Page 4 - Instrumentation and Measurement

2.5 Flow Measurement………………………………………………………………………..28
2.5.1 Differential Pressure Methods……………………………………………………28
2.5.2 Turbine Meter…………………………………………………………………….30
2.5.3 Ultrasonic Time of Flight Flow Meter……………………………………………31

2.6 Other Measurements……………………………………………………………………...31
2.6.1 Viscometer………………………………………………………………………..31
2.6.2 Oil Mist Detector…………………………………………………………………32
2.6.3 Oxygen Analyser…………………………………………………………………33

3. CONTROL SYSTEMS 35

3.1 Introduction……………………………………………………………………………….35
3.2 Control Systems…………………………………………………………………………..35
3.3 Open- and Closed-Loop Control………………………………………………………….37
3.4 Basic Elements……………………………………………………………………………39
3.5 Basic Elements of a Closed-Loop System………………………………………………..39
3.6 Case Studies………………………………………………………………………………42

3.6.1 Control of Fuel Pressure………………………………………………………….42
3.6.2 Control of Liquid Level…………………………………………………………..43
3.6.3 Fluid Flow Control………………………………………………………………..44
3.7 Discrete-Time Control Systems…………………………………………………………..44
3.8 Digital Control Systems…………………………………………………………………..46
3.9 Hierarchical Control………………………………………………………………………48

4. PROCESS CONTROLLERS 49

4.1 Introduction………………………………………………………………………………49
4.2 Basic Terms………………………………………………………………………………49

4.2.1 Direct and Reverse Actions………………………………………………………49
4.2.2 Dead Time………………………………………………………………………..50
4.2.3 Capacitance………………………………………………………………………50
4.3 On-Off Control…………………………………………………………………………...50
4.4 Proportional Control……………………………………………………………………...53
4.4.1 Proportional Band………………………………………………………………...55
4.4.2 Limitations of Proportional Control………………………………………………57
4.5 Derivative Control………………………………………………………………………..59
4.5.1 PD Control………………………………………………………………………..60
4.6 Integral Control…………………………………………………………………………...62
4.6.1 PI Control…………………………………………………………………………63
4.7 PID Control……………………………………………………………………………….65
4.8 Tuning…………………………………………………………………………………….66

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