chapter10.industrial electronic jm304
Upcoming SlideShare
Loading in...5
×
 

Like this? Share it with your network

Share

chapter10.industrial electronic jm304

on

  • 1,934 views

 

Statistics

Views

Total Views
1,934
Views on SlideShare
1,934
Embed Views
0

Actions

Likes
0
Downloads
35
Comments
1

0 Embeds 0

No embeds

Accessibility

Upload Details

Uploaded via as Adobe PDF

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

chapter10.industrial electronic jm304 Document Transcript

  • 1. E3065/10/1 TELEMETRY AND DATA ACQUISITION UNIT 10TELEMETRY AND DATA ACQUISITION OBJECTIVESGeneral objective : To understand the concept of telemetry and data acquisition.Specific objectives : At the end of the unit you should be able to:  Identify the main concept of telemetry system and data acquisition.  Describe the structure of data collection system.  Define the specification of data acquisition system.  Identify the types of telemetry system.  Explain the function of multiplexing system.
  • 2. E3065/10/2 TELEMETRY AND DATA ACQUISITION INPUT10.1 INTRODUCTION OF TELEMETRY. Telemetry means the transmission of data for monitoring and control over longdistances. Data can be sent directly as a DC voltage or current up to a few meters. At longdistances speed is severely limited, and noise becomes a serious problem. The original Morsetrans-Atlantic cables of 19th century used DC which transmitted at less than one word perminute. For longer distances, we convert DC voltage or current to audio tones and send themover wire. This is called modulation, and the reverse (i.e. converting the varying signal to data)is called demodulation. A device to perform it is called a modem. An analog signal is a continuously varying wave. If we measure its height at specificpoints in time, we obtain a series of voltages with numeric values. These values can berepresented in binary form and transmitted as a series of bits. A bit is a binary digit, either 0 or1, whose combination in form of a code represents information in digital communication. Figure 10.1(a) : Converting the analog to digital signal. In other words, as indicated earlier, sensors in telemetry systems generate electricalsignals which change in some way in response to changes in physical characteristics. Anexample of a sensor is a thermistor, a device used to measure temperature. A thermistor’sresistance varies inversely with temperature: as the temperature increases, the resistance
  • 3. E3065/10/3 TELEMETRY AND DATA ACQUISITIONdecreases. The thermistor is usually connected into some kind of a resistive network, such as avoltage divider or bridge, and also to a DC voltage source. The result is a DC output voltage,which varies in accordance with temperature and which is transmitted to a remote receiver formeasurement, readout, and recording. The thermistor becomes one channel of an frequencydivision multiplexing (FDM) system. Other sensors have different kinds of outputs. Many simply have varying DC outputs,while others are AC in nature. Each of these signals is typically amplified, filtered, andotherwise conditioned before being used to modulate a carrier. All of the carriers are thenadded together to form a single multiplexed channel.10.2 STRUCTURE OF DATA ACQUISITION SYSTEMS. Data acquisition system are used to measure and record signals obtained in basicallytwo ways:a. signals originating from direct measurement of electrical quantities, these may include dc and ac voltages, frequency or resistance and are typical found in such areas as electronic component testing, environmental studies and quality analysis work.b. Signals originating from transducers such as strain gage and thermocouple. Data acquisition systems are used in a large and ever-increasing number of applicationsin a variety of industrial and scientific areas, such as the biomedical, aerospace and telemetryindustries. The type of data acquisition system whether analog or digital, depends largely onthe intended use of the recorded input data. In general, analog data systems are used when widebandwidth is required or when lower accuracy can be tolerated. Digital systems are used whenthe physical process being monitored is slowly varying (narrow bandwidth) and when highaccuracy and low per-channel cost is required. Digital systems range in complexity fromsingle-channel dc voltage measuring and recording systems to sophisticated automatic multi-channel systems that measure a large number of input parameters, compare against presetlimits or conditions and perform computations and decisions on the input signal. Digital dataacquisition systems are general more complex than analog systems, both in terms of theinstrumentation involve and the volume and complexity of input data they can handle. Data acquisition systems often use magnetic tape recorders. Digital system requireconverts to change analog voltages into discrete digital quantities or numbers. Conversely,digital information may have to be converted back into analog form such as a voltage or acurrent which can then be used as a feedback quantity controlling an industrial process. Instrumentation systems can be categorized into two major classes, analog systems anddigital system. Analog system deal with measurement information in analog form. An analog
  • 4. E3065/10/4 TELEMETRY AND DATA ACQUISITIONsignal may be defined as a continuous function, such as a plot of voltage versus time, ordisplacement versus pressure. Digital systems handle information in digital form. A digitalquantity may consist of a number of discrete and discontinuous pulse whose time relationshipcontains information about the magnitude or the nature of the quantity. Data acquisition is divided by two types, analog data acquisition and digital dataacquisition. 10.2.1 ANALOG DATA ACQUISITION. An analog data acquisition system typically consists of some or all of the following elements, a. Transducers – translating physical parameters into electrical signals. b. Signal conditioners – amplifying, modifying, or selecting certain portions of these signals. c. Visual display devices – continuous monitoring of the input signals. These devices may include single-channel or multi-channel oscilloscope, storage oscilloscope, panel meters, numerical display and others. d. Graphic recording instruments – obtaining permanent records of the input data. These instruments include stylus and ink recorders to provide continuous records on paper chart, optical recording systems such as mirror galvanometer recorders and ultraviolet recorders. e. Magnetic tape instrumentation – acquiring input data, preserving their original electrical form, and reproducing them at a later date for more detailed analysis. 10.2.2 DIGITAL DATA ACQUISITION. A digital data acquisition included some or all of the elements shown in figure 10.2.2. The essential function operations within a digital system include handling analog signals, making the measurement, converting and handling digital data and internal programming and control. The function of each of the system elements of figure 10.2.2 is listed below. a. Transducer – translate physical parameters to electrical signals acceptable by the acquisition system. Some typical parameters include temperature, pressure, acceleration, weight displacement, and velocity frequency, also may be measured directly. b. Signal conditioner – generally includes the supporting circuitry for the transducer. This circuitry may provide excitation power, balancing circuits, and calibration
  • 5. E3065/10/5 TELEMETRY AND DATA ACQUISITION elements. An example of signal conditioner is a strain- gage bridge balance and power supply unit.c. Scanner or multiplexer – accept multiple analog inputs and sequentially connects them to one measuring instrument.d. Signal converter – translates the analog signal to a form acceptable by the analog- to-digital converter. An example of signal converter is an amplifier for amplifying low-level voltages generated by thermocouples or strain gages.e. Analog –to-digital (A/D) converter - Converts the analog voltage to its equivalent digital form. The output of the A/D converter may be displayed visually and also available as voltage outputs in discrete steps for further processing or recording on a digital recorder.f. Auxiliary equipment – This section contains instruments for system programming functions and digital data processing. Typical auxiliary functions include linearizing and limit operation. These functions may be performed by individual instruments or by a digital computer.g. Digital recorder – Records digital information on punched cards, perforated paper tape, magnetic tape, typewritten pages, or a combination of systems. The digital recorder may be preceded by a coupling unit that translates the digital information to the proper form for entry into the particular digital recorder selected. Fig. 10.2.2: Elements of digital data-acquisition system.
  • 6. E3065/10/6 TELEMETRY AND DATA ACQUISITION Activity 10ATEST YOUR UNDERSTANDING BEFORE YOU CONTINUE WITH THE NEXTINPUT…!10.1 Name THREE places where telemetry is used.10.2 What is the basic principles of telemetry ?10.3 Describe that TWO categorized system of instrumentation.10.4 What the differential between analog and digital data acquisitions ? Hii !!!!!…..Good Luck and Try your best ….
  • 7. E3065/10/7 TELEMETRY AND DATA ACQUISITION Feedback To Activity 10A10.1 Three places used a telemetry : telephone system, modern radio and TV broadcasting, semiconductor industries, control system and others.10.2 Telemetry means the transmission of data for monitoring and control over long distances. For longer distances, telemetry convert DC voltage or current to audio tones and send them over wire. This is called modulation, and the reverse (i.e. converting the varying signal to data) is called demodulation. A device to perform it is called a modem.10.3 Instrumentation systems can be categorized into two major classes, analog systems and digital system. Analog system deal with measurement information in analog form. An analog signal may be defined as a continuous function, such as a plot of voltage versus time, or displacement versus pressure. Digital systems handle information in digital form. A digital quantity may consist of a number of discrete and discontinuous pulse whose time relationship contains information about the magnitude or the nature of the quantity.10.4 The type of data acquisition system whether analog or digital, depends largely on the intended use of the recorded input data. In general, analog data systems are used when wide bandwidth is required or when lower accuracy can be tolerated. Digital systems are used when the physical process being monitored is slowly varying (narrow bandwidth) and when high accuracy and low per-channel cost is required. Digital systems range in complexity from single-channel dc voltage measuring and recording systems to sophisticated automatic multi-channel systems that measure a large number of input parameters, compare against preset limits or conditions and perform computations and decisions on the input signal. Digital data acquisition systems are general more complex than analog systems, both in terms of the instrumentation involve and the volume and complexity of input data they can handle.
  • 8. E3065/10/8 TELEMETRY AND DATA ACQUISITION INPUT10.3 FREQUENCY OF TELEMETRY. In the frequency of telemetry process, the carrier frequency is varied above and belowits center value (modulated) in accordance with the amplitude of the data signal. The rate atwhich the carrier frequency deviates from its center value is a function of the frequency signal.The amplitude and frequency characteristics that define the data signal are therefore containedin the frequency variations of the frequency telemetry carrier around its center value. Whenthis modulated frequency demodulator by detecting the number and rate of zero crossings. It is clear that frequency telemetry recording is extremely sensitive to variations in tapespeed (flutter) because tape speed variations introduce apparent modulation of the carrier andare interpreted by system as unwanted signal (noise). Instability in tape speed therefore reducesthe dynamic range of the system. Since the data signal is contained entirely in the frequency characteristics of thefrequency carrier, the system is not sensitive to amplitude instability. Two important factors intelemetry recording are deviation ratio and percentage deviation. Deviation ratio is defined asthe ratio of deviation of the carrier from the center frequency to the signal frequency, or  =  m where  = deviation ratio  = carrier deviation from center frequency m = data signal frequency
  • 9. E3065/10/9 TELEMETRY AND DATA ACQUISITION10.4 MULTIPLEXING SYSTEM. Multiplexing is the process of simultaneously transmitting two or more individualsignals over a single communications channel. Multiplexing has the effect of increasing thenumber of communication channels so that more information can be transmitted. There are many instances in communication where it is necessary or desirable totransmit more than one voice or data signal. The application itself may require multiple signalsand money can be saved by using a single communications channel to send multipleinformation signals. Telemetry and telephone applications are good examples. In satellitecommunications, multiplexing is essential to making the system practical and for justifying theexpense. The concept of a simple multiplexer is illustrated in figure 10.7(a). Multiple inputsignals are combined by the multiplexer into a single composite signal that is transmitted overthe communications medium. Alternatively , the multiplexed signals may modulate a carrierbefore transmission. At the other end of the communications link, a demultiplexer is used tosort out the signal into their original form. Figure 10.4(a) : Concept of multiplexing.
  • 10. E3065/10/10 TELEMETRY AND DATA ACQUISITION There are two basic types of multiplexing, frequency division multiplexing (FDM) andtime division multiplexing (TDM). Generally speaking , FDM systems are used to deal withanalog information and TDM systems are used for digital information.10.4.1 FREQUENCY DIVISION MULTIPLEXING. Frequency division multiplexing is based on the idea that a number of signal can sharethe bandwidth of a common communications channel. The multiple signal to be transmittedover this channel are each used to modulate a separate carrier. Each carrier is on a differentfrequency. The modulated carriers are then added together to form a signal complex signal thatis transmitted over the single channel. Figure 10.4.1(a) shows a general block diagram of FDM system. Each signal to betransmitted feeds a modulator circuit. The carriers for each modulation fc is on a differentfrequency. The carrier frequencies are usually equally spaced from one another over a specificfrequency range. Each input signal is given a portion of bandwidth . the result is illustrated infigure 10.4.1(b). As for the type of modulation any of the standard kinds can be used includingAM, SSB, FM or PM.
  • 11. E3065/10/11 TELEMETRY AND DATA ACQUISITIONFigure 10.7.1(a) : The transmitting end of an FDM system. Figure 10.7.1(b) : Spectrum of an FDM signal.
  • 12. E3065/10/12 TELEMETRY AND DATA ACQUISITION The modulator output containing the sideband information are added together in alinear mixer. In a linear mixer, modulation and the generation of sidebands do not take place.Instead , all the signals are simply added together algebraically. The resulting output signal is acomposite of all carriers containing their modulation. This signal is then used to modulate aradio transmitter. Alternatively, the composite signal itself may be transmitted over the singlecommunication channel. Another option is that the composite signal may become one input toanother multiplexer system.10.4.2 TIME DIVISION MULTIPLEXING. In FDM, multiple signals are transmitted over a single channel by sharing the channelbandwidth. This is done by allocating each signal a portion of the spectrum within thatbandwidth. In TDM , each signal can occupy the entire bandwidth of the channel. However ,each signal is transmitted for only a brief period of time. In other words, the multiple signalstake turns transmitting over the single channel. This concept is illustrated graphically in figure10.4.2(a). Figure 10.4.2(a) : The basic TDM concept Here, four signals are transmitted over a single channel each signal is allowed to use thechannel for a fixed period of time, one after another. Once all the signals have beentransmitted, the cycle repeats again and again. Time division multiplexing may be used with both digital and analog signals. Totransmit multiple digital signals, the data to be transmitted is formatted into serial data words.For example, the data may consist of sequential bytes. One byte of data may be transmittedduring the time interval assigned to a particular channel. For example , in figure 10.4.2(a), eachtime slot might contain 1 byte from each channel. One channel transmits 8 bits. The third
  • 13. E3065/10/13 TELEMETRY AND DATA ACQUISITIONchannel then transmits its data word and so on. One transmission of each channel completesone cycle of operation called a frame. The cycle repeats itself at high rate of speed. In this way,the data bytes of the individual channel are simply interleaved. The resulting single –channelsignal is a digital bit stream that must somehow be deciphered and reassembled at the receivingend.
  • 14. E3065/10/14 TELEMETRY AND DATA ACQUISITION Activity 10BTEST YOUR UNDERSTANDING BEFORE YOU CONTINUE WITH THE NEXTINPUT…!10.5 Describe the concept of multiplexing process.10.6 Describe briefly the differential between , frequency division multiplexing (FDM) and time division multiplexing (TDM).10.7 Referring to equation 10(a), what is the meaning of ,  and m . Equation 10(a):  =  m Are you ready to check your answer ??
  • 15. E3065/10/15 TELEMETRY AND DATA ACQUISITION Feedback To Activity 10B10.5 Multiplexing is the process of simultaneously transmitting two or more individual signals over a single communications channel. Multiplexing has the effect of increasing the number of communication channels so that more information can be transmitted. There are many instances in communication where it is necessary or desirable to transmit more than one voice or data signal. The application itself may require multiple signals and money can be saved by using a single communications channel to send multiple information signals. Telemetry and telephone applications are good examples. In satellite communications, multiplexing is essential to making the system practical and for justifying the expense.10.6 Please refer to Input 10.4.1 and Input 10.4.2 for the answer.10.7 The answer for this question,  is deviation ratio,  = carrier deviation from center frequency and m = data signal frequency
  • 16. E3065/10/16 TELEMETRY AND DATA ACQUISITION SELF-ASSESSMENT You are approaching success. Try all the questions in this self-assessment section and check your answers with those given in the Feedback on Self-Assessment given on the next page. If you face any problems, discuss it with your lecturer. Good luck.Question 10-1 a. Based on figure 10(b), what is an analog signal ? b. Referring to figure 10(b), describe that how to convert the analog signal to digital signal ? c. Describe the function of thermistor according to telemetry concept. Figure 10(b) : Converting the analog to digital signal.Question 10-2 a. Data acquisition system is used to measure and record signals obtained in basically two ways. Describe that the two ways of data acquisition system. b. List FIVE elements in analog data acquisition and describe each item.
  • 17. E3065/10/17 TELEMETRY AND DATA ACQUISITIONQuestion 10-3 a. Referring to Figure 10(c), describe the relationship of each element according to digital data acquisition. b. Referring to multiplexer diagram, describe briefly the concept of multiplexer and de-multiplexer. List TWO basic types of multiplexer. Figure 10(c): Elements of digital data-acquisition system.
  • 18. E3065/10/18 TELEMETRY AND DATA ACQUISITION Feedback To Self-AssessmentAnswer 10-1 a. An analog signal is a continuously varying wave. b. If we measure its height at specific points in time, we obtain a series of voltages with numeric values. These values can be represented in binary form and transmitted as a series of bits. A bit is a binary digit, either 0 or 1, whose combination in form of a code represents information in digital communication. c. A thermistor is a device used to measure temperature. A thermistor’s resistance varies inversely with temperature: as the temperature increases, the resistance decreases. The thermistor is usually connected into some kind of a resistive network, such as a voltage divider or bridge, and also to a DC voltage source. The result is a DC output voltage, which varies in accordance with temperature and which is transmitted to a remote receiver for measurement, readout, and recording. The thermistor becomes one channel of an frequency division multiplexing (FDM) system.Answer 10-2 a. Two way of data acquisition system are used to measure and record signals is, i. signals originating from direct measurement of electrical quantities, these may include dc and ac voltages, frequency or resistance and are typical found in such areas as electronic component testing, environmental studies and quality analysis work. ii. Signals originating from transducers such as strain gage and thermocouple. b. An analog data acquisition system typically consists of some or all of the following elements, i. Transducers – translating physical parameters into electrical signals. ii. Signal conditioners – amplifying, modifying, or selecting certain portions of these signals.
  • 19. E3065/10/19 TELEMETRY AND DATA ACQUISITION iii. Visual display devices – continuous monitoring of the input signals. These devices may include single-channel or multi-channel oscilloscope, storage oscilloscope, panel meters, numerical display and others. iv. Graphic recording instruments – obtaining permanent records of the input data. These instruments include stylus and ink recorders to provide continuous records on paper chart, optical recording systems such as mirror galvanometer recorders and ultraviolet recorders. v. Magnetic tape instrumentation – acquiring input data, preserving their original electrical form, and reproducing them at a later date for more detailed analysisAnswer 10-3 a. Refer to figure 10(c), the function of transducer is translate physical parameters to electrical signals acceptable by the acquisition system. Some typical parameters include temperature, pressure, acceleration, weight displacement, and velocity frequency, also may be measured directly. Signal conditioner ; generally includes the supporting circuitry for the transducer. This circuitry may provide excitation power, balancing circuits, and calibration elements. An example of signal conditioner is a strain- gage bridge balance and power supply unit. Scanner or multiplexer; accept multiple analog inputs and sequentially connects them to one measuring instrument. Signal converter; translates the analog signal to a form acceptable by the analog-to- digital converter. An example of signal converter is an amplifier for amplifying low- level voltages generated by thermocouples or strain gages. Analog to digital (A/D) converter ; converts the analog voltage to its equivalent digital form. The output of the A/D converter may be displayed visually and also available as voltage outputs in discrete steps for further processing or recording on a digital recorder. Auxiliary equipment; This section contains instruments for system programming functions and digital data processing. Typical auxiliary functions include linearizing and limit operation. These functions may be performed by individual instruments or by a digital computer. Digital recorder; Records digital information on punched cards, perforated paper tape, magnetic tape, typewritten pages, or a combination of systems. The digital recorder may be preceded by a coupling unit that translates the digital information to the proper form for entry into the particular digital recorder selected. b. Multiple input signals are combined by the multiplexer into a single composite signal that is transmitted over the communications medium. Alternatively , the multiplexed signals may modulate a carrier before transmission. At the other end of the communications link, a de-multiplexer is used to sort out the signal into their original form.
  • 20. E3065/10/20 TELEMETRY AND DATA ACQUISITION Figure 10.4(a) : Concept of multiplexing. There are two basic types of multiplexing, frequency division multiplexing (FDM) and time division multiplexing (TDM). Generally speaking , FDM systems are used to deal with analog information and TDM systems are used for digital information. CONGRATULATIONS !!!!…..May success be with you always….HAVE A FUN AND NICE DAY.