PWM Function inside Cyclic Interrupt OB

Mert Turgut

Ok I will use ctrl pwm in function or function block.

My pwm is opetaring according to cyclic interrupts's cyclic time.

 Can you please explain your reasoning for using cyclic interrupt, it may very well be valid and I am interested to learn new ways of doing things.

Mert Turgut

QW1000 and QW1002 which is the pulse of PWM are controlled via PID.

I re-read one of your replies and thought I should clarify something. QW1000 and QW1002 do not actually produce output but are duty cycle (Pulse Duration) settings. They are not tags for the outputs to be turned On and Off at the pulse rate...no. They hold the value of the Pulse Durations

 I used cyclic interrupt because I used PID function. And as far as I know to use PID function we should use them in a cyclic interrupt.

and I enclosed the ob 30 cyclic interrupt in .pdf format at the attachment.

In network 1 there is a PID_3Step function it is controlling a solenoid valve which has two relay.

In network 2 it is used to make auto mode PID compact function

In network 3; there is a reference value, and one value is added to reference vaue one value is subtracted from reference value so maximum and minimum vales are obtained. and the pneumatic clinder should stop between these value.

In network 4: to stop pneumatic cylinder between max. and mimimum value an output is used.

In network 5: PID Compact function it is used to adjust initial pulse duration of the pulse width modulation. 

In network 6: the other PID_Compact function and like first PID Compact function it is used to adjust initial pulse duration of the second pulse width modulation.

In network 7: First CTRL_PWM

In netwroks 8: Second CTRL_PWM

After trying to explain the ob 30 program I can summerize my thoughs and problems.

First; OB30 has 100 ms cyclic time but PWM has 15 ms cyclic time, and I placed PWMs inside OB30, PWM has shorter cyclic time than OB30. According to these values PWM can work in their cyclic time or should I use CTRL_PWM inside another Function or function block.

Second: When m1000.0 bit is activated, the cylinder should be stopped. But even m1000.0 bit is activated the CTRL_PWM is continuing to work and the cylinder is not stopped. 

I do not understand why pwm is staying enabled when m1000.0 is activated the CTRL_PWM should not be enabled.

Best regards...

Kal.A

 

Can you please explain your reasoning for using cyclic interrupt, it may very well be valid and I am interested to learn new ways of doing things.

I re-read one of your replies and thought I should clarify something. QW1000 and QW1002 do not actually produce output but are duty cycle (Pulse Duration) settings. They are not tags for the outputs to be turned On and Off at the pulse rate...no. They hold the value of the Pulse Durations

 

Mert Turgut

 I used cyclic interrupt because I used PID function. And as far as I know to use PID function we should use them in a cyclic interrupt.

and I enclosed the ob 30 cyclic interrupt in .pdf format at the attachment.

In network 1 there is a PID_3Step function it is controlling a solenoid valve which has two relay.

In network 2 it is used to make auto mode PID compact function

In network 3; there is a reference value, and one value is added to reference vaue one value is subtracted from reference value so maximum and minimum vales are obtained. and the pneumatic clinder should stop between these value.

In network 4: to stop pneumatic cylinder between max. and mimimum value an output is used.

In network 5: PID Compact function it is used to adjust initial pulse duration of the pulse width modulation. 

In network 6: the other PID_Compact function and like first PID Compact function it is used to adjust initial pulse duration of the second pulse width modulation.

In network 7: First CTRL_PWM

In netwroks 8: Second CTRL_PWM

After trying to explain the ob 30 program I can summerize my thoughs and problems.

First; OB30 has 100 ms cyclic time but PWM has 15 ms cyclic time, and I placed PWMs inside OB30, PWM has shorter cyclic time than OB30. According to these values PWM can work in their cyclic time or should I use CTRL_PWM inside another Function or function block.

Second: When m1000.0 bit is activated, the cylinder should be stopped. But even m1000.0 bit is activated the CTRL_PWM is continuing to work and the cylinder is not stopped. 

I do not understand why pwm is staying enabled when m1000.0 is activated the CTRL_PWM should not be enabled.

Best regards...

 Thanks for sharing.

Placing CTRL_PWM in interrupt OB is not the cause for the pulse generator to remain enabled; the problem is in code.

As I mentioned earlier the cycle time of PWM is completely independent of CPU scan cycle or any OB you place it in. The hardware controls the pulse generator based on the initial setting you put in the hardware configuration and downloaded to the CPU. Your program can then Enable the generator and change the Pulse Duration and/or Cycle Time.

The only very slight advantage that I see in putting CTRL_PWM in that specific interrupt is that the M1000.0 will be immediately updated saving few milliseconds; if even that.

Back to your issue, you should be able to figure this out pretty quick by replacing the stop bit M1000.0 with a global tag that you can set yourself for testing purposes.

First I would change the M1000.0 coil assignment resulting from the comparison to be a "Set Output" and you can reset it later in the code as you want to make sure the output stops until the condition changes.

Second, does the integer you are comparing ever falls outside those limits even for a moment? IF so then that is your problem which can be mitigated by what I describe above, using Set and Reset but I would still look further intro refining that comparison if that was the problem.

Thanks in advice.

Allso you mean it is not problem where ctrl pwm is used. It is working according to its own cyclic time.

M1000.0 bit is used to stop the system if it is enabled to postion between desired values. According to my idea to use set command is not suitable. Because it will set m1000.0 while the cylinder is moving between desired values. But if the cylinder moved out of the desired value it will stay in set mode. 

I want to stop the cylinder if is in position between my desired values.

Mert Turgut

Thanks in advice.

Allso you mean it is not problem where ctrl pwm is used. It is working according to its own cyclic time.

M1000.0 bit is used to stop the system if it is enabled to postion between desired values. According to my idea to use set command is not suitable. Because it will set m1000.0 while the cylinder is moving between desired values. But if the cylinder moved out of the desired value it will stay in set mode. 

I want to stop the cylinder if is in position between my desired values.

 Yes, where CTRL_PWM is used does not affect "its own cycle time".

You do not have to use Set Output , that was just a suggestion to help resolve the issue you were having. I don't have access to all your code, if it works and you like it then that's the way it stays. And of course it says set until you reset it, that's the whole idea. It remains set to insure it does what it's supposed to and somewhere else in the code you reset it based on another condition.

Let's say your cylinder is within those desired values and M1000.0 goes high and stops PWM outputs but the cylinder continues to move because of momentum or load and it gets outside those values what's going to happen is M1000.0 will go low and PWM output will turn on. Now I don't know anything about your system and what the cylinder does and if it could coast or how its position is monitored so my concerns may not be valid at all. Just something to consider while troubleshooting your problem.

Thanks in advice.

I am on holiday. On monday I will be in my workshop and I can take a video and upload it to youtube. Maybe When you watch it, you can have more idea about my system. 

When I used stable pwm I controlled the system very well. But in this case pwm is stable also initial duration time ia stable, I change the system and I wanted to control initial duration time of pwm by using pid compact function. But in this case the problem occurred I mentioned.

And there is another problem I faced in this application.

I could solve it very simple way but it is realy a solition way or not I am not sure.

I applied two pid compact function for two ctrl pwm function.

One of them has Qw1000 and the other has Qw1002.

If the setpoint is less than input also real value one pid compact adjust the pwm which has Qw1000.

And if the setpoint is more than input the other pid compact should adjust the other pwm which has Qw1002.

But in the second case pid is making nothing..

What I did to solve this problem.

In the second pid function I changed the setpoint and input. Also setpoint always bigger than input value.

But this is a real solution way, or is there another way to solve this type problems I do not know.

Best regards ...

Hello Mert,

I have very little knowledge of PID I would not be of any help to you. My suggestion is to start another topic specific to this problem to attract the right kind of help.

Cheers

Kal

Kal.A

Hello Mert,

I have very little knowledge of PID I would not be of any help to you. My suggestion is to start another topic specific to this problem to attract the right kind of help.

Cheers

Kal

 I opened a title ragarding to this problem.

I hope there would be a simple solution method for this type problem.