Client Goal

• Manage 11 filters with automatic backwash sequence
• Automatically control water inventory
• Log critical plant data for DHEC (Department of Health and Environmental Concerns)
• Provide uninterrupted operation during changeover
• Ensure that critical plant data is viewable at all times

Project Overview

A southeastern municipality water plant had installed a number of different control systems over its three decades of operation. The systems ranged from 30-year-old technology to underutilized current technology. The oldest systems posed an increasing risk to uninterrupted water production due to hardware obsolescence and increased downtime. In addition, none of the existing PLC or HMI systems had been documented. The challenge was to leverage the newer technology, replace the outdated systems, and enhance system capabilities through integrated software without interrupting the plant’s production of the required 28 million gallons of water per day during the conversion.

The previous control system comprised Bristol relay controls, single loop controllers, obsolete Foxboro Spec 200 analog control boards, and PLCs performing manual control. The system also included strip chart recorders for trending, and an alarm panel. Operator interface functions were performed via manual devices and two PC stations equipped with outdated Intellution software. The operators opened manual switches for backwashing filters and established flow set points via manual switches and HMI stations. The system was difficult to use and heavily dependent on the operator’s direct involvement.

Tegron was chosen to upgrade the system to a current platform and enhance system performance for future growth. As a cost-effective solution, existing technology would be leveraged and new hardware installed to replace obsolete systems. The goals for the new system were to centralize control, automate the backwash sequence, enable uninterrupted plant operation, provide system documentation, and enhance data collection. It was required that this be accomplished with minimal downtime and disruption to the plant operations.

The new system would consist of 16 Modicon PLCs, 2 iFix servers, and one iFix client, all communicating over an Ethernet network. A total of 12 LCD monitors would display plant data and provide operator control.

Tegron employed the function block capabilities of the Modicon Quantum PLC to develop standard controls for each equipment type. The HMI was developed using a standard screen navigation and graphics for ease of use, and iHistorian software was selected to store data for regulatory requirements. These provided consistent programming for system operations and maintenance troubleshooting. The enhanced resolution capabilities of iFix enhanced a 12-monitor display using three PCs, for a cost-effective approach. Upon completion of the commissioning phase, Tegron provided the with a comprehensive electrical documentation package, documented PLC and HMI configuration files, and a user’s manual on CD to ensure that the system would be properly serviced and maintained. Tegron also provided comprehensive training for system operators and maintenance personnel to better familiarize them with the installed system.

Scope of Supply

• CAD Documentation
• Commissioning & Start-up
• Control Panel Fabrication
• Electrical Control Design
• Human Machine Interface Development
• PLC Software Development
• System Training
• Emergency Support
• Support Agreements
  

The Outcome

Production Benefits:

• Centralized control
• Efficient backwash sequences
• Consistent operation
• Chemical cost savings
• Enhanced engineering data for high rating