Programmable Logic Controller, Digital Logic Control and Fuzzy Logic Training

Programmable Logic Controllers

Programmable logic control or PLC is the most commonly used industrial automation technique in the world. It is universally applied for factory automation, process control and manufacturing systems. Programmable logic control originated from the creation of computerised versions of relay control systems used to control manufacturing and chemical process systems. The programming is done using a special technique called ladder logic, which allows sequences of logical actions to be set up, interlinked and timed. A standard task in logic control is batch control and sequencing in a process system, as demonstrated in the PLC Trainer. This piece of equipment allows practical PLC systems to be built using a Programmable Logic Trainer based upon industry standard systems and a PLC Process equipped with relay control valves, contact switches and other standard logic control hardware found in batch production.

Digital Logic Circuit Trainer

Logic circuits are the basis of most electrical equipment and control systems. Devices such as AND gates, OR gates and XOR logic gates are basic blocks, that together with devices like flip flops, shift registers, encoders and decoders, are used in all logic circuit implementations. Implementing these in hardware blocks during training or prototyping is expensive, so a number of software packages for logic circuit development have been developed. Professional packages are too complex for simple systems and training, and so logic circuit simulation packages like the Logic Circuit Trainer is used. This combines a simple graphical user interface with screens that allow simulated logic circuits to be built by dropping icons of logic blocks on to a graphical representation of a circuit board on the computer screen and 'wired' together using simple mouse and keyboard operations. The logic circuit trainer has a built in real time interface which allows external logical actuators, sensors and outputs to be attached to the simulation. This allows standard logic problems such as stepper motor control and position encoders to be simulated and standard practical problems such as traffic light sequencing to be investigated.

Fuzzy Logic Control

Fuzzy logic control has been a very significant practical breakthough for implementing simple control systems. Fuzzy logic is easy to implement because it uses simple linguistic rules to incorporate uncertainty into logical control. For example, a building heating control system for an office which gets lots of sun in the summer might include the fuzzy logic rule

IF afternoon AND summertime THEN {heatingoff AND ventilationhigh}

Fuzzy logic can be complicated to understand initially because it is a different approach to control, and so the Fuzzy Logic Trainer has been developed to show clearly how the various fuzzy logic elements in a fuzzy system operate. The Fuzzy Logic Trainer contains handware blocks for fuzzification, de-fuzzification, plus fuzzy AND, OR and other fuzzy logic statements. These blocks can be connected together to implement a wide range of fuzzy logic control systems, ranging from simple fuzzy PI control to a fuzzy logic washing machine control cycle.

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