PID Loop Conversion

  • Thread starter Shahid Waqas Chaudhry
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Thread Starter

Shahid Waqas Chaudhry

Dear List,

One of our client who wants to replace his old SIngle Loop Controller based system (in a Chemical Recovery Plant) to a newer PLC based system. The new system installed is SIEMENS SIMATIC S7.

The old controllers were Fischer & Porter Micro DCI. I have a list of their parameters. However, there is no conversion factors that could
translate them into the SIMATIC S7 PID block (FB41, Continous Control). If anyone has done a similar job or know the conversion parameters, then it would be a great help to easily convert the loops instead of re-tuning all of them.

Also, in the same plant, there is a boiler that burns black liqour (coming from the fibre mill after it is used to cook pulp). This boiler
has a Drum Level cascade loop, which has no available information. Any information about this would be welcome.

Thanks in advance,

I have used FB 41. I found it cumbersome.

I have used different controllers and PLC's for PID loops. The parameters (P,I &D along with others) change whenever the make changes. This could be because of changes in the way the PID algorithm is implemented in different
instruments by different manufacturers.

In S7 that I used the PID was executed every 100ms as compared to 250ms for some controllers. This too seems to act on tuning parameters. Plus the I and D in S7 are based on time values. Making it really complex while moving from

Use the tuning parameters for basic tune up. I do not recollect but S7 could be proportional band which is the inverse of gain. First Convert Proportional band or gain to proper format.
Convert the Integral and derivative components to time formats. Check that the scaling of process variable, and setpoint are proper in the
S7 controller FB. Start your tuning from these parameters.

What is the problem with drum level control. is it 2 element or 3 element or simple drum level control?

If the details are more specific then the solution can be better presented.

However no matter what you do, you may not be able to totally avoid tuning, you can only succeed in reducing the effort.

Anand Iyer