Before proceeding and understanding how sensors and actuators are wired to the input/output modules of PLC, we need to understand the concept of sourcing and sinking. here plc inputs and outputs explained in detail

This is required to appropriately select the sensors, actuators as well as the input and output modules of the PLC in the project.

Consider the circuit diagram shown here.

We can see a power source and a switch and a lamp in series with it.

When the switch is closed, current flows through the circuit and the lamp turns on.

As we can observe, the current first enters the switch and then the lamp.

Here switch is sourcing type.

Now let us modify this circuit a bit.

Let us first connect the lamp to the power source and then connect the switch in series.

In this circuit, when we close the switch, the lamp turns on.

However, here the current first enters the lamp and then the switch.

Here the switch acts as sinking type, as the current sinks in the switch.

In a simple way…

Plc inputs and outputs explained:


  • If a device provides current when it is ON, it is said to be
    sourcing current.
  • If a device receives current when it is ON, it is said to be sinking
    current.

Isolated AC/DC Inputs :

  • Isolated input interfaces operate like standard AC/DC modules except that each input has a separate return, or common, line.

TTL Inputs :

  • Transistor-transistor logic (TTL) input interfaces allow controllers to accept signals from TTL-compatible devices, such as solid-state controls and sensing instruments.

Register/BCD Inputs :

•Multibit register/BCD input modules enhance input interfacing methods with the programmable controller through the use of standard thumbwheel switches.

•This register, or BCD, the configuration allows groups of bits to be input as a unit to accommodate devices requiring that bits be in parallel form.

Output types :

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