Ladder logic program examples lamp sequence

#Ladder logic program examples lamp sequence manual#

ThatвЂ™s not a bad idea actually, and IвЂ™ve always left them in Program Scope because I only ever reference these tags from the low level machine control routines inside the same program.Д«y default it gave the new instruction (and tag) a name of Stop_000. However, youвЂ™ll quickly realize it always creates the tags in Program Scope, not Controller Scope. This is a nice feature, and beats having to create each coil tag by hand, like we do during ladder logic programming. That inserts the new Stop instruction and attaches it into the diagram after the transition:Д®very time you create an SFC instruction, it automatically creates a tag to store the instruction state. First select the Transition element, then click the Stop instruction on the tool bar above the editor: We need a Stop condition to tell the sequential function chart when the auto sequence is complete (so we can re-start the sequence). If you want, you can also use Structured Text language expressions here too, like вЂњNOT(SomeBOOLTag)вЂќ.ДЄs you can see, the editor provides an initial state for us, but doesnвЂ™t include a Stop condition. You can also use BOOL tags directly in your transitions, which means you can drive the transition logic from ladder logic conditions if you like. WeвЂ™ll use that bit in our lower level machine control routines elsewhere in the Washing Machine program. So, weвЂ™re going to make a bunch of steps (Step 1, Step 2, Step 3), and each one represents a bit that will turn on only while that step is active. These sequential function charts have a lot of advanced functionality, but I want to show you what I think is the simplest and most powerful use of themвЂ¦ just think of every step as a bit, or boolean condition, thatвЂ™s only on when that particular state is active. We attach a True/False condition to the Transition, and when the condition is true, we move from the step before the transition to the step after the transition. The little cross mark under the step is a Transition. This means that we always start our sequence here. The fact that it has a double border means itвЂ™s the Initialization step for the SFC. If youвЂ™ve never seen an SFC routine before, this might be a little overwhelming, but itвЂ™s pretty simple. In the dialog that pops up, enter the name Ab_Auto_Sequence, but remember to select Sequential Function Chart in the Type drop down box:Дouble click on the new routine to open it: Right click on the Washing Machine program and click New Routine. Start by adding a new SFC routine to our Washing Machine program. Add a new Sequential Function Chart Routine ItвЂ™s perfectly suited to laying out your auto mode logic. Thanks to the IEC 61131-3 specification, RSLogix 5000 now includes the sequential function chart (SFC) language which is kind of a cross between the two. However, state machines are easier to write and troubleshoot if you can express them as state transition diagrams or flowcharts. You can create readable finite state machines in ladder logic, and IвЂ™ve certainly done that on occasion. TheyвЂ™re extremely difficult to troubleshoot, especially for someone who only knows basic ladder logic. When PLCs were invented, they created the sequencer instruction as a way to port existing mechanical drum sequencer logic into the PLC. Before the advent of PLCs this was done with drum sequencers.

When you write auto mode logic, whether you realize it or not youвЂ™re creating a finite state machine. (Then you can write the rest of your program in the hotel room at night.) State Machines

#Ladder logic program examples lamp sequence manual#

You need to be ready to download your program and start the electrical checkout long before you have enough time to finish programming the machine.ДЄt this point, you already have all of your low level machine control (and hopefully your HMI manual mode screens) laid out, so you can actually download the program to the PLC and start assisting with the checkout.

Real projects have many things going on in parallel, such as design, programming, ordering, panel building, mechanical assembly, electrical field wiring, checkout, commissioning, etc. We did that first because in real life you rarely have enough time to completely write a program before you have to commission it. So in the last section we created the low level machine control routines, but we left AFI instructions as placeholders where we needed to insert commands from our automatic mode logic. This is part of an RSLogix 5000 Tutorial.