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pid control and analog input value processing

Created by: madarlag at: 1/8/2015 9:34 PM (11 Replies)

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1/8/2015 9:34 PM	Rate (0)
madarlag Posts: 8 Rating: (0)	Hello! I've just started to program PLC's a few week ago and I have a project what I have to solve. The part of the exercise is to make a pid control for frequency converter. I have a 0-20 mA pressure sensor. The minimum pressure is 7 bar. At 8 bar it has to start a motor at 10% and it has to raise up constantly. When it reaches 10 bar, the motor has to work at 100%. The system has to shut down if it reaches 16 bar. I know how to use the pid block but I have no idea how to process the value from analog input. Please for help!
madarlag Posts: 8 Rating: (0)
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1/8/2015 11:03 PM	Rate (0)
MicroMan Platinum Member Joined: 11/29/2011 Last visit: 2/4/2025 Posts: 1362 Rating: (233)	madarlag Hello! I've just started to program PLC's a few week ago and I have a project what I have to solve. The part of the exercise is to make a pid control for frequency converter. I have a 0-20 mA pressure sensor. The minimum pressure is 7 bar. At 8 bar it has to start a motor at 10% and it has to raise up constantly. When it reaches 10 bar, the motor has to work at 100%. The system has to shut down if it reaches 16 bar. I know how to use the pid block but I have no idea how to process the value from analog input. Please for help! Hi, That sounds like Ratio Control. Have a look at this thread for some background info: https://www.automation.siemens.com/tf/WW/en/Posts/111488 1st Question: How to use analog Input? You can connect the input word to the PV_PER directly. You can convert the RAW input value to REAL and connect the variable connect it to PV_IN input of PID. Read about both options in this Manual: http://support.automation.siemens.com/WW/view/en/89515142 You can read about the Annalog Value representation for example in the manual below(Chapter 11): http://support.automation.siemens.com/WW/view/en/105037964 I hope I could help! Cheers
	- What you read here, please check with manuals and your requirements. - Do not forget to Test, Test and Test... - If the post is helpful, please RATE it! MicroMan
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1/9/2015 8:11 AM	Rate (0)
madarlag Posts: 8 Rating: (0)	Hi! Thanks for reply! I don't think that it is like ratio control. It looks like a simple pid temperature control what I have done before in RSLogix5000. I think that I will use the PV_PER input. The analog process manual doesn't seem helpful. Can you be more specified?
madarlag Posts: 8 Rating: (0)
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This contribution was helpful to 1 thankful Users MicroMan

1/9/2015 9:41 AM	Rate (0)
MicroMan Platinum Member Joined: 11/29/2011 Last visit: 2/4/2025 Posts: 1362 Rating: (233)	madarlag Hi! Thanks for reply! I don't think that it is like ratio control. It looks like a simple pid temperature control what I have done before in RSLogix5000. I think that I will use the PV_PER input. The analog process manual doesn't seem helpful. Can you be more specified? Hi, A simple PID control have a Set Point and dinamically adjust its output to keep the minimize the Error signal(Difference between Set Point and Process Value). By your descrition I tought you have linear connection between the Speed an Pressure. Maybe your PID have Low "cut off" and high "cut off" point. How do you plan to realize the "cut off"? Do you try to TRACK it? Maybe take it out to Manual? I attached the Analog input manual as reference to explain how the analog values represented in chanel. Just some bacxkground literature. Regards:
	- What you read here, please check with manuals and your requirements. - Do not forget to Test, Test and Test... - If the post is helpful, please RATE it! MicroMan
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1/9/2015 9:47 AM	Rate (0)
madarlag Posts: 8 Rating: (0)	Some details about the PID block settings For setpoint I added "Setpoint" which is an integer. For Input_PER I added "Pressure" which is an analog input and it is also an integer and this integer has to be given by the pressure sensor. For Output_PER I added "Frequency_converter" which is an analog output. I am just wondering that is it possible to solve it with the help of SCALE function which would be Real to Integer. I would add to MIN: 0 MAX: 27648 VALUE: "Pressure" ( the same tag what I use at the PID block) OUT: "Frequency_converter" (the same tag what I use at the PID block) Any oppinion or suggestion?
madarlag Posts: 8 Rating: (0)	Last edited by: madarlag at: 1/9/2015 9:55 AM
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1/9/2015 10:16 AM	Rate (0)
MicroMan Platinum Member Joined: 11/29/2011 Last visit: 2/4/2025 Posts: 1362 Rating: (233)	HI, You need to convert the output. See this manual at page9633: http://support.automation.siemens.com/WW/view/en/89515142 It tells you how to scale it, but you still need to convert to the analog card. Cheers:
	- What you read here, please check with manuals and your requirements. - Do not forget to Test, Test and Test... - If the post is helpful, please RATE it! MicroMan
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1/9/2015 11:24 AM	Rate (0)
madarlag Posts: 8 Rating: (0)	Thanks for your answers so far you helped a lot. How can I convert it to the analog card?
madarlag Posts: 8 Rating: (0)
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1/9/2015 11:57 AM	Rate (2)
MicroMan Platinum Member Joined: 11/29/2011 Last visit: 2/4/2025 Posts: 1362 Rating: (233)	HI, If the response was helpfull you can always use the thank and Rate buttons! Anyhow. The analog conversion is described here: http://support.automation.siemens.com/WW/view/en/77316903 Cheers
	- What you read here, please check with manuals and your requirements. - Do not forget to Test, Test and Test... - If the post is helpful, please RATE it! MicroMan
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This contribution was helpful to 2 thankful Users hdhosseini madarlag

1/9/2015 1:28 PM	Rate (0)
madarlag Posts: 8 Rating: (0)	Hi again The thing is that I downloaded the zip file but I have no clue how to put the block inside the S7 software. Any idea?
madarlag Posts: 8 Rating: (0)
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1/9/2015 2:27 PM	Rate (0)
madarlag Posts: 8 Rating: (0)	I just found another solution. I will use Div calculation instead of scaling. But anyway thank you very much! Regards
madarlag Posts: 8 Rating: (0)
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