1. INTRODUCTION TO ELECTRONIC INSTRUMENTATION
Chapter 8 INTC 1305 – 11
LOOP THEORY
Paul Kilger

2. Chapter 7 Review - VIBRATION
Vibration is a random movement of an object
Vibration meters are used to measure velocity, acceleration or displacement
Usually have a sensor, amplifier and output devices
Vibration is measured in large or high speed equipment to prevent catastrophic failure

3. Speed Speed = Distance traveled per unit of time
Velocity = Speed with a direction
Speed is measured with a sensor and a readout
Sensors include tachometers, induction measurement, or magnetic proximity signal
Speed is either rectilinear (mph) or rotational (rpm)
Car speed is measured by rpm and tire circumference

4. Preview of Chapter 8 Learn Process control Determine Set Point
Understand Control Loops
Identify
Sensing
Transmitting
Controlling
Final Control Element
Signals – Pneumatic, electronic, digital, mechanical

5. INTRODUCTION Concept of controlling processes
Mixes various elements to create a specific process
Either Open or Closed
Components of a loop:
1) Sensor
2) Transmitter
3) Controller
4) Final Control Element

6. SIGNALS
Pneumatic
Electronic
Digital
Mechanical

7. ORDER OF CONTROL Process variable is measured First - sense a variable
Pressure
Temperature
Flow pH
Speed
First - sense a variable
Second - transmit the information
Third - compare the variable with a Set Point
Forth – Control some element

8. Process Control A process variable is a quantity such as temperature
A process control is the act of regulating one or more variables
A variable must first be sensed and measured
Then the variable has to be compared to a Set Point
Next is a comparison of variable with the Set Point
Then something has to happen

9. Control Loop Consists of a Sensor Transmitter
Controller – Compares and manipulates
Final control element

10. Control Loops
A group of instruments working together to control a process variable Two Types – Open – car without cruise Closed – car with cruise on Open – A signal path without feedback Closed – A signal is measured compared and sends a signal to correct – with feedback

11. Loops
Sense

12. Loops
Sense
Transmit

13. Loops
Sense
Transmit
Controller

14. CLOSED LOOP Corrects errors in process Sense Transmit Controller
Final Control Element

15. CONTROL LOOPS Loops can control a single element
Each variable is measured by itself and then compared to the “normal” variable
The difference or comparison is determined to be high or low as compared to the Set Point

16. TWO TYPES OF CONTROLS
OPEN – Direct action and no comparison - no feedback
CLOSED – compares and reacts – has feedback

17. CLOSED LOOP
Cruise control – adjusts fuel in response to Set Point of speed

18. OPEN LOOP
Driving without using the cruise control

19. SENSING
Pressure gauge or thermometer
Senses process variable

20. TRANSMITTING
Once a variable has been sensed it has to be converted for transmission.
3 – 15 psi Or
4 – 20 mA
Transducer must respond accurately
Precision defines the repeatability of a reading

21. CONTROLLER
Has the job of comparing the instantaneous reading to a set point checking for difference (error).
Then it has the job of sending the difference information to the Final Control Element
This is where the magnitude and direction are determined

22. TRANSDUCER Converts one form of data to another
Usually converts electric to pneumatic OR
Converts pneumatic to electric

23. FINAL CONTROL ELEMENT Commonly an actuated valve
The Final Control Element have I/P (Current to Pneumatic) transducer, a positioner, an actuator and a valve.

24. LOOP BLOCK DIAGRAM
Pressure Gauge
Process

25. LOOP BLOCK DIAGRAM
Transmitter
Process

26. CLOSED LOOP BLOCK DIAGRAM
Input Signal Conditioner
Process

27. Input Signal Conditioner
LOOP BLOCK DIAGRAM
SP - Comparator
Input Signal Conditioner
Process

28. Input Signal Conditioner
LOOP BLOCK DIAGRAM
Determine
Amount
SP - Comparator
Input Signal Conditioner
Process

29. Input Signal Conditioner
LOOP BLOCK DIAGRAM
Determine
Amount
Determine Direction
SP - Comparator
Input Signal Conditioner
Process

30. Input Signal Conditioner
LOOP BLOCK DIAGRAM
Determine
Amount
Determine Direction
SP - Comparator
Input Signal Conditioner
Send
Signal
Process

31. Input Signal Conditioner
LOOP BLOCK DIAGRAM
Determine
Amount
Determine Direction
SP - Comparator
Input Signal Conditioner
Send
Signal
Transmitter
Final Control
Element
Process

32. Signal Transmission FOUR TYPES: Pneumatic (Analog)
Electronic (Analog) – current is preferable to voltage because current has a higher immunity to electrical and electromagnetic interference . Current can be compared with water: water in = water out
Digital – Binary numbers
Mechanical – Link or linkage – must be close

33. PNEUMATIC Has a range of 3 – 15 psig – slower than elec
Always represent 0 to 100%
Every pneumatic system needs an air supply
Generally 20 psig for a 3 – 15 psig device
Signal travels through tubing
The signal usually travels short distances
Travels at the speed of sound

34. ELECTRONIC - ANALOG Continuously variable sensor Range of 4 – 20 mA
Current is preferred to voltage because current not affected by resistance
Much faster than pneumatic- travels near the speed of light
Distance may be increased by the use of an amplifier

35. ELECTRONIC (DIGITAL) Binary number – coded transmission
Tremendous variation by manufacturer

36. MECHANICAL (Link / Linkage)
Must be close together
Conveys a linear motion or rotary motion

37. LOOP ERROR Manufacture defines
Error = √Sum of Error of each component squared

38. LIVE ZERO
A standard error or bias has been added to an instrument to perfect calibration