Introduction to Data Acquisition and Real
Contents
1. gt theta_1 deg Calibration deg V D a 0 Display2 HIL Terminator Read th Analog 2 P K gt Timebase 31 Tachometer w_1 rpm HIL Read Analog Calibration ad Timebase rpm V HIL 1 D gt Terminator1 Display HIL Read 0 PK gt Encoder Encoder enc theta_1 deg HIL Read Encoder Calibration HIL 1 deg count Figure 4 2 Simulink model to send voltage to the SRV 02 as well as to obtain various readings from the SRV 02 30 CHAPTER 4 INTRODUCTION TO DATA ACQUISITION AND REAL TIME CONTROL 4 3 In Lab Assignment and Post Lab Report Assume that the encoder gives you perfect differential position information You should actually convince yourself that the encoder measurements are quite accurate by rotating the gear 360 man ually and comparing your visual reading with the calibrated encoder reading On the other hand the potentiometer voltage range is not exactly 5V you can actually measure the potentiometer with a multimeter and its electrical range is not exactly 345 1 Think about a way of re calibrating the potentiometer voltage so that the position information obtained via the potentiometer tracks very closely the position information via the encoder up to a constant of course since potentiometer gives absolute position information whereas the encoder gives diffe2. Quanser NI terminal Board 27 28 CHAPTER 4 INTRODUCTION TO DATA ACQUISITION AND REAL TIME CONTROL 4 2 2 Building and running a QuaRC code using Simulink 1 2 3 Log in the account nobody which is not password protected Launch MATLAB and start Simulink Create a new folder EE351L in My Documents and save all files you will create throughout the experiment in this EE351L folder To apply a voltage to to the DC motor on SRV 02 follow the steps in subsection 4 1 of 3 with the following changes a Set the Board Type field in the HIL Initialize Block to ni pci 6251 instead of qd or q8 b Use a HIL Write Analog Block instead of a HIL Write Block Important To protect the equipment do not set the amplitude and the frequency in the Signal generator to values higher than the ones indicated in the manuals To measure the potentiometer voltage on SRV 02 follow the steps in subsection 4 2 of 3 with the following additional changes a Use a HIL Read Analog Timebase Block instead of a HIL Read Timebase Block Set the Samples in Buffer field to 1 in the HIL Read Analog Timebase Block b The potentiometer we have is model 138 instead of model 132 It has an electrical range 345 4 according to 1 Therefore use the scaling factor 345 10 instead of 352 10 in potentiometer calibration To measure the tachomet
3. you will follow 3 with some minor changes These changes are again due to the difference in our Data Acquisition Card Some of the QuaRC blocks mentioned in 3 are not available for NI PCI 6251 and hence they will have to be replaced by those blocks that have similar functions and are available for NI PCI 6251 These changes are outlined in subsection 4 2 2 For more information see 4 or type doc quarc in the Matlab prompt and go to User s guide QuaRC Data Acquisition card Support 4 2 1 Wiring Procedure This experiment requires four items to be connected 1 Rotary Motion Servo Plant SRV 02 2 Quanser NI Terminal Board 3 Universal power module UPM 4 Data Acquisition Card NI PCI 6251 This card is installed within the PC hence it is not readily visible but it can be accessed through the NI cable with a 68 pin blue connector lying on the bench 26 CHAPTER 4 INTRODUCTION TO DATA ACQUISITION AND REAL TIME CONTROL The proper connection of these elements is crucial and particularly confounding in the tight spaces on the lab bench Follow the steps below to wire the equipment 1 Turn off UPM using the kill switch located on the back of the UPM Important This is the only fail safe method to cut power to the SRV 02 system Whenever you run an experiment one team member must be assigned to operate this power switch Mistakes do happen so to protect yourself your teammates and the equipment always have someo
4. Chapter 4 Introduction to Data Acquisition and Real Time Control The objectives of this laboratory session are 1 Gain familiarity with the Rotary Motion Servo Plant SRV 02 the Data Acquisition Card NI PCI 6251 and the QuaRC Software 2 Understand the basic input output I O connections 3 Design a Simulink model using blocks from the QuaRC library to run the DC motor on the SRV 02 4 Design a Simulink model using blocks from the QuaRC library to measure the various signals on the SRV 02 4 1 Pre Lab Assignment Read this entire chapter as well as the references 1 2 3 Digital control of a continuous time systems has become very popular as the price and reliabil ity of digital computers has improved Digital sensors like thermocouples in thermostats and a computer like an integrated circuit perform calculations to emulate the analog controllers like bi metal strips they replace Very complicated control structures can be implemented easily using a digital controller whereas an analog controller would require complex hardware Digital controllers are more adaptable to parameter changes than their analog counterparts Furthermore analog em ulation and real time control provide advanced features such as adaptive self tuning multivariable control expert systems and the ability to communicate over a local area network Typically the computer replaces the cascade controller The measured data is converted from ana
5. egration Student Manual 4 QuaRC Data Acquisition Card Support
6. er voltage on SRV 02 follow the steps in subsection 4 3 of 3 with the following additional changes a Set the Analog channels field in the HIL Read Analog Timebase block to 0 1 2 3 instead of 0 2 Adding the analog channels 1 and 3 seems unnecessary since you will not use them However for some unknown reason the tachometer voltage does not seem to show up at the analog channel 2 otherwise b The SRV 02 is in the high gear configuration therefore use the corresponding scaling factor for tachometer calibration To measure the encoder signal on SRV 02 follow the steps in subsection 4 4 of 3 with the following additional changes a An encoder channel is not available in the HIL Read Analog Timebase block There fore use an HIL Read Encoder block from the QuaRC Targets library under Data Acquisition Generic Immediate I O Tip Use Figure 4 2 as a guide to build your Simulink models for this experiment 4 2 LABORATORY PROCEDURE 0000 00 gt Signal Generator Amplitude V 1 D 1 Constant Offset V HIL Initialize HIL 1 ni_pci_6251 0 Quat contrabr development made tsy Vi a Saturation Motor Calibration gt V V gt Vm V HIL Po Write Analog HIL Write Analog HIL 1 29 Display1 Po Potentiometer
7. log to digital form by the analog to digital converter ADC This is accomplished by the data acquisition system DAQ which is the eyes and ears of the digital computer The computer receives and manipulates the signal in digital binary form and the output is then converted to analog by the digital to analog converter DAC This process is the hands and arms of the computer The full scale output is usually determined by an external reference voltage The DAC resolution is defined as the smallest possible change in output For an N bit converter the resolution is given by Eq 4 1 100 Resolution gn 4 1 24 4 2 LABORATORY PROCEDURE 25 For example the resolution of a 10 bit DAC is 100 100 210 1024 0 09766 The resolution of an ADC is defined as the smallest detectible change in input which is also given by 4 1 When the computer reacts to external events as they occur it is referred to as real time control An important consideration in real time control is the update rate During one controller cycle three things must happen before the next cycle can begin 1 Sensors are read ADC inputs 2 The microprocessor computes updated commands and 3 The commands are converted to analog signals DAC outputs Between cycles the commands outputs are held constant If the controller is updated every 0 01 seconds the output of the controller would look like a staircase with steps 0 01 seconds wide As expec
8. ne ready to cut power in the event of an accident Turn off the PC Follow the steps in subsections 6 1 and 6 2 of 1 to wire the equipment with the following changes a As mentioned above Quanser NI Terminal Board is slightly different from the one in 1 n NS However similar to the one in 1 Quanser NI Terminal Board has all the analog I O channels and the encoder input channels mentioned in 1 although the numbers and the locations of these channels are different from the one shown in 1 Another minor difference is that Quanser NI Terminal Board will be connected to NI PCI 6251 using the NI cable with a 68 pin blue connector lying on the bench Fig ure 4 1 which is to replace Figure 21 in 1 shows Quanser NI Terminal Board and the connections Finally make sure that the jumper on the analog input channels 0 3 of the Quanser NI Terminal Board is set to D which stands for differential In QuaRC the analog mode is set to the default mode for the Data Acquisition Card which is differential for NI cards As a result the jumper on the Quanser NI Terminal Board must be configured to match the default analog mode of NI PCI 6251 4 Have the instructor check your wiring 5 Turn on the PC Make sure the LED on the terminal board is illuminated If it is not then the fuse needs replacement Contact the instructor 4 2 LABORATORY PROCEDURE NI PCI 6251 N 4e ot O me O Figure 4 1
9. rential position information Before doing this assignment you should have reviewed 1 which explains how the potentiometer and the encoder work 2 Estimate the rate based on the encoder measurement Compare the rate obtained from the tachometer measurement with the estimated rate based on the encoder measurement Are they sufficiently close or do the tachometer measurements need to be re calibrated as well Tip For this assignment you can apply a constant voltage 1V with a saturation 10 V s as shown in Figure 4 2 As a result the gears will start rotating at a constant rate Do not apply arbitrary voltages with high amplitudes or high frequencies Save all of your data and figures Submit a typed and well organized lab report to the instructor by the beginning of the next lab session In you report explain your reasoning and what you did clearly but concisely Include at least one figure illustrating that the re calibrated potentiometer voltage closely tracks the position information via the encoder Include at least one figure com paring the rate obtained from the tachometer measurement with the estimated rate based on the encoder measurement In both questions you can superimpose two trajectories on top of each other and or plot the difference etc Tip Use the subplot command in MATLAB to save space Bibliography 1 Quanser SRV 02 User Manual 2 Quanser UPM User Manual 3 Quanser Rotary Experiment 00 QuaRC Int
10. ted the faster the dynamics of the system being controlled pouring water versus pouring molasses the faster the update rate must be Modern real time control systems use computer aided software engineering CASE such as MATLAB s Real Time Workshop to automatically generate C code from a graphical control model like Simulink Often the sensors or other components of the DAQ system are proprietary Vendors now provide Simulink blocks along with their hardware in order to ease the graphical modeling of their product In this lab we will focus on gaining familiarity with the Data Acquisition Card NI PCI 6251 and the QuaRC software In addition you will explore the effects of A D and D A conversion that are built into the NI PCI 6251 through which all the control signals pass 4 2 Laboratory Procedure The laboratory procedure consists of two main steps 1 Wiring the equipment For this you will follow the wiring procedure detailed in Section 6 of 1 with some minor changes The Data Acquisition Card we have is an NI PCI 6251 instead of a Quanser Q4 or Q8 As a result we use an appropriate Quanser NI Terminal Board to access NI PCI 6251 which is slightly different from the Quanser Q8 terminal board mentioned in 1 The minor changes in the wiring due to this difference are pointed out in subsection 4 2 1 2 Building and running a QuaRC code using Simulink to run the SRV 02 as well as to measure various signals from the SRV 02 For this
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