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calling PID

Created by: jruz1 at: 5/9/2014 8:38 AM (8 Replies)

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5/9/2014 8:38 AM	Rate (0)
jruz1 Regular Member Joined: 4/26/2014 Last visit: 8/25/2023 Posts: 26 Rating: (0)	hdhosseini And the final way would be using functions.I came across the idea from HERE.The original user program was deleted due to "copy right" issues because it contains a function from "Standard PID Control Package".The important point would be how to interface the PID related data to global data.See the attachment for more information.It is worth mentioning when an FB presents in the "Blocks" folder in STEP7,You can create instance data block with same data structure. Hihdhosseini, You are very helpful and that I may need your input. I am new to Step 7 Siemens. I have read some samples of the PID FB41 and sounds confusing to me, until I came up with PDF files of yours. I'll be using CONT_C into 3 controls valves (input/output are continuous), and I can see base on samples that I might need 3 Instance DB (am I right?). I plan to use your Fourth.zip docs way of calling the PID, that is (correct me if I am wrong) I'll be creating 1 FC1 (to call FB41:DB41, FB41:DB42, and FB41:DB43). And after this, I will be calling the FC1 on my OB35. I tried these things in pure ladder, and I cannot figure out the rest of the parameters you have on OB35 after calling FC1. Also, I cannot understand calling FC twice under OB35? I would appreciate for your help. If there is an easy way aside using your Fourth method, please share just a sample program and serve as my reference. Thanks again. Jruz :)
	Last edited by: O_Moderator at: 5/9/2014 12:01 PM new subject after splitting from /tf/WW/en/Posts/72787#top
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5/9/2014 11:28 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 9/25/2023 Posts: 6822 Rating: (1349)	Hello, I downloaded my own attachment to see the whole condition. Currently, I can not share a solution but it is not difficult to implement: You can pass DBs through input of FCs. You can make copy of same DB from template of FB41 or any other FB Develop the logic like what I did Call FC as many time you like and just change the DB numbers Good Luck! Hamid Hosseini
	Demo Channel on Youtube
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5/27/2014 5:35 AM	Rate (0)
jruz1 Regular Member Joined: 4/26/2014 Last visit: 8/25/2023 Posts: 26 Rating: (0)	Hi, Its only now that I've tested a PID. I just copied this to one of the samples. I was able to feed in and get the output under the manual mode, however, in auto it acts unexpectedly. When I switch to auto mode, it tries to calculate continously until LMN reaches down to zero or sometimes to 100. I am just modifying the value of the IW100, refer to my attached file. The calculation goes on even if the IW100 is constant. Shouldn't the LMN stays on its first calculated value, and will change again if the IW100 change? Please help. Thanks. Jruz Attachment OB35_DB41.JPG (183 Downloads)

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5/27/2014 6:35 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 9/25/2023 Posts: 6822 Rating: (1349)	jruz1 Hi, Its only now that I've tested a PID. I just copied this to one of the samples. I was able to feed in and get the output under the manual mode, however, in auto it acts unexpectedly. When I switch to auto mode, it tries to calculate continously until LMN reaches down to zero or sometimes to 100. I am just modifying the value of the IW100, refer to my attached file. The calculation goes on even if the IW100 is constant. Shouldn't the LMN stays on its first calculated value, and will change again if the IW100 change? Please help. Thanks. Jruz Good Morning World, Check the following points: What is range of PV and setpoint? In case of oscillatory LMN,Your PID parameters need adjustment(gain,Ti) LMN should not be constant even input is zero, PID algorithm works with error and it is a dynamic equation in Laplace domain! Hope these comments help you! Hamid Hosseini
	Last edited by: hdhosseini at: 5/27/2014 10:27 AM // typo Demo Channel on Youtube
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5/27/2014 7:02 AM	Rate (1)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 9/26/2023 Posts: 4477 Rating: (830)	jruz1 .......... I cannot understand calling FC twice under OB35? ..... Hello, Before starting PID programming, please read our PID Genius"Hamid Hossieni's"posts and tags. Different ways to call PID controller' FBs. Hamid Hossieni Tags. In the above link, you will found all tags that was created by experts. Most of them was created by Hamid and it contains important posts for PID. I recommend you and any one to read it carefully. To understand why we call PID FBs in cyclic OBs like OB35. I will tell you in a simple way. Cyclic OBs (OB3x) are organization blocks which are called cycliclly every certain interval of time. This "certain interval" is editable in HW config. And it is beining called every this interval in case of no any other interrupt OB with higher priority is being called. What we want to do exaclty is to call PIB FB once every certain fixedinterval. Because we have to take samples once every certain equal intervals to do calculations. It's called sampling time and should be entered in FB as well. jruz1 Hi, Its only now that I've tested a PID. I just copied this to one of the samples. I was able to feed in and get the output under the manual mode, however, in auto it acts unexpectedly. When I switch to auto mode, it tries to calculate continously until LMN reaches down to zero or sometimes to 100. I am just modifying the value of the IW100, refer to my attached file. The calculation goes on even if the IW100 is constant. Shouldn't the LMN stays on its first calculated value, and will change again if the IW100 change? Please help. Thanks. Jruz Hello it seems to be that you need to make PID tunning. Please find here attached guidelines to tune PID loops. The attached sheets are part of this manual: Closed-Loop Control Module IP262 Hope this helps. Attachment PID tunning.pdf (374 Downloads)
	Ayman Elotaify
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5/27/2014 8:44 AM	Rate (0)
jruz1 Regular Member Joined: 4/26/2014 Last visit: 8/25/2023 Posts: 26 Rating: (0)	Ayman Elotaify jruz1 .......... I cannot understand calling FC twice under OB35? ..... Hello, Before starting PID programming, please read our PID Genius"Hamid Hossieni's"posts and tags. Different ways to call PID controller' FBs. Hamid Hossieni Tags. In the above link, you will found all tags that was created by experts. Most of them was created by Hamid and it contains important posts for PID. I recommend you and any one to read it carefully. To understand why we call PID FBs in cyclic OBs like OB35. I will tell you in a simple way. Cyclic OBs (OB3x) are organization blocks which are called cycliclly every certain interval of time. This "certain interval" is editable in HW config. And it is beining called every this interval in case of no any other interrupt OB with higher priority is being called. What we want to do exaclty is to call PIB FB once every certain fixedinterval. Because we have to take samples once every certain equal intervals to do calculations. It's called sampling time and should be entered in FB as well. jruz1 Hi, Its only now that I've tested a PID. I just copied this to one of the samples. I was able to feed in and get the output under the manual mode, however, in auto it acts unexpectedly. When I switch to auto mode, it tries to calculate continously until LMN reaches down to zero or sometimes to 100. I am just modifying the value of the IW100, refer to my attached file. The calculation goes on even if the IW100 is constant. Shouldn't the LMN stays on its first calculated value, and will change again if the IW100 change? Please help. Thanks. Jruz Hello it seems to be that you need to make PID tunning. Please find here attached guidelines to tune PID loops. The attached sheets are part of this manual: Closed-Loop Control Module IP262 Hope this helps. I thank you again for your help guys. I have read all of his notes before I tried implementing this PID. It might be with the range of my SP and PV, and I think I have seen the PV range 0-200, and cannot figure out where to see SP range (hope someone else can let me see this, could it be another scaling?). I will also try to check on your tuning tips. Thanks again. I'll get back soon. jruz

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5/27/2014 8:49 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 9/25/2023 Posts: 6822 Rating: (1349)	It might be with the range of my SP and PV, and I think I have seen the PV range 0-200, and cannot figure out where to see SP range (hope someone else can let me see this, could it be another scaling?). As you are using my FB41 Sample , I defined PV_FAC=2.0 and informs the FB41 the range is 0~200. To avoid this error ,use the default value PV_FAC=1.0 .In this case PV will be scaled internally in range of 0~100.You should keep the same rule for setpoint for trouble-free operation of the whole PID loop! Enjoy your exploration of PID controllers, HD Hosseini
	Demo Channel on Youtube
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5/27/2014 8:49 AM	Rate (0)
jruz1 Regular Member Joined: 4/26/2014 Last visit: 8/25/2023 Posts: 26 Rating: (0)	hdhosseini jruz1 Hi, Its only now that I've tested a PID. I just copied this to one of the samples. I was able to feed in and get the output under the manual mode, however, in auto it acts unexpectedly. When I switch to auto mode, it tries to calculate continously until LMN reaches down to zero or sometimes to 100. I am just modifying the value of the IW100, refer to my attached file. The calculation goes on even if the IW100 is constant. Shouldn't the LMN stays on its first calculated value, and will change again if the IW100 change? Please help. Thanks. Jruz Good Morning Worlg, Check the following points: What is range of PV and setpoint? In case of oscillatory LMN,Your PID parameters need adjustment(gain,Ti) LMN should not be constant even input is zero, PID algprithm works with error and it is a dynamic equation in Laplace domain! Hope these comments help you! Hamid Hosseini What is range of PV and setpoint? - PV is 0-200, and SP could it be another scaling ? In case of oscillatory LMN,Your PID parameters need adjustment(gain,Ti) - the adjustment is linear, if LMN goes down, it continously approach zero. LMN should not be constant even input is zero, PID algprithm works with error and it is a dynamic equation in Laplace domain! - thanks for the input

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5/27/2014 10:31 AM	Rate (0)
jruz1 Regular Member Joined: 4/26/2014 Last visit: 8/25/2023 Posts: 26 Rating: (0)	jruz1 hdhosseini jruz1 Hi, Its only now that I've tested a PID. I just copied this to one of the samples. I was able to feed in and get the output under the manual mode, however, in auto it acts unexpectedly. When I switch to auto mode, it tries to calculate continously until LMN reaches down to zero or sometimes to 100. I am just modifying the value of the IW100, refer to my attached file. The calculation goes on even if the IW100 is constant. Shouldn't the LMN stays on its first calculated value, and will change again if the IW100 change? Please help. Thanks. Jruz Good Morning Worlg, Check the following points: What is range of PV and setpoint? In case of oscillatory LMN,Your PID parameters need adjustment(gain,Ti) LMN should not be constant even input is zero, PID algprithm works with error and it is a dynamic equation in Laplace domain! Hope these comments help you! Hamid Hosseini What is range of PV and setpoint? - PV is 0-200, and SP could it be another scaling ? In case of oscillatory LMN,Your PID parameters need adjustment(gain,Ti) - the adjustment is linear, if LMN goes down, it continously approach zero. LMN should not be constant even input is zero, PID algprithm works with error and it is a dynamic equation in Laplace domain! - thanks for the input Thanks for you guys, I think I got it already. I overlooked the basics of this PID when in simulation.

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