Experiment 6: Perform different operations over conveyor belt PLC setup.

Hardware:

In the hardware section a Alen Bradly MicroLogix 1500 LSP series C PLC is used. It has 10 input and 10 output ports. There are different sensors and actuators used with this PLC. And they are accessed by the PLC with their unique address through the software.  The sensors and actuators and their unique address is listed below:

Sensors or Input Elements
Sl no	Name	Address
1	Start switch (Green)	I:0/0
2	Stop switch (Red)	I:0/1
3	IR sensor 1	I:0/2
4	IR Sensor 2	I:0/3
5	Reed switch 1	I:0/4
6	Reed switch 2	I:0/5
7	Reed switch 3	I:0/6
Actuators or output element
1	Green LED	O:0/0
2	Red LED	O:0/1
3	Motor (Conveyor Belt)	O:0/2
4	Cylinder 1	O:0/3
5	Cylinder 2	O:0/4
6	Cylinder 3	O:0/5

Sensors or Input elements: there are seven sensors are used through which we can give instructions to the PLC. These are

Green and Red switch: they are two push button switches. Normally they are push to ON switches. The green switch is called start switch and red switch is called stop switch. When the switch is pushed it sends a logic HIGH pulse to the PLC and sends logic LOW when not pressed.

IR sensor Pair: There are two IR sensor pair has been used. The sensor pair consists of an IR LED and a photo diode and they are placed front to front. When an object comes in between a pair it sends logic LOW pulse to the PLC and sends logic HIGH if there is no object in between them.

Reed switches: There are three Reed switches attached to the three Pneumatic Cylinders. It sense the position of the piston inside the cylinder. When the piston is pulled out from the cylinder by the air pressure the reed switch connected to it sends logic HIGH pulse to the PLC. Otherwise it gives logic LOW pulse.

Output elements: There are six output elements are used through the PLC acknowledges the sensors. These are

Green and Red LED: They are two normal LED which are used for indication purpose. When a logic HIGH pulse is given to the LED they glow.

Motor: It is a simple 12V DC gear motor. A conveyor belt is attached to it with a support at the other end. It starts rotating when it gets logic HIGH pulse.

Pneumatic cylinders: There are three pneumatic cylinders are used. Each cylinder has a piston inside it and a reed switch attached outside. When the air pressure comes inside the cylinder it pulls out the piston. The air pressure is generated by a compressor and it is controlled by a solenoid valve. When the valve gets logic HIGH pulse from the PLC it opens and allows the air to flow into the cylinder.

Software:

The software used to program the PLC is RSLogixMicro. The ladder diagram is drawn here and is downloaded to the PLC.

When the software is opened the IDE will look like this. The center area is for ladder diagram. Just above the ladder window there is a function tab where you can find and pick the tools to use in the diagram. The left side window is called the project window. In the function tab there are lots of tools which are used in the ladder diagram. Frequently used tools/instructions  are

Every line or row of the ladder diagram is called rung. This symbol is to create new rung. When this symbol is clicked a new blank rung comes right above the present rung.

This symbol is used to make a branch or a parallel rung. When it is clicked it comes to the main rung. Then click on the right or left bottom edge and drag it to make a parallel branch with other tool.

This is normally open switch (NO). Just click on it and drag then drop it in the left side of the rung when you see a square changed from red to green color. This switch replicates the physical switch in the software. Means when this symbol is assigned to a physical switch, the switch behaves normally. That is when the switch is pressed it gives a logic HIGH and LOW for not pressed.

This is normally connected switch (NC). It is reciprocal to the NO switch. Means when it is assigned to a physical switch, the switch gives logic LOW when pressed and logic HIGH when not pressed.

This symbol is to energize the output element. Just click on it, drag and drop at the right side of the rung when see the green square. Assign it to an output element by proper addressing. It keeps the output energize as long as the input side of the rung gives logic HIGH.

This symbol is called latch output and it is used to latch or hold the output always energized after being triggered once by the input switch. Another switch is used to de-energize the out put by using unlatch symbol.

This symbol is called unlatch output. It is used to unlatch the output which would have been latched by the latch output symbol. The address of the output element should be same. The switch which is used to unlatch the output gives a triggering pulse once to de-energize the output.

This instruction is called ON delay. It comes under timer tab. The Timer ON (TON) instruction is used to turn an output ON or OFF after a certain preset time interval has passed. The parameters of the Timer ON instruction are:

Timer: this is the timer address,T4:1.

Time Base: This specifies the time interval that each incremental step of the timed count takes. There are three time base settings for the TON instruction, 1.0, 0.01, 0.001, all are in seconds.

Preset: This is the number of incremental steps that the timed count must take. Preset = Required Time(sec)/ Timer Base. Therefore for getting a 2 sec interval with Time Base of 0.01sec, the Preset value should be 200.

Accum: This is the accumulated value of the timed count. The number in the accumulator (Accum) increases by one with each incremental count.

EN: Thisis the enable bit. While the rung of TON instruction is true, the enable bit will be true. If once timing is completed and the rung is still true, EN bit will remain active. The EN bit is only false when the rung is false.

DN: This is the Done bit. This bit is set true when timed count is completed (accumulator value is equal to preset value). If once timing is completed and the rung is still true, DN bit will remain stay at true.

When the rung containing the TON instruction becomes true, the timer will start timing. the accumulator value will increment in time intervals determine by the Time Base until the accumulator value equals the Preset value. once this occurs, the Done bit will set true.

This instruction is called Timer OFF and it does the same thing what TON does. The only difference is in DN bit and starting of time count. When the rung containing the TOF instruction goes from true to false, the EN bit goes from true to false, the timer will start counting, and both the timing bit and DN bit will be active. The accumulator value will increment in time intervals determined by the Time Base until it equals the Preset value. Once this occurs the DN bit becomes false.

Procedure to Start:

Click on the RSLogix Micro English from the start menu.

Then go to New from the file menu or directly click on the shortcut.

   Now choose the processor “MicroLogix 1500 LSP Series C” and click OK.

Then this window will open.

Now draw your ladder diagram. And save it in a folder. Switch ON the power of PLC hardware setup. Then click on Download.

Click on Yes.

Again click on Yes.

The program is being downloaded to the PLC.

Click on Yes to get connected online with PLC.

Now the hardware and software are online, means the changes in hardware will be reflected to the software. Here if you want to edit your program you can’t do, you must go offline to do this.

Click on go offline and do make changes to your program if needs.