E-Book ; Practical Process Control for Engineers and Technicians

288 Index impact on the overall control loop, 44 pressurized vessels, 43 backward error propagation Linear variable differential transformer, 33 (the delta rule), 162 limitations/disabilities, 34 Loop time constant (LTC) method, 119–20 forward output flow, 161 neural sigmoidal functions, 161–2 Magmeter, 38 neural networks, 159 Neoprene, 39 learning process, 159 Non-PID-controller see Ideal PID-controller neuron actions in ‘learning’, 160 neuron input calculation, 159–60 On–off control, 78–9 neuron internal function transform, 160 closed control loop, 81–2 neuron output, 160 combination of feedback and feedforward plotting and creating a fuzzy patch, 157 control, 83 rules of, 156 concepts of open and closed loop control, 83 training a neuron network, 162 control modes in closed loop control, 82 avoiding overparameterization, 163 reverse or direct acting controllers, 82 changing learning tolerance, 163 modulating control, 79 changing the momentum term, 163 open loop control, 79 increasing middle layer value, 163 examples of open loop control, 80 noise and repeated data, 163 function of open loop or feedforward re-initialize the weights, 162 control, 80 step changes to existing weights, 162–3 use of open loop control, 79 use of fuzzy patches, 157–8 ratio control, 80 Gain scheduling controller, 166 Open loop reaction curve, procedure to obtain: advantages, 166 changing the process, 114 disadvantages, 166–7 controller mode, 114 obtaining and analyzing the reaction curve, 115 Hard rubber, 40 recording the PV response, 114 IC sensors, 26 Orifice plate, 35–6 cryogenic temperature measurements, 26 advantages, 36 ranges and accuracy, 26 limitations/disabilities, 36–7 Ideal PID-controller, 108–9 Pessen: description of, 108 tuning for no overshoot on start-up, 126 ideal process variables, 109 tuning for overshoot on start-up, 127 tuning constants, 127 Industrial process in practice, 87–9 Instrumentation and transducer considerations: PID equations: dependent and independent gains, 127–8 materials of construction, 47 noise, 46–7 independent gains equation, 129–30 ISA equation, 128 reduction techniques, 47 Pressure transmitters: signal conditioners, 46 applications, 35 signal linearization, 47–8 capacitance, 32–3 signal transmission pneumatic vs electronic, linear variable differential transformer, 33 optical sensors, 34 45–6 strain gage, 28 Integral control, 16 terms of pressure reference, 28 vibrating wire/resonant wire transducers, 31 KENT K90 controllers PID algorithm, 111 Process control: definition of error in, 19 Lead function – derivative control with filter: definitions and terms, 13 lead algorithm for derivative control, 110 types/modes of operation: Level transmitters, 42–3 installation: atmospheric vessels, 43 future technologies, 44

Process control (Continued ) Index 289 closed loop or feedback control, 14 feedforward control, 14 resistance temperature detectors, 24–6 modulating control, 14 selection of temperature transducer design and on–off control, 13 open loop control, 14 thermowells, 26–7 thermistors, 26 Process deadtime, 150 thermocouples, 22–3 compensation, 154 Smart transmitter, 50–1 example of, 151–2 Smith Predictor model, 152 overcoming, 152 disturbance-free PV, 152–3 predicted PV, 153 Process responses: in reality, 153–4 response deadtime, 86 in theoretical use, 153 response process gain, 85–6 Soft rubber, 40 response process lag, 86 Statistical process control (SPC), 167–8 calculating control limits, 173–4 Production process, improving: formulated approach, 175 controlled variations problem, 168 structural approach, 174 uncontrolled variations problem, 169 information required for, 169 distributions of measurements, averages and Proportional control, 16 ranges, 172–3 Radiation pyrometers, 27 example of stable process, 171–2 developments in infrared optical pyrometry, 27 recording averages and ranges for a stable Real PID-controller: process, 170 description of, 109–10 recording averages and ranges for an unstable real process variables (field originated), 110 process, 170–1 Resistance temperature detectors (RTDs), 24 statistical inference, 169 application in digital environment, 24–5 using sub-groups to monitor the process, 169 construction of, 24 logic behind control charts, 175 range sensitivity and spans of, 24 uniform product, 168 self-hating problems associated with, 26 controlled variation, 168 uncontrolled variation, 168 Selection criteria and considerations, 48 Strain gage, 28 application, 48–9 composition of, 28–9 economics, 49 measurement errors for, 30 environmental and safety, 50 pressure transducer specifications, 31 installation, 49 sensitivity and gage factor, 29–30 measuring devices and technology, 50 performance, 49 Teflon (PTFE), 39 processed material properties, 49 Thermistors, 26 vendor supply, 50 values, range and sensitivity, 26 Self-tuning controllers, 165 Thermocouples, 22 controller synthesizer, 166 implementation requirements of, 167 Peltier and Thomson effects on operation, 23 self-tuning operation, 166 principle of operation, 22 system identifier, 165–6 reference or cold junction compensation, 23 types of, 22 Sensors, 18 Time constants, process: dynamics, 21 first order response, 6 optical, 34 high order response, 10 advantages, 34–5 second order response, 9–10 disadvantages/disabilities, 35 Transducers: selection of sensing devices, 21 characteristics of: temperature, 22 IC sensors, 26 dynamic and static accuracy, 17 radiation pyrometers, 27 hysteresis, 21 precision, 19–20

290 Index rangeability, 57–8 size and design pressure, 57 rangeability, 20–1 types of, 56 repeatability, 20 pinch, 58–9 resolution, 20 design pressure, 59 sensitivity, 20 design temperature, 59 span, 21 rangeability, 59 definition of, 18 size, 59 vibrating wire/resonant wire, 31 plug, 59–60 advantages, 32 design pressure, 60 limitations/disabilities, 32 design temperature, 60 Turbine or rotor flow transducer, 37–8 rangeability, 60 advantages, 37 size, 60 limitations/disabilities, 37–8 types, 60 sliding gate, 63 Ultrasonic flow measurement, 41 design pressure, 63 advantages, 42 design temperature, 64 Doppler effect, 41 rangeability, 64 limitations/disabilities, 42 size, 63 transit-time, 41 types, 63 special valve design, 64 User models in measuring transducers: dynamically balanced plug valves, 64 cold junction compensation, 45 expandable element in-line valves, thermocouple linearity, 44 voltage generation of a thermocouple, 44 65–6 fluid interaction valve, 66 Valve sizing, 76–7 Suanders diaphragm, 61–2 Valves, types of control: design pressure, 62 design temperature, 62 ball, 52–3 rangeability, 62 design temperature, 53 size, 62 rangeability, 53–4 types, 62 size and design pressure, 53 types of, 53 Ziegler–Nichols: continuous cycling method, 120–1 butterfly, 54 calculation of tuning constants, 122 design temperature, 55 stages of obtaining (closed loop tuning), rangeability, 55 121–2 size and design pressure, 55 open loop method using POI, 117–18 types of, 56 open loop tuning method, 116 hysteresis problems encountered in, 120 digital, 55 P control algorithm, 116 applications, 56 P, I and D open loop control algorithms, design pressure limits, 55–6 117 design temperature, 55 PI control algorithm, 116 rangeability, 56 size, 55 globe, 56 design temperature, 57 flow characteristics, 57