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PV FACTOR in FB41

Created by: malbec at: 6/12/2014 11:34 AM (5 Replies)

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6/12/2014 11:34 AM	Rate (0)
malbec Posts: 54 Rating: (0)	I'm trying to do a PID loop in STEP7 with FB41. The proccess value comes from an analog input. The analog input has a range of 0-4096 (10V gives a reading of 4096). I don't understand how to calculate the PV FACTOR parameter. I reached, by trail and error, the value of 276 to make it work correctly. What value do I need if the analog input has a different range (e.g 0-32767)?
malbec Posts: 54 Rating: (0)
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6/12/2014 11:53 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 12/27/2025 Posts: 6889 Rating: (1368)	malbec I'm trying to do a PID loop in STEP7 with FB41. The proccess value comes from an analog input. The analog input has a range of 0-4096 (10V gives a reading of 4096). I don't understand how to calculate the PV FACTOR parameter. I reached, by trail and error, the value of 276 to make it work correctly. What value do I need if the analog input has a different range (e.g 0-32767)? Hello, When you are using the "PV_PER " to process value in FB41, algorithm only converts a value in range 0~ 27648 into 0~100.This is true in case of "PV_FAC =1 and PV_OFF=0 ". If you encounter such exception that I can not guess the reason, process the process value out of PID controller and feed it to FB41.For this you need "PVPER_ON =FALSE" and transfer the converted process value to PV_IN .You have option of using FC105 from standard library in STEP 7 but I think it is also valid in range 0~ 27648. In brief, in case of different range from standard blocks, you should write your own block for processing the analog input or consult the manual of the module for recommendation of manufacturers.Please, find more information for FB41 and FC105 in STEP 7 online manual. I hope it helps, Hamid Hosseini
	Demo Channel on Youtube
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11/13/2014 7:27 PM	Rate (0)
manestras Posts: 4 Rating: (0)	hello i am in the same situation like malbec but i want to give the values to analog input by a slider in hmi.I have an analog input 12 bit and i want to simulate the slider as a sensor.How i will scale and fill the parametres in fb41 to achive this?I will use PV_PER or PV-IN?Is it necessary to use PIW256?In plcsim piw256 shows me as max value 32767(why?).Is it possible a slider to play the role of the sensor in this situation? Do any one have an Answer ? Rergards! manestras
manestras Posts: 4 Rating: (0)
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11/13/2014 8:34 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 12/27/2025 Posts: 6889 Rating: (1368)	manestras hello i am in the same situation like malbec but i want to give the values to analog input by a slider in hmi.I have an analog input 12 bit and i want to simulate the slider as a sensor.How i will scale and fill the parametres in fb41 to achive this?I will use PV_PER or PV-IN?Is it necessary to use PIW256?In plcsim piw256 shows me as max value 32767(why?).Is it possible a slider to play the role of the sensor in this situation? Do any one have an Answer ? Rergards! manestras Hello, Only select PVPER_ON =FALSE and transfer a value from the HMI to PV_IN of instance DB related to the loop you are testing.You also have option of limiting the output of slider to 0~100. I hope this helps, Hamid Hosseini
	Last edited by: hdhosseini at: 11/13/2014 8:39 PM Demo Channel on Youtube
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11/13/2014 9:21 PM	Rate (0)
manestras Posts: 4 Rating: (0)	Thanks for the reply.Sorry but i need further clarification cause i am new on plcs.I am trying to give values to an analog input from a slider but there is something wrong with formats.You said to transfer value from hmi slider to fb 41 PV_IN but it needs real format.You will help me if you tell me what exactly i have to do.Do i have to scale the values?Sorry again but as i said i am new..
manestras Posts: 4 Rating: (0)
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11/13/2014 10:04 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 12/27/2025 Posts: 6889 Rating: (1368)	manestras Thanks for the reply.Sorry but i need further clarification cause i am new on plcs.I am trying to give values to an analog input from a slider but there is something wrong with formats.You said to transfer value from hmi slider to fb 41 PV_IN but it needs real format.You will help me if you tell me what exactly i have to do.Do i have to scale the values?Sorry again but as i said i am new.. Hello again, Call FB41 and assign an instance DB to it say "DB41".Writing to peripheral input addresses is not generallly possible, so you can simulate a input from a field device from an HMI.Assign the variable of slider to DB41.DBD10 that is a floating point variable regards PV_IN parameter in FB41(PID algorithm).About scaling, I think it is goood to map the slider to 0~100 and also consider same range for set-point. Please , read more the online manual plus check the clustered threads here : HD_PID Control Package - FB41 Samples And this is what you shoud start from and develop more: // write from HMI to this address DB41.DBD 10 CALL "CONT_C" , DB41 COM_RST := MAN_ON := PVPER_ON:=FALSE P_SEL := I_SEL := INT_HOLD:= I_ITL_ON:= D_SEL := CYCLE := SP_INT := PV_IN := PV_PER := MAN := GAIN := TI := TD := TM_LAG := DEADB_W := LMN_HLM := LMN_LLM := PV_FAC := PV_OFF := LMN_FAC := LMN_OFF := I_ITLVAL:= DISV := LMN := LMN_PER := QLMN_HLM:= QLMN_LLM:= LMN_P := LMN_I := LMN_D := PV := ER := NOP 0 I hope this helps, Hamid Hosseini
	Demo Channel on Youtube
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