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How to store the count values in Siemens S7-1200

Created by: Joseph Antony Christoper at: 9/16/2014 6:12 AM (9 Replies)

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9/16/2014 6:12 AM	Rate (0)
Joseph Antony Chr... Posts: 4 Rating: (0)	Here is the simle project that i am doing. From rotary encoder that i connected to the rotating device, i get the pulse outputs to measure the number of counts. From the rotary encoder to the PLC and display it on the Siemens HMI KP300 basic - mono, and i also need to store the previous 5 counts values... So basically i programmed with an Up counter and move the count value to new memory location when a slice button is pressed and it worked fine for storing just one previous count value... but i do not know how to store previous 5 count values... Any help with my Ladder Logic PLC Prgramming will be much appreciated...
Joseph Antony Chr... Posts: 4 Rating: (0)
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9/16/2014 8:56 AM

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Jens_app

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Joseph Antony Christoper
Here is the simle project that i am doing. From rotary encoder that i connected to the rotating device, i get the pulse outputs to measure the number of counts. From the rotary encoder to the PLC and display it on the Siemens HMI KP300 basic - mono, and i also need to store the previous 5 counts values... So basically i programmed with an Up counter and move the count value to new memory location when a slice button is pressed and it worked fine for storing just one previous count value... but i do not know how to store previous 5 count values... Any help with my Ladder Logic PLC Prgramming will be much appreciated...

Dear Joseph,

what you could do is use an array to storethe number of counts, use avariable index to access the different components of your array.

This can either be done by STL(not applicable for S7-1200), SCL and in S7-1500(not sure about S7-1200) it can also be done in LADDER.

(	How do you implement an array access with an S7-1500 with variable index?)

For SCL programming following syntax can be used:
"<Data block>".<ARRAY>["i"] // one-dimensional ARRAY

For STL, check previous link, an example is given there. (not applicable for S7-1200)

Another option is using multiple move blocks which are enabled with a comparator function.
You'd want to compare the current counter value with a fixed value.
For example:
If index =0 then move countvalue to dbw0
If index =1 then move countvalue to dbw2
If index =2 then move countvalue to dbw4
...
Increase your index number upon clicking the button on your hmi.

PEEK/POKE can also be used for S7-1200. ( PEEKinstruction is used to write a memory address to a memory area without specifying a data type.)

So lots of possibilities, you can choose whichever one suits you best.

Let us know what you think.

Kind regards,
Jens

Last edited by: Jens_app at: 9/16/2014 9:02 AM

added peek/poke (optional)

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9/16/2014 3:00 PM	Rate (1)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 10/4/2024 Posts: 15264 Rating: (2422)	Joseph Antony Christoper Here is the simle project that i am doing. From rotary encoder that i connected to the rotating device, i get the pulse outputs to measure the number of counts. From the rotary encoder to the PLC and display it on the Siemens HMI KP300 basic - mono, and i also need to store the previous 5 counts values... So basically i programmed with an Up counter and move the count value to new memory location when a slice button is pressed and it worked fine for storing just one previous count value... but i do not know how to store previous 5 count values... Any help with my Ladder Logic PLC Prgramming will be much appreciated... What you have done already is nearly what you need to do for the remaining 4 count values as Jens_app said. When you accept the slice button input to push onto the STACK of max size fixed to 5, you first MOVE #4 to #5 (so you do not lose #4). MOVE #3 to #4, MOVE #2 to #3, MOVE #1 to #2, MOVE current-count to #1. Now you have 5 values plus the current count value. Do not overlook your zero or reset function. Also ensure when you startup you activate that function appropriately for your application. RESET, INIT, FAULT HANDLER for your counts should be part of your design consideration. Making them likewise easy to do will save you headache and make your code easier to understand and maintain. You know they will never want the last 10, right? You know they will never want to auto-reset after 4, right? You know they will not ask for the counters to reset when a new product is run, right? Also that init could possibly store/restore values from stored (retained) memory from perhaps the last time this product or process was run. You may have already considered these. However, if not, now you have a little more to consider as you develop your count saving solution. NOTE: the above suggestion of successive moves is not the move efficient approach. It is simple and easy to explain and fix. It however is not easy to adapt to change without making code changes. There are more adaptable methods if you need them.
	science guy
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9/17/2014 5:06 AM	Rate (0)
Joseph Antony Chr... Posts: 4 Rating: (0)	I tried all ways... putting parallel move blocks, and moving 4 to 5, 3 to 4, 2 to 3, 1 to 2 and current count to 1.... and then tried giving time delay between the move blocks... but it all results the same problem... If count value is xxx, and when i press that slice button all the previous values changes to same xxx value.... I am trying this non-stop for 2 days... some experts please help me... if there is any similar programs, please upload... The tags i have used in the diagram attached is, Tag 23-Previous count 5 Tag 22-Previous count 4 Tag 21-Previous count 3 Tag20-Previous count 2 Tag14-Previous count 1 Tag10-Current Count Attachment IMG_20140916_114839816_HDR.jpg (1065 Downloads)
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9/17/2014 9:03 AM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 6/15/2024 Posts: 815 Rating: (123)	Joseph Antony Christoper I tried all ways... putting parallel move blocks, and moving 4 to 5, 3 to 4, 2 to 3, 1 to 2 and current count to 1.... and then tried giving time delay between the move blocks... but it all results the same problem... If count value is xxx, and when i press that slice button all the previous values changes to same xxx value.... I am trying this non-stop for 2 days... some experts please help me... if there is any similar programs, please upload... The tags i have used in the diagram attached is, Tag 23-Previous count 5 Tag 22-Previous count 4 Tag 21-Previous count 3 Tag20-Previous count 2 Tag14-Previous count 1 Tag10-Current Count Hi Joseph, offcourse they update all simultaneously when you put the move blocks in parallel without any conditions in between. You have to enable your move blocks depending on an index value. I'll try to explain it in more detail. 1) We create an array that can store 5 values (lets call it "Dataarray[0..4] of int") 2) You want to store the countervalue everytime you push a button, so we increase the #index (int) everytime a button is pushed (can be achieved with CU) 3) We want that for every #index value the countvalue is stored to another location (can be achieved by comparing the #index value with a fixed number 0-4 and the MOVE function (check attachment) 4) We want to create a cyclic buffer, so everytime the #index reaches it maximum value we want it to reset to 0 (can be achieved by compare and move) 5) You're done... simple as that... Some notes You might want to put your datablock in retain mode, so you don't lose data on plc restart. The programin attachment is just a snippet from the complete program, you'll still have to implement some of the previously mentionned steps. So this is not the complete program! I hope this helps you further. Kind regards, Jens Attachment StoreToDataArrayAcToCU.jpg (833 Downloads)
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9/17/2014 9:50 AM	Rate (0)
Palo PLC Experienced Member Joined: 5/15/2012 Last visit: 5/21/2024 Posts: 39 Rating: (7)	Hello I thing the problem is: If you push the button new value isn't write once but X times. You need use positive edge for button. It make only by change state of button will be new value write. palo Attachment Edge.jpg (830 Downloads)

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9/17/2014 9:56 AM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 6/15/2024 Posts: 815 Rating: (123)	Palo PLC Hello I thing the problem is: If you push the button new value isn't write once but X times. You need use positive edge for button. It make only by change state of button will be new value write. palo Dear Palo, we are using an increasing index, which means after a push button the index is increased, which means we stop writing in the same dataarray component and move on to the next; So there is no need for any edge detection here. Kind regards, Jens
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9/17/2014 3:15 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 10/4/2024 Posts: 15264 Rating: (2422)	Jens_app Palo PLC Hello I thing the problem is: If you push the button new value isn't write once but X times. You need use positive edge for button. It make only by change state of button will be new value write. palo Dear Palo, we are using an increasing index, which means after a push button the index is increased, which means we stop writing in the same dataarray component and move on to the next; So there is no need for any edge detection here. Kind regards, Jens I still think the edge detection of the HMI PB press is simpler with that small sequence of MOVE commands. Yes, there are plenty of options, and of the one I originally proposed, the -[P_TRIG]- before the MOVE blocks would handle that minor problem and the original poster could finish the task. As they get more familiar with PLC programming, they may revisit the task and use your alternative (and more general and in my opinion better) approach.
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9/18/2014 10:40 PM	Rate (1)
TrueB Posts: 22 Rating: (6)	Hello Joseph, I just wanted to provide another solution encase it helps you or any others that may find this post. To restate the problem as I understand it: When the user presses the slice button you want to capture the current encoder reading and store it together with the previous four readings in a FIFO (first in first out) manner. Proposed Solution: Of course there are many ways to accomplish this. I prefer SCL do to its inherent readability. It's very easy to create an SCL program block and as you'll see the code is short and readable. Code: //if the button input is true but was not true last scan cycle //this will assure a single capture per button press if di_sliceButton and not sliceButtonLastScan then //shift all of the previous encoder readings in a FIFO manner previousEncoderCount5 := previousEncoderCount4; previousEncoderCount4 := previousEncoderCount3; previousEncoderCount3 := previousEncoderCount2; previousEncoderCount2 := previousEncoderCount1; //capture the current encoder reading previousEncoderCount1 := currentEncoderCounts; end_if; //assign last scan status sliceButtonLastScan := di_sliceButton; Explanation: In the if statement we look for the button input to be true but its value to have been not true on the previous scan; this gives us positive edge detection. This is critical as we want to make sure this only happens once per button press. After the if statement, all that is needed is to capture the status of the button input during this scan cycle. Instead of using 5 separate tags to store the previous readings you could also use an array. I chose not to in this example for the sake of readability since you only have 5 tags. I hope you and anyone else that finds this may find it helpful and give SCL a try. Its powerful stuff! Cheers
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9/19/2014 12:21 AM	Rate (0)
Joseph Antony Chr... Posts: 4 Rating: (0)	Thank you so much... it worked... The other array and index are complicated and did not understand... Can you explain why the normal move did not work and how did this P_TRIG work, and why is there a memory on it I just inserted this P_TRIG before each move block and the program worked... Please explain if you have the time...
Joseph Antony Chr... Posts: 4 Rating: (0)	Last edited by: Joseph Antony Christoper at: 1/5/2015 3:39 PM
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Created by: Joseph Antony Christoper at: 9/16/2014 6:12 AM (9 Replies)

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