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Variable Filter

Created by: Control Boy at: 5/29/2014 3:29 PM (26 Replies)

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5/29/2014 3:29 PM	Rate (0)
Control Boy Posts: 60 Rating: (0)	Hi, I have created a filter / buffer to smooth out a rapidly updating value. The function works fine but I would like to refine if possible. Firstly, the "update" input is triggerd by a timer with a positive edge contact that I can set to any time base - ideally i would like this inside the function with the time setting adjustable from outside the function. not sure of the timer code in SCL. Secondly, after my math I reset the buffer array to 0 one section at a time. Is there a way of setting the whole array to 0? i.e Array[all]:=0?? likewise this would hel when adding all the array values together. Code below IF #Update =True THEN; #Busy:=True; #Buffer[#i]:=#Input; #i:= #i+1; #Done:=True; END_IF; IF #i >9 THEN; #Output:=(#Buffer[0]+#Buffer[1]+#Buffer[2]+#Buffer[3]+#Buffer[4]+#Buffer[5]+#Buffer[6]+#Buffer[7]+#Buffer[8]+#Buffer[9])/10.0; #i:=0; #Buffer[0]:=0; #Buffer[1]:=0; #Buffer[2]:=0; #Buffer[3]:=0; #Buffer[4]:=0; #Buffer[5]:=0; #Buffer[6]:=0; #Buffer[7]:=0; #Buffer[8]:=0; #Buffer[9]:=0; END_IF; #Busy:=False; #Done:=False; //*) Attachment Buffer!.GIF (1033 Downloads)
Control Boy Posts: 60 Rating: (0)
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5/29/2014 4:15 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2461)	B&C Ltd Hi, I have created a filter / buffer to smooth out a rapidly updating value. The function works fine but I would like to refine if possible. Firstly, the "update" input is triggerd by a timer with a positive edge contact that I can set to any time base - ideally i would like this inside the function with the time setting adjustable from outside the function. not sure of the timer code in SCL. Secondly, after my math I reset the buffer array to 0 one section at a time. Is there a way of setting the whole array to 0? i.e Array[all]:=0?? likewise this would hel when adding all the array values together. Code below IF #Update =True THEN; #Busy:=True; #Buffer[#i]:=#Input; #i:= #i+1; #Done:=True; END_IF; IF #i >9 THEN; #Output:=(#Buffer[0]+#Buffer[1]+#Buffer[2]+#Buffer[3]+#Buffer[4]+#Buffer[5]+#Buffer[6]+#Buffer[7]+#Buffer[8]+#Buffer[9])/10.0; #i:=0; #Buffer[0]:=0; .. #Buffer[9]:=0; END_IF; #Busy:=False; #Done:=False; //*) A few suggestions come to mind. Have you looked at the OSCAT open source library? There is a smoothing function in that library. Maybe one of the filters will work for you. If not or you are not ready to deal with importing the library into Portal, you might consider using thefill_blk instructions for your zero set: FILL_BLK(IN:=0, COUNT:=10, OUT=>#buffer[0]); As for your algorithm, it only updates once every 10 calls to this function right? Is that fast enough? What you probably really want is a circular buffer of the last 10 values and an average of those last 10 values. That might improve your system response considerably.
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5/29/2014 6:14 PM	Rate (0)
Control Boy Posts: 60 Rating: (0)	Thanks Huggy, Your right about the OSCAT, I do look in the library but for inspiration only. I’ll try the "fill" method. Regarding the circular buffer, I’m curious! Can you provide an example?
Control Boy Posts: 60 Rating: (0)
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5/29/2014 6:18 PM	Rate (0)
William_B Posts: 5225 Rating: (1197)	huggy_d1 A few suggestions come to mind. Have you looked at the OSCAT open source library? There is a smoothing function in that library. Maybe one of the filters will work for you. If not or you are not ready to deal with importing the library into Portal, you might consider using the fill_blk instructions for your zero set: FILL_BLK(IN:=0, COUNT:=10, OUT=>#buffer[0]); As for your algorithm, it only updates once every 10 calls to this function right? Is that fast enough? What you probably really want is a circular buffer of the last 10 values and an average of those last 10 values. That might improve your system response considerably. Hi there. "huggy_d1" has already given valuable info. Do try the OSCAT route. To add more ideas, please find attached a PDF printout of how the S7-200 does its filtering. I admire the concept where a quick change is also accommodated. A general tip: (how does the SCL version of TON work?) Inside the TIA design environment you have a toolbar drawer on your right marked as INSTRUCTIONS. Even in SCL the instruction seen there can be click-and-drag into the coding. Hovering on the instruction brings out a tooltip which is selectable. From the tooltip the help on that instruction can be opened. I miss the examples the S7-200's software gave for their help, but the text is helpful. I hope this was of value to you. Good luck. w Attachment S7-200 - Built in analog input filters_System Block Configuration.pdf (649 Downloads)
William_B Posts: 5225 Rating: (1197)
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5/29/2014 6:33 PM	Rate (3)
William_B Posts: 5225 Rating: (1197)	B&C Ltd Thanks Huggy, Your right about the OSCAT, I do look in the library but for inspiration only. I’ll try the "fill" method. Regarding the circular buffer, I’m curious! Can you provide an example? Rotary buffer concept.. [code]// Assume values declared, initiated and seeded. // Coding is not the actual SCL needed. // track values already recoded if less than array maximum count := count + 1; if count > index_max then count := index_max; end_if; total := total - buffer[index] + reading; average := total / count; buffer[index] := reading; //ensure rotary action index := index + 1; if index > index_max then index := 0; end_if; [/code]
William_B Posts: 5225 Rating: (1197)	Last edited by: William B. at: 5/30/2014 8:21 AM add: coding is NOT actual SCL (sorry)
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5/29/2014 11:20 PM	Rate (0)
Control Boy Posts: 60 Rating: (0)	Thank you William. I will try look at your example also.
Control Boy Posts: 60 Rating: (0)
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5/31/2014 6:44 PM	Rate (0)
Control Boy Posts: 60 Rating: (0)	Hi, so I had a go and the code compiles but the PLC is in error! not really following the code - any pointers? cheers // #reading declared as real /input // #total declared as real / inout // #average declared as real / inout // #count declared as int / temp // #index declared as int / temp // #index_max declared as int / temp // #buffer declared as array 0-9 real / temp #index_max:=9 ; #count := #count + 1; IF #count > #index_max THEN ; #count := #index_max; END_IF; #total := #total - #buffer[#index] + #reading; #average := #total / #count ; #buffer[#index] := #reading; //ensure rotary action #index := #index + 1; IF #index > #index_max THEN #index := 0; END_IF;
Control Boy Posts: 60 Rating: (0)	Last edited by: Control Boy at: 5/31/2014 7:19 PM Last edited by: Control Boy at: 5/31/2014 7:05 PM Last edited by: Control Boy at: 5/31/2014 6:57 PM
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5/31/2014 7:21 PM	Rate (0)
Control Boy Posts: 60 Rating: (0)	this is the error from the buffer Attachment area error.GIF (619 Downloads)
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5/31/2014 8:45 PM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 11/29/2024 Posts: 815 Rating: (123)	Control Boy this is the error from the buffer Hello Control Boy, I see #count isdefined as atemp, but it is not initialized at the start of your program. Temp variables always need to be initialized at the start of your program. By initializing the TEMP I mean defining it's start value at the beginning of your code, for example; #count := 0; Now by the looks of your codeI don't think #count should be a temp, but rather a inout or a static(if you use a fb). Because in this case, everytime the functions exits the temp variable is deleted. So the program never knows what the last #count value was. Try changing #count to an inout and see what happens. Same for #index, it is also a TEMP andnot initialized at the start. So the program doe snot know which component of the buffer array he needs to access. Also here try changing it to inout if it needs to be remembered afterthe function finishedor initialize it at the start. This should fix your problems. Kind regards, Jens
	Last edited by: Jens_app at: 5/31/2014 8:47 PM Added some more info Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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5/31/2014 10:42 PM	Rate (1)
William_B Posts: 5225 Rating: (1197)	Hi, The designer's intent is important to understand any coding. Sorry.. I should probably left the bit out where "count" is used. Please see the code below that has more detail filled in. This is also attached to this post. Hopefully the code will speak for itself. If still not.. please ask. Knowing my skills as programmer, I would advise you to check and test the code. My first versions of anything I design is full of bugs. [code]FUNCTION_BLOCK "MovingAverage" TITLE = Calculating average over a sample { S7_Optimized_Access := 'TRUE' } AUTHOR : WilliamB FAMILY : TOOLS VERSION : 0.01 VAR_INPUT RESTART { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : Bool; // Restart data recording and zero values TRIGGER { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : Bool; // Trigger next recording and calculate next average READING { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : DInt; // Reading needing to be averaged END_VAR VAR_OUTPUT FILTERED { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : Bool; // Filtered reading value END_VAR VAR count { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : USInt; // Counter keeps track of values recorded.. useful when less than maximum index { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : USInt; // Next read/write position in the buffer total { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : DInt; // Sum of the recorded values average { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : DInt; // Running average output buffer { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False'} : Array[1..10] of DInt; // Buffered values; Circular buffer END_VAR VAR CONSTANT index_max : USInt := 10; END_VAR BEGIN // CLIENT...Siemens A&D Forum, User: Control Boy // DATE.....31 MAY 2014 // PURPOSE..USE CIRCULAR BUFFER TO CALCULATE A MOVING AVERAGE. // AUTHOR...William B. // Clear all relevant values. IF #RESTART OR #index < 1 THEN #count := 0; #index := 1; //..buffer is from 1 to 10 #total := 0; #average := 0; FILL_BLK(IN := 0, //clear all buffer values COUNT := #index_max, OUT => #buffer[1]); END_IF; // cancel further actions if next recording not triggered. IF NOT #TRIGGER THEN #FILTERED := #average; //ensure there is an output RETURN; END_IF; // Track values already recoded, if less than array maximum after RESTART IF #count < #index_max THEN #count := #count + 1; // ..always: count <= index_max END_IF; // Calculate the new average. // Remember buffer and total was seeded to zero values at RESTART #total := #total - #buffer[#index] + #READING; // ..oldest buffered value now removed #average := #total / #count; // Absorb a new reading into the circular buffer #buffer[#index] := #READING; //ensure circular action #index := #index + 1; IF #index > #index_max THEN #index := 1; END_IF; #FILTERED := #average; END_FUNCTION_BLOCK [/code] Is this of value to anyone? Attachment FB1050_MovingAverage 2.zip (653 Downloads)
William_B Posts: 5225 Rating: (1197)	Last edited by: William B. at: 5/31/2014 11:21 PM version 2 of code..previously the output did not receive a value.
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