Contents
What are the two types of signal that the PLC can process?
A PLC interfaces numerous types of external electrical and electronic signals. These signals can be AC or DC currents or voltages.
What are ways a PLC see an input turned on?
The normally closed contact will turn on the input to the PLC card in its ‘normal state. The NO contact when activated will complete a circuit and turn on the PLC input. Ladder logic will then turn on if you use a normally open (Examine On) input in your program.
How does PLC read analog input?
When the analog input signal enters the PLC it goes through an A/D converter or analog to digital converter. This is the component in the PLC analog input card that transforms the analog signal to digital signals. It is these digital signals that will eventually give our binary value representation in the PLC.
How does a PLC read the data from field transmitters?
The PLC has an analog input module that detects the output of the temperature transmitter. Virtually all analog input modules are voltmeters, even though they are listed as milliamp inputs.
How does the PLC read the rung logic?
As the PLC begins to process the rung, it reads the instructions on the left and determines if the Logic on that side of the rung is set to TRUE. The Logic evaluates to TRUE when a hypothetical current is able to pass through the instructions. Each instruction has a set of conditions that make it TRUE or FALSE.
What does I / O mean in a PLC system?
I/O overview PLC I/O is the part of the PLC that connects the brain of the PLC, the CPU, to the outside world, the machines. In a PLC system there will usually be dedicated modules for inputs and dedicated modules for outputs. An input module detects the status of input signals such as push-buttons, switches, temperature sensors, etc..
What should I know about plc part 3?
Welcome to part 3 of the “Beginner’s PLC Overview” series! Before we get started, if you have not read Part 1 and Part 2, I recommend that you do that now before continuing this post. Ok, moving on, in this post we are jumping into PLC inputs and outputs, often referred to simply as I/O. But before we do that, let’s do a little review.