What are some of the skills and tools you need to master relay logic vs PLC?

Relay logic (ladder logic) is also just one of the ways to program modern PLCs. This represents big advantage because it gives electricians and technicians a very understandable picture of how intended logic circuit works, since it has nearly identical logic flow as the physical relay logic circuitry. It also looks nearly identical to the relay logic electrical diagram and therefore makes that particular audience very potent and capable PLC ladder logic programmers.

- An example of relay logic commonly used is what’s known as the (three wire circuit) in this case voltage travels through a normally closed contact (stop or off button) it supplies power to a normally open (start or on button) when the start or on button is pressed voltage is allowed to travel through the stop button, and through the start button completing a circuit to close a coil or relay. Another variant of this logic will cause the relay to stay engaged or (seal in) until the stop button is pressed, interrupting the voltage to the start button and coil.

One characteristic of relay logic is the ability to latch and hold its state indefinitely until it is reset. This electromechanical ability is similar to the semiconductor technology which is equivalent to one bit of memory.

Important to understand: PLC takes a snapshot of the inputs at the beginning of the operation, followed by the program logic scan to determine all of the decisions to be made and finally finished with the actual outputs update.

I have extensively worked on "physical" relay logic from small scale logic & control operations to heavy equipments relay based logics. I noticed that electromechanical relays are rugged, having higher current ratings, easy to maintain, requires no handling softwares, easy to physically interface with various discrete sensors (plug & play), faces zero cyber threats & lastly served as the programming basis for soft logic controllers (PLC, Loop Controllers). The problems with relays are requirements of comparatively wider physical space for installation, huge wiring connections and environmental effects. Nevertheless relay logic serves as the backup for mostly ESD systems.

Compact in nature, requires less space and physical connections compared to hard relay networks, easy to manipulate & program and higher flexible nature while it comes to interfacing with various sensors (Analog and digital), make things possible and easy compare to hard relay networks. But it still face facing cyber threats, programming bugs/virus, conservative nature while interfacing with different communication protocols and softwares, proprietary nature of softwares, communications standards, different vendor compatibility etc. But despite all it stills replacing Hard wired relays in industries.

When looking at a relay operated control panel, it can often look cluttered and confusing, but having the blue print on hand can be very useful. The more you understand relay logic, the more similar it becomes to plc logic. PLC’s will take that system and do it all internally through inside bits and instructions, while relay operated systems have relays that communicate to other relays. They are like internal bits that communicate that a certain condition is met, and now another process can begin. I just hope your wires in your system are labeled!

The best way to start learning the basics of a PLC is to wire up one with some inputs and outputs (wiring them in should be simple, but if you need help there’s information online), and make a system. Start out by hooking up some switches, buttons, lights, maybe even a motor, then craft a real life system model. I started out by making a model of a car wash, I had a stepper motor reach limit switches that would represent certain “stations”, and anytime the “car” would make it to a certain station, a light would represent an action, like rinsing, soaping, or drying. Just starting off with something simple, that you can picture, and something that will push you to learn the program more.