Simultaneous start.

[Dionntes]

I'm super new to the Controls world. This is my first controls job and i never went to school or have a background. I was just a technician that was hungry and wanted to learn. I was tasked with making some code that when I push the Start button at the control cabinet 16 conveyors start at once. They all have a local start button.
My question, is there an easy way to do it?, do i just branch around the local push button? is there an instruction that can take the input of the button and write to all the outputs? Or do i have to do 16 different rungs with the same input but different outputs?




Or am I completely wrong?


Any help is much appreciated.

 

[JeremyM]

Your last approach is probably most sound. With a rung per output, you’ll be able to condition each device individually, troubleshooting will be easier, and you’ll have set up a basic framework for more elaborate sequencing or state handling from the start.

What part of Texas are you from?

 

[parky]

In general there are things to consider, 16 direct on-line conveyors starting at the same time not generally a good idea, first thing to consider is the initial load on the supply, the starting current can be quite high i.e. over double or even 4-5 times higher tha the running current. so this could put a load way above the supply current of the system. this will all depend on the type of motors, if VFD's or soft starters are used etc.
generally, you phase start them i.e. for conveyors start at the outfeed & start them in sequence for example a few seconds between each one, this serves two purposes 1. reduce initial load on the system, 2. allows product on the conveyors to seperate or they can be started in banks.
I suggest you think carefully about the control, if these were manuallly started then the probability is that the power supply & components were designed for that mode not starting all at the same time. It all depends on the system as above.
Phasing is pretty simple start the first conveyor (or bank of conveyors), then run a timer of a few seconds, start the next & so on, there are many ways to do this, i.e. a counter driven off a pulse generated from a reciprocating timer & compares for turning on the conveyors, for example create a pulse every second, use that to count up a counter, the first conveyor (s) start when counter is equal to or grater than 0, the next will start when the compare of the counter is equal to or greater than 3 & so on.
See pic of two ways to sequence conveyors. One uses a timer for each conveyor (s), the other uses a counter & compares

 

[Dionntes]

Your last approach is probably most sound. With a rung per output, you’ll be able to condition each device individually, troubleshooting will be easier, and you’ll have set up a basic framework for more elaborate sequencing or state handling from the start.

What part of Texas are you from?

Thanks for the reply, I'll work on building the code so i can test it..
I am in the Fort Worth area. What about yourself?

 

[Dionntes]

In general there are things to consider, 16 direct on-line conveyors starting at the same time not generally a good idea, first thing to consider is the initial load on the supply, the starting current can be quite high i.e. over double or even 4-5 times higher tha the running current. so this could put a load way above the supply current of the system. this will all depend on the type of motors, if VFD's or soft starters are used etc.
generally, you phase start them i.e. for conveyors start at the outfeed & start them in sequence for example a few seconds between each one, this serves two purposes 1. reduce initial load on the system, 2. allows product on the conveyors to seperate or they can be started in banks.
I suggest you think carefully about the control, if these were manuallly started then the probability is that the power supply & components were designed for that mode not starting all at the same time. It all depends on the system as above.
Phasing is pretty simple start the first conveyor (or bank of conveyors), then run a timer of a few seconds, start the next & so on, there are many ways to do this, i.e. a counter driven off a pulse generated from a reciprocating timer & compares for turning on the conveyors, for example create a pulse every second, use that to count up a counter, the first conveyor (s) start when counter is equal to or grater than 0, the next will start when the compare of the counter is equal to or greater than 3 & so on.
See pic of two ways to sequence conveyors. One uses a timer for each conveyor (s), the other uses a counter & compares

Thank you so much for this, I had never even thought about all the problems that could surface upon starting them all at once. I will discuss with my manager to make clarify what exactly he wants.

 

[parky]

Yes I would definitely look at phasing the conveyors, as I said, they could be done in banks of 2, 3, 4 etc. another way is use a timer with a larger time SP, then just use compares with the timer elapsed time i.e.
Start first conveyor (or bank), compare timer CV with say 3 secs, start next bank, compare for 6 secs start next bank & so on.

 

[dbozic]

I agree with sequential starting of conveyors, not all at once.
Have seen a few time main circuit breaker goes off because of simultaneous start.
When I was starting in this field, happened to me at my first job as well, around 10 pumps all at once started and caused inrush and tripping.
If there are many motors/conveyors I would as said start the first one/or last (depends on preferences) and use a timer (or clock memory and counter) that is stopped when the last one starts.
Compare the elapsed values with values for each pump/conveyor to start and give enough time in between to eliminate inrush.

 

[cardosocea]

If there are many motors/conveyors I would as said start the first one/or last (depends on preferences) and use a timer (or clock memory and counter) that is stopped when the last one starts.

I don't think this should be down to preference. The first to turn on is the last (in the direction of product travel) conveyor to empty it downstream and not have the potential for product hitting a stopped conveyor if you start the first conveyor.

To stop them, the reverse applies, you'd want to stop the first one to allow the others to transport whatever is on them. You can be precious about this and if you know the speed at which each conveyor travels, calculate how much it should run to empty its belt thus ensuring it stops empty. (assuming, of course, that we don't have a way to detect whether it has something in them or not.

 

[dbozic]

I don't think this should be down to preference. The first to turn on is the last (in the direction of product travel) conveyor to empty it downstream and not have the potential for product hitting a stopped conveyor if you start the first conveyor.

To stop them, the reverse applies, you'd want to stop the first one to allow the others to transport whatever is on them. You can be precious about this and if you know the speed at which each conveyor travels, calculate how much it should run to empty its belt thus ensuring it stops empty. (assuming, of course, that we don't have a way to detect whether it has something in them or not.

I fully agree with you. For conveyors I would do like that.
But as I was referencing both pump/conveyors same rules don't apply, so I wasn't definite and left a room of preference, depending on the situation/process.

 

[cardosocea]

But as I was referencing both pump/conveyors same rules don't apply, so I wasn't definite and left a room of preference, depending on the situation/process.

Sorry, my misunderstanding.

 

[drbitboy]

I'm super new to the Controls world. This is my first controls job and i never went to school or have a background. I was just a technician that was hungry and wanted to learn.

Good for you. I suggest you start here and here.

The first link is @Ron Beaufort's PLC boot camp video series, which will explain the scan cycle in less than an hour. Watch the first several videos repeatedly until you can confidently explain the scan cycle to someone else. PLCs are about time, and the scan cycle is the fundamental "unit" of PLC time.

The other, and probably more, important concept that those videos teach is that ladder logic rungs are not circuits. This is an admittedly nuanced point, as most rung behavior is similar to circuit behavior. 99% of the time you will find thinking that way will be good enough, but when that 1% case comes around you will be glad you have the details of how rungs actually work in your back pocket.

The second link shows most of the canonical patterns of PLC Ladder Logic. Study especially the Input Map, the Seal-In, the Start/Stop and the State Coil patterns; you will use the last two, or some a form similar to those, over and over again. In @parky's example in Post #3, the first rung uses the Stop/Start Circuit pattern.

I was tasked with making some code that when I push the Start button at the control cabinet 16 conveyors start at once. They all have a local start button.
My question, is there an easy way to do it?, do i just branch around the local push button?

The simplest answer is yes (but see Caveats below!): if I assume there are 16 Start/Stop patterns, one for each conveyor, then ORing* the Control Panel [Start_All] in an XIC/NO instruction with the local [Start_Conveyor_N] XIC/NO instruction would be one way to start any conveyor that is not already running.

* OR i.e. you want to start any conveyor if

• EITHER the local start button for that conveyor is pressed
• OR the global Control Panel [Start_All] button is pressed

I say OR because an instruction "branching around" (i.e. in parallel with) the local start button instruction functions as a logical OR.

Caveats

The caveats are issues like the discussion here about not starting all the conveyors at once. Also we on the forum are blissfully unaware of your particular process: are these conveyors in series or in parallel; how many of the conveyors can be started simultaneous;y without overloading the power supply system; are there safety issues e.g. if conveyor N fails to start, is it safe to start convey N+1; etc.?

is there an instruction that can take the input of the button and write to all the outputs? Or do i have to do 16 different rungs with the same input but different outputs?

Yes there is, but it depends on the layout of the discrete outputs' bitboxes**. Specifically, if the discrete outputs' bitboxes are contiguous and compose all or part of a single data word (typically an integer of some kind), then yes, they can all be written with one bitwise-OR instruction***:

​

Note that when the START_ALL_CONVEYORS bitbox is 1, Rung 0004 could instead bitwise-OR the value 3840 into the word B3:0, which would trigger all of the Start/Stop seal-in branches to evaluate to True.

** see video above
*** four conveyor Start/Stop patterns shown on Rungs 0001-0004, plus one global Start button on Rung 0000; this approach could be expanded for up to 16 or even 32 conveyors

 

[parky]

Where is the STOP all conveyors but I like the idea.

 

[JeremyM]

Thanks for the reply, I'll work on building the code so i can test it..
I am in the Fort Worth area. What about yourself?

Great. Keep us posted.

I'm in Dallas/Plano/McKinney. What industry do you call home?

 

[James Mcquade]

one more thing to consider, how to start them.
by that i mean you will need interface wiring to start.
you may need a signal back to indicate it is running and stopped , e-stopped.
interface wiring is yellow or orange ( it has changed and i cannot remember)
you may want to buy an illustrated NEC70 codebook and NFPA 79 - electrical standard for industrial machinery.
james

 

[parky]

Reading your post again, some questions come to mind.
The local Start/stop buttons are they wired back to one main control cabinet.
Are they actually hard wired to the contactors or are they through an existing PLC.
Do you need to have local control as well as auto start.
And of course, any modification must upgrade the system to any current legislation in force regarding control of those conveyors.
Depending on a number of factors (and local regulations) how you modify the control is important.
Assume all start/stops go back to PLC inputs then not a real problem, however, if the start/stops are hard wired then perhaps hand/off/auto selector is required, so if in manual the switch to pass through off so the conveyors stop then in auto can be re-started, same goes for reverse of this.
Also if the local stops are to be active during auto control then the ouputs to start the conveyors would need to be pulsed i.e. only on for enough time to "LATCH" in the existing hard wired start/stop.
Perhps a warning beacon & sounder should also be implemented for a few seconds before auto start to warn any operatives the system is about to start, also perhaps warning signs about auto start. local isolators also may be needed.
perhaps if hand/off/auto is used, the power to the hand controls & auto control be switched so that when in auto the local starts do not operate.
As mentioned, all this depends on the system as a whole, what safety is in place, does it meet current legislation, risk assesments etc.
you are about to enter into a project where what the company want, but in many cases I have seen before you will be the doom & gloom guy, management will want it done as cheap as possible, legislation says you need to make sure it's safe.
One scenario comes to mind, we were invited to quote for a complete upgrade of a latex dipping plant, this consisted of 5 stages the existing control was done by 5 klockner adaptable boxes that controlled each stage, the machine was a real mess of wires, we quoted & my boss not being very tactile mentioned that the wiring was a rats nest & unsafe, we did not get the job, some months later, the company called us, an unfortunate employee had been electricuted & died, apparently he was doing something on a motor, put one hand on the motor casing & one on the machine frame. The factory inspector closed the factory until the plant was made safe. we managed to design, build, install & commission a new control system in three weeks.
This included zoned areas with explosion proof controls etc. the cost nearly doubled the original quote & we actually did two other systems for them on the back of the original project. We have no idea of the total cost of lost production, fines by HSE & the prosecutions that may have been done but make sure that you are bullet proof & stand your ground.