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instrumentation > Final > Flashcards

Final Flashcards

1
Q

Two chemical reaction types.

A

Exothermic - gives off heat

Endothermic - absorbs heat

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2
Q

Self-Regulating process

A

Tank filling up while depleting

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3
Q

3 Process dynamic attributes

A

Gain - ratio of output to input
Lag - first change to completion
Deadtime - first change to first sensed

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4
Q

2 things that contribute to lag in a process

A

Resistance

Capacitance

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5
Q

Difference between error and offset?

A

error - Difference in PV & setpoint

Offset - Permanent difference in measurement between PV and SP

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6
Q

2 types of control loops

A

Open loop - feedforward

Closed loop - feedback

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7
Q

Bump-less transfer?

A

Seamless transition from manual control to automatic control.

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8
Q

Two different control actions

A

Direct Control - as input increases output increases

Reverse Control - input increase output decreases

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9
Q

Deadband

A

Range of value where a change in measurement does not result in out change.

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10
Q

Four common control strategies

A

On/off - Two switch control, on & off
Proportional - changes output proportional to error.
Integral - changes output proportional to error and also factors in time.
Derivative - Changes output proportional to rate of change in a process.

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11
Q

3 types of AI

A

Diagnostic - finds faults in a process
Knowledge - finds faults and probable cause
Expert - finds faults, probably cause, and a solution.

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12
Q

Proportional Gain

A

Input is proportional to the output

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13
Q

Cascade Control

A

Multiple loop control strategy that alters the PV by changing the setpoint of the second loop.

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14
Q

3 components of automatic control

A

Process variable - Dependent variable to be controlled.
Control variable - Independent variable used to adjust depend variable.
Controller - Device that compares a process measurement to a setpoint and changes the CV to bring the PV back to setpoint.

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15
Q

Controller tuning

A

Altering various inputs of a controller to achieve a desired output.

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16
Q

The performance standards can often be defined by the ___ loop response of a ___ order system.

A

Closed, Second.

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17
Q

3 common controller performance standards.

A

Deadtime - time between change is first made to first sensed.
Overshoot - Change of a PV that exceeds the uppder deadband.
Decay Ratio - How quickly an overshoot decays from one oscillation to the next.

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18
Q

Two reasons for using the most common performance standard.

A

It is easy to judge

Response is close to optimal

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19
Q

3 Controller performance standards used in industry.

A

Rise time - the length of time required for PV to cross ultimate value.
Dynamic response time - Time it takes for pv to remain within 5% of its ultimate value
Gain margin - Gain is increased tot he point of instability.

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20
Q

3 steps taken as a pretuning check.

A

Determine whether direct or indirect
Know if its proportional, integral, or derivative.
Know initial tuning values

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21
Q

4 manual tuning methods used for controller tuning.

A

Setpoint step change method - making small changes and observing.
Tuning Map Method - compares process curves to numerous others.
Ziegler-Nichols closed loop tuning - increasing gain to the point of instability
Ziegler Nichols open loop tuning - tuning based on open loop response to a step input.

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22
Q

Most common tuning method

A

Setpoint step change method - very easy to judge.

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23
Q

Another tuning method that is intended to achieve one-quarter decay ratio?

A

Ziegler Nichols tuning method

24
Q

Digital controller

A

Controller that uses microprocessor technology, digital version of electric controller.

25
Q

Two differences between a DCS and PLC.

A

PLC’s are more rugged

PLC’s are faster

26
Q

What are the two types of electric controllers

A

Null Balance

Analogue

27
Q

3 operator interfaces

A

Stand alone display
PC based display system
Digital Recorder

28
Q

5 commonly used configuration formats utilized in digital control systems.

A

Pick and choose - Picking and choosing between a config from a list of available functions.
Ladder logic - 2 rails with sequential logic between them.
Function Block - Library of functions provided by the manufacturer.
Structured Text - Format similar to the C++ & microsoft visual basic
Sequential Function Chart - series of conditional statements, parallel paths, and action block. Begins with start & ends with existing scan.

29
Q

What is final element.

A

Receives a control input and adjusts material and energy accordingly.

30
Q

How are the valve flow characteristics represented graphically?

A

Percent flow vs percent open

31
Q

3 Valve flow characteristics

A
  1. Quick-opening valve
  2. Linear Valve
  3. Equal-percentage valve
32
Q

List and explain two phenomena that affect the control valves in liquid services.

A
  1. Flashing - Liquid to vapor during pressure drops

2. Cavitation - Vapor bubbles in liquid collapse inside a valve as pressure increases.

33
Q

What is critical pressure ratio?

A

The ratio of downstream pressure to upstream pressure where gas out of a valve is at sonic velocity.

34
Q

Cv

A

Valve coefficient, Q x √p/ΔP, number of gallons of water per minute at 60F.

35
Q

What is the advantage of using a double ported valve over a single port valve?

A

Double ported valve reduces the force on the valve plug, and smaller actuator.

36
Q

Name four types of rotary shaft valves

A
  1. Butterfly
  2. Ball
  3. Plug
  4. Eccentric Cam Control Valve
37
Q

What is the difference between a pressure regulator and a back pressure regulator?

A

Pressure regulator monitors downstream pressure, while a back pressure regulator monitors upstream pressure.

38
Q

List and Explain three types of dampers.

A
  1. Parallel-blade Damper - A damper with adjacent blades that are in parallel.
  2. Opposed-blade Damper - Damper, parallel blades, move in opposite direction.
  3. Round-blade Damper - Damper that has a circular blade.
39
Q

List four requirements of an actuator.

A

Speed
Power
Precision
Resolution

40
Q

List four types of actuators used on control valves.

A
  1. Diaphragm and Spring Actuator
  2. Pneumatic Sliding Stem Piston Actuator
  3. Pneumatic Rotary Piston Actuator
  4. Electric Actuator
41
Q

What is the key feature of a typical valve positioner that allows for accurate positioning?

A

Feedback

42
Q

Give two examples of processes that would use split range control.

A
  1. pressure control

2. Heating and cooling control valves

43
Q

List and Explain the four types of pressure regulators.

A
  1. Spring-Loaded Pressure Regulator - Valve plug that is controlled by spring opposition.
  2. Air-Loaded Pressure Regulator - Uses air pressure to oppose and control downstream pressure.
  3. Pilot-Operated Pressure Regulator - Uses upstream fluid pressure to power the diaphragm of a larger valve.
  4. Differential Pressure Regulator - Controls pressure difference between the outlet pressure and inlet pressure.
44
Q

Define PPE

A

Persona protective equipment, any clothing or device worn to protect injury.

45
Q

What applications are safety vales, relief valves, and safety relief valves used?

A

Safety valves - conditions where valves must open quickly to reduce dangers.
Relief valves - Used for unfired vessel applications, protection against overpressure down stream of pressure regulators.
Safety relief valves - unfired vessels i.e. compressed air receiver vessels.

46
Q

Difference between a safety valve and a safety relief valve?

A

Safety relief valves can act as both saefty valves and relief valves.

47
Q

Pressure relief with the above valves must conform to codes established by whom?

A

ASME International (american society of Mechanical Engineers)

48
Q

4 worst-case pressure-relieving conditions

A

Fire
runaway chemical reaction
blocked discharge
thermal expansion

49
Q

List and explain the four types of rupture disc.

A

Conventional metal - metal sheet placed between holders, with pressure applied to the concave side
Reverse Buckling - metal sheet between holders, pressure on convex side.
Composite - metal sheet with holes combined with thin polymer sheet.
Graphite Composite - disc made of graphite powder in a polymer cement, used in corrosive conditions.

50
Q

Name 2 types of hazardous atmosphere detectors.

A

Combustible gas detector

Toxic gas detector

51
Q

3 electrical classifications for hazardous locations

A

Divisions
Groups
Classes

52
Q

4 Electrical protections commonly used for instruments

A

Nonincendive protection
Dust ignition proof protection
Explosion proof protection
Intrinsically safe protection

53
Q

What is SIS

A

Safety Instrumented System, brings a process to a safe state when normal conditions are violated.

54
Q

The use of an SIS to determine the required degree of safety is very complex, but the evaluation needs to consider ___, which is comprised of event ___ and event ___ and the ___ level needed to protect against it.

A

Risk
Severity
LIkelyhood
Integrity

55
Q

Difference between step change & load change

A

A load changed must be compensated for by the CV, whereas step change is compensated by the controller.

instrumentation (4 decks)

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