Multiple Inputs-Question

Heres my problem. THe way it is now(Look at the picture) it works. C1 and C2's are momentary PB's on a panel attached to the PLC. Now I have another input X4(taken from a AUTO/MANUAL pushbutton from the stand) when it is ON it is in AUTO and if it is OFF stand is manual. I want to make it work in parellel to what i have in the picture. That means if C1 is ON and X4 is OFF Y1 should energize and C2 is ON and X4 is ON Y2 should energize. C1 is momentary so I need a Y1 latch and X4 ON or OFF. I tried ORing X4's across C1 and C2. Y1 or Y2 latch creates the problem. If i remove them it doesnt work either. It doesnt seems to be working. Any help is appreciated.

Thanks

Won't work with that arrangement. You will need the second set of buttons to have 2 seperate inputs for Manual PB and Auto PB.

Kim

I'll assume X4 is a maintained pushbutton. The question you have to ask yourself is - what if the momentary from the screen and this X4 pushbutton don't agree? Who wins?

If the physical button is a momentary then Kim's observation is correct. You'll need a second input. (eg X4 momentary on = set Auto, X5 momentary on = set Manual)

If X4 was a momentary push button then perhaps this will work for you. X4 is a push on (flip) push again (flop)

I would do away with the input X4, add another momentary pb to the stand and have them energize C1 and C2 too. It makes everything easier to understand when control panels have matching buttons etc.

I am a little confused on the program, the PBs C1 etc. should be X1 etc, why are you using C bits?

Firstly, I do not understand your question. When you say you want the buttons to be working in "parallel" do you mean OR?
C1 is ON or X4 is OFF --> Energize Y1
C2 is ON or X4 is ON --> Energize Y2

Is X4 coming from a MOMENTARY PUSHBUTTON or from a MAINTAINED PUSHBUTTON (very unlikely) OR a SELECTOR SWITCH??? I think you meant SELECTOR SWITCH.

Is this what you are trying to do? If yes then you need to use a one-shot with your selector switch input and thus make it act like a momentary input. Then you need to use both the momentary inputs in parallel. However, this is not advisable since then the selector switch position might disagree with the actual mode of the process and this is very non-intuitive. If the operator does not / cannot look at the touch panel, he/she has no means of knowing what the actual mode is.

Also, another good programming practice in such cases is to use the SET and RST instructions in DirectSoft32. Use (SET) Y1 in parallel with (RST) Y2 for Manual mode and (RST) Y1 in parallel with (SET) Y2 for Auto mode. This way you dont have to worry about breaking the latches. One breaks when the other makes.

Now, if instead of parallel (OR), you meant series (AND) then it is actually easier. On rung 1 put XIC C1 in series with XIO X4 to SET Y1 and RST Y2 (in parallel). On rung 2 put XIC C2 in series with XIC X4 to SET Y2 and RST Y1 (in parallel again). Now, your selector switch (X4) acts as a permissive only. Based on the state of X4, C1 and C2 are allowed to change the mode respectively. And the state of X4 will never disagree with the actual mode. However, in this case, having two input sources (panel and switch) does not make much sense because one cannot function without the other.

Finally, if you want to make it a little smart, you can try this. Any of the two (panel or selector) can put the system in MANUAL but only the source which put the sytem in MANUAL can change it back to AUTO. This can be used to avoid safety hazards of two different people operating a system without knowledge of one another. I have tried this and can give you more details if you want. I think this is the best way to do it.

Summarizing,

If you want OR operation then both sources have independent control of the mode but the switch position can disagree with the actual mode -- safety concern.

If you want AND operation then the panel is dependent on the selector switch which only acts as a permissive to change the mode. However, saftey wise you are good.

Best option is to hand the control over to the one that operated it last. If MANUAL mode is safer than AUTO (usually it is) then the source that put system in MANUAL should be the only one to put it back it AUTO. This way, both can switch from AUTO to MANUAL but not vice versa.

rsdoran said:

I am a little confused on the program, the PBs C1 etc. should be X1 etc, why are you using C bits?

Click to expand...

Ron, My guess is he is trying to add somthing to an exsiting program that he did not write himself.

milldrone said:

Ron, My guess is he is trying to add somthing to an exsiting program that he did not write himself.

Click to expand...

I reckon, just seems to me that if auto and manual are actual PBs then the code should use their input directly, no need for the internal bits.

If they are adding another control panel then they need to have it match the original, this way you can parallel NO and series NC contacts.

I reckon, just seems to me that if auto and manual are actual PBs then the code should use their input directly, no need for the internal bits.

Click to expand...

Ron, he said the "C1 and C2's are momentary PB's on a panel attached to the PLC". This might be an Automation Direct PLC (DL-06 model and others) with attached LCD graphic operator panel, like this one:

http://web1.automationdirect.com/adc/Overview/Catalog/PLC_Hardware/DirectLogic_06/PLC_Units

If so, some of the PLC internal "C" memory bits are mapped directly to the operator panel pushbuttons. No "X" PLC inputs are required for the Panel pushbuttons in that case.

Then again it might be something else. Don't you love the guessing game? Guessing the equipment is as much fun and a lot more difficult than the piddling little old problem.

Thanks for all your replies. It took me while to get back to you guys. Sorry. Anyway lancie is correct. I am using a DL-06 PLC with a OP-640 panel. PLC internal "C" memory bits are mapped directly to the operator panel pushbuttons. i.e C1 and C2. These PB's does not control the stand actually. Y1 and Y2 are for status lights. There is a an exisiting AUTO/Manual PB(Maintained) on the stand. This is what actually put the stand in AUTO/Manual mode. So when I press this PB or the PB's on the OP-640 panel, I want the staus light to be turned ON. Yea and if the real PB on the stand in not in AUTO, pressing PB on the OP-640 should not be doing anything. Hope this helps.

Thanks

lilocomotiv said:

These PB's does not control the stand actually. Y1 and Y2 are for status lights. There is a an exisiting AUTO/Manual PB(Maintained) on the stand. This is what actually put the stand in AUTO/Manual mode. So when I press this PB or the PB's on the OP-640 panel, I want the staus light to be turned ON. Yea and if the real PB on the stand in not in AUTO, pressing PB on the OP-640 should not be doing anything.

Click to expand...

lilocomotiv said:

That means if C1 is ON and X4 is OFF Y1 should energize and C2 is ON and X4 is ON Y2 should energize

Click to expand...

When I bring these two quotes together the only action I get is
When X4 is on = auto
When X4 is off = manual
The status of C1 and C2 make no difference in the quotes.


Kim Gold, bernie_carlton, and puravdagli all saw this problem and tried to point it out to lilocomotiv.

I get the feeling lilocomotiv wants something different.

lilocomotiv, please explain this so We can understand what you want.

When using 2 control panels they should match controls as close as possible, just makes it easier to understand.

What you could do is use one input X4 from the stand and say C1 (also maintained) and default is AUTO

 

     C1       X4               Auto

|---| |------| |----------------(y1)--| 

|   Y1                         Manual

|---|/|-------------------------(y2)--|

If either C1 or X4 get pushed (goes off) then it goes into manual.

You can can change the arrangement where default is manual or auto, your choice.

Here is What You Asked For...

A Working Version of What You Asked For:

1. When X4 Maintained PB = OFF, Y1 Manual Status Light is ON, regardless of whether Momentary C2 Auto PB is pressed. If C1 is pressed, Y1 stays ON.

2. When X4 Maintained PB = ON, Y2 Auto Status Light is ON, regardless of whether Momentary C1 Man PB is pressed. If C2 is pressed, Y2 stays ON.

Question: Is this what you really need?

Comment: As many have said before me, the maintained pushbutton will always have more weight that the momentary C1 and C2 pushbuttons, like an elephant and and two fleas in a glassware shop. For all of C1 and C2's influence, you might as well delete them. Perhaps a rethinking of the operating logic is needed here....



Here is another version. It LOOKS more useful, but contains another useless top branch in each rung. If I remember in state tables and Karnaugh mapping these are examples of "Don't Care" conditions.

Lancie, this is what I said earlier. If you use the two input sources (X4 and C1+C2) in series, then C1+C2 becomes useless as X4 is the main permissive. If you use the two input sources in parallel then thats a safety hazard because X4 will sometimes disagree with the actual mode.

The best way according to me is to use the third method I have suggested. The source that first put the system in MANUAL is the only one thats allowed to change it back to AUTO. However, in AUTO, both can put the system to MANUAL.

I hope this makes some sense...

Puravdagli,
You have me convinced. Now convince the customer! Perhaps a ladder example of your third-method logic would help.