DIY PLCs
Most programmable logic controllers, or PLCs, are programmed using relay logic wiring schematics, which was the original PLC programming method. Relay logic uses inputs to control the flow of power through hot rails to outputs and eventually to a neutral rail. Under the right circumstances, the PLC will tell an output device to perform a certain task, allowing for the development of complex machinery operation with simple programming that non-programmers can perform.
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Instructions
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Determine where the input comes from. Inputs control the PLC and can come from sensors or switches.
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Determine the output device. The power will flow through the PLC and power on an output device, such as a motor.
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Configure the top rung, which consists of two inputs that can be turned on or off. If one input is on and the other is off, power flows through the output to activate the connected device. If both inputs are on or off, the output will remain off.
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Configure the rung underneath the top rung. Several combinations of inputs can turn the output on, depending on the configuration of the device.
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Run ladder logic PLC programming software. These programs usually let you create a ladder diagram through Ladder Mode. Ladder diagrams are schematics found in industrial documents. The Ladder Mode has a comment section, Custom and Standard Labels and a Ladder Rung. The Ladder (Draw) Mode lets you find and select the functions you want to incorporate, including the contact source, contact number and contact type, through the Contact Editor.
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Create your own labels using this software. The Output Editor lets you develop a program on the right side of the ladder rung. Control blocks of ladder logic using the Master Control Relay to save time.
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Use Shift and Reset Shift to create a variable size shift register to store each step. Make any changes to the math functions using the Math Function Editor. In addition to add, subtract, multiply and divide, you can also compare math data.
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Use Data ports to read inputs into the accumulator as numbers to use in the program. You can also load and write values to the accumulator. Correlate bits of accumulator with relay coils using Pack and Unpack. Relay coils are electromagnetic relays made from coils of wire that are surrounded by soft iron coke, an iron yoke, moveable iron armature and at least one set of contacts.
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Tips & Warnings
If you wish to replace all the data with new data, use the System Reset.
