Rslogix 500 PID controller

[Dani610]

Hello All,

This forum has been of great help for me
As i mentioned in my earlier posts that I am a learner so pardon me if I ask silly questions.

I am trying to do a ladder logic for a cool room it has a temperature gauge and a cooling fan. As soon as the temperature goes up above the specific point the fan starts and when it comes back to the normal point the fans stops. Then I have to show this on my HMI and enable the HMI to enter set point of room temperature and enter the room temperature manually.

I know that I have to use PID controller for that I tried looking online to find any similar example for that to get me started but couldn't.

Any help in this regard is highly appreciated.

Thank you

 

[Mickey]

This is not a PID application. It's a simple on/off control with a deadband.

Use compare instructions, if x is greater then set point turn on fan, is x is less then setpoint minus y turn off fan.

x=room temp
y= value of deadband

 

[Dani610]

This is not a PID application. It's a simple on/off control with a deadband.

Use compare instructions, if x is greater then set point turn on fan, is x is less then setpoint minus y turn off fan.

x=room temp
y= value of deadband

Thank you for your reply

One thing i forgot to mention is that my fan speed is 0-50hz need to control that as well so that’s why i need to use PID. The fan speed will work according to the raise in temprature

 

[Mickey]

So the fan is controlled by a VFD?

If so then yes a PID instruction will do.

It may help if you can tell the forum which controller you have as RSLogix500 is used to program the SLC and Micrologix series of controllers. The PID instruction is a little different in those controllers.

See link..

https://www.google.com/search?sourc...k1j0i67k1j0i131i67k1j0i20i264k1.0.NXLL4ATDJGM

 

[Dani610]

So the fan is controlled by a VFD?

If so then yes a PID instruction will do.

It may help if you can tell the forum which controller you have as RSLogix500 is used to program the SLC and Micrologix series of controllers. The PID instruction is a little different in those controllers.

See link..

https://www.google.com/search?sourc...k1j0i67k1j0i131i67k1j0i20i264k1.0.NXLL4ATDJGM

Yes it is controlled by VFD

Controller I am using is Micrologix 1400.

Thanks for the link I tried this searching online before posting but couldn’t understand fully how I can use this in this particular application that’s why.

Thanks

 

[Dani610]

Hello All,

This forum has been of great help for me
As i mentioned in my earlier posts that I am a learner so pardon me if I ask silly questions.

I am trying to do a ladder logic for a cool room it has a temperature gauge and a cooling fan. As soon as the temperature goes up above the specific point the fan starts and when it comes back to the normal point the fans stops. Then I have to show this on my HMI and enable the HMI to enter set point of room temperature and enter the room temperature manually.

I know that I have to use PID controller for that I tried looking online to find any similar example for that to get me started but couldn't.

Any help in this regard is highly appreciated.

Thank you

I have attached a pic of my .RSS file. What I am trying to do is controlling the temperature. My logic is I have a temperature gauge and a fan in a room whenever the temperature goes up say from 50 the fan goes on and vice versa. The frequency of my fan is 0-50Hz.

As you can see in my logic first I have given an analogue input(temperature gauge input) and then converted it and store it then in my PID I have given that input to Process Variable and my Control Variable is N7:1. then again I have converted that and given that to analogue output( I suppose that will go to the fan).
I have only changed set point to 50 in setup screen of PID.

Now can you tell me if I am going n the right direction if not then guide me kindly and if yes even then guide me how can I get this working. One more thing I need is to show this all on my HMI and be able to enter the temperature of temperature gauge manually from HMI and can change my set point from my HMI.

PS: Fan is controlled by VFD

Thank you

 

[Mickey]

Now can you tell me if I am going n the right direction if not then guide me kindly and if yes even then guide me how can I get this working

.

Off to a good start. You need to make an attempt to configure the PID instruction.

Tuning parameters ( at least a gain setting)
If you want to enter a set-point in engineering units you will need to set the Setpoint min/max values ( this should correspond to the input scaling range)
You should set the CV min/max e.g 0-100
Time mode?
Control mode?
etc.

Read thru the manual and give it a shot.

It's always best to post the whole program it's .RSS file (zip it first)

 

[daba]

Please bear in mind that the fan motor may not be VFD rated, and will not like running at below 10% of it's full speed. It will probably run hotter when running slower, due to the motor cooling fan (the one inside the cowl on the motor) providing ineffective cooling for the motor body.


I suspect that a simple on-off control would be better in this application, otherwise you will have to provide it anyway for when the PID is working at less than 10% output.


Most cold rooms work with just a simple thermostatic switch, maintaining the temperature at +/- 2 or 3 degrees of setpoint, and a PID is not necessary.

 

[Mickey]

I suspect that a simple on-off control would be better in this application, otherwise you will have to provide it anyway for when the PID is working at less than 10% output.
Most cold rooms work with just a simple thermostatic switch, maintaining the temperature at +/- 2 or 3 degrees of setpoint, and a PID is not necessary.

I agree with daba. As I stated in my post #2.

 

[Dani610]

.

Off to a good start. You need to make an attempt to configure the PID instruction.

Tuning parameters ( at least a gain setting)
If you want to enter a set-point in engineering units you will need to set the Setpoint min/max values ( this should correspond to the input scaling range)
You should set the CV min/max e.g 0-100
Time mode?
Control mode?
etc.

Read thru the manual and give it a shot.

It's always best to post the whole program it's .RSS file (zip it first)

Thanks
Yes I am playing around with once I make some improvement then i will post the .RSS file to get better suggestions

Please bear in mind that the fan motor may not be VFD rated, and will not like running at below 10% of it's full speed. It will probably run hotter when running slower, due to the motor cooling fan (the one inside the cowl on the motor) providing ineffective cooling for the motor body.


I suspect that a simple on-off control would be better in this application, otherwise you will have to provide it anyway for when the PID is working at less than 10% output.


Most cold rooms work with just a simple thermostatic switch, maintaining the temperature at +/- 2 or 3 degrees of setpoint, and a PID is not necessary.

Thanks for this I am learning the working of PID