Connecting Legacy Generators to a Modern PLC at a Municipal Storm Water Facility

Extracting Modbus RTU data from aging generator sets — without breaking the budget

A water and wastewater integration firm in the southeastern United States had a clear task: get data out of two backup generators at a municipal storm water pump station and into the Allen-Bradley PLC (Programmable Logic Controller) controlling the site. 

The pump station draws water from drainage infrastructure and discharges it into a nearby river. The generators keep it running when the power goes out. 

The facility wanted to know when those generators were running and whether any faults had occurred — five data points, nothing more.

The generators communicated over Modbus RTU. The control system ran on EtherNet/IP (EIP). Bridging those two protocols required a gateway. And because this was a public works project, cost shaped the decision from the beginning.

"For municipalities and government work, they pay a lot more close attention to price than industrial customers," said the system engineer leading the project.

A gap between two protocols

The generators had been in place for years and worked reliably. No one wanted to replace them. The goal was simply to make their data visible in the existing control system.

Keeping everything on EtherNet/IP was the priority. It meant remote access, easier reconfiguration, and a consistent architecture the team already knew how to support. What was missing was a device to bridge the gap: a Modbus RTU to EIP gateway that could sit between the generators and the PLC without requiring a full system overhaul.

To complicate things further, this was the first hands-on Modbus integration for the systems engineer leading the project.

"It was about time I dipped my toes into Modbus."

$200 versus $1,400

The well-known option for this type of integration — a ProSoft module with built-in Studio 5000 add-on profiles — runs about $1,400 per unit. With two generators requiring separate converters, that was nearly $3,000 before any other project costs. A steep price for what the facility was looking for.

A search for alternatives turned up the Net485 from Grid Connect. Under $200 per unit and the documentation suggested it could handle the job. The engineer ordered two.

"I knew there was a little bit more legwork I'd have to do on my end, but I was down to try that."

When the documentation runs out, support matters

The initial setup wasn't without friction. Some software tools referenced in the product manuals had gone offline. The documentation itself was written for engineers already comfortable with Modbus, which the engineer candidly acknowledged he wasn't yet.

"It wasn't necessarily written for someone who is entry level to Modbus."

He opened a support ticket. After a few exchanges, he was connected directly with the engineer who had developed the product. They got on a video call.

"I had a direct line with him to walk me through how to set up this device. We went through all the details, and it was very helpful."

The developer walked through the full configuration, provided a copy of a discontinued EtherNet/IP tools package that was no longer publicly available, and answered every question the engineer had. By the end of the call, the engineer had a step-by-step procedure and a list of fallback options to try if anything went sideways in the field.

Installation: one day, two generators, five data points

On site, the engineer worked through the configuration with both units. The NET485 required an active connection to the Modbus server to complete the data mapping, so some of the setup had to happen in the field rather than from the office. He anticipated that and came prepared.

"I made really good notes, and I had a list of things to try. The developer offered to let me call if I had any trouble in the field."

The first device took the most time. Once the approach was confirmed, the second — same generator model, same configuration — followed without surprises.

"I wired it up myself and powered it, and it worked as expected."

Both units were online by the end of an eight-hour day.

The result

The PLC now receives live run states and fault states from both generator sets. That data flows through the facility's control system and onto the city's network. Operators can log in from tablets to check status without setting foot on site.

At under $200 per unit, the Net485 didn't just fit the municipal budget — it outperformed the expectation. Legacy generators, a modern PLC, five data points, and operators checking status from a tablet. The price made it worth trying. The support made it work.

"The support was really good. The value seemed great for the solution it offered."