Greetings to All:
I am in a problem here. The hardware plateform is SLC 5/04. The thing is, i have to go to the site and fix a problem in ladder logic that is not written by me. I understood the logic and trying to figure it out the problem. I dont have the logic with me otherwise i would have posted it but Here is the working history first:
WORKING: There is a Master Controller PID in the program, who has two inputs: Input 1 is the output of inlet pressure pid(Control variable in percentage) and Input 2 is the output of the outlet pressure pid (Control variable in percentage). There are 2 outputs of the Master controller, output 1 is the percentage output for the recyling valve, and the output 2 is the percentage output for the speed of the engine. The way Master controller works is, it takes a low select(the low input, out of 2 inputs) and it uses a split range method on its two outputs. Hence it first reacts on the speed and then on the recyling valve. Actually it keeps a cross eye on both inlet pressure and outlet pressure pid outputs (which are the inputs of master controller). Outlet pressure pid loop is reverse acting and inlet pid loop is direct acting. Dpending upon what the master controller selects it operates its output in the following order:
1) Speed
2)Recycling valve
For example if the outlet pressure is higher than its setpoint, the master controller will lower down the speed of teh engine so that to keep track of outlet pressure,it will lower down the speed till the minimum speed reaches. At this point if the outlet pressure is still out of setpoint range, it start openning up the recyling valve.
PROBLEM: Now the problem is, everything working just fine the way it works, but there are few problems that makes this program unstable:
1) First the outlet pressure does not keep track of the setpoint, for example, if the SP for the outlet pressureis set at 3000, then the PV for the outlet pressure will go to 4000, and keeps on increasing, but after a long delay the master outputs come into play, it lowers down the speed and then the recyling valve but there is a huge delay in while doing it. So the whole system shuts down.
The Pid tunning paameters for the inlet and outlet pressure loops are as follows:
Inlet:
P = 8
I = 2
D = 0
Outlet:
P = 8
I = 2
D = 0
For both the pids the internal RG bit is not set and hence the resolution is 0.1.
The solution that i came up with are, there might be tunning issues with teh outlet pressure pid loop, But even if the loop is badly tunned, it should work, why the pressure keeps on increasing to 4000........
I also came to know that the speed output from the master controller goes into engine system which again acts as a setpoint for the engine system pid, that might be a problem, may be the engine system pid is badly tunned and takes a long time to react.......Thats all i came up with.....
But guys i need a lot of your suggestions and ideas before i go to field which is most likely tomm or day after...... so any ideas will be appreciated...thanks in advance
I am in a problem here. The hardware plateform is SLC 5/04. The thing is, i have to go to the site and fix a problem in ladder logic that is not written by me. I understood the logic and trying to figure it out the problem. I dont have the logic with me otherwise i would have posted it but Here is the working history first:
WORKING: There is a Master Controller PID in the program, who has two inputs: Input 1 is the output of inlet pressure pid(Control variable in percentage) and Input 2 is the output of the outlet pressure pid (Control variable in percentage). There are 2 outputs of the Master controller, output 1 is the percentage output for the recyling valve, and the output 2 is the percentage output for the speed of the engine. The way Master controller works is, it takes a low select(the low input, out of 2 inputs) and it uses a split range method on its two outputs. Hence it first reacts on the speed and then on the recyling valve. Actually it keeps a cross eye on both inlet pressure and outlet pressure pid outputs (which are the inputs of master controller). Outlet pressure pid loop is reverse acting and inlet pid loop is direct acting. Dpending upon what the master controller selects it operates its output in the following order:
1) Speed
2)Recycling valve
For example if the outlet pressure is higher than its setpoint, the master controller will lower down the speed of teh engine so that to keep track of outlet pressure,it will lower down the speed till the minimum speed reaches. At this point if the outlet pressure is still out of setpoint range, it start openning up the recyling valve.
PROBLEM: Now the problem is, everything working just fine the way it works, but there are few problems that makes this program unstable:
1) First the outlet pressure does not keep track of the setpoint, for example, if the SP for the outlet pressureis set at 3000, then the PV for the outlet pressure will go to 4000, and keeps on increasing, but after a long delay the master outputs come into play, it lowers down the speed and then the recyling valve but there is a huge delay in while doing it. So the whole system shuts down.
The Pid tunning paameters for the inlet and outlet pressure loops are as follows:
Inlet:
P = 8
I = 2
D = 0
Outlet:
P = 8
I = 2
D = 0
For both the pids the internal RG bit is not set and hence the resolution is 0.1.
The solution that i came up with are, there might be tunning issues with teh outlet pressure pid loop, But even if the loop is badly tunned, it should work, why the pressure keeps on increasing to 4000........
I also came to know that the speed output from the master controller goes into engine system which again acts as a setpoint for the engine system pid, that might be a problem, may be the engine system pid is badly tunned and takes a long time to react.......Thats all i came up with.....
But guys i need a lot of your suggestions and ideas before i go to field which is most likely tomm or day after...... so any ideas will be appreciated...thanks in advance