Emerson Exchange 365

• Not Answered

How does the BIAS block work?

Dear all,

I have come across a module that has a master PID, the output of the PID goes to a splitter and the output of the splitter goes to two BIAS/GAIN blocks.

The output of the BIAS/GAIN block goes to the CAS_IN of two other PID blocks. Each PID block is wired with a valve.

How does it work or what is the function of the BIAS/GAIN blocks?

Thank you very much.

Regards,

RAguilar

• 7 Dec 2022 12:10 PM
• Cancel

1 Reply

• Lou Heavner

  

  • 7 Dec 2022 3:24 PM

  Imagine you have a steam header and you are trying to control the pressure. Imagine further that you have 2 boilers providing steam to the header. You could have a PID block for pressure control that outputs to a splitter block. The splitter block outputs to the boiler master for each boiler. If the pressure drops and the demand for steam rises, the boiler masters would increase fuel and air to provide the required steam. But suppose the boilers were different sizes and that sometimes you just want to base load one of the boilers. Or maybe, you have an "optimizer" that calculates the efficiency of each boiler and makes decisions on how to allocate the steam load optimally between the 2 boilers. You could configure the boiler masters as bias/gain blocks. The block modes can be adjusted to allow the operators to set the seam load. The gain could be adjusted to account for the relative sizes of the boilers. A bias could be applied for whatever reason. This isn't the only way to solve the problem, but it is a straight forward way, where you have parallel slave loops or final control elements and you may need to allocate the load between the 2 in some way.

  • Cancel