We have around 400 RTDs in the plant which is to be designed. We are going with FF for AI/AOs and in a process of deciding what to do with RTD I/Ps. One way is with TT with FF. Second option is with Multiplexers. Or maybe just with Junction Boxes.

Can somebody pull his experiance to help me out in this situation?

Regards,

Rishi

 

Rosemount model 848T is an FF device that can accept up to 8 sensors - RTDs (2,3 wire), thermocouples, mV, ohms. The channels are individually configurable.

This is a cost-effective alternative to the solution you have in mind - using individual temperature transmitters.

 

We used a Honeywell HC-900 as an I/O front end for 420 thermocouple points spread out over 5 I/O racks. An OPC server took the data out of the controller. The Honeywell AI card does either T/Cs or RTDs, it's universal so it would apply to your RTDs.

The approach offered the flexibility of ethernet cabling remote-rack-back-to-controller which fit the topology of the plant (remote I/O racks in dispersed areas), ethernet for OPC, and the ease of 'copying' function block configuration from page to page in the development software.

The cost came to $112USD/point for all the hardware and software for that portion of the project.

But I don't recall anything about that model being FF, so this approach probably doesn't fit your situation.

Bud