PLC Valve Control Ladder Logic Programming

Digital Inputs for PLCs

  1. Valve Open Feedback
  2. Valve Close Feedback

PLC Valve Control Ladder Logic Programming

Any pneumatic valve that wants to function needs an instrument air supply. In order to set the needed air supply to the valve and remove any liquid or particle matter from the instrument air supply, an air filter regulator is utilized.

A solenoid valve connects the air filter regulator’s output to the valve actuator. The instrument air supply to the valve actuator is controlled by this solenoid valve, which turns it on and off.

Consider the normally closed (NC) type solenoid valve (SOV). The instrument air supply will be cut off because the SOV is normally closed in the usual position, which is also known as the off position or de-energized state. The SOV becomes normally open (NO) when the PLC sends the instruction to activate it, allowing the instrument air supply to pass through.

Several people frequently mix up the terms valve actuator and solenoid valve. ON/OFF valves have limit switches or proximity switches to detect when the valve is fully open or fully closed. They are therefore linked to the digital inputs of the PLC. PLC can therefore determine if a valve is fully open or fully closed in the field and communicate this information to the operator using graphics.

Think about our ON/OFF valve as The valve is open when it is of the normally-open kind. In other words, the proximity or limit switch for open feedback will be activated by default, while the switch for close feedback will be in the de-powered state.

PLCs are commonly used in industrial automation systems to monitor and control the performance of numerous pieces of machinery and processes. Controlling the operation of valves, which are used to manage the flow of fluids and gases throughout industrial operations, is one of a PLC’s primary responsibilities. Ladder logic programming, which is a graphical programming language created specifically for Allen Bradley PLCs, can be used to achieve the valve control function.

The fundamental steps to writing a ladder logic program for valve control are as follows:

1. Define the inputs:

The status of the switches and sensors that determine the location and operation of the valve, such as limit switches, position sensors, and pressure sensors, will often comprise the program’s inputs. These inputs will be used to assess the valve’s state right now and to start the proper control processes.

2. Define the outputs:

The signals from the program’s outputs will be used to control how the valve operates, such as signals for opening and closing the valve, controlling pressure or flow rate, or giving the operator feedback.

3. Create the ladder logic diagram:

The ladder logic diagram illustrates the control logic that specifies the steps that must be taken in order to control the valve. The illustration consists of rungs, each of which stands for a distinct control operation.

4. Add the control logic:

A set of directives that specify the actions to be conducted in response to the input signals make up the control logic. The control logic would activate the proper output signal to open the valve, for instance, if the position sensor detected that the valve was closed and the operator signaled for the valve to be opened.

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Some common ladder logic instructions used in valve control programming include:

Set and reset coils: These instructions are used to, depending on the input signal, turn an output on or off, respectively.

Instructions for a timer and a counter: These instructions are used to create timed or counted delays in a program, which can be used to order operations or limit the length of a certain action.

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