An HMI migration can be a separate project from field-controller replacement. GDS's Medina County work replaced Wonderware with VTScada while retaining Motorola RTUs and field communications.
Identify What Will Change
Identify the existing application, servers, workstations, controllers, gateways, and communications. State which components remain and which change. Confirm the interface requirements before assuming the new application can communicate with the retained system.
Review Operator Tasks
Use the existing screens as a starting point, then review how operators navigate sites, interpret equipment status, acknowledge alarms, and find historical information. Identify changes they need as part of the new application scope.
Define Data and Alarm Requirements
List the points, scaling, alarm behavior, notification recipients, trends, reports, and required historical data. Specify whether existing historical data must be retained or transferred. A new historian does not automatically include the old records.
Plan User Access and Redundancy
Define user roles, remote access needs, workstation locations, and required redundancy with the system owner. These requirements should be reflected in the software, hardware, and testing scope.
Agree on Cutover and Acceptance
Identify how the new application will be checked against the field system, who coordinates the transition, and what documentation and training operators will need. GDS's ADOT project included an operating guide for its Ignition pumphouse application.