

output.

18. List the basic components of magnetic recorders. (May 2007- R 01)

The basic components of magnetic recorders are

i) Recording Heat

ii) Magnetic Tape

iii) Reproducing Head

iv) Tape Transport Mechanism

v) Conditioning Devices.

19. State typical digital instrument accuracy specification .compare the accuracy of

analog and digital multimeters.(Nov 2007)


The best analog instrument are rated usually within ±0.1 percent of full

scale. Digital instrument can be made to much greater accuracies

20. A frequency meter with 1 MHz clock source is used for measuring the time

period of input wave. Determine the measured time period when 1560 pulses are

registered on the display.(Nov 2007)

21. Write briefly on serial interfacing.(May 2008)

This type of interfacing enables exchange of data between microprocessor

and peripherals such as printers, external drives, scanners etc.

22. How much loss will be experienced if a fiber of Numerical aperture of 0.3 is the

source for a fiber with a numerical aperture of 0.242?.(May 2008)

When the source fiber has a broader cone of acceptance there will be a loss and this

can be calculated by

Loss = 20 log (NA1/NA2) larger NA is NA1 and smaller is NA2

Energy that is lost through the cladding of the receiving fiber

Loss = 20 log(0.3/0.242)

= 1.87 dB.

23. List different instruments used as signal analyzers. (May 2009)

Spectrum analyzer, distortion analyzer, Wave analyzer, logic analyzer, FFT

analyzer, Network analyzer

24. A counter which has a 3 digit display, gated period of 10 milliseconds, is

selected to measure an unknown frequency. The readings is 045.What is the

frequency of the system? (Nov 2009)

25. What is a vector voltmeter?(Nov 2009)

Vector voltmeter are used to measure the phase difference between two points in a

circuit at the same time the voltage between these two point is measured .

26. What are the problems that are associated with the measurement of pulsed

signals? .(May 2010)

27. Explain how prescaler can be used to extend the range of frequency

counter.(May 2010)

28. What are the advantages of digital meters over analog meters?

High accuracy

High precision

Better resolution

No parallax error

No observation error


29.What are the disadvantages of digital meters?

They need external power supply unit because of the use of ICs.

Testing of diodes cannot be done normally, and a special additional circuit

has to be provided for this purpose in some meters.

30.What is a digital voltmeter?

The digital voltmeter displays measurements of DC or AC voltages as discrete

numerals instead of a pointer deflection on a continuous scale as in analog devices.

31. List the characteristics of a DVM.

Input range

Accuracy

Stability

Resolution

Calibration

32. Define sensitivity.

It is the smallest change in voltage that the meter can respond.

33. Define resolution.

The resolution of a D/A converter is defined as the smallest change in the analog

output voltage corresponding to the change of one bit in the digital input signal.

34. Define stability.

It is the constancy of the fullscale output with age and variations in temperature

and power supply.

35.What is a frequency counter?

A frequency counter is a device that counts selected input signal transitions for a

fixed period of time and displays the resultant frequency on a multidigit display.

36.What is called extension of frequency range?

The measurement of frequencies greater than 50 MHz often presents problems as

these frequencies are often beyond the upper range of frequency counters. This is

overcome by using either one of the plug- in modules such as prescalers, frequency

converters etc.

37.Write the use of digital multimeter.

This is used for measuring quantities such as AC voltage, AC current, DC voltage, DC

current and resistance.

38. List the main parts of digital multimeter.

Current to voltage converter

DC voltage attenuator

AC voltage attenuator

AC to DC converter


39. List the special features of DMM.

Diode test

Touch hold

Peak hold

Bar graph display

Digital interface

40. Give the disadvantage of DVM.

The direction and relative magnitude of a signal’s change during an adjustment

may be less apparent using digital voltmeter.

41. State the principle of heterodyne frequency converter.

The principle states that it is used to extend the upper range of frequencies that

can be measured with electronic counters.

42. State the properties of analog instruments.

They require no power supply

They give a better visual indication of the changes

They suffer less from electrical noise and isolation problem.

They are simple and inexpensive.

PART B

1. Comparison of analog and digital instruments


2.Explain how dual slope A/D converter used in DVM (NOV/DEC 2011) With necessary diagrams explain Ramp type digital voltmeter. (8)(April/May 2011)


3.Explain with a neat block diagram, the operation of successive approximation type Digital voltmeter 4.Explain with a neat block diagram, the operation of Dual slope integrating type

digital Voltmeter


5.Explain with a neat block diagram, the operation of digital multimeter

DIGITAL MULTIMETER

The resolution of a multimeter is often specified in "digits" of resolution. For

example, the term 5½ digits refers to the number of digits displayed on the display

of a multimeter.

By convention, a half digit can display either a zero or a one, while a three-quarters

digit can display a numeral higher than a one but not nine. Commonly, a three-

quarters digit refers to a maximum value of 3 or 5. The fractional digit is always the

most significant digit in the displayed value. A 5½ digit multimeter would have five

full digits that display values from 0 to 9 and one half digit that could only display 0

or 1.[3] Such a meter could show positive or negative values from 0 to 199,999. A

3¾ digit meter can display a quantity from 0 to 3,999 or 5,999, depending on the

manufacturer.

While a digital display can easily be extended in precision, the extra digits are of


no value if not accompanied by care in the design and calibration of the analog

portions of the multimeter. Meaningful high-resolution measurements require a

good understanding of the instrument specifications, good control of the

measurement conditions, and traceability of the calibration of the instrument.

Modern multimeters are often digital due to their accuracy, durability and extra

features. In a digital multimeter the signal under test is converted to a voltage and

an amplifier with electronically controlled gain preconditions the signal. A digital

multimeter displays the quantity measured as a number, which eliminates parallax

errors.

Modern digital multimeters may have an embedded computer, which provides

a wealth of convenience features. Measurement enhancements available

include:

Auto-ranging, which selects the correct range for the quantity under test so that the

most significant digits are shown. For example, a four-digit multimeter would

automatically select an appropriate range to display 1.234 instead of 0.012, or

overloading. Auto-ranging meters usually include a facility to 'freeze' the meter to a

particular range, because a measurement that causes frequent range changes is

distracting to the user. Other factors being equal, an auto-ranging meter will have

more circuitry than an equivalent, non-auto-ranging meter, and so will be more

costly, but will be more convenient to use.

Auto-polarity for direct-current readings, shows if the applied voltage is positive

(agrees with meter lead labels) or negative (opposite polarity to meter leads).

Sample and hold, which will latch the most recent reading for examination after the

instrument is removed from the circuit under test.

Current-limited tests for voltage drop across semiconductor junctions. While not a

replacement for a transistor tester, this facilitates testing diodesand a variety of

transistor types.

A graphic representation of the quantity under test, as a bar graph. This makes


go/no-go testing easy, and also allows spotting of fast-moving trends.

A low-bandwidth oscilloscope. Automotive circuit testers, including tests for

automotive timing and dwell signals

Simple data acquisition features to record maximum and minimum readings

over a given period, or to take a number of samples at fixed intervals integration

with tweezers for surface-mount technology.

A combined LCR meter for small-size SMD and through-hole components. Modern

meters may be interfaced with a personal computer

Specifying "display counts" is another way to specify the resolution. Display counts give

the largest number, or the largest number plus one (so the count number looks nicer)

the multimeter's display can show, ignoring a decimal separator. For example, a 5½

digit multimeter can also be specified as a 199999 display count or 200000 display

count multimeter. Often the display count is just called the count in multimeter

specifications.

6. Draw the block diagram of a multiplexed display used in frequency counter and

explain?

Explain how to extend the frequency range of counter (Nov/Dec 2012) (NOV/DEC

2011)


7.How to make automatic polarity and automatic range indication in digital

instruments? (Nov/Dec 2012)

AUTOMATION IN DIGITAL INSTRUMENTS

Modern multimeters are often digital due to their accuracy, durability and extra features. In a

digital multimeter the signal under test is converted to a voltage and an amplifier with

electronically controlled gain preconditions the signal. A digital multimeter displays the

quantity measured as a number,which eliminates parallax errors. Modern digital multimeters

may have an embedded computer, which provides a wealth of convenience features.

Measurement enhancements available include:

Auto-ranging, which selects the correct range for the quantity under test so that the most

significant digits are shown. For example, a four-digit multimeter would automatically select

an appropriate range to display 1.234 instead of 0.012, or overloading. Auto-ranging meters

usually include a facility to 'freeze' the meter to a particular range, because a measurement

that causes frequent range changes is distracting to the user. Other factors being equal, an


auto-ranging meter will have more circuitry than an equivalent, non-auto-ranging meter, and

so will be more costly, but will be more convenient to use.

Auto-polarity for direct-current readings, shows if the applied voltage is positive (agrees with

meter lead labels) or negative (opposite polarity to meter leads)

Sample and hold, which will latch the most recent reading for examination after the

instrument is removed from the circuit under test.

Current-limited tests for voltage drop across semiconductor junctions. While not a

replacement for a transistor tester, this facilitates testing diodes and a variety of transistor

types.

A graphic representation of the quantity under test, as a bar graph. This makes go/no-go

testing easy, and also allows spotting of fast-moving trends.

A low-bandwidth oscilloscope. Automotive circuit testers, including tests for automotive

timing and dwell signals

8. How computer controlled measurement system is used for testing radio receiver?

(8) APRIL/MAY 2011

COMPUTER CONTROLLED TEST SYSTEMS

Computer Controlled Test System provides the capability to automatically test digital

networks such as; large scale integrated arrays (MOS, BIPOLAR), complex integrated

circuits, printed circuit cards, and other digital subsystems. Multiplexing is provided for

operating four test stations with one FST-1 computer. Each test station can test different

electronic devices or modules with up to 120 pins.

Each test station pin capability is expandable in groups of 30 up to a maximum of 120 pins.

Two 120 pin test enclosures may be used for up to a 240 pin test configuration. Each pin has

the capability to be defined either as an input pin or an output pin. Through system software

it is possible to instruct the tester to perform various operations on the device-under-test

such as assign input/output pins, execute tests, indicate Go/No-Go results and print test

results.

Basically, the system performs two types of tests; functional tests (that determine whether

the device performs the intended logic operations) and precision DC tests (that determine

whether component parameters meet device specifications). Functional tests are performed

by forcing programmed logic levels on the input pins of the device-under-test and

comparing the device outputs with programmed expected outputs. Absolute DC tests allow

programmable measurement of network parameters such as saturation voltage and input

leakage.


In addition, the magnitude of all test system reference voltages and currents such as Go/No-

Go thresholds, device supply voltages and functional logic level forcing magnitudes are

programmable. The number of tests required to adequately test an array has a large

influence not only on test throughput rate but also on test system configuration. The

maximum test rate is approximately 286,000 functional tests per second and 250 DC tests

per pin

per second.The maximum number of tests that can be performed on a single device without

using programming loops, is approximately 130,000. Using loops, programs can be extended

to any length.

TYPICAL SYSTEM CONFIGURATION

The Fairchild FST-l computer is the primary controller. Tester instructions are held in bulk

storage (disc or magnetic tape) and are transmitted to the computer memory when required.

The test head, power supplies and timing controls receive their instructions from core

memory under control of the computer


For functional tests, the tester applies logic levels representing forcing functions to the

input pins of the unit under test and compares actual outputs to the predicted

responses on a "Go/No-Go" basis. The expected output thresholds are programmable

as are the input logic levels.

For DC tests, a single pin can be addressed with an instruction that calls for a DC

(Absolute) measurement. A switching network then connects the Precision

Measurement Unit to the addressed pin and executes the measurement. A pin is

always restored to its previous functional test condition prior to being connected to, or

released from, the DC measurement unit.

The computer can control the unit-under-test device handler such that wafer indexing

and "class" sorting is automatic, depending on the result of tests performed. A fifteen

bit storage register is available for this purpose.

Figure 1-2 shows a test system with multiple test stations. The configuration allows

independent testing of devices of different design, therefore increasing the testing

throughput rate. The amount of peripheral equipment required per system varies

according to the environment of operation. For example, test engineering may require

the most peripherals since these groups will be continually generating new-design test

programs and new test techniques.

The operations are typical electronic data processing operations and are most

efficiently done only if a card reader, magnetic tape, disc, printer, and teletype are

available. In the production wafer-test environment, a minimum of peripherals are

required. Prepared programs on magnetic tape can easily be transferred to the disc.

There can be 350 programs of an average length of 1450 tests stored on the disc for

immediate access. Figure 1-3 shows probable peripheral configurations for the

engineering, wafer-test, and package test systems.

TESTER OPERATING FEATURES

There are three basic modes of operation for the test system:

(1) Automatic,

(2) Manual,


(3) Monitor.

Automatic

In the Automatic mode the test system operation is self-contained within the program.

This mode of operation is primarily intended for the production environment where there

is little need for operator intervention:

Manual

In the Manual mode a single programmed instruction is executed each time the "start"

button is depressed. This mode of operation is useful for program verification where the

operator needs to single step through a program. With a multiple test system, any or all

stations may be in Manual operation simultaneously A manual station will not inhibit

other stations from testing. After executing a single step at Station A, the controller will

accept start requests from other stations before returning to Station A.

Monitor

In the Monitor mode the operator is provided the opportunity to intervene with the

programmed control of the test system. This mode is primarily intended for use in the

prototype the operator has a variety of options such as, modifying programmed

delays, selecting datalogging conditions, modifying programmed voltages, etc.

(Voltages may be modified in any mode by the control panel override.)

9. What is virtual instrument? List the advantages of virtual instrument over conventional instrument (8)(Apr/May 2011) explain the need of virtual instrument with example (Nov/Dec 2012) VIRTUAL INSTRUMENTS

Virtual instrumentation is an interdisciplinary field that merges sensing, hardware and

software technologies in order to create flexible and sophisticated instruments for

control and monitoring applications. There are several definitions of a virtual

instrument available in the open literature.

Santori defines a virtual instrument as "an instrument whose general function

and capabilities are determined in software".


Goldberg describes that “a virtual instrument is composed of some specialized subunits,

some general-purpose computers, some software, and a little know-how".

Although informal, these definition capture the basic idea of virtual instrumentation

and virtual concepts in general - provided with sufficient resources, “any computer

can simulate any other if we simply load it with software simulating the other

computer“ [Denning01]. This universality introduces one of the basic properties of a

virtual instrument – its ability to change form through software, enabling a user to

modify its function at will to suit a wide range of applications.

The concept of virtual instrumentation was born in late 1970s, when microprocessor

technology enabled a machine's function to be more easily changed by changing its

software [Santori91]. The flexibility is possible as the capabilities of a virtual instrument

depend very little on dedicated hardware - commonly, only application-specific signal

conditioning module and the analog-to-digital converter used as interface to the

external world. Therefore, simple use of computers or specialized onboard processors

in instrument control and data acquisition cannot be defined as virtual instrumentation.

Virtual Instrument Architecture

A virtual instrument is composed of the following blocks: o Sensor

Module,

o Sensor Interface,

o Medical Information Systems Interface,

o Processing Module,

o Database Interface, and

o User Interfac

Figure 1 shows the general architecture of a virtual instrument.


Figure 1: Architecture of a virtual instrument

The sensor module detects physical signal and transforms it into electrical form, conditions the

signal, and transforms it into a digital form for further manipulation. Through a sensor interface,

the sensor module communicates with a computer. Once the data are in a digital form on a

computer, they can be processed, mixed, compared, and otherwise manipulated, or stored in a

database. Then, the data may be displayed, or converted back to analog form for further

process control. Biomedical virtual instruments are often integrated with some other medical

information systems such as hospital information systems. In this way the configuration settings

and the data measured may be stored and associated with patient records. In following sections

we describe in more details each of the virtual instruments modules.

Sensor module

The sensor module performs signal conditioning and transforms it into a digital form for further

manipulation. Once the data are in a digital form on a computer, they can be displayed,

processed, mixed,compared, stored in a database, or converted back to analog form for further

process control. The database can also store configuration settings and signal records.

The sensor module interfaces a virtual instrument to the external, mostly analog world

transforming measured signals into computer readable form. Table # summarizes some of

the often used human physiological signals


converter.

The sensor detects physical signals from the environment. If the parameter being measured

is not electrical,the sensor must include a transducer to convert the information to an

electrical signal, for example, when measuring blood pressure.

The signal-conditioning module performs (usually analog) signal conditioning prior to AD

conversion, such as . This module usually does the amplification, transducer excitation,

linearization, isolation, or filtering of detected signals.

The A/D converter changes the detected and conditioned voltage into a digital value. The

converter is defined by its resolution and sampling frequency. The converted data must be

precisely time -stamped to allow later sophisticated analyses

Sensor interface

There are many interfaces used for communication between sensors modules and the computer

According to the type of connection, sensor interfaces can be classified as wired and

wireless.

1. Wired Interfaces are usually standard parallel interfaces, such as General Purpose

Interface Bus (GPIB), Small Computer Systems Interface (SCSI), system buses (PCI

eXtension for Instrumentation PXI or VME Extensions for Instrumentation (VXI), or serial

buses (RS232 or USB interfaces)

2. Wireless Interfaces are increasingly used because of convenience. Typical interfaces include

802.11 family of standards, Bluetooth, or GPRS/GSM interface.Wireless communication is

especially important for implanted sensors where cable connection is impractical or not possible

. In addition, standards, such as Bluetooth, define a selfidentification protocol, allowing the

network to configure dynamically and describe itself. In this way, it is possible to reduce

installation cost and create plug-and-play like networks of sensor. Device miniaturization

allowed development of Personal Area Networks (PANs) of intelligent sensors Communication

with medical devices is also standardized with the IEEE 1073 family of standards . This

interface is intended to be highly robust in an environment where devices are frequently

connected to and disconnected from the network .

Processing Module

Integration of the general purpose microprocessors/microcontrollers allowed flexible

implementation of sophisticated processing functions. As the functionality of a virtual

instrument depends very little on dedicated hardware, which principally does not perform any


complex processing, functionality and appearance of the virtual instrument may be completely

changed utilizing different processing functions.Broadly speaking, processing function used in

virtual instrumentation may be classified as analytic processing and artificial intelligence

techniques.

Analytic processing

Analytic functions define clear functional relations among input parameters. Some of the

common analyses used in virtual instrumentation include spectral analysis, filtering,

windowing, transforms, peak detection, or curve fitting. Virtual instruments often use various

statistics function, such as, random assignment and biostatistical analyses. Most of those

functions can nowadays be performed in real-time.

Artificial intelligence techniques

Artificial intelligence technologies could be used to enhance and improve the efficiency, the

capability, and the features of instrumentation in application areas related to measurement,

system identification, an control. These techniques exploit the advanced computational

capabilities of modern computing systems to manipulate the sampled input signals and

extract the desired measurements. Artificial intelligence technologies, such as neural

networks, fuzzy logic and expert systems, were applied in various applications, including

sensor fusion to high-level sensors, system identification, prediction, system control,

complex measurement procedures, calibration, and instrument fault detection and isolation .

Various nonlinear signal processing, including fuzzy logic and neural networks, are also

common tools in analysis of biomedical signals.Using artificial intelligence it is even possible

to add medical intelligence to ordinary user interface devices.

For example, several artificial intelligence techniques, such as pattern recognition and machine

learning, were used in a software-based visual-field testing system

Database interface

Computerized instrumentation allows measured data to be stored for off-line processing, or to

keep records as a part of the patient record

Many virtual instruments use DataBase Management Systems (DBMSs) . They provide

efficient management of data and standardized insertion, update, deletion and selection.


Most of these DBMSs provided Structured Query Language (SQL) interface, enabling

transparent execution of the same programs over database from different vendors. Virtual

instruments use these DMBSs using some of programming interfaces, such as ODBC,

JDBC, ADO, and DAO .

MEDICAL INFORMATION SYSTEM INTERFACE

Virtual instruments are increasingly integrated with other medical information systems, such as

hospital information systems. They can be used to create executive dashboards, supporting

decision support, real-time alerts and predictive warnings. Some virtual interfaces toolkits, such

as LabView, provide mechanisms for customized components, such as ActiveX objects. That

allows communication with other information system, hiding details of the communication from

virtual interface Code.

In Web based telemedical applications this integration is usually implemented using Unified

Resource Locators (URLs). Each virtual instrument is identified with its URL, receiving

configuration settings via parameters. The virtual instrument then can store the results of

the processing into a database identified with its URL

Presentation and control

An effective user interface for presentation and control of a virtual instrument affects

efficiency and precision of an operator do the measurements and facilitates result

interpretation. Since computer’s user interfaces are much easier shaped and changed than

conventional instrument’s user interfaces, it is possible to employ more presentation effects

and to customize the interface for each user. According to presentation and interaction

capabilities,

we can classify interfaces used in virtual instrumentation in four groups:

interfaces, and

Terminal User Interfaces


First programs for instrumentation control and data acquisition had character-oriented terminal

user interfaces. This was necessary as earlier general-purpose computers were not capable of

presenting complex graphics. As terminal user interfaces require little of system resources,

they were implemented on many platforms.In this interfaces, communication between a user

and a computer is purely textual. The user sends requests to the computer typing commands,

and receives response in a form of textual messages.

Presentation is usually done on a screen with fixed resolution, for example 25 rows and 80

columns on ordinary PC, where each cell presents one of the characters from a fixed character

set, such as the ASCII set. Additional effects,such as text and background color or blinking, are

possible on most terminal user interfaces. Even with the limited set of characters, more

sophisticated effects in a form of character graphics are possible. Although terminal user

interfaces are not any more widely use on desktop PCs, they have again become important in a

wide range of new pervasive devices, such as cellular phones or low-end personal digital

assistants (PDAs). As textual services, such as SMS, require small presentation and network

resources they are broadly supported and available on almost all cellular phone devices. These

services may be very important in distributed virtual instrumentation, and for emergency alerts

Graphical User Interfaces (GUI)

Graphical user interfaces (GUIs) enabled more intuitive human-computer interaction, making

virtual instrumentation more accessible . Simplicity of interaction and high intuitiveness of

graphical user interface operations made possible creation of user-friendlier virtual instruments.

GUIs allowed creation of many sophisticated graphical widgets such as graphs, charts, tables,

gauges, or meters, which can easily be created with many user interface tools (Figure #). In

addition, improvements in presentation capabilities of personal computers allowed for

development of various sophisticated 2-D and 3-D medical imaging technologies

Distributed Virtual Instrumentation

Advances in telecommunications and network technologies made possible physical

distribution of virtual instrument components into telemedical systems to provide medical

information and services at a distance. Distributed virtual instruments is naturally integrated

into telemedical systems. Figure illustrates possible infrastructure for distributed virtual

instrumentation, where the interface between the components can be balanced for price and

performance


Infrastructure for distributed virtual instrumentation

10. Explain in detail about computer controlled test system?

mahalakshmi 4.pdf · brief the principle of digital phase meter. (nov’ 2005 ece) a digital phase...

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