Intro Flashcards
What is Instrumentation
(according to ISA) A
collection of instruments or their application for
the purpose of observation, monitoring, and
control.
What is Control
To regulate, to have power, to rule
Scope of Instrumentation and Control
1. Computers, IT, Communications, Telecommunications, Data Handling, Telemetry 2. Aerospace/Avionics 3. Marine Science/Marine Biology 4. Metrology 5. Automation – Mechanical 6. Automation – Process 7. Analytical 8. Bio-medical 9. Cryogenics 10.Nuclear Instrumentation 11.Power Instrumentation 12.Others/unclassified
Process Automation covers the measurement and control of what process variables?
pressure, temperature,
flow, level, viscosity, humidity, specific gravity,
ph, thickness, weight, conductivity, oxygen level,
etc
In order to monitor a process
a characteristic
or parameter of the process must be
measured.
The accuracy and repeatability of the
measurement
is a must before the controller
can do its job of controlling the process.
What is Process Control
a technique of balancing supply and demand
over a period of time at a predetermined level
of operation called the Set Point (SP).
How to attain Process Control
the controller compares the
measured variable (Process Variable) with the
set point and then makes the adjustment in
the final control element based on the
difference between the set point and the
process variable
What is an error signal?
difference between the
set point and the process variable.
What is the objective of process control
Its objective is to make e equal to zero
Why is process control important?
high quality products and safety
Why is process control necessary?
To minimize/eliminate the effect of
disturbances
How is control design documented?
Process and Instrumentation Diagrams (P and
ID’s provide the documentation.
Why Process and Instrumentation Diagrams are used?
- system is too complex to describe in text.
- standard symbols must be used.
Seven Control Objectives:
- Safety
- Environmental Protection
- Equipment Protection
- Smooth Operation
- Product Quality
- Profit
- Monitoring and Diagnosis
What is a flash separator
or vapor–liquid separator?
is a
device used in several industrial
applications to separate a
vapor–liquid mixture.
In a flash separator, how is SAFETY / ensured?
High pressure drum is dangerous, therefore a pressure controller is used
In a flash separator, how is ENVIRONMENTAL PROTECTION ensured?
Hydrocarbons are never released to the atmosphere. Excess hydrocarbons are burned
In a flash separator, how is EQUIPMENT PROTECTION ensured?
No flow could damage the pump
In a flash separator, how is SMOOTH OPERATION PRODUCTION RATE ensured?
Flow Control is used to make a continuous feed to the pressure tank
In a flash separator, how is PRODUCT QUALITY ensured?
Adjust L.Key by adjusting the heating
In a flash separator, how is HIGH PROFIT ensured?
Use the least costly heating
In a flash separator, how is Monitoring and Diagnostic ensured?
Calculate and plot key parameters
What happens when the seven control objectives are not achieved
It will lead to UNPROFITABLE or UNSAFE operation
When we control a process,
we reduce the
variability of key variables to achieve the seven
control objectives.
Variability is moved from?
controlled variable to
the manipulated variable.
What is process performance
efficiency, yield, production rate, etc. It measures performance for a control objective
Note when calculating the process performance
Use the distribution not the average value of the key varable
AAH Co
Analyzer Alarm High Carbon Monixide
FE
Flow Element (for example, orifice)
FIC
Flow Indicating Controller
FO
Flow Orifice (Restricting Orifice used in a pump bypass loop to maintain a minimum flow through the pump)
FSH
Flow Switch High
HC
Hand Control (manual Control)
LG
Level Glass or Gage Glass
LR
Level Recorder (maintains record of level over several days or months)
PDC
Pressure Differential Controller
PP
Pressure Point (test point)
PRC
Pressure Recorder and Controller
PSD
Pressure Safety Disc (Rupture disc which fails at high pressure and or temperature to protect vessel from damage
PSV
Pressure Safety Valve
PV
Pressure Valve (located on the pipeline)
SIC
Speed Indicating Controller
SSH
Speed Switch High
SSHH
Speed Switch High High
TIC
Temperature Indicating Controller
TW
Temperature Well (used to protect temperature measuring element from harsh environment of a process)
Instrument supply or connection to process
_________________________
Undefined Signal
______/_________/_________
Pneumatic(air) signal
______//________//_________
Electric Signal
______///________///_________
or
————————————————–
Hydraulic Signal
________L_______L_________
Capillary Tube or filled system
_________X_______X________
Electromagnetic or sonic signal (guided)
_________~________~________
Electromagnetic or sonic signal (not guided)
~ ~
Software or Data Link
_______O__________O_______
Mechanical Link
_______(.)__________(.)________
Pneumatic Binary signal (on-off)
______//\__________//\_______
Electric Binary Signal (on-off)
______///\__________///\_______
or
————-———————–-—————–
Instrument Supply: AS
Air Supply 7000 kPa
Instrument Supply: ES
electrical supply 24v dc
Instrument Supply : SS
Steam Supply 350 kPa
Instrument Supply: WS
Water Supply: 350 kPa
Instrument Supply: NS
Nitrogen Supply: 210 kPa
Pneumatic Signal is typically in what range?
20 to 100 kPa oe 3-15 psig
pneumatic signal medium
air, natural gas or nitrogen
electrical signal is typically in what range?
4 to 20 mA
Common Hydraulic medium
oil filled system
What is a capillary tube
sensing line which connects the process to the instrument.
What is a capillary tube filled with?
filled with inert material (silicone oil)
What is the use of silicone oil in capillary tubes?
To protect the instrument from the deleterious effects of the process fluid
What are sonic signals
frequency signals, guided in a co-axial cable or not guided as in radio telemetry or satellite transmission
What is included in sonic signals?
it includes nuclear radiation and light
What does DCS mean?
Distributed Control System
Controller Properties
Good Performance - feedback measures
Wide Applicability - adjustable parameters
Timely Calculations - avoid convergence loops
Switch to/from manual - bumplessly
extensible - enhanced easily
Time Domain and Transfer Function and Final Value after Disturbance of Proportional Controller
Mv(t) = Kc*e(t) + Ip (bias constant) Gc(s) = MV(s)/E(s) = Kc Cv(t) = deltaD*Kd/(1+Kc*Kp)
Time Domain and Transfer Function and Final Value after Disturbance of Integral Controller
Mv(t) = Kc/Ti integral of e(t) from 0 to infinity + Ii(bias constant) Gc(s) = MV(s)/E(s) = Kc*Ti * 1/s Cv(t) = 0
Time Domain and Transfer Function and Final Value after Disturbance of Derivative Controller
Mv(t) = Kc*Td d(e(t))/dt+ Id(bias constant) Gc(s) = MV(s)/E(s) = Kc*Td * s Cv(t) = deltaD*Kd
Integral mode is also known as
persistent mode
Derivative mode is also known as
predictive mode
What is open loop test
A test of process characteristics with the loop controller in manual mode. The feedback loop has been “opened” and is no longer a complete loop
Three major classification of process response
Self Regulating
Integrating
Runaway
What is self regulating response?
responds to a step change in the final control element’s status by settling to a new, stable value
What is an integrating response?
responds by ramping either up or down at a rate proportional to the magnitude of the final control element’s step change
What is a runaway response?
by ramping either up or down at a rate that increasing over time, headed toward complete instability without some form of corrective action from the controller
Self regulating processes are characterized by?
their natural ability to stabilize at a new process variable value following changes in the control element value or loads
Self regulating processes absolutely require what controller?
it requires integral controller action to eliminate offset between process variable and setpoint
Faster integral controller action results in?
quicker elimination of offset
The amount of integral controller action tolerable in a self-regulating process depends on?
the degree of time lag in the system.
Too much integral action will result in?
oscillation, just like too much proportional control action
Example of integrating response?
filling a water tank and the water level acting as the process variable
What is mass balance?
Process variable (pressure, level) will remain constant if and only if incoming mass = outgoing mass
What is energy balance?
Process variable (temperature, speed) will remain constant if and only if incoming energy = outgoing energy
common examples of integrating processes
liquid level control, gas pressure control
storage bin control (conveyor belt)
temperature control (energy balance)
speed control (energy balance)
Integrating processes are characterized by?
ramping of the process variable in response to a step-change in the control element value or load
The integration occurs as a result of either _________ or ______________ in and out of the process
Mass flow imbalance or energy flow imbalance
integral controller action guarantees __________ in a purely integrating process
setpoint overshoot
some integral controller action will be required in integrating processes to _____________
compensate for load changes
The amount of proportional controller action tolerable in an integrating process depends on?
the degree of time lag and process noise in the system
Too much proportional action will result in _____ or ________
oscillation (time lags), erratic control element motion (noise)
Runaway processes are characterized by ?
exponential ramping of the process variable in response to a step change in the control element value or load(s)
what causes runaway processes?
it is a result of some form of positive feedback happening inside the process
Runaway processes cannot be controlled with proportional or integral controller action alone. What does it require?
it always requires derivative action for stability
some integral controller action will be required in runaway processes to?
compensate for load changes
Example of runaway process?
nuclear fission reaction when mother atoms split to daughter atoms to continue the nuclear reaction; pendulum in a cart
how can runaway processes be self regulating
if sufficient feedback is naturally introduces, as in the case with water moderated fission reactors
Example of a lag time?
inserting a square wave in an rc filter.
gravity drained level control process exhibits similar response to?
a sudden change in control valve position
What is stated in newton’s cooling law?
Higher temperature results to faster rate of cooling
what is one time constant?
the amount of time required for the variable to change 63.2 percent of the way from its starting point to its terminal value
How is lag time defined?
the difference in time between when the process variable ramps to a certain value and when it would have ramped to that same value were it not for the existence of the first order lag in the system
example of lag time involving heating?
heating a potato wrapped in aluminum foil. A lag time exist between the temperature of the element, temperature of the oven and temperature of the potato
What is dead time?
it refers to a period of time during which a change in manipulated variable produces no effect whatsoever in the process variable
Types of lag in a system
first-order lag-time, multiple order lag time, pure dead -time response
Dead time is also referred to as?
transport delay,
why is dead time also called transport delay?
because the mechanism of dead time is often a time delay caused by the transportation of material at finite speed across some distance
What is the difference between a lag time and dead time
a lag time function has a phase delay and a corresponding different gain. Dead time has only phase delay with unity response
What is the difference between first-order, second-order and higher order response?
The higher the order of the response, the longer the higher the phase delay
What is a hysteresis?
There is a lack of responsiveness to a change in direction.
