We are going to change old plc of fired heater with new one. There is no data available about software implemented in old plc but every thing is ok. but there is one doubt only: orifice meter volumetric flow compensated by pressure & temperature transmitters installed on fuel gas line to heater to control the process fluid temperature. Up to here every thing is ok. But in addition to above mentioned instruments, there is one density meter on fuel gas line also which wired to plc and we don't know what is the purpose of it. Does anybody knows about its function?

 

Quite likely, the PLC is programmed to calculate mass flow of fuel by
multiplying flow times density. You might see what it is doing with that
calculation. It might be important.

Walt Boyes
Editor in Chief
Control and ControlGlobal.com
555 W. Pierce Rd Suite 301
Itasca, IL 60143

wboyes [at] putman.net
www.controlglobal.com

 

There is often a good reason to use density and not temperature and pressure which relates to the limitations of the PTZ calculation but price is often also a factor... PTZ is cheap, density is not cheap but accurate.

A source of information is here:
http://www.documentation.emersonpro...mi/documents/instruction_manuals/78125040.pdf

And here:
http://www.documentation.emersonpro...mi/documents/instruction_manuals/hb511020.pdf
These manuals have some useful reading in the appendices.