ISE 212: Engineering Computing Spring 2015
PLC Assignment:
Design and demonstrate ladder logic programs that will carry out the following tasks:
1) Turn each signal light (3) on/off by opening and closing a separate switch for each light.
2) A motor (green light) is switched on by pressing a start switch and the motor remains on until another stop switch is pressed.
3) Either of two normally open switches has to be closed for a coil (red light) to be energized and operate an actuator.
4) A heating element (yellow light) is turned on for 7 seconds. The heating element is turned on 5 seconds after receiving a signal (switch #3) that a part has arrived.
5) Simulate the following operation of an index machine.
> Start an index machine in motion when a start button is pressed (switch #1).
> The index machine takes exactly 3 seconds to change position. (green light).
(The green light must stay on for exactly 3 seconds to simulate the indexing motion).
> A signal is sent to lower & turn on a vertical drill press (red light), which takes
exactly 10 seconds to complete. This also includes the time to raise the drill press
back to its original position. (The red light must stay on for 10 seconds to simulate
the drill press operation).
> A signal is also sent to an automated parts feeder (yellow light) that takes exactly
4 seconds to load. (The yellow light must stay on for 4 seconds to simulate the
loading of a part).
> A safety switch (switch #2) will stop the index machine if needed.
> Make sure to keep a count of parts processed through your system in your program
for review.
ISE 212: Engineering Computing Spring 2011
Allen Bradley Micrologix 1000 Programmable Logic Controller
Equipment (P27 Lab)
A-B Micrologix Programmable Controller
Computer with Rockwell Software – RS Logix
Training box with switches and lights
Reading
Allen-Bradley User Manual for the fundamentals of programming the MicroLogix 1000
Safety Precautions
Do not open training boxes to remove wires on the PLC.
The Allen Bradley PLC consists of a built-in power supply, central processing unit, inputs (switch device), and outputs wired to colored signal lights.
The processor provides control through the use of a processor file. The processor file contains other files that break-up the program into more manageable parts. The processor file contains controller information, the main ladder program; interrupt subroutines and any subroutine programs.
The basic instructions used in the ladder programs represent hardwired logic circuits used for the control of a machine or equipment. The basic instructions are separated into three groups: bit, timer, and counter. The bit instructions operate on a single bit of data. During operation, the controller may set or reset the bit, based on the logical continuity of the ladder rungs. The timer and counter instructions consist of accumulator and preset values. Once the accumulator value is equal to the preset value, the rung changes from false to true.
Sensing devices located on a machine detect changes in the machine’s condition. For example, a part arriving at a workstation contacts and closes a limit switch, the sensing device. As a result, a signal goes to the control panel. At the control panel, the signal enters a bank of relays or other devices such as the solid-
ISE 212: Engineering Computing Spring 2010
state modules. Circuits within the control panel open or close causing additional signals to go to output devices at the machine. A relay may energize a clamp, which secures the part at the workstation.
Systems run by programmable controllers operate in much the same way. Input sensing devices report machine conditions; output devices respond to the commands. Wiring between the machine and the controller provide electrical paths from the sensing devices to the controller and from the controller to the output devices.
The hardware must be properly addressed so that is relates to the ladder diagram program. In the ladder diagram program, the input to the output instruction address is associated with a particular I/O terminal and is identified by the 5-digit address.
Input and output devices are connected to the processor’s input and output module terminals. Each terminal corresponds to a memory bit that reflects the state of that device. If the device goes on, then we say the corresponding bit in the data table is set to 1. If the device goes off, we say the corresponding bit in the data table is reset to 0.
Output instructions are programmed at the end of the ladder-diagram rungs. Only one output instruction can be programmed on each rung and it is executed only if the instructions preceding it are true. The Bit controlling instructions are used to set memory bits on or off in any area of the data table, excluding the processor work areas.
Timer and Counter instructions are output instructions within the processor. They provide many of the capabilities available with timing relays and solid-state timing and counting device. Usually conditioned by examine instructions, timers and counters keep track of timed intervals or counted events according to the logic continuity of the rung. Each timer or counter instruction has two 3-digit values. Each value requires one word of data-table memory.
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