Need help in PID

[Nitin_110051]

Hello ,

I am Trying to implement PID loop but facing some issues.

Input :- Feedback from motor in terms of PWM fixed duty cycle and varying frequency .

Output :-  is fixed frequency and varying duty cycle .

Observation is irrespective of set point motor is running in the range defined by PID output range .

Please help to resolve this thing .

Attachment :- Output by running Vi & Vi also attahced .

[GerdW · Accepted solution]

Hi Nitin,

so you limit the PID output range to a very small range - and then you wonder, why the PID control doesn't go outside of that small working range???

Output :-  is fixed frequency and varying duty cycle .

Btw. Why do you set the output to [1700, 1900] when you want to have a duty cycle as output value? What kind of duty cycle uses values like "1800"?

[Nitin_110051]

Good morning Gerd,

Even if i change the output range to 0 to 6000 , then i am getting the graph in which pulse is coming 0 to 6000 .

Practically it should maintain speed to setpoint, but i observe its behaving with ouptut range only .

Duty cycle :- this 1800 or whatever values in terms of 100 are the Rpm for the motor and i am coverting into duty cycle by dividing with the factor 6000.

Thanks & regards

Nitin

[GerdW]

Hi Nitin,

can you attach your VI in LV2011?

[Nitin_110051]

Hi Gerd,

Please refer the attachment in 2011 version .

Thanks & regards

Nitin

[GerdW]

Hi Nitin,

thanks for conversion.

On your VI:

- Why are you using so many local variables, causing race conditions?

- Why are there controls and indicators with exactly the same name ("frequency")?

- Why is "Output PID" set as control, when it just displays a value like an indicator?

- Why are you reading "N samples" from your frequency input, but using just one sample for the PID?

- Why are you manipulating the measurement value with an Abs() function?

- Why are you providing a dt=0.0001 to the PID function, when you use a WaitForMultiple set to multiples of 180ms?

There is so much wrong with your VI! Please correct all other problems before you even attempt to integrate a PID control…

From an UX point of view: Why do you use gauges as input controls?

[Nitin_110051]

HI Gerd

Thanks for information .

I tried with your observations , its working now . Some problems are still there like if i change the parameters(Kp=1.0,Ki=0.001,Kd=0.000 to Kp=2,Ki=0.001,Kd=0.001) its osciallting to much in the output range . and also if i hold the motor with hands softly  it is gaining speed and not coming back while holding the motor, once i realeased motor it is coming back .

Awnser's

On your VI:

- Why are you using so many local variables, causing race conditions? I  didn't know that variables can create race condition , can you suggest me some document regarding this ?

- Why are there controls and indicators with exactly the same name ("frequency")? :- Changed Now

- Why is "Output PID" set as control, when it just displays a value like an indicator? :-  Changed Now

- Why are you reading "N samples" from your frequency input, but using just one sample for the PID?  if i am using single samples  it is not working at all .

- Why are you manipulating the measurement value with an Abs() function? Changed Now

- Why are you providing a dt=0.0001 to the PID function, when you use a WaitForMultiple set to multiples of 180ms? Removed Now

There is so much wrong with your VI! Please correct all other problems before you even attempt to integrate a PID control…  Corrected

From an UX point of view: Why do you use gauges as input controls?I used gauges just for representation .

Attachment :- New VI

[GerdW]

Hi Nitin,

Why are you using so many local variables, causing race conditions? I  didn't know that variables can create race condition , can you suggest me some document regarding this ?

The LabVIEW help explains the term "race condition"… (Googling for "labview help race condition" gives a lot of documentation!)

Why are there controls and indicators with exactly the same name ("frequency")? :- Changed Now

Now there are controls without a label: this is no good idea either…

Why are you providing a dt=0.0001 to the PID function, when you use a WaitForMultiple set to multiples of 180ms? Removed Now

 Now there is no timing at all in the loop - and you still provide the PID a wrong timing of 1e-4…

From an UX point of view: Why do you use gauges as input controls?I used gauges just for representation .

You still use gauges for inputs…

Some problems are still there like if i change the parameters(Kp=1.0,Ki=0.001,Kd=0.000 to Kp=2,Ki=0.001,Kd=0.001) its osciallting to much in the output range

Do you know how to get estimates for PID parameters? Have you heard about Ziegler-Nichols? Wikipedia explains this with a lot of details!

[Nitin_110051]

Thanks Gerd

Now its working , But stil i am not able to set derivative .