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MM440 Enabling PID after time delay

Created by: amel at: 8/17/2010 10:46 AM (8 Replies)

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8/17/2010 10:46 AM	Rate (0)
amel Posts: 4 Rating: (0)	I have a system that controls a pump to a flow set point using the PID and it works fine. I want to change the operation so that on start up the pump runs for a time at a fixed frequency. I set a fixed frequency and used timer one output P2852 to drive PID enable P2200 where previously I had a value of one. Timer 1 enabled by On 52.2 . The behaviour was not as I expected. During the timer run period the drive ran at the fixed frequency but on enabling the PID the drive went to full speed P1082 even though the max PID output is restricted by P2291 to 63% of P1082. The drive remains like this and the PID control does not seem to pick it up. I notice that the PID calculation appear to run at all times and the block diagram shows the enable switching in the PID output. Because during the timer run at fixed frequency the process variable is above set point, I would expect that the initial PID output would be at minimum. Can anyone explain why the PID does not start to control when enabled. Thank in anticipation, Amel
amel Posts: 4 Rating: (0)
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8/17/2010 11:41 AM	Rate (0)
joher Regular Member Joined: 6/12/2010 Last visit: 1/30/2023 Posts: 22 Rating: (0)	Hello Amel, I think drive is working ok,because when drive is switch to PID it takes some time to settle as it works on error signal generated between actual & setpoint.settle time depends on time taken to generate error signal. Regards joher

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8/18/2010 2:42 PM	Rate (0)
amel Posts: 4 Rating: (0)	joher I do not think it is just a case that the PID needs time to take control because 1) I have allowed time and it does not change, 2) If the PID was working normally the output would be limited to the PID max output I have set in P2291 and it is not, it goes to max output set in P1082. Thanks amel
amel Posts: 4 Rating: (0)
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8/19/2010 11:20 AM	Rate (0)
joher Regular Member Joined: 6/12/2010 Last visit: 1/30/2023 Posts: 22 Rating: (0)	Hello Amel If set value is P2280>P2291 than the speed will go to the value set in P2280 ie Fmax.

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8/19/2010 12:55 PM	Rate (0)
amel Posts: 4 Rating: (0)	joher P2280 is proportional gain which is set at 0.1 so I do not really understand your point. The PID loop works perfectly when enabled from start up and all I have changed is to use a timer to dely the enabling of the loop for 60 seconds during which time the drive uses a fixed frequency. I am starting to wonder if the loop must be enable on startup. Amel
amel Posts: 4 Rating: (0)
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8/24/2010 6:35 AM	Rate (0)
Vithani Platinum Expert Joined: 7/8/2009 Last visit: 8/5/2024 Posts: 1976 Rating: (477)	It is not like that the loop should be start inly at start up. I used application where I enabled PID by selector switch in between. What I wonder is, you might have change any Parameter by mistake which affect the operation have you observed PID output at r2294?? What is your setpoint in P1070?? How you are switching setpoints between PID and Fixed Frequency? And upload Parameter Set if possible Regards, Devesh Vithani
	I dont Like people driving Fast, thats the reason I overtake them ;)
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8/27/2010 10:01 AM	Rate (0)
amel Posts: 4 Rating: (0)	Thank you for your help. 2294 is at the maximum set by 2291 so it is clear that the PID is output is not being passed through to take over the drive frequency control.In P1070, I have 1024. I am trying to use the output of timer 1 to switch between fixed frequency and PID by putting timer 1 P2852 into PID enable P2200. If I have 1 in P2200 PID control works from start up fine. If I change to using the timer output, I get the fixed frequency for the time period, then I get max frequency P1082 when the timer times out. The PID set point is from fixed PID set point. I have noticed that with the drive stopped, and the PID not enabled P2200 = 0 or (timer 1 O/p off), the set point P2260 ramps up to a high value 160%.(true value is 48%). I then changed some of the unused fixed frequency settings to zero and this reduced the 160 to 80% but I still do not see why the PID set point is being linked to fixed frequencies. I think I do not really understand the function of P1070. This may irrelevant as the issue seems to be with getting the PID output mapped to control frequency after fixed frequency has been in us .I haveattcached the .dnl files I am using with drive monitor. Note the fixed start up/PID control is only required in 3rd command set (2). Amel Attachment WithTimerPIDenable.zip (251 Downloads)
amel Posts: 4 Rating: (0)
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8/27/2010 6:10 PM	Rate (0)
innovations Experienced Member Joined: 5/21/2008 Last visit: 10/24/2024 Posts: 91 Rating: (0)	dear amel, as far as linking of fixed frequency is concerned you have p1016=p1017=p1018=p1019=1 and also P1020.2=P1021.2=1, it means that when enabled the FF1+FF2(P1001+P1002) will be setpoint of frequency. but as you said that when you have set other fixed frquency to 0 & that is also indicated in your .dnl file that P1001=40 it gives a final output of 40 hz in r1024 which is also 40hz ( because now P1002=0). The same is alsotrue for r2224( fixed pid setpoint) for the others issues i have to check ..... sehgal

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8/28/2010 6:20 AM	Rate (0)
Vithani Platinum Expert Joined: 7/8/2009 Last visit: 8/5/2024 Posts: 1976 Rating: (477)	amel Thank you for your help. 2294 is at the maximum set by 2291 so it is clear that the PID is output is not being passed through to take over the drive frequency control.In P1070, I have 1024. ..This may irrelevant as the issue seems to be with getting the PID output mapped to control frequency after fixed frequency has been in us .I haveattcached the .dnl files I am using with drive monitor. Note the fixed start up/PID control is only required in 3rd command set (2). Amel I think you made things complicated.. By the way, you are using Fixed PID setpoint.. Check out Function Diagram No 3300 and make proper logic such that you get your set fixed frequency in r2224. Because, in your case, frquency setpoint is being added. Now regarding, P1070 - Its main Setpoint parameter. You have set it to 1024 so you have to trace it by reading r1024. By checking online will be easier because you can get values in read parameters. Check that from where your Frequency is being increased. I am not sure from your backup that your PID would have run properly with this setting without timer also. You should have just switch over Setpoint in P1070 from 1024 - your Desired Fixed frequency to r2294 PID output. That would have been much easier. Any ways, try using Starter. You can easily trace your setpoint using Starter as it is having good graphical representation One more thing I dont understand is why you switched to 3rd CDS as your first is free... Regards, Devesh Vithani
	I dont Like people driving Fast, thats the reason I overtake them ;)
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