How Do PLCs Work?

 

How Do PLCs Work?

PLCs are often described as small industrial computers with modular components designed to automate control processes. PLCs are the controllers behind most modern industrial automation. There are many components to a PLC, but most of them are often put within the following three categories:

• Processor (CPU)
• Inputs
• Outputs

PLCs are complex and powerful computers. But, we will describe the function of a PLC in simple terms. The PLC takes inputs, performs logic on the information within the CPU, then activates or off outputs supported that logic. We'll get into more detail later, except, for now, consider it like this:

The CPU monitors the inputs' status (ex. switch on, proximity sensor off, valve 40% open, etc.)

The CPU takes the knowledge that it gets from the inputs, performs logic on the information.

The CPU operates the outputs logic (ex. close up the motor, open valve, etc.)

See the flowchart below for a visible representation of the steps above.

Let's use a well-known example, for instance, how PLCs work. Your dishwasher. Many dishwashers have microprocessors that function similarly to PLCs. The dishwasher has inputs, outputs, and, of course, a CPU. a number of the information in the dishwasher controller would be the buttons on the front, the water sensors, and therefore the door switch. The dishwasher outputs would be the water valves, the warmth elements, and consequently, the pumps. Now let's believe how the dishwasher uses those various components.

• The user pushes the cycle mode button (input detected)
• The user pushes the beginning button (input detected)
• CPU verifies that the door is closed (input detected)
• Fill valve opens, and therefore the dishwasher begins filling with water (output activated)
• CPU waits until the proper water level is reached (input detected)
• Fill valve closes, and water flow stops (output activated/deactivated)
• The heating element is turned on (output activated)
• CPU waits until the proper water temperature is reached (input detected)
• Soap dispenser opens (output activated)
• Water pump activates to force water through sprayers (output activated)
• CPU begins timing counting on cycle type (logic timer activated)
• Water pump turns off (output deactivated)
• The heating element is turned off (output deactivated)
• The drain valve opens, and therefore, the dishwasher begins draining the dirty water (output activated)
• CPU waits until it detects the water level to be low enough (input activated/deactivated)
• Drain valve closes (output activated/deactivated)
• Fill valve opens again to rinse dishes (output activated)
• Water pump activates to force water through sprayers (output activated)
• CPU begins timing (logic timer activated)
• Water pump turns off (output deactivated)
• The drain valve opens, and therefore, the dishwasher begins draining rinse water (output activated)