PLC Number Interface?

[Barry1492]

I have a machine that counts pails on a conveyor belt as part of its process. If the machine is maualy operated, it resets the count to zero.

I want to interface something into the PLC that will allow an operator to input what the count should be after resetting. I'm assuming there should be some sort of number pad that I can plug in.

In my experience, I've messed with pressure sensors that output either a voltage (0-5v) or a current (4-20 mA) that is then read by a program (Labview). I'm assuming a PLC would need binary inputs instead.

Any advice??

 

[analogkid2digitalman]

Depending on the make/model of the PLC, the manufacturer may have an off-the-shelf user interface display, keypad, or programming pendant to connect to it to allow modification of register contents. You will probably have to edit the ladder logic so the program prompts for a count entry after a reset. But with enhanced interface comes security and 'tweaking' issues if operators are not locked out of various functions.

Another approach could be to interface a BCD thumbwheel switch array to inputs of the PLC. Again, modify the program to read the count it is set to after a reset is performed.

PLC's, when outfitted with the approprate modules can read analog and frequency inputs and also generate such signals as outputs. But I think a BCD count is probably the best route to take.

Having said that, it has been almost 20 years since I touched a PLC or edited code for one- things may be a bit different today, so let's hear from others with more recent exposure

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[itsmoked]

Barry1492 since you have not said much about your process I am only guessing. But why would someone automatically zero the bucket count just because the system is switched to manual. Why not ALWAYS count the buckets and reset the bucket count ONLY when you want to zero it? Seems to me
that having people manually enter bucket counts is a good way to really have problems. "Was that 238 buckets or 138?"
or worse; "This shift needs more throughput! Increase the number by 100 buckets"

Does this make sense?

 

[Barry1492]

It's a palletizer. Basicaly, it puts buckets into stacks of 3 and then pushes those stacks of three into 16 stacks on the pallet.

The counter I'm referring to only counts from 1 to 16. Basicaly, it says, "OK....this is the 6th stack that has come through. Push them onto this spot on the pallet."

For whatever reason, once the machine is operated manually, it assumes the next stack goes into position 1, etc.

I want a simple input that the operators can use that will let them say, "ok, there were four stacks on the pallet before we start this thing up again. Push (4) then enter." Now the machine knows to push the next stack into position 5...etc....

 

[itsmoked]

Interesting. Thanks for the clarification.

Still seems that the the PLC programming could be slightly altered to not reset the count. This would be easier to rectify than adding the "enter the number" feature to the PLC code and the required hardware.

But if you still want that feature you might consider, (if you have the room), of just adding 16 small numbered individual buttons. This would need 16 Digital Inputs but would be less finger work, more robust, and easier to code.

 

[logbook]

A hexadecimal keypad might be simpler. There is still only one button to press and hopefully four binary switch lines. Only problem is the 0 to 15 (F), ie offset by one from what you requested.

 

[MacGyverS2000]

If 0-9 and A-F is an issue, maybe some paint or stickers would change that easily enough to 1-16. They may have to be repainted/restickered every year, but still cheaper and easier.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

U can get Hex keyboards with no labeling. Not a bad idea as it does allow only 4 digital inputs.

 

[Fchild]

Could you just have one two position spring to center switch to increment or decrement the count? You could even set it up if the button was held longer than a second or two to increment faster. Simple, one button two inputs. It is not as fancy as an input pad but it's cheap and easy.

 

[itsmoked]

Except don't you need a display for a blind kind of switch?

 

[Barry1492]

I like the sound of that. That is pretty simple. What I'd need would be a display.

ie....what ever the pail count is on the palletizer will be shown on the display. This button you speak of can be used to move the count up 1 each time it is pressed. That should be real simple to program.

 

[itsmoked]

Barry1492; Yes, I agree the button is reeeeeeeeeeal simple.
But the display is reeeeeeeeeeeeeeeeeeal hard.

simple + hard = not "the" simplest. Unless you know of a convientient PLC display unit. Even if you do this would still take more programming and far more hardware than just a HEX keypad.

 

[Rheinhardt]

What about the incrementing/decrementing function and then flashing the amount selected on pilot light. You must also have a confirm button. To confirm the count to the PLC where the operator must ensure the right count and then confirm it. The PLC will only load this value once you confirm it and not on any key strike up or down. as for flahing codes use a long pulse for over ten followed by short pulses for count.

BY having a input facility you are already putting the onus onto the operator, it is critical that you maybe use keyswitch on multi-directional selection switch.

This system would include 1multi directional spring return selection switch (up/down) confirm push button 1 pilot light and some software obviously for count,confirm, display.

Just a option.

Regards

--Off all the things i've lost , i miss my mind the most--

 

[MacGyverS2000]

How about one of those switches that has several decades to it, and you change each decade by pressing an up/down button. The number is displayed mechanically on the switch itself, and a separate button press sends the data in one fell swoop to the controller.

For example, how about the 3U0210002 from ITT Industries? About $7.50/decade from DigiKey in singles, BCD output, display is taken care of automatically. They also have thumbwheel versions if that will be better.

http://www.ittcannon.com/media/pdf/catalogs/Leaf/SW_thumbwheel_3u.pdf

For the money spent and the minimum of time needed for interfacing, I think this type of switch is ideal for this application.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

macgyvers2000; That's a pretty good idea though a little more expensive than a hex pad I bet. But if they often start the load at some specific count that would be a nice solution they could just leave it set and hit the ol'button.

 

[analogkid2digitalman]

BDC switch was mentioned 2 weeks ago- no display needed.
Just do it!!!! Git R Done!!!


Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[skills]

From reading the above posts, I would say that by far the easiest and possibly the least expensive way to do this would be to use an EZTEXT-PLC that integrates a text panel and control buttons to a small easily programmed plc that costs about $225 and has I/O modules for most basic tasks. The software to program the text panel and the plc is about $100 and you don't need to swap cables to program the different units. I don't know how much you value your time; but, you could do this in about 30 minutes vs some serious time trying to redesign a control system yourself.

 

[plcsavvy]

I think I would try to determine why the count value is getting lost when a manual operation is performed.
Look for code that either resets the counter or places a value in the register that the counter is using. I would start by performing a search on the counter register. Some PLCs can use as many as 3 registers to control a counter.
register 1 for example could be for updating the accumulated value of the counter. Register 2 for eaxample could be used to update the preset value (value the counter reaches before turning on a counter done bit.
and register 3 could be used for resetting the counter.
Other PLCs use a prefix at the end of the counter register. An allen bradley SLC 5xx programmed using RSlogix 500 programming software uses one register for the counter. An example is C5:0 to view or make changes to the accumulated value you simply use c5:1.ACC (accumulated value. To view or change the preset value you use C5:0.PRE.
I would bet also that when the machine is powered down it loses count. The way to prevent this is to move the accumulated value of a counter to a non volatile register.
In an Allen_bradley PLC you can use a move instruction to move C5:1.ACC for example, to a non volatile register such as N7:0

What brand and model of PLC is controlling the machine?

If you can fix the problem by making code changes to the PLC, you can save yourself a lot of time and money.

best regards, PLCSAVVY.