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Old March 17th, 2017, 06:56 PM   #31
Bering C Sparky
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Smile

I saw this tread come back around and since I have a DoMore set up on my bench, I thought I would try this out on this platform and see whats, what.

Well, I did not see an "Unlatch" instruction in the DoMore library, but there are "Set" and "RST" instructions.

The RST instruction in DoMore does not act like the OTU instruction in Allen Bradley though.

I tested it with the rungs you see below and it did not work.
I was toggling (NOT FORCING) the bits in Data View and left the C0 instruction true, to simulate a stuck HMI button....... A 0 was not moved to the C0 bit box when C3 on rung 2 became true and fired the one shot at the RST. It did not unlatch the instruction as it would have using OTU on an Allen Bradley platform.
(If you have a rig on your bench, give it a try)

So question to you guys using DoMore......How would you perform this function? (In other words, along the same lines as this thread has followed, how would you do the same in DoMore to insure a stuck HMI button unlatches, using the PLC programming to do it.)

Maybe I am just overlooking that DoMore has another instruction I am not seeing that will do this. IDK, but I do know the RST instruction does not work as OTU would in this case.

(and yes, I know the z in the one shot pictured below is backwards to represent a rising edge one shot, but use your imagination....it is correct in the program I am testing with )


BCS
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File Type: jpg HMI UNLATCH 2.jpg (9.3 KB, 72 views)
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Old March 18th, 2017, 11:20 AM   #32
Bering C Sparky
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Ok, I got an answer to my above post from over on the AD forum.
It seems that the One Shot instruction in DoMore is not a stand alone instruction as it is in Allen Bradley.
You do not need to give the One Shot its own unique tag name and precede it with logic on the rung for it to work.

You have to apply the same tag name as the output on rung one in my example (C2) to the One Shot Instruction and then the logic works fine.

Seems I have to start forgetting old habits and learning some new ones, in order to begin triving and prospering in this new world.

Below is the quote that was posted to answer my question on the AD forum and a corrected drawing of how the logic should look in DoMore.

Quote:
It's because with Do-more (or any AD PLC, really) you don't need a second bit to create a one-shot (a definite plus of AD PLC's over anything Allen-Bradley). All you need to do is make your C2 in the second rung a one-shot rising and eliminate the C3 entirely.
EDIT: Just to clarify something I said earlier....The RST instruction was not the problem I was having, it was that I was using the One Shot instruction incorrectly for the DoMore application.

BCS
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Last edited by Bering C Sparky; March 18th, 2017 at 11:32 AM.
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Old March 18th, 2017, 11:51 AM   #33
Steve Bailey
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The biggest hurdle to overcome when trying to learn a new brand is the expectation that it behaves just like the brand you're already familiar with.
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Old March 18th, 2017, 12:06 PM   #34
robertmee
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Quote:
Originally Posted by proof View Post
I disagree. When I press the STOP button on the HMI, I do not want the PLC to override my STOP. The STOP should come off when I release the button. The HMI should be set up so that the operator presses and release the stop even if the PLC shows the HMI stop already On.
I don't understand this reasoning at all....for the plc to reset the bit it has to have seen it which means it performed the function associated with a stop....if your plc code requires you to hold in a stop button that's crazy talk. Conversely let's say your start bit gets stuck on from the hmi because you lost the io server....that's a much more common and dangerous proposition.
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Old March 18th, 2017, 12:36 PM   #35
Bering C Sparky
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Quote:
Originally Posted by Steve Bailey View Post
The biggest hurdle to overcome when trying to learn a new brand is the expectation that it behaves just like the brand you're already familiar with.
So true, and its the little simple stuff that gets you.

Oh its just a one shot, I already know how that works so no need to read up on it. Just program it in and off we go.......Nope, not in this case anyway.

I am still torn as to, do I feel excited to learn all this again.....or frustrated?

Either way does not matter, it has to be done, so time to be like Nike and "Just Do It"


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Old March 20th, 2017, 08:24 AM   #36
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Quote:
Originally Posted by robertmee View Post
I don't understand this reasoning at all....for the plc to reset the bit it has to have seen it which means it performed the function associated with a stop....if your plc code requires you to hold in a stop button that's crazy talk. Conversely let's say your start bit gets stuck on from the hmi because you lost the io server....that's a much more common and dangerous proposition.
If I am pressing the stop button on the HMI, and don't want another person pressing the start button on another HMI start it back up. Your method will allow me to stop the motor, but doesn't prevent the second operator from starting it back up.
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Old March 20th, 2017, 10:25 AM   #37
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Quote:
Originally Posted by proof View Post
If I am pressing the stop button on the HMI, and don't want another person pressing the start button on another HMI start it back up. Your method will allow me to stop the motor, but doesn't prevent the second operator from starting it back up.
I've done work on 100s of manufacturing and utility sites around the US in my 25 years in this industry and what you are describing would never be SOP on any of them. Either you need a separate enable/disable or, if it's a maintenance/safety issue, execute the LOTO procedure.

One case where you would not want the PLC to reset the button bit would be for a jog (or similar) operation, where the duration of the "button on" press determines how long/how much the logic executes a function.

Last edited by BAJ; March 20th, 2017 at 10:34 AM.
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Old March 20th, 2017, 08:46 PM   #38
robertmee
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Quote:
Originally Posted by proof View Post
If I am pressing the stop button on the HMI, and don't want another person pressing the start button on another HMI start it back up. Your method will allow me to stop the motor, but doesn't prevent the second operator from starting it back up.
Serious? So you're telling me that your SOP is to hold an HMI button in to prevent something from being started somewhere else? That's insanity. I can't picture an operator standing at an hmi holding a button in on a screen as a means to prevent something from running. I would fire someone for doing that.
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