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johnny61

need help on 2 ladder diagram

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I have draw 2 ladder diagram based on the question.I think there are some mistake in it ladder diagram and may be I miss some part. Can someone please give some comment and advice.thanks. question.pdf Q2C.doc Q3C.doc Q2c_update.doc Q3cupdate.doc Edited by johnny61

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First why don't you add some descriptions to your data to make it a little easier to follow then we can probably walk you through it

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I am sorry that I forget to add description on my ladder diagram.I will add it.

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I've got to hand it to you. GOOD JOB for atleast making some EFFORT.....

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Had a little more time to look at it and the first question I have johnny61 is do you understand the different data types. The main ones I am thinking about for this one are: Binary (B) Timer (T) Counter (C ) Integer (N) Floating (F) Also, and no this will not affect my helping you, I know your are learing PLCs but are you going through some help book or are you in an actual class. This has more to do with knowing where you are at in your learning. Edited by TWControls

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my first ? is do you have a way of opening a .RSS file? Next is if you have a input variable at the begining of a rung then you also need a output whether it be a OTE, OTl, OTU, counter, Timer, or a jmp. over all it is looking pretty good for someone just starting out but my comrads are right about we need to know where you stand in your learning process so we can better help you if need you can email me directly and i will do anything to help you out even if it means a ph call or 2 back and fourth. krwillis@cox.net

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thanks for everyone help.Acually ,I am taking a part time PLC program.I just learn about PLC for 3 weeks and I can understand the basic instruction in PLC such as counter,timer.

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Q2c Ok, in your studies before now, you should have learned about binary (example-B3) bits. You need to add some of these to make your logic work. Beyond that you have done very well besides a few things. I'm not going to tell you where to put them but I will show you the problems. Rung 0 – Your logic makes it so the start button must be held until the level 1 sensor is made Rung 1 – This is going to cause problems when you try to drain the tank. When draining the tank and it drops below level two, Valve 2 Actuator is going to turn back on Rung 4 and 5 – Once T4:2 is done, the sequence will not start up. You should be about to fix this with 3 B3s, but I would suggest you take another look at Panic Modes example in your previous thread. It actually gives you a good example of stepping through sequences without sequencers. Fix those problems then repost your program and we will work on it a little more. And add a new post to your thread to put your new files, don't add them to your original post Edited by TWControls

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One of my tech guys wrote a program not to long ago that I helped him write. In other words I taught him. This is his first program after my direction in the simplest form I could tell him without getting to complex. I did not teach my tech guy the sequencer because he didn't have a basic understanding of PLC yet. So I will explain some basics I believe are good to start with. There are many different ways to write a program. This program is one of the simpler ways to write a sequence using only Inputs, Outputs, Control Bits (B3 bits) and Timers. Currently I use integer type stepping in my programs today but I was teaching a beginner so I did not want to explain how an integer works just yet. (N7 file) When you write PLC logic, I recommend doing these steps: 1. Write down your sequence of operation on a piece of paper. Example: I have a R&D pump project I was working on a couple of days ok. I wrote down the pump sequence. Record each motion. step 1: Dispense Valve Extend step 2: Plunger Valve Extend step 3: Dispense Valve Retract step 4: Fill Position Valve Extend step 5: Plunger Valve Retract step 6: Fill Position Valve Retract My valves are air valves. They are all single solenoid type, so I must "latch" or hold the solenoid valve "on" to keep the device I am controlling in the extended position until the next operation is complete or I tell the valve to retract. So understanding a little about the valves you are controlling is a plus whether you have single valves or double valves (which don't have to be held on). 2. I used global "control bits" to control a sequence. I still do that in my logic now. I have an "Ok" bit, an "Incycle" bit, a "Start Single Shot", or "Go", and a "Done" bit. These global bits control the overall operation of the device I am controlling. 3. Always use control bits throughout your sequence. NEVER put an output in your sequence. If you look at the example program. You see that all B3 bits are used until the end where the control bits actually turn on the outputs near the end. Use control bits in your sequence. You should have a control bit for each motion or sequence. Since you already wrote it done, it should be each for you to create the sequence control bits. 4. Try to CLEARLY comment everything. Even sections of your code. It will help you and help others understand what you have done. Granted this information does not apply to sequencers, which is your assignment, but it gives you some foundation and rules to try to follow. PUMP.RSS PUMP.pdf

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No he doesn't. In his previous thread he was using a RsSimulator. Have to convert to PDF as Chakorules did or use screen captures

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Just a little note here, if you an integrator, that this rule often changes depending on who the customer is. I've had customers specify that inputs and outputs must be mapped to internal coils (you'll see them only once in the program, being mapped) and I've had customers specify that this practice is forbidden (all logic must address inputs and outputs directly, no mapped internal coils) and exceptions must be approved. Its usually in the customer's controls specification. Personally, I'm somewhere in the middle.

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note:I forget to change the preset tiem for both timer to 6000 and 1800. Q2cupdate2.doc Edited by johnny61

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I must not get the question. Are you saying your class or your simulator will not let you use binary? Or are you asking if binary is an acceptable thing to use? Maybe I should ask what "Standard Functions" include in the instructions for this exercise? And did you look at Panic Modes example in your previous thread where you asked about sequencers?

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I did look at the panic modes example whch he use the B3:0 function.My friend said that we can only use the normal instruction such as timer,counter and relay to solve the problem.I will double check again with my lecturer this weekend.how about the Q3c ladder diagram?I think I miss the timer relay part? Edited by johnny61

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A B3 data file does use normal instructions. Mainly you use OTE, OTL, and OTU. The B3 is just a storage space. In the way you need to use it will pretty much be like an output without the physical output or an internal relay. You could do it without them but it is not the normal way of programming and definitely not the way I have seen any student assignments. Just clarify which way your professor wants it done and we will see if we can guide you through it.

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how about the q3c ladder diagram?The question never mention about the instruction so I can use any step or instruction to solve it.

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Rung 0 - Your assignment never mentions a stop button so take it out Rung 1 - This is where you need to latch an internal bit to keep this rung from being true again when the tank is draining. Also what to you have the timer bit in this one for? Rung 2 - This on needs the same type of internal bit as rung 1 to keep the valve from reopening when the tank is draining Rung 3 - Looks good Rung 4 - Think you already know but your preset is wrong Rung 5 - Looks good Rung 6 - Preset wrong Rung 7 - Once you get Rungs 0-6 working you will need to put something in to start the process over since it is suppose to continuously cycle Edited by TWControls

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thanks for the Q2c guide.I would like to know about the the Q3c ladder diagram which is about the automatic door control system.

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I think it would be easier if you finished the Q2c first. The Q3c is pretty much the Q2c with counters added

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can you please guide me on using the b3 function,I would like to know how to use it. From what I found out that in plc: "Individual data bits can be accessed in the bit memory. These can be very useful when keeping track of internal states that do not directly relate to an output or input. The bit memory can be accessed with individual bits or with integer words" What I don't understand is how can I use the bit function it in application?Do I have to use instruction such as 'BSR' 'NEQ' such as the one used in the 'tank program' 'OSR' in order to use the bit function.

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Don't worry about the bit shift instructions yet. Just use the B3 in place of inputs and outputs for internal relays. Do you know how to use OTL and OTU instructions? Edited by TWControls

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Here is the new ladder diagram.So now I have to replace the output for Y0,Y1 and Y2 with the OTL and OTU? 2QC.doc

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No you would not use the OTL and OTU to on the outputs. Use them on B3 bits to track your process. Your steps are 1. fill to level 1 with valve 1 2. fill to level 2 with valve 2 3. Spin for an amount of time 4. Drain for an amount of time Everytime you finish a step OTL a B3 bit to say that step is done. Use these bits to fix the problems I stated were wrong with Rungs 1 and 2. When you have drained the tank, OTU the bits that were tracking which step you were at to start the process over

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Almost. As a general rule you can't have two output in series so you must use a branch as shown below. Then B3/0 is already used to start the sequence so you would need to use a different address such as B3/1 in rung 1 and again a different address in rung 2 and etc. Once you have done that, you must use those bits as conditions for turning on the particular output so it will not turn on again during the draining process Edited by TWControls

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