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S7-1200 PID limiting output

Created by: Darius at: 1/13/2010 3:05 PM (8 Replies)

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1/13/2010 3:05 PM	Rate (0)
Darius Platinum Expert Joined: 9/28/2005 Last visit: 11/6/2023 Posts: 2957 Rating: (242)	Dear all, Recently I've tried to use PID on S7-1200 and sometimes I need feature called as output limit. So I go into DB configuration and saw option like that, but one problem. I can change high output limit with no restrictions, but low limit I can change in range [-100...0]%. What is that ? What is purpose for this ? Suppose I control current output 0..20mA and I want control range 8..20mA. Is it possible with S7-1200 PID controller ?
	Best regards, Darius
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1/19/2010 4:18 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 12/4/2023 Posts: 4281 Rating: (1378)	Hi, At this momment, the only way to realise this is working with offset. You will need add a offset to the PID output.
	Denilson Pegaia Siemens Industry Sector Technical Support
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This contribution was helpful to 2 thankful Users Darius dekelec

7/24/2011 12:03 AM	Rate (0)
HydroPLC Posts: 13 Rating: (0)	Hello Pegaia, In a PID Control, if only P (proprtional control) is needed and there is no need for using Integral and Derivative controls, can simple math logic be used in S7-1200. In this case, the psudologic is simple; PID ERROR= SETPOINT minus PROCESS VARIABLE (PV) MANIPULATED VARIABLE = PID ERROR times GAIN. Assuming no auto-tuning is desired, to achieve this simple PID, only SUB (subtraction) and MUL (Multiply) functions are needed from instruction set. Other tasks such as manual opertion, error checking etc can be programmed using other functions provided. Looks like this method is easier for P only control in PID. What is your opinion? Comments from other PID experts will be appreciated. Thanks
HydroPLC Posts: 13 Rating: (0)
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7/25/2011 3:18 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 12/4/2023 Posts: 4281 Rating: (1378)	Hi, I don't have anything agains to do your PID algorithimus by yourself (in special if your usage is simple). I by myself, have alread done one. Take a look at: /tf/WW/en/Posts/45886#top Maybe you could use it as first step to your logic.
	Denilson Pegaia Siemens Industry Sector Technical Support
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6/21/2012 11:00 AM	Rate (0)
Hjorleifur Posts: 2 Rating: (0)	Hi, I have the same problem as Darius,that isI have to limit the output value of the PID Compact. I put in the instance DB values for "sPid_Cmpt r_Lmn_Hlm" and "sPid_Cmpt r_Lmn_Llm". The high limit works but the low limit does not. This PID for example has to work in the range of 70% to 100%. Do you have any solution on that? With regards, Hjorleifur
Hjorleifur Posts: 2 Rating: (0)
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6/22/2012 8:43 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 12/4/2023 Posts: 4281 Rating: (1378)	Hi, The suggestion that I think at this momment is to work with 0-100% range, and "recalculate" this range when connecting the LNM to the output (f(x)=ax+b) in his case, F(x) = x/10030+70=x0.3+70
	Denilson Pegaia Siemens Industry Sector Technical Support
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9/6/2012 10:01 PM	Rate (0)
waiz55ss Posts: 2 Rating: (0)	Pegaia Hi, The suggestion that I think at this momment is to work with 0-100% range, and "recalculate" this range when connecting the LNM to the output (f(x)=ax+b) in his case, F(x) = x/10030+70=x0.3+70 Hi, my problem with PID compact: at start moment of PID-compact i need to init output value, for example 25%. Is it possible?
waiz55ss Posts: 2 Rating: (0)
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9/6/2012 10:35 PM	Rate (0)
waiz55ss Posts: 2 Rating: (0)	waiz55ss Hi, my problem with PID compact: at start moment of PID-compact i need to init output value, for example 25%. Is it possible? Del problem!! PID compact is not so bad)).
waiz55ss Posts: 2 Rating: (0)
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1/15/2016 4:13 PM	Rate (0)
Marko80 Posts: 24 Rating: (0)	Hello, I would like to refresh this post. Is this possible to set LMN_HLM and LMN_LLM at PIDC_Compact or not? The same as it is in S7 Classic PID CONT_C - Continous control PID LNM_HLM - manipulated value high limit LNM_HLM - manipulated value low limit Thanks for answer
Marko80 Posts: 24 Rating: (0)
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