GE 90-30 PLC Sweep Time and PID ISA

[turbohamad]

Dear Fellows;
Good day. Here i share two images one is PLC Sweep Time control and Monitor Screen and the other one PID Control Screen.
First i define the problem. The Program control the fuel of the Gas Turbine but when we start the turbine it is not stop at the given set point and speed overshoot and tripped.

In PLC Sweep time i think it is the scan time in GE 90-30 am i right?
If you see the image the actual sweep time of the program is 14 mSec while it set to 100 mSec. In my point of view that PID sets its parameters CV after 100 mSec?

In the Second Image the detail of PID i want to understand that

1. If i change the Upper clamp value from 32000 (20 mA) to 18000 then CV not going to beyond 18000 and limited to this value regardless how much error (SP-PV)?

2. Near the bottom of integral value there is a 32000 value appear it means the SP and PV are compared in Counts or can i say that SP (%R) and PV (%AI) are in counts. Is it god technique to calculate the error by counts or convert counts to EU (Frequency for speed sensor) for calculate error?

3.The sample period is 10 mSec is it correct value according to Sweep time?

4. Can i fix the Sweep time that program must scan in 25 mSec instead of 14 mSec because the fuel control mechanism is Electro Hydraulic (Response time is slow) ?

5.I want to understand Dead band +/- , Bias, and slew time?

6. Can i change the Ki (Proportional) by using the Move instruction at different speeds like
If speed between 35 to 55 then update KI is 8.0,
If speed between 55 to 62 then update KI is 6.0
and so on?

Regards



Regards

 

[Steve Bailey]

The PLC sweep time setting of "Normal" means that it will take whatever time it requires to complete a full cycle of Input updates, program scan, output updates, external communications service and other housekeeping items. While the cursor is on the 'Normal' field you can hit the tilde (`) key to change to "Fixed" which will force the PLC to take the number of milliseconds you specify for a full scan cycle.
The PID sample period indicates how often the PID will be updated when it is enabled. If the sample period is less than the PLC scan time the PID will be updated every scan. If the PID sample period is longer than the scan time, the PID will be updated in only the scans when the sample time has elapsed since the last update. ten milliseconds is the fastest update frequency you can set.
All of the parameters can be changed in ladder logic if you dare.
I'm not going to get into a detailed explanation of the parameters. They are covered in the Logicmaster manual GFK-0467