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Old December 28th, 2017, 02:41 PM   #1
stu
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Pvp help for step sequence on a weighing system

Hi guys
Im after some ideas to display a weighing system on a hmi to help with easy fault find?
We have a micrologix 1400 and pvp 700 all on a working machine
We have a few step sequence flour delivery, discharge, water delivery,liquids
Each step sequence have about 8 steps
I thought about having something like a flowchart of the step sequence?
Or lamps on for step bits ??
Any creative ideas welcome thanks stu
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Old December 28th, 2017, 04:14 PM   #2
Aardwizz
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So many questions

Do you have one stored recipe, or several?
  • Is the sequence the same for all recipes, or variable?
  • Do you want to program the recipes from the PV, or just have them in the PLC code?
  • Does your sequence have prompts that the operator must respond to? Is there a time limit for response?
  • Do you plan to have traditional S88 states or Idle |Running | Holding | Held | Restarting | Aborting | Aborted ? Or just a simplified version of Idle | Running | Held | Aborted. (i.e, no need to do a controlled stopping, just stop the flour blower, RAL & chute, turn off liquid pumps, close valves) ?
  • What security / whodoneit tracking?
  • Any lot / RM tracking?

Basic premise: a sequence consists of ACTIONS and TRANSITIONS. Separate the two when coding.

"easy fault find" == tell the operator what each transition is waiting for.

Making the sequence work is the easy part. How to let the operator know when you've fallen from the "straight and narrow" ("Flour overfill") and how to guide him to recovery -- that's why we get paid the big buck.

A MicroLogix 1400 is not a lot of room to play in, depending on your recipe requirements.

You might consider re-inventing Rockwell's Logix Batch & Sequence Manager (LBSM). It's a PlantPAX add-on (i.e., free), but I'm not sure if it has a PVP component. I did something very similar to LBSM decades ago, using SQO commands, both to drive my outputs, the process setpoints and the sequence. Each action ("add flour", "add liquid", "mix") was a row, with a setpoint and a series of checkboxes.. Each checkbox corresponded to a row/column in a bit array, and indicated which action(s) wre being performed on which step. It could do things simultaneously, like add Flour B to the weigh hopper, adding liquid to the mixer, while also doing timed Mix1). The column (step) that was active was highlighted. Again, look at Rockwell's LBSM documentation. What I did looked very similar, although the implementation was simpler (and open).

You are correct to focus on the display. How you want to present what's happening to operator will drive how you code it. An SFC-style display as you describe ("flow chart") is another option, but not necessarily as flexible, if flexibility is a requirement.
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Old December 29th, 2017, 06:20 AM   #3
stu
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Adardwizz thanks for that you are very informative,
We have about 40 recipe in the plc ,
The issue we have is we have 4 systems connected to the mixer , but we have the system fall over and the less technical engineers/ ops can’t see the issue due to lack of alarms, can’t see the sequence where it stopped
I am after ideas on the best way to display the cycle on the hmi
And the flow chart was one idea , plus it’s a learn curve that I’m looking forward to getting more knowledge
Thanks stu
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Old December 29th, 2017, 06:56 AM   #4
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You don't want to show too much info usually.
But the operator needs to know what the sequence is doing.
And if it fails it needs to show him why. It's advisable to have a service page where you can see more details including I/O for troubleshooting, because eventually someone has to check a sensor or do something and they have to know which one it is.

Have timeout alarms so that when something takes too long the operator gets an alarm.

And then of course regular alarms on objects like motors, valves etc and their feedback signals.

You can also have alarms on weight changes, for instance to indicate that when something is filling up but there is no weight change.

Last edited by Pete.S.; December 29th, 2017 at 06:59 AM.
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Old December 29th, 2017, 07:25 AM   #5
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Hi Pete thanks for that info
That's what I was thinking have info for the operator and then a service page for the engineers.
I/O info would help ? Do you think individual virtual lamps for i/o or Aoi ??
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Old December 30th, 2017, 08:01 AM   #6
Pete.S.
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Quote:
Originally Posted by stu View Post
Hi Pete thanks for that info
That's what I was thinking have info for the operator and then a service page for the engineers.
I/O info would help ? Do you think individual virtual lamps for i/o or Aoi ??

Yes, individual virtual lamps for the I/O and show analog I/O in engineering units, % or mA. Whatever makes the most sense.

The goal should be to be able to provide enough information to diagnose any error with just the electrical schematics, a multimeter and the HMI.

99% of all errors are sensors in the field, so many times just being able to view the status of the sensor is a big help and speeds up the troubleshooting. It's also a way to see if the I/O works because if you measure say 24V at the input but the PLC shows that it is 0 then you know the I/O is probably faulty.

I usually make flowcharts for complex sequences as part of the documentation for the programming, but they are intended primarily for anyone that needs to do changes to the sequences and not for troubleshooting.

Last edited by Pete.S.; December 30th, 2017 at 08:04 AM.
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Old December 31st, 2017, 07:57 AM   #7
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OK. So you've already got a working system, and NOW you're thinking about visualization. That's a bit "cart before the horse", but that's where you're at.

Pete S. is absolutely right: don't drown the operators with information. They'll never be able to find the important information in the midst of clutter.

Since you have a PanelView, you may consider having the PLC force screen changes to better allow them to see what's going on. One screen that tells them ONLY what step they're on, what it's sharing for (SP & PV), and how long it's been on that step, would be cleaner than an SFC that they might struggle to interpret.

If something goes wrong, force navigation to another page for details.

Obviously you don't want to interfere with their own curitsity, so you'll need to one-shot screen changes, clear the Remote Page Control register after a successful move, perhaps monitor the Current Screen number so that, if they're navigating, the PLC doesn't change the screen, at least for a few minutes. Things like that.

Without knowing how you've coded your sequencer, it's hard to recommend a way to visualize it.
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Old December 31st, 2017, 04:10 PM   #8
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I use sequencers a fair bit. To help with trouble shooting, I make an array of strings and use [1] to say [20] as a description of what the PLC is waiting for, eg: 'Waiting for tank full sensor' or ' Waiting for left actuator to extend'

Every rung that is active on the sequencer copies that part of the array to [0] and the HMI displays the [0] part.

That way everyone can see what the PLC is waiting for.

As said, 99% of the time, it sensors or reeds switches etc etc to be made.

If you get a phone call, ask them what the screen says and 9 /10 you can give them clear instructions on what the PLC is waiting for in order to advance.
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