PID For Tank Level Control

[JoseM 0]

Please guys. I need help creating my first PID code in RSLogix5000. I have a tank where water comes in at the top and water comes out in the bottom with a pump. I have a pressure sensor that is used to calculate the tank water level. I have a electrical actuator that opens a butterfly valve from 0 to 90 degrees. The actuator is 0 degree = 4 ma and 90 degree = 20 ma. I'm using a 1794-OF4I analog output module to control the electrical actuator. The output module I think is set as 4ma = 0 and 20ma = 7878.

[kaiser_will 65]

Class assignment?

[Michael Lloyd 85]

2 hours ago, kaiser_will said:

Class assignment?

If it isn't whoever designed the system should be drawn and quartered at a minimum :)

[kaiser_will 65]

1. Research the PID itself and understand the differences in undershoot, overshoot, unstable conditions, etc.

2. Break the problem description down into blocks.  Bit-size morsels is how we code.

3. Learn and understand the PID (or PIDE) function block; it is only 1 block.  A code example for 1 rung and 1 block...probably not going to happen.

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1756-rm003_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1756-rm006_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/wp/logix-wp008_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1756-rm094_-en-p.pdf

[JoseM 0]

I'm trying to figure out how do I go about configuring the 1794-OF4I. I read that I need to configure the output range for the output module because there are many available options. The configuration is based on a combination of four bits to tell if it is a 4-20 ma or 0-20ma, etc.

Edited 1 Nov 2016 by JoseM

[kaiser_will 65]

1794-OF4I => Isolated 4-channel analog output module.  In Logix5000, when you add a PLC module, Logix automatically creates read and write configuration words , tags, for you.  If you pull up the Controller Tags list, and drill to the rack and analog output module, there will be input and output words.  Read the literature; these cards can be used in a multitude of ways, so look for your desired example.  You will need to set/reset certain bits to get the desired configuration.  

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1794-in037_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1794-um008_-en-p.pdf

[JoseM 0]

Thank you all for your replies. All the information provided has helped me understand almost everything I need to know I believe. I will like to ask an additional question in regards of PID instruction on CLX.

I will like to see if its possible to have an HMI screen that has a field for the "Setpoint" of the PID instruction where I can adjust this number to change the level of my tank.