2. Computer-Based Instrumentation 11/12/01 ISAT 300

3. The generalized measurement system – Figure 2.1 Sensing element Signal modification subsystem Indicator or recorder Measurand Computer E.g., for temperature measurement, could be a thermocouple or a thermistor

4. Computer-Based Instrumentation Connection Module Computer Thermocouple or thermistor

5. Computer-Based Instrumentation

6. Measurand Sensing element Signal modification subsystem Indicator or recorder

7. Computerized Data Acquisition System – Fig. 4.1 What we want to know about

8. What’s a MUX? (Multiplexer) – Fig. 4.4 What if we want to monitor several measurands? (several temperatures, pressure, humidity, illumination,etc.)  We need to monitor several sensors. In most cases, each sensor is connected to a separate channel of the computerized data acquisition system. The computer reads information from the various channels one at a time using a device called a multiplexer (MUX). The MUX is an electronic switch.

9. What’s a MUX? (Multiplexer) – Fig. 4.4 The computer instructs the MUX to select a particular channel and the data are then read and processed. The computer then instructs the MUX to select a another channel …

10. Computerized Data Acquisition System – Fig. 4.1 What we want to know about

11. Computerized Data Acquisition Information in computers is stored in bistable devices, called “flip-flops”. Flip-flops can have two possible states. The “on” state is assigned a numerical value of 1. The “off” state is assigned a numerical value of 0. We need to know a little bit about binary. The analog-to-digital converter converts an analog signal (generally a voltage) to a digital (binary) code.

12. Everything I need to know I learned in kindergarten “Sing a song of sixpence, a pocket full of rye, Four and twenty blackbirds baked in a pie” 24 2 tens + 4 ones

13. Another example (decimal system) 1224 10 digits = 10 possibilities 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

14. Binary system 1011 2 digits = 2 possibilities 0, 1

15. Binary numbers--what’s it worth? 1 0 1 0 128 64 32 16 8 4 2 1 0000 1111 b = 15 d 1111 1111 b = 255 d 0000 1111 1111 1111 b = 4095 d 1111 1111 1111 1111 b = 65,535 d 8 bits = 1 byte

16. Examples: converting binary to decimal 0000 0101 b = ? d 0000 1111 b = ? d 0010 1010 b = ? d 1101 0101 b = ? d

17. Adding in binary 0 0 1 1 +0+1+0+1 0 1 110

18. Subtracting in binary 1 11110  0  1  1  1 1 010 1

19. 3 +3 6 More adding in binary 11 +11 110 compare to decimal:

20. Converting decimal to binary least significant bit (lsb) most significant bit (msb) “zero padding” 92 d = 0101 1100 b

21. Examples: converting decimal to binary 12 d = ? b 75 d = ? b 1215 d = ? b

22. Representing negative numbers – 2’s complement 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 -8 -7 -6 -5 -4 -3 -2 4 bits of numbers 3 bits of numbers, 1 bit of sign

23. 2’s complement--hard for us, easy for the computer 1) Convert the magnitude of the number to binary-- have at least one “leading zero” 2) Invert all of the bits--0’s become 1’s, 0’s become 1’s 3) Add 1 to the result To get positive numbers: 1) Convert the magnitude to binary--but you must have at least one “leading zero” To get negative numbers:

24. 1) Convert the magnitude of the number to binary-- have at least one “leading zero” 2) Leave it alone--it’s positive! 2’s complement--hard for us, easy for the computer Example: +92 01011100

25. 1) Convert the magnitude of the number to binary-- have at least one “leading zero” 2) Invert all of the bits--0’s become 1’s, 0’s become 1’s 3) Add 1 to the result 2’s complement--hard for us, easy for the computer Example: - 92 01011100 10100011 +1 10100100

26. 2’s complement--example +19 d = ? b -19 d = ? b Use one byte = 8 bits for both