(Sequence Table) You will notice that we have a memory retentive output and the actual output to activate the solenoid. It is turned on by the start signal and off by the full sensor switch. The filling of the tank is done through Solenoid A. From the sequence table, we know that we need to have the timer done and the empty sensor off to reset the sequence. The first thing in our program is to control the start and stop functions. In our example, we will use the ‘V Memory’ areas. Since we must continue the sequence when the power goes off, memory retentive locations in the PLC must be used. I am writing the PLC sample ladder logic program for the process mixer. It will help prevent you from continuously re-writing the PLC logic. This is the step where you can save a lot of work by understanding everything about the operation. Knowing all of these answers upfront is vital in developing the PLC program. What happens when electrical power and/or pneumatic air is lost? What happens when the input / output devices fail? Do we need redundancy? It will also prompt questions like the following. How is the PLC example program solve the logic?Ī flow chart or sequence table is used to understand the process entirely.
Timer 3 minutes – (Internal) 3 – Develop a logical sequence of operations: Timer 3 minutes done bit – On/Off (Internal) Stop Pushbutton – Normally Closed – On/Off Start Pushbutton – Normally Open – On/Off What sensors will be used in the PLC program? The start button is pressed to repeat the sequence. The empty sensor switch opens to de-energize solenoid B when the tank is empty. When the agitate motor stops, solenoid B is energized to empty the tank. The mixer motor starts and runs for 3 minutes to mix the liquid. When the tank is complete, the full-level sensor switch closes.
As the tank fills, the empty level sensor switch closes. When the start button is pressed, solenoid A energizes to begin filling the tank. 1 – Define the task:Ī normally open start and normally closed stop pushbuttons are used to start and stop the process. We will discuss each step of the PLC program development. The process mixer will be programmed using ladder logic. We will apply the five steps to PLC Program development to our following programming example of a process mixer.
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