Distributed Controls

Question Set 1

1. Produce a fully-labelled sketch to show the components of a Direct Digital Control system.

2. State the minimum number of printed-circuit cards required to construct a basic controller, naming each of the cards.

3. Produce a sketch to show the construction of the data words on the data highway.

4. Explain the use of the different MODES of control available in a controller of a Distributed Control System.

5. The Instrument Engineer, designing a Distributed Control System, has available to him Basic Controllers and Advanced Controllers. List all the reasons why an Advanced Controller might be used in preference to a Basic Controller, making reference to the full processing capabilities of the advanced controller.

6. Describe the difference between notified status and change detect points and list the types of cards to which this applies.

7. Describe the main purpose of sequence programmes and state what would require to be done in the writing of a programme which was too long to fit in one sequence slot, making reference to the problem which this could cause.

Question Set 2

1. Describe the data presented to the operator on the Detail page display of the operator station. List six different items of data which would be presented for a control loop data point, and state whether the operator would be able to change the values pertaining to these items.

2. State the limitations of the data highway system and what attributes of the advanced distributed control system help to overcome these.

3. Explain the token passing technique used for advanced distributed control system communications on the LAN, describing the procedure for a newly powered up module to join the system.

4. Describe in detail the different types of alarm generated on the advanced distributed control system.

5. Using the information below, produce a set of calibration figures for the control loop TICA1495.

TI1495 range = 100 to 420°C
TICA1495 SP = PV = 300°C
TCV1495 = 30%.

6. An operator, using the operator interface, will have the operator station in operator personality. Describe the requirement for 'personalities' within the DCS, making reference to other personalities available, and explain how different functions are denied to unauthorised persons within the operator personality.

7. Describe a procedure for adding a new data point to the distributed control system data base and making this new point available to the operator.

Question Set 3

1. Provide a list of the five major factors to be taken into account when considering the choice of a distributed control system for any given installation, stating the benefits to be gained from the use of DCS for an offshore oil and gas processing plant.

2. Describe the differences in communication protocol between the Honeywell TDC2000 and Honeywell TDC3000 distributed control systems. State the name of the device used to enable these two systems to talk to each other.

3. All of the distributed control systems have the ability to use a data historian module. List the main tasks of a data historian attached to a DCS.

4. Describe the use of Group Points, stating which of the manufacturer's systems these apply to.

5. Describe the functions of a Highway Traffic Director, and state which of the manufacturer's systems does not require the use of this device.

6. Where would an HIA be installed and what are its functions?

7. Explain the reasons behind the installation of distributed control systems in refineries for the control of natural gas liquids fractionation plant.