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Understanding Computer Data Acquisition Systems | Learn about Sensors, Signal Conditioning, and More | Lecture on Instru

Explore the fundamentals of computer data acquisition systems, including sensors, A/D conversion, and transducer signal conditioning. Discover the components like sensors, I/O panels, and DAQ boards, along with trigger timing and digital control circuitry. Learn about ADC, signal transmission, and serial communication, as well as analog-to-digital conversion theory and ADC types. Gain insights into parallel and serial data transmission techniques with examples and comparisons of ADC systems.

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Understanding Computer Data Acquisition Systems | Learn about Sensors, Signal Conditioning, and More | Lecture on Instru

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  1. Universiti Malaysia Perlis ENT356 INSTRUMENTATION SYSTEM Lecture 6.1: Computer Data Acquisition System Sem 2, 2010/2011

  2. General Computer DAQ System Transducer Signal Conditioning A/D Conversion Computer Sem 2, 2010/2011

  3. A data acquisition (DAQ) system is a collection of add-on hardware and software components that allow your computer to receive real-world information from sensors. It consists of • Sensors • I/O terminal panel(s) • DAQ board(s) • Software Sem 2, 2010/2011

  4. Trigger Timer Digital Control Circuit Interrupt Sensor Instrumentation Amplifier Input Strobe + Parallel/Series Input Port Computer A/D Filter S/H - Bridge Display Parallel/Series Output Port D/A Control Output Strobe Example of Computer DAQ System DAQ Board Sem 2, 2010/2011

  5. Inside the Case of a Computer It contains a system board (mother board). This board hosts most of the circuits connecting : CPU, memory, I/O ports. buses, expansion slots, storage Power supplier Sem 2, 2010/2011

  6. Elementary Bus Structure Micro- processor Monitor ROM Optional User ROM System & User RAM User Input/Output Address Bus Data Bus Keyboard System Input/Output Display Sem 2, 2010/2011

  7. Analog-to-Digital Conversion An ADC converts an analog voltage to a digital number. The digital number represents the input voltage in discrete steps with finite resolution. ADC resolution is determined by the number of bits that represent the digital number. Sem 2, 2010/2011

  8. Signal Transmission in DAQ Analog input voltage Transmission Link Sample & Hold A/D Conversion Parallel to Serial Signal Transmitter Signal Receiver Sample and hold output Analog output Hold Hold Voltage Sampled Sampled Sampled 1 1 0 1 1 1 1 0 0 1 0 1 0 1 0 1 PCM signal Time Sem 2, 2010/2011

  9. Bits The smallest unit in digital signal is the bit, a contraction of the more descriptive phase of binary digit. A bit is a single element in digital signal, having only two possible states: on (indicating 1) or off (indicating 0). Off 0 On 1 Sem 2, 2010/2011

  10. Off 0 Off 0 Off 0 Off 0 Off 0 Off 0 On 1 On 1 Bytes Bits are organized into larger units called bytes, the basic unit of information in a computer system. A basic byte contains 8 bits. The total amount of information it can convey is 28 (=256) possible combinations. Sem 2, 2010/2011

  11. How Many Bytes? Since each byte can represent only one single character or command, to do anything useful requires a lot of bytes. The common sizes of bytes groups are KB, MB, GB, and TB. Name Shorthand Size Byte bit 20 1 210 1 KB 1 Kb Kilobyte Kilobit 1 MB 1 Mb Megabyte Megabit 220 1 GB 1 Gb 230 Gigabyte Gigabit 1 TB 1 Tb Terabyte Terabit 240 Sem 2, 2010/2011

  12. Vin C Out 1 Volt Vref 1 Comparator Vref =. 5 V 0 0 Volt VOut Vin 1-bit Analog-to-Digital Conversion • A comparator is the most basic ADC • This is a 1-bit Flash ADC • Out = 0 if Vin < Vref • = 1 if Vin > Vref Sem 2, 2010/2011

  13. N-bit Digital Output Analog Input N-bit ADC 3-bit ADC Scale 1 Volt 111 . 875 110 . 75 Volt 101 . 625 100 . 5 V 011 Step Size = = 0.125 V . 375 010 . 25 V 001 . 125 000 0 Volt Digital Output Code Analog-to-Digital Converter Theory Analog Input Signal Sem 2, 2010/2011

  14. Data Range 0-10 volts 8-bit A/D 256 distinct possible values ADC Types There many different types of analog-to-digital converters (ADC) available for DAQ systems. Different ADC types offer varying resolution, accuracy, and speed specifications The most popular ADC types are the parallel (flash) converter, the successive approximation, and the voltage-to-frequency ADCs. Sem 2, 2010/2011

  15. Example of Encoding (8-bit system) Sem 2, 2010/2011

  16. Encoding (8-bit Bus, 0-5 V Input) Sem 2, 2010/2011

  17. ADC Comparisons Sem 2, 2010/2011

  18. Parallel Data Communication • Parallel data communication is usually used in high speed and short distance communication in a laboratory type environment (with relatively low electrical interference) • IEE 488/IEC 625 standard:16-line bus: 8 lines for data (7-bit ASCII + parity check bit) 3 lines for “handshaking” 5 lines for bus activity control • Up to 15 devices can be connected onto the bus. Sem 2, 2010/2011

  19. Serial Data Transmission • Data bits of serial digital signals are transmitted one bit at a time in a chain along a single path. It is often referred as pulse code modulation (PCM). • Typically, serial is used to transmit ASCII data using 3 transmission lines: (1) ground, (2) transmit, and (3) receive. The important serial characteristics are baud rate, data bits, stop bits, and parity. • baud rate: a speed measurement for communication. • data bits: the actual data bits in a transmission. • stop bits: used to signal the end of a data communication. • parity: a simple form of error checking in serial communication. Sem 2, 2010/2011

  20. Signal Transmission Characteristics TTL (Transient-Transistor Logic) RS-232 is the most commonly used serial interface specification. RS-232 specifies 25 interchange circuits that govern the data flow between the data terminal equipment (DTE) and data communication equipment (DCE). A signal is considered to be ON when the voltage is between +3 and +15V, to be OFF when it is between -3 and -15V. The range between -3 and +3V is a TRANSITION region 5 V 0 V Time Voltage Space 15 V Positive range ON function 3 V Transition region 0 V Time -3 V Negative range OFF function -15 V Mark Sem 2, 2010/2011

  21. Baud Rate When we refer to the clock speed of serial transmission, we mean the baud rate. If the protocol calls for a 4800 baud rate, then the clock is running at 4800Hz. It means that the serial port is sampling the data line at 4800Hz. Common baud rates for telephone lines are 14,400; 28,800; and 33,600. Baud rates greater than these are possible, but these rates reduce the distance by which devices can be separated. Sem 2, 2010/2011

  22. Digital Transmission Links • Simplex: One way communication from A to B where B is not capable of transmitting back to A. • Half Duplex: Transmission from A to B and B to A but not simultaneously. The sample rate for m multipexed signals can be estimated: • Full Duplex: Simultaneouslytransmission from A to B and B to A. Sem 2, 2010/2011

  23. Transmission Bandwidth To estimate the bandwidth required for selecting a transmission link, it is necessary to find the extent of the frequency spectrum of PCM signal. • bit rate of the PCM signal: 1 baud = 1 bit/s • for a single signal: R = nfs • for m multiplexed signal: R = nmfs Where: fs is the sampling rate (samples/sec.) n is the size of data bits Sem 2, 2010/2011

  24. Transmission Bandwidth Calculation In a general case of a single signal, sampled at fS, and encoded into an n-bit code, the minimum PCM bandwidth is determined by For m multiplexed signals, each sampled as fS=1/t, the time in the HOLD state is m/ t. This means that an n bits of information must be transmitted during time t /m, the corresponding PCM bandwidth in this case is Sem 2, 2010/2011

  25. Example: Serial-Com System Design 16 analog signals, each with a frequency spectrum between 0 and 5 Hz, are input to a time division multiplexer. The multiplexed signal passes to a serial digital (PCM) transmitter consisting of a sample/hold device, 12-bit binary ADC and a parallel to serial converter. (1) Suggest a suitable sampling frequency for each input signal. (2) What is the corresponding number of samples per second for the multiplexed signal? (3) What is the maximum length of time the sample hold device can spend in the HOLD state? (4) Find the bit rate and minimum transmission bandwidth for the PCM signal. Sem 2, 2010/2011

  26. Example: Serial-Com System Design (1) Sampling rate should satisfy: (2) Sampling rate for the multiplexed signal.(3) Maximum length of time in the HOLD state (4) Bit rate and bandwidth Sem 2, 2010/2011

  27. Plug-In Data Acquisition Boards Plug in data acquisition board is a good solution for systems that don't need portability. Key Benefits • Lowest cost • Large selection to choose from • Established platform Sem 2, 2010/2011

  28. Computer Data Acquisition Board A plug-in data acquisition board is inserted directly into computer’s bus and transfer data directly to computer’s memory. It utilizes computer hardware: • cables & buses • power supply • back panel, etc. It is designed for particular bus structure, and unaffected by computer’s internal electrical noise. CPU transfers to RAM Display CPU retrieves from RAM Display Display Sem 2, 2010/2011

  29. Bus Structures of Plug-in Board The are several types of local bus structures commonly used for plug-in boards : • AT • NEC PC-9800 • Parallel Port • PCI • PCMCIA • PXI • USB • Others Sem 2, 2010/2011

  30. DAS-8 Series The DAS-8 family is a series of 4 kHz analog and digital boards for IBM compatible computers. Major Models • DAS-8 base model, 8-channel, 12-bit • DAS-8/LT modified model for laptop • DAS-8PGA programmable inputs, clock • DAS-8/AO include 2 analog output channels DAS-8 is a product made by Keithley Instruments Inc., USA Sem 2, 2010/2011

  31. Specifications of DAS-8PGA Sem 2, 2010/2011

  32. Preliminary SettingsBase Address Switch DAS-8 family boards need eight consecutive address locations in I/O space. To avoid conflict with other devices, DAS-8 boards base address may be set by the base address DIP switch to any 8-bit boundary anywhere in the IBM-PC-decoded I/O space. DAS-8/PGA Board Base Address 9 8 7 6 5 4 3 1 2 3 4 5 6 7 8 Recommended I/O address choice for the DAS-8 boards are Hex &H300, &H308, &H310 (Decimal 768, 776, & 784). Usually, the DAS-8 boards are shipped with &H300 address. Sem 2, 2010/2011

  33. Address BA +0 +1 +2 +3 +4 +5 +6 +7 Read A/D Lo Byte A/D Hi Byte Status reg. Status & gain Read Ctr 0 Read Ctr 1 Read Ctr 2 - Write 8-bit A/D conv. 12-bit A/D conv. Control register Gain cntrl reg. Load Counter 0 Load Counter 1 Load Counter 2 Counter control ProgrammingI/O Address Map Since the A/D provides 12 bits of data, it requires two bits to handle each word of data. Data is held as Low Byte first, the High Byte. This sequence is a convenience for Assembly Language programmers. Sem 2, 2010/2011

  34. ProgrammingDriver Installation A Device Interface Driver is required to pass the Base Address and corresponding Interrupt Level of a DAS-8 family board to a user program. Driver installs automatically at boot-up and can handle up to five boards in a computer system. Example of syntax for device definition of a single board located at 300 (hex): DEVICE = DAS8DI.SYS/B:&h300 Sem 2, 2010/2011

  35. Preliminary SettingsSE/DIFF DIP Switch The DAS-8/PGA uses an 8-position DIP switch foe selecting between Single-Ended (SE) and Differential (DIFF) operation. The eight switch position allow each channel to be individually set. S2 Ch 0 1 2 3 4 5 6 7 DAS-8/PGA Board 1 2 3 4 5 6 7 8 SE DIFF Sem 2, 2010/2011

  36. Mode Descriptions (incomplete) Sem 2, 2010/2011

  37. 19 37 18 36 17 35 16 34 15 33 14 32 13 31 12 30 11 29 10 28 9 27 8 26 7 25 6 24 5 23 4 22 3 21 2 20 1 Connector Pin Assignment DAS-8 family boards use a standard 37-pin D male connector for analog/digital I/O. The connector diagram of DAS-8/PGA is shown on left. IN 0 - IN 1 - IN 2 - IN 3 - IN 4 - IN 5 - IN 6 - IN 7 - DIG COM OP 4 OP 3 OP 2 OP 1 OUT 2 OUT 1 CLK 1 OUT 0 CLK 0 +12 V IN 0 + IN 1 + IN 2 + IN 3 + IN 4 + IN 5 + IN 6 + IN 7 + +5 V DIG GND IP 3 IP 2 IP 1 INT IN GATE 2 GATE 1 GATE 0 -12 V Sem 2, 2010/2011

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  41. What kind of DAQ did u used for your lab? What kind of software? THANK YOU Sem 2, 2010/2011

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