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Making curves with math.

Created by: Tomnord at: 10/25/2013 1:24 PM (2 Replies)

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10/25/2013 1:24 PM	Rate (0)
Tomnord Member Joined: 2/2/2013 Last visit: 11/7/2024 Posts: 4 Rating: (0)	Hello. I need to make a curve that consist of 5 individual adjustable points. With linear scaling inbetween them. Please look at attached picture. Is this something that is easely done? I have the "calc" block for a linear curve, but I just cant wrap my head around hov to use these to get the result I need. Im stuck here so I would really appreciate all the help I can get. I need both outside temp and PV-temp on each point to be adjustable. Really looking forward to some good advice! regards, Tom Attachment graph.jpg (270 Downloads)

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10/25/2013 1:53 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 11/26/2024 Posts: 6854 Rating: (1365)	Tomnord Hello. I need to make a curve that consist of 5 individual adjustable points. With linear scaling inbetween them. Please look at attached picture. Is this something that is easely done? I have the "calc" block for a linear curve, but I just cant wrap my head around hov to use these to get the result I need. Im stuck here so I would really appreciate all the help I can get. I need both outside temp and PV-temp on each point to be adjustable. Really looking forward to some good advice! regards, Tom Hello, from products in range of SIMATIC,I can say "NONLIN" function from PID Professional package has the same functionality you want.But that package is used for S7 300/400 in TIA Portal.Same discussion we had before here.You have option of checking OSCAT library.But, for a programmer, that should not be really difficult to make such a function if points are limited.It is peicewise linear approximation of a arbitary function,define boundreis and in each boundry define the Y=AX+B formula. Hope these comments help Hamid Hosseini
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10/27/2013 5:41 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	It can be done in many ways,.... if you need only linear lines between points is very simple. Below ispart of my program which calculates setpoint temperature in relation to days. T=(Tn-Tn_1)/(dn-dn_1)(d-dn_1)+Tn_1 where: T..setpoint Tn...setpoint temperature for n-th point Tn_1..setpoint temperature for (n-1)-th point dn-dn_1...difference of time between n-th point and(n-1)-th point d..currenttime #CurveHours:=SINT_TO_DINT(#CurveCalcDays)24+#CurveCalcHours; (* T=(Tn-Tn_1)/(dn-dn_1)(d-dn_1)+Tn_1 ) #CurveVentOFF:=false; #CurveHeatOFF:=false; IF #CurveEnable THEN IF (#CurveHours<-72) THEN //>-3 #CurveVentOFF:=true; #CurveHeatOFF:=true; ELSIF (#CurveHours>=-72) AND (#CurveHours<-24) THEN //-3 to -1 //dn=-24 //dn_1=-72 //dn-dn_1=48 #CurveVentOFF:=true; #Temp_SP:=(#CurveTempSP[1]-#CurveTempSP[0])(DINT_TO_REAL(#CurveHours)+72.0)/48.0+#CurveTempSP[0]; ELSIF (#CurveHours>=-24) AND (#CurveHours<0) THEN //-1 t0 0 //dn=0 //dn_1=-24 //dn-dn_1=24 #CurveVentOFF:=true; #Temp_SP:=(#CurveTempSP[2]-#CurveTempSP[1])(DINT_TO_REAL(#CurveHours)+24.0)/24.0+#CurveTempSP[1]; ELSIF (#CurveHours>=0) AND (#CurveHours<72) THEN //0 to 3 //dn=72 //dn_1=0 //dn-dn_1=72 #Temp_SP:=(#CurveTempSP[3]-#CurveTempSP[2])(DINT_TO_REAL(#CurveHours)+0.0)/72.0+#CurveTempSP[2]; ELSIF (#CurveHours>=72) AND (#CurveHours<168) THEN //3 to 7 //dn=168 //dn_1=72 //dn-dn_1=96 #Temp_SP:=(#CurveTempSP[4]-#CurveTempSP[3])(DINT_TO_REAL(#CurveHours)-72.0)/96.0+#CurveTempSP[3]; ELSIF ............. for you : ELSIF (#OutsideTemp>=OutTemp[1]) AND (#OutsideTemp<OutTemp[2] ) THEN #Temp_SP:=(#CurveTempSP[2]-#CurveTempSP[1])*(#OutsideTemp - OutTemp[1]) /(OutTemp[2] -OutTemp[1] )+#CurveTempSP[1]; and so on if, if only i didn't make a mistake.
	Last edited by: Marko Bursic at: 10/27/2013 6:06 PM
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