Need to skip a station

Good day all. I have kind of an odd question. Is there a way to have a processor skip an input whilst reading all the remaining input signals? What I have is 9 tanks for a cleaning process that uses a crane. Because of the cost, I could not get a servo motor and encoder approved so I had to use a single prox switch, two pushbuttons and dawgs placed over each tank, to display the cranes position, in the system. Everything works fine except now we have added two new tanks, one a process tank, the other a rinse tank. The problem is, the new process tank is identified as tank "0", then the next process tank is tank "1". So when the crane is at tank 0, it is ok. Then when it moves to tank 1, because there is a tank between 0 and 1, it now displays tank 1 as tank 2. What I'm trying to do is have the processor ignore the input as far as a counting position is concerned, when the crane lands on the rinse tank between process tanks 0 and 1. I still need that input however because that is what is used to tell the crane it is over a tank and enables the lift/drop instruction for the rinse tank. I'm sure this is probably terribly confusing but I don't know how else to ask this. It is for a SLC 5/03 processor. Thank you.

So your crane travels along this rail, and there are inputs that it sees as it moves and it uses these inputs as a counting method to determine what tank it is currently at?

Starts at Tank 0, sees a switch, says "OK Now at Tank 1". Sees a second switch says "OK Now at Tank 2".

A switch/tank was added between Tank 0 and "Old" Tank 1, and now it it counts twice when it reaches the "Old" Tank 1 and says it is Tank 2?

Are these switches all coming back to the same input. Paralleled to a high speed counter or something? Or does each individual switch come to a separate input?

Are you using a couter or a add to count the tanks? If you are 1 higher than you need to be just subtract 1 at all tanks except tank.

Sounds mechanical to me also. You prox should be counting a specific target. Just don't have a target on the tank you don't want.

You will need two sets of numbers. One set identifies how many switches have passed. The second set will identify the tank.

Logic will have to translate a count of '2 switches' tho 'Tank 1'. You can decide whether this translation is for the benefit of a display only or if it will be used in the actual processing.

Are the processes in the same order as the placement of the tanks? So a new tank and process has been added between the first two tanks. Go ahead and 'name' the tanks and processes 'Tank 0', 'Rinse', 'Tank 1' etc but have them tied to counts of 0, 1, 2 etc. You don't need to be a total slave to what they have chosen to name the external equipment. Don't try skipping the count, just use it properly.

Tharon said:

So your crane travels along this rail, and there are inputs that it sees as it moves and it uses these inputs as a counting method to determine what tank it is currently at?

Starts at Tank 0, sees a switch, says "OK Now at Tank 1". Sees a second switch says "OK Now at Tank 2".

A switch/tank was added between Tank 0 and "Old" Tank 1, and now it it counts twice when it reaches the "Old" Tank 1 and says it is Tank 2?

Are these switches all coming back to the same input. Paralleled to a high speed counter or something? Or does each individual switch come to a separate input?

Click to expand...

Yes, all of them back to the same input. As it passes by a dawg, it updates a counters accumulator value.

I understand he has a single prox on the traveling portion and a seperate target at each tank. So there is only one input which pulses once (hopefully) att each station/target. So in my previous post:

One set identifies how many switches have passed

Should have been phrased as

One set identifies how many targets have passed

I'd say the easiest solution is to change the accumulator values that identify your tanks.

Before, 2 (or 1?) was tank 1, now 3 (or 2?) will be tank 1.

bernie_carlton said:

Are the processes in the same order as the placement of the tanks? So a new tank and process has been added between the first two tanks. Go ahead and 'name' the tanks and processes 'Tank 0', 'Rinse', 'Tank 1' etc but have them tied to counts of 0, 1, 2 etc. You don't need to be a total slave to what they have chosen to name the external equipment. Don't try skipping the count, just use it properly.

Click to expand...

No, there are different recipes which call upon different tanks, times, and temps.
I'm not sure what you mean by "Don't try skipping the count, just use it properly".

Thank you

The idea is easy for me to think of, but hard for me to convey to you without knowing exactly how you are doing it in your program now.

Maybe Bernie can explain it? But if you can, post your ladder program and others could help you identify the changes needed to be made to properly identify the tanks in all your recipes.

Basically instead of changing the hardware, just change how the program identifies the Tank. I can only make assumptions now, but if I were programming it I'd have a bit set in the program somewhere by the counter value. I'd change that counter value to the correct count for that recipe selection rather than trying to skip the input for that recipe selection.

I think the best way to handle this is
1. the PLC has the crane stop at each tank no matter what.
2. the product based recipe tells the crane what to do at that tank. If nothing then recipe in PLC tells crane you are done at tank X go to tank X + 1.

Dan Bentler

I'm sure this is probably terribly confusing but I don't know how else to ask this. It is for a SLC 5/03 processor. Thank you.

Click to expand...

CeilingWalker,
If you will post the relevant parts of your SLC 5/03 program, then I am sure that we can help you figure out the best cure. If that is not possible, then make a simple block diagram of your tank layout, showing the tanks and the prox targets and prox switch.

It seems to me that the problem is that you need to use the prox-switch targets for TWO separate-but-related functions: to keep up with the Crane's tank poition, but then you only want to "count" certain tanks for certain operations. That problem can be taken care of in a program by separating the logic into TWO separately-operating functions: a crane-tracking position function, and then the operational Tank Numbering function. Remember that in a PLC program, prox switch inputs can be used more than once, as many times as needed.