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Instrumentation, Measurement and Control > Control system architecture > Flashcards

Control system architecture Flashcards

1
Q

Production scheduling level

A

Level 4

Production scheduling

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2
Q

production control level which does not directly control the process, but is concerned with monitoring production and monitoring targets

A

Level 3

Production control

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3
Q

contains the supervisory computers, which collect information from processor nodes on the system and provide the operator control screens

A

Level 2

Plant supervisory

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4
Q

Contains the industrialised input/output (I/O) modules, and their associated distributed electronic processors

A

Level 1

Direct control

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5
Q

contains the field devices such as flow and temperature sensors, and final control elements such as control valves

A

Level 0

Field Level

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6
Q

What HART stands for

A

Highway Addressable Remote Transducer

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7
Q

What digital systems allow for

A

Intelligent Device Management (IDM)

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8
Q
  • Hybrid analogue and digital protocol
  • Uses existing 4-20mA instrument current loops for 2 way communication of additional information

Shares the existing wires
Backward compatible (no rewiring)

A

HART

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9
Q

Uses conventional analogue signal, information is sent only one way, either from the device to the host (inputs) or from the host to the device (outputs)
Digital information on the other hand, can travel in both directions ising the HART digital communications signal
Primary variable and control signal information on conventional 4-20mA.
Additional information available on the same lines

A

HART

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10
Q

Advantages of HART

A
  • Allows an instrument that only receives control signal information from a host to also send the host information about that’s happening at the valve
  • A transmitter that only sends a process variable to the host can now also receive information such as configuration settings
  • Established mature techonology
  • Dedicated wiring to each field device avoids knock on effects in the case of a wiring fault
  • HART signals can be used for diagnostics/ calibration but 4-20mA is still needed for control
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11
Q

HART applications

A
  • Configuration of the instrument remotely
  • Receiving instrument status
  • Receiving instrument diagnostics
  • Performing instrument troubleshooting
  • Gathering additional measurements beyond the analogue signal
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12
Q

Typically a DCS, PLC, or computer based central control or monitoring system

A

Primary master

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13
Q

Can be connected almost anywhere on the network and communicate with field devices without disturbing communication with the primary master

A

Secondary masters

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14
Q

only speaks when spoken to by a master

A

a field (slave) device

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15
Q

… can communicate with slave devices in a HART network at the same time

A

Two masters (primary and secondary)

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16
Q

Disadvantages of HART

A
  • Costly in terms of cabling, labour and checking of each connection
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17
Q

Do not need a wired infrastructure and can communication both control signals and Intelligent Device Management (IDM)

A

Wireless Hart

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18
Q

Wireless HART Advantages

A
  • do not need a wired infrastructure
  • Best suited for remote locations where wiring costs are prohibitive - good for retrofitting, can be powered locally or with batteries
  • This is the slowest of the technologues - especially when using batteries. this can limit the applications
19
Q

International fieldbus communications standard for linking process control and plant automation modules

A

Profibus

20
Q

In PROFIBUS, used to connect all devices with high speed, bi directional, serial messaging used for transfer of information - instead of running individual cables from a main controller to each sensor and actuator

A

Single multi-drop cable

21
Q

PROFIBUS advantages

A
  • can use a single connection wire with spurs for each unit
  • significant wiring savings
  • quicker to install
  • entirely digital system completely eliminating the need for analogue 4-20mA signals
  • the devices are expensive but the cost is offset by savings in wiring, installation and checking
22
Q

PROFIBUS disadvantages

A
  • Complex and harder to troubleshoot
  • Replacement of exisitng 4-20mA system would require full rewiring - retrofitting is less likely
  • Vulnerable if the key wires break
23
Q
  • Decentralised peripherals
  • Carries communication data between a controller and field devices
A

PROFIBUS-DP

24
Q
  • a “string” is connected through a coupler or linking device to enable typical process automation (PA) application
  • spurs for each unit
A

PROFIBUS-PA

25
Q
  • Centrally housed input output modules
  • Devices on factory floor
  • Many pairs of cables over potentially long distance
A

Traditional system

26
Q
  • Input output modules move to the factor floor
  • DP carries communication data between a controller and field devices
  • Shorter cables to I/O
  • Single cable to PLC
A

PROFIBUS-DP (Decentralised Peripherals)

27
Q
  • Removes I/O modules and cabling
  • All sensor to one “bus”
A

PROFIBUS-PA (Process automation)

28
Q

good for configuration, calibration,
diagnostics, and viewing internal variables –
what is usually referred to as intelligent device
management (IDM)

A

HART

29
Q

used for IDM and also for real-time
closed loop control

A

Fieldbus

30
Q

Fastest

A

HART

31
Q

Slowest

A

Wireless HART

32
Q

What PLCs stand for

A

Programmable Logic Controllers

33
Q

A ruggest computing device for the process environment
- dedicated to single tasks
- tolerant to heat, moisture, dust etc.

A

PLCs

34
Q
  • Typically used for unit operations that operate independently
  • Uses ladder logic as means of programming, based on the standard DI, DO, AI & AO signals
  • Good for stand alone fucntions
  • Would not be used on a large compex site
A

PLC

35
Q
  • Input instructions enters on left
  • Output instructions enters on right
  • Processor scans ladderrings: Top to bottom, left to right
  • If input conditions are TRUE output action occurs
  • If input conditions are FALSE output action does not occur
A

PLC Ladder logic

36
Q

Handles the normal communication or exchange of data with the slaves assigned to it for PROFIBUS

A

Class 1 Master

37
Q

Special device primarily used for commissioning slaves and for diagnostic purposes

A

Class 2 master

38
Q

—[ ]—

INPUT

A

Normally open contact, closed whenever its corresponding input which controls
it is energized. (Open contact at rest)

39
Q

—[]—

INPUT

A

Normally closed (“not”) contact, closed whenever its corresponding input which
controls it is not energized. (Closed contact at rest)

40
Q

—( )—

A

Normally inactive coil, energized whenever its rung is closed. (Inactive at rest)

Outputs

41
Q

—()—

A

Normally active (“not”) coil, energized whenever its rung is open. (Active at rest)

Outputs

42
Q

Terminology used originally for hard wired relays and named for historical reasons
Notional devices with no physical presence

A

Contacts and coils

43
Q
A

Instrumentation, Measurement and Control (12 decks)

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