Replacing Foxboro 762CNA-AT with something more modern

Hello, I have been tasked with replacing 16 aging Foxboro 762CNA-AT controllers (as well as some other process displays) with something more modern.

The setup is as follows:
There are 8 water filtration basins, each one having two Foxboro controllers. One unit controls effluent flow through that filter (either manually in GPM, or in automatic mode distributing the influent flow evenly across all active filters). The other Foxboro unit manually controls a common backwash valve (all 8 backwash units control the same valve) supplying backwash water to the filter set. (Backwash is done manually, one filter at a time.)

There are also two 7-segment LED displays for each filter, showing effluent turbidity and head loss.

They have asked me to replace all this with something more modern, because the Foxboro controllers are dying frequently, requiring $1000+ repair bills each time.

I've found some units like the MicroMod 53SL6000 units, which look very similar, and may provide a drop-in solution, and there are other multiloop controllers available, but it may be more preferable to go with a PLC-based system and replace the controllers and displays with a single touchscreen at each filter. I've had good luck with the inexpensive AutomationDirect CLICK PLC series, and the Kinco 10" touchscreens seem to work well while being very reasonably priced.

I would welcome any suggestions or ideas on how to approach this.

Thanks!

IMO standalone loop controllers are for cost savings and when a plant doesn't have the resources to maintain a real control system.

I almost always vote to replace them with PLCs, especially when there are more than one. It's just so much more flexible, easy to troubleshoot, and likely more reliable.

The Micro-DCI communications is "RS-485", meaning their proprietary protocol ("secure DataLink protocol") not Modbus or Ethernet/IP or Profibus. That is not modern in my book. That's back to 1990. What SCADA or HMI do you use with "secure Datalink"?

Siemens discontinued their 353 "process controller" (same footprint as the Foxboro) a couple years ago and at the time Yokogawa and ABB had similar footprint process controllers, but I can't recall the model numbers. It isn't clear how much longer those stand-alone process controllers will be around.

Because those controllers were used extensively on boilers, there were a number functions implemented with respect to manual mode, that you might want to check into with your customer to make sure that you understand exactly what has to be accomplished in manual mode (and any associated bumpless transfers into or out of manual mode are needed), to make sure that whatever you replace it with has that functionality.

Micro-Mod (maybe affiliated with Micro-DCI?) was a unit claiming to be Siemens 353 compatible.

MicroMod 53SL6000 series controllers

Hello Ryan.

I have worked with stand alone process controllers, DCS systems and PLCs both in industry and education.

You've mentioned a replacement for your for old Foxboro units; the MicroMod 53SL6000 controllers.

For your application, I believe you've hit the 'nail on the head'. I've used the 53SL6000 units for many years and found them to be the most user friendly, adaptable and reliable controllers I have ever worked with, especially when used with MicroMods LoopMaster configuration software. I've never seen a PLC that can match them for the variety they can provide you with.

OK, I do agree with danw, re the communications module interface ( RS232 and RS 485. However, I've been told that MicroMod are re engineering the controller in the first quarter of this year (2020) and are considering new communications modules and a graphical display among other updates.

Any other questions on this you can contact me at [email protected]. You can also contact the manufacturer, who is a US company by Googling their website.

Best wishes,

Ray Miller