Question

Objective:

The objective of this practical exercise is to introduce to develop a ladder diagram from a word problem using interlocking and safety operation techniques.

Equipment:

·         Computer with installed software to control and program the PLC

Process Application: Water Tank Level

The process shown in the Figure below is to be used to control the level of water in a storage tank by turning a discharge pump on or off. The modes of operation are to be programmed as follows:

Operation
OFF Position	the water pump will stop if it is running and will not start if it is stopped
Manual Mode	the pump will start if the water in the tank is at any level except low
Automatic Mode	if the level of water in the tank reaches a high point, the water pump will start so that water can be removed from the tank, thus lowering the level. When the water level reaches a low point, the pump will stop.

Status Indicating
green	Water pump running
red	Low water level status
yellow	High water level status

Note: Man/Auto = 1 means Auto mode and Man/Auto = 0 means Manual mode.

Understanding the process first!

Procedure

1.       Draw the system truth table: (NF: On/OFF, MA: MAN/AUTO, HS: High Sensor, LS=Low Sensor)

NF	MA	HS	LS	G	R	Y
0	0	0	0
0	0	0	1
0	0	1	0
0	0	1	1
0	1	0	0
0	1	0	1
0	1	1	0
0	1	1	1
1	0	0	0
1	0	0	1
1	0	1	0
1	0	1	1
1	1	0	0
1	1	0	1
1	1	1	0
1	1	1	1

2.       Write the logic functions for the outputs:

G =

R =

Y =

3.       Write a ladder diagram for the field devices.

4.       Simulate the program

5.       Take a snap picture of your running (contacts turn green) program under the three operational modes described above.

6.       In the table below summaries the status of system switches, sensors and lights

OFF/ON	MAN/AUTO	Low level	High Level	Green	Red	Yellow

·         Draw the logic circuit that describes the operation of this process

·         Draw below and send a copy of the ladder diagram to the instructor’s email address.

Ladder Diagram	comments

Answer 1