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BUMPLESS PID

Created by: MS10 at: 5/18/2011 7:38 AM (49 Replies)

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5/18/2011 7:38 AM	Rate (0)
MS10 Posts: 53 Rating: (0)	Hi, I have programmed my PID loop using FB 41 and realised that everytime I switch from manual to auto mode, the PID is not bumpless.. the controlled variable always starts from 0 instead of from the last manual value. Any idea how to make this PID bumpless? Also, do we have to set COM_RST to be on all the time? Snapshot of my programme attached. Thanks, MS Attachment pid.pdf (1487 Downloads)
MS10 Posts: 53 Rating: (0)
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5/18/2011 1:55 PM	Rate (1)
Aret Posts: 2348 Rating: (264)	PID algorithm uses following statement: IF Switch to auto mode THEN Setpoint value := Actual input value. Please post your code here if you have code-related problems.
Aret Posts: 2348 Rating: (264)
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This contribution was helpful to 1 thankful Users BWoost

5/19/2011 12:26 AM	Rate (0)
MS10 Posts: 53 Rating: (0)	Hi Aret, Thanks for your reply. Find attached the pdf of my code for the particular FC. We are controlling a steamcontrol valve to achieve the desired cooktemperature. The temperature setpoint for the is set from the HMI (db95.dbd74). network no 5 is to ensure the transition from Auto to manual is bumpless but not sure why it's not bumpless from manual to auto. please advise. Thanks, MS Attachment FC52.pdf (1323 Downloads)
MS10 Posts: 53 Rating: (0)
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5/19/2011 12:55 PM	Rate (1)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	MS10 Find attached the pdf of my code for the particular FC. We are controlling a steamcontrol valve to achieve the desired cooktemperature. The temperature setpoint for the is set from the HMI (db95.dbd74). network no 5 is to ensure the transition from Auto to manual is bumpless but not sure why it's not bumpless from manual to auto. Hi You have option of using Modular PID Control as a software package from SIEMENS.I think 3 function of this package would be helpful: 2.1.20 PID: PID Algorithm parameter SMOO_CHG ,smooth change over from the manual mode to the automatic mode. 2.1.23 ROC_LIM: Rate of Change Limiter Ramp functions are used when the process must not be subjected to a step change at the input. For example when the set point or gain of PID algorithm change suddenly(Jump in these crucial parameters). 2.1.13 LMNGEN_C: Output Continuous PID Controlle parameter LMNRC_ON ,manipulated value rate of change on,ensures bumpless switchover in manipulated variable. regards
	Last edited by: hdhosseini at: 6/1/2012 2:51 PM Demo Channel on Youtube
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5/20/2011 1:53 AM	Rate (0)
MS10 Posts: 53 Rating: (0)	Hi Hdhosseini, Thank you for your suggestion. I will have a read of the modular control PID but at this stage I'm at the last stage of programming my code. FB41 has worked in the past for me I'm just not sure why it's not bumpless this time although I've feed the manual CV back to the block. If anyone else has a suggestion it will be much appreciated. Thanks, MS
MS10 Posts: 53 Rating: (0)
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5/20/2011 5:02 AM	Rate (1)
H-H Platinum Member Joined: 7/2/2008 Last visit: 9/30/2024 Posts: 928 Rating: (309)	Hello MS10, 1st make sure that auto mode resets manual bit and manual mode resets automatic bit. 2nd make sure that db102.dbw4 is the right word for valve position. If I may suggest, Try making it easy for yourself and use only one bit for automatic and manual and also use the output parameter LMN IF *"DB_PID".COOK_TEMP_PID.Manual_Mode* = 0 Movethe output parameter LMN to *"DB_PID".COOK_TEMP_PID.Manual_CV* Also as explained earlier by ARET, in manual mode it's better to transfer the process value to the setpoint So, IF *"DB_PID".COOK_TEMP_PID.Manual_Mode* = 1 Move the *the output parameterPV* to *"DB_PID".COOK_TEMP_PID.Setpoint* If you still face problems then It will be better if you upload your programhere somembers can check it for you. Best regards. H-H Attachment FC52 with comments.pdf (977 Downloads)

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5/20/2011 7:37 AM	Rate (0)
MS10 Posts: 53 Rating: (0)	Hi H-H, Thanks for the response. First of all, I have made sure that auto mode reset manual bit and vice versa. I have also made sure that I'm using the right address for valve position and in my exisiting code, i transfer the output to manual CV in Auto mode. I used LMN_PER instead of LMN so I dont have to scale the output. I didnt have to move the PV to SP in the past but i will try it this weekend. Just a question on the range of SP. is it limitedfrom 0-100? let's say my Process variablerange is 0-200, does this mean that I have to scale my SP from 0-200 to 0-100? I have attached my code for the relevant block. thanks, MS
MS10 Posts: 53 Rating: (0)	Last edited by: MS10 at: 6/1/2011 9:03 AM
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5/20/2011 10:09 PM	Rate (2)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	MS10 Just a question on the range of SP. is it limitedfrom 0-100? let's say my Process variablerange is 0-200, does this mean that I have to scale my SP from 0-200 to 0-100? Dear MS10 SP and PV normally have same physical dimensions i.e same type of signal.If PV is temperature which is limited from 0 centrigrade to 500.0 centigrade, the SP can also take this values.But it depends on the project and physical constrains. SP and PV are real vaalues in FB41, so they have mathematical limits of real value. As you require bumpless operation on your actuator in your process, I propose using the following rate limiter function which is simple and can be developed or customized for your case. The drawback of the functions is : "it can not support negative inputs".The function change all step changes to ramp. FUNCTION_BLOCK FB67 TITLE ='rate limiter' AUTHOR : hdhosseini VERSION : '1.0' // Block Parameters VAR_INPUT // Input Parameters input:REAL; rst:BOOL:=false; step:REAL:=0.1; //100ms call factor:REAL:=1.0; high:REAL:=100; low:REAL:=0; END_VAR VAR_IN_OUT // I/O Parameters first:BOOL:=true; END_VAR VAR_OUTPUT // Output Parameters out:REAL; END_VAR VAR_TEMP // Temporary Variables END_VAR VAR // Static Variables buffer:REAL:=0; in:REAL; END_VAR // Statement Section IF rst=true THEN buffer:=0; //first:=true; out:=0; in:=0; ; ELSE IF first= true THEN buffer:=in; first:=false; END_IF; IF input >= high THEN in:=high; END_IF; IF input <= low THEN in:=low; END_IF; IF (input > low) AND (input<high) THEN in:=input; END_IF; IF in > (buffer+step) THEN buffer:= (buffer+(step* factor)); END_IF; IF in < (buffer-step) THEN buffer:= (buffer-(step*factor)); END_IF; IF in = buffer THEN buffer:=in; END_IF; ; out:= buffer; END_IF; ; END_FUNCTION_BLOCK regards
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5/20/2011 10:26 PM	Rate (1)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	Hi See the attachment Attachment rate_limiter.zip (2090 Downloads)
	Last edited by: hdhosseini at: 10/29/2011 4:23 PM Demo Channel on Youtube
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5/21/2011 3:24 PM	Rate (0)
MS10 Posts: 53 Rating: (0)	Hi Hdhosseini, Thanks again for your help. I will try your FB and let you know how's the progress. Just still don't get it why I can't make my PID bumpless this time around. Thanks also for the answer on the range of the SP.. The manual said that the range is -100 to 100 so I got confused although I know I didnt have to scale my SP to be within this range last time. Will update soon. Thanks, MS
MS10 Posts: 53 Rating: (0)
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