Reference no: EM132903684 , Length: 10 pages

Question 1

a) Briefly explain THREE (3) differences between open loop system and closed loop system. You need draw diagrams to illustrate your answers.
b) Explain all elements in the typical process control closed loop system
c) The temperature of steam distillation plant is controlled by On-Off controller. The heater is located at the bottom of the distillation tank with RTD is used to monitor the temperature of the plant.

i. Draw a block diagram indicating all the components and variables in the system.
ii. Briefly explain the operation of ON-OFF controller in this application.
iii. List TWO (2) advantages and TWO (2) disadvantages of ON-OFF controller.
iv. Suggest TWO (2) improvement could be made to the system to prolong the life of the heater.

Question 2

a) A linear liquid-level control system has input control signal of 0 to 10 V is converts into displacement of 1 to 5 m.

i. Determine the relation between displacement level and voltage.
ii. Find the displacement of the system if the input control signal 50% from its full-scale
b) A PT100 RTD temperature sensor has a span of 25°C to 250°C. A measurement results in a value of 115°C for the temperature. Specify the error if the accuracy is:

i. ±0.4% full-scale (FS)
ii. ± 0.2% of span
iii. ±1.0% of reading

c) A controller output is a 4 to 20 mA signal that drives a valve to control flow. The relation between current, I and flow, Q:
Q = 25 [I - 3 mA] ½ liter/min.

i. What is the flow for 10 mA?
ii. What current produces a flow of 1.5 liter/min?

Question 3

a) List 3 basic elements needed in a programmable logic controller (PLC) and briefly descript each one of them.
b) Draw a diagram to show the basic structure of a programmable logic controller (PLC). Label your diagram correctly.
c) List two operations mode of a programmable logic controller and briefly explain each of them.
d) In the context of process control, the controller operating on a discontinuous mode initiates a discontinuous change in the controlled variable. Name two basic operations in the discontinuous mode and explain each of them

Question 4

a) Figure 1 shows a pictorial view of an oven, along with the associated input and output signals. All inputs and outputs are two-state variables, and the relation of the states and the variables is indicated. Construct Boolean equations that implement the following events:

Figure 1

i. The heater will be on when the power-switch is activated, the door is closed, and the temperature is below the limit.
ii. The fans will be turned on when the heater is on or when the temperature is above the limit and the door is closed.
iii. The light will be turned on if the light switch is on or whenever the door is opened.

b) Develop the control system of an automatic coffee-vending machine. Insertion of a coin and pushing of buttons provides a paper cup with coffee that can be black, with sugar, with cream, or with both. Describe the features of the machine as a discrete-state system.

c) Prepare a flow chart to describe the event sequence of the coffee-vending machine based on Q4b.