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PID - changing Gain parameter

Created by: BryanG2001 at: 6/27/2013 3:14 PM (15 Replies)

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6/27/2013 3:14 PM	Rate (0)
BryanG2001 Posts: 113 Rating: (22)	S7-1215, TIA Portal V11 SP2 Upd5 I have an application where I need to be able to vary the Gain on a PID controller, well actually it is just a PI controller. I would expect that if PV and SP are near enough the same and I modify the Gain by 10% that there would be little change in the output of the PI loop. It is how the PID controller in the S7-200 used to behave, it is how all other PID loops I have used behave.. What I have found though is that if I increase the Gain by 10% I get a 10% increase in output, which then drops back to the correct value as the PI loop does it stuff. Similarly if I decrease the Gain by 10% the controller output drops by 10% before moving back to match the SP. I know that the Gain affects all components in the S7-1200 PID loop system, so I tried changing the 'Proportional action weighting' which just affects the P component but that cause the same problem. I can work around it by switching to Manual for one cycle of the PID loop but that is not ideal. The same problem doesn't affect changing the I component, there the PID loop behaves as expected. Current PID settings: Input - General 0-100% from a calculated value. Output - General 0-100% P (gain) = 0.8 I = 10.0 D - not used, left at 0.0 Loop is reverse acting. Sampling every 2 seconds. Anyone know of another work around or do I need to contact tech support.
BryanG2001 Posts: 113 Rating: (22)
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6/27/2013 4:11 PM	Rate (0)
Ton Verra Gold Member Joined: 4/20/2007 Last visit: 12/13/2024 Posts: 728 Rating: (43)	Are you using a dead band?

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6/27/2013 4:25 PM	Rate (0)
DS SURESH KUMAR Bronze Member Joined: 4/17/2012 Last visit: 11/26/2024 Posts: 474 Rating: (10)	BryanG2001 S7-1215, TIA Portal V11 SP2 Upd5 I have an application where I need to be able to vary the Gain on a PID controller, well actually it is just a PI controller. I would expect that if PV and SP are near enough the same and I modify the Gain by 10% that there would be little change in the output of the PI loop. It is how the PID controller in the S7-200 used to behave, it is how all other PID loops I have used behave.. What I have found though is that if I increase the Gain by 10% I get a 10% increase in output, which then drops back to the correct value as the PI loop does it stuff. Similarly if I decrease the Gain by 10% the controller output drops by 10% before moving back to match the SP. I know that the Gain affects all components in the S7-1200 PID loop system, so I tried changing the 'Proportional action weighting' which just affects the P component but that cause the same problem. I can work around it by switching to Manual for one cycle of the PID loop but that is not ideal. The same problem doesn't affect changing the I component, there the PID loop behaves as expected. Current PID settings: Input - General 0-100% from a calculated value. Output - General 0-100% P (gain) = 0.8 I = 10.0 D - not used, left at 0.0 Loop is reverse acting. Sampling every 2 seconds. Anyone know of another work around or do I need to contact tech support. Hi, In TIA you have the auto tunning option .It will done within 10 Min to 20 min. In PID Compact block you will get a commissioning sysmbol on right side top corner of that block,,.... you have to select that and follow the instruction thats all it will start tune the PID values and it set the gain also.. here i attach the screenshot of that auto tunning... Attachment all.jpg (1351 Downloads)

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6/27/2013 4:38 PM

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hdhosseini

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BryanG2001
S7-1215, TIA Portal V11 SP2 Upd5

I have an application where I need to be able to vary the Gain on a PID controller, well actually it is just a PI controller. I would expect that if PV and SP are near enough the same and I modify the Gain by 10% that there would be little change in the output of the PI loop. It is how the PID controller in the S7-200 used to behave, it is how all other PID loops I have used behave.. What I have found though is that if I increase the Gain by 10% I get a 10% increase in output, which then drops back to the correct value as the PI loop does it stuff. Similarly if I decrease the Gain by 10% the controller output drops by 10% before moving back to match the SP. I know that the Gain affects all components in the S7-1200 PID loop system, so I tried changing the 'Proportional action weighting' which just affects the P component but that cause the same problem. I can work around it by switching to Manual for one cycle of the PID loop but that is not ideal. The same problem doesn't affect changing the I component, there the PID loop behaves as expected.

Current PID settings:
Input - General 0-100% from a calculated value.
Output - General 0-100%
P (gain) = 0.8
I = 10.0
D - not used, left at 0.0
Loop is reverse acting.
Sampling every 2 seconds.

Anyone know of another work around or do I need to contact tech support.

Hello,

it is recommended to change those parameters shown in attachment(mostly static variable of PID controller) in "inactive" mode to avoid malfunction of controller.It is recommendation from manual and I think better to be followed as we don't know what is really happening inside.

TIA Online Manual

Note
Edit the variables listed in this table in "Inactive" mode to avoid malfunction of the PID controller. The "Inactive" mode is forced by setting variable "sRet.i_Mode" to "0".

You method to put the controller to manual and back to auto again can be done by programming while error is near zero (SP=PV) But please make sure of bumpless transitions.

Best regards
Hamid Hosseini

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parameters.pdf (1374 Downloads)

Last edited by: hdhosseini at: 6/27/2013 4:41 PM

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6/27/2013 5:56 PM	Rate (0)
BryanG2001 Posts: 113 Rating: (22)	Thanks for the replys guys. Sorry I haven't figured out how to do quotes on this forum so I have used italics instead. Are you using a dead band? No, no deadband. In TIA you have the auto tuning option .It will done within 10 Min to 20 min TIA Auto Tuning was a big disappointment for me, I tried it multiple times on another project and the results left a system that was very slow to react, I tuned it better by hand. On this job, Auto Tune could never work because the parameters of the system change, I would have to Auto Tune in each mode and then use an average. It is recommended to change those parameters shown in attachment(mostly static variable of PID controller) in "inactive" mode to avoid malfunction of controller.It is recommendation from manual and I think better to be followed as we don't know what is really happening inside. I don't have that list in my version of the manual 04/2012 A5E02486680-06, I guess I will have to get the latest version. It is strange that one of the parameters you aren't supposed to change unless in Inactive mode is sRet.i.Mode which is what you use to put the controller in Inactive Mode. You method to put the controller to manual and back to auto again can be done by programming while error is near zero (SP=PV) But please make sure of bumpless transitions. Fortunately I had to make the system bumpless a while back, so Auto to Man and Man to Auto is bump free, even PID Fault to Man. So Siemens have managed to make a controller where you can't change parameters whilst the controller is active - 'Now that's what I call Automation inefficiency!!' If you have seen the training videos you will understand the reference. I guess I will dump their controller and try the PID lean controller instead.
BryanG2001 Posts: 113 Rating: (22)
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6/27/2013 6:42 PM	Rate (0)
DS SURESH KUMAR Bronze Member Joined: 4/17/2012 Last visit: 11/26/2024 Posts: 474 Rating: (10)	Hi, For bumpless control what is the parameters i have to change???

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6/27/2013 7:33 PM	Rate (0)
BryanG2001 Posts: 113 Rating: (22)	There isn't a parameter to change. What you are trying to do is avoid any sudden changes in speed as you go from Man to Auto and Auto to Man. It helps if you can vary the Gain when moving from Man to Auto because you can have an acceleration phase with a lower Gain and then move to a higher Gain for normal operation. As we have found the only way to get that effect with the TIA PID loop is to move to Auto with a lower Gain and then briefly switch back to Manual whilst you change the Gain to a 'working' level. The Auto to Manual change is easier depending on what you want to achieve. One way would be whenever the PID is in Auto you can feed back the output, in to the Manual speed settings, so as you go from Auto to Manual there is no change is speed. Another method would be to introduce averaging on the output at the Change from Auto to Manual so that the system still changes speed, but more slowly.
BryanG2001 Posts: 113 Rating: (22)
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6/27/2013 9:21 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 1/19/2025 Posts: 6858 Rating: (1366)	Hello again, as it is getting a long story, I just summarize some important points: Each controller is designed for a determined ranges of machinery,for controlling small machines controllers such S7 200 and S7 1200 are suitable. (Hans Berger, automating with SIMATIC). Gain scheduling is existing in SIMATIC range of product but not for S7 1200. If you think there is some missing points in manuals related to PID compact in TIA, use this feature to inform moderators (Moderator). For more advance options in regulation and process control use specialized tools and better controllers.Have a look here. Hope that helps Hamid Hosseini
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6/27/2013 9:58 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 1/19/2025 Posts: 6858 Rating: (1366)	Ton Verra Are you using a dead band? about dead band in PID compact ,read it here: PID Compact S7-1200 Deadband hdhosseini Wardyp Is there a deadband setting or similar on the PID compact instruction for S7-1200? I would like something similar to the DEAD_W on the CONT_C controller on the S7-300. You can refer to online help of PID compact you are using. As it shown in the attachment there is no dead band function after error calculation (SP-PV).For newer version, consult the manual. Note:Deadband is used right after the error calculation block. DS SURESH KUMAR Hi, For bumpless control what is the parameters i have to change??? and case for related to bumpless switchover from manual to automatic and vice versa please refer to the following discussed topic in details: PID fb41 auto to manual mode FB58,Bumpless manual to automatic switchover
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6/28/2013 9:53 AM	Rate (0)
BryanG2001 Posts: 113 Rating: (22)	I appreciate you summary.... but. Gain scheduling is existing in SIMATIC range of product but not for S7 1200. Gain Scheduling worked in the S7-200 and so I expect it to work with the S7-1200. If Siemens had released information that Gain Scheduling wasn't going to be allowed for the S7-1200 then I could have made the decision to use a controller from another manufacturer. If you think there is some missing points in manuals related to PID compact in TIA, use this feature to inform moderators (Moderator). I really shouldn't have to tell a moderator that the manuals are deficient, I would suggest that it would be Siemens job to know that the manuals are deficient. For more advance options in regulation and process control use specialized tools and better controllers.Have a look here. This job won't stand the extra cost of an S7-300. The S7-200 performed the job perfectly well. If the S7-1200 is intended to be the replacement for the S7-200 then it should perform at least the same functions. I appreciate all the 'bells and whistles' that they have added to the S7-1200 and TIA Portal but I would suggest that perhaps they should have got the basics right before adding all the fancy stuff. You might not like people writing complaints about Siemens here, and maybe, in a couple (or more) of years when they have sorted out all the problems people will have less things to complain about. To give some perspective I created my first folder for S7-1200 related files 16 August 2010, Siemens have had almost 3 years to get things right. How long do we have to wait and how long do Siemens think that we will stay loyal to the brand?
BryanG2001 Posts: 113 Rating: (22)
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Created by: BryanG2001 at: 6/27/2013 3:14 PM (15 Replies)

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