Automation & Controls:
- There are two ways to migrate a code, the first is without rewriting the software and the second involves rewriting it.
- After performing an auto-migration, verify that all software blocks (e.g., OBs, FCs, FBs) are identical to the original program. Pay special attention to functions that may have been automatically converted to a different implementation.
Example: A PID block such as CONT_C may be migrated from an FC to a Technology Object, potentially altering DB numbers, tag names, and HMI connections.
- If any portion of the code was rewritten, confirm that its behavior matches the original logic. Give extra attention to sequences and non-standard tuning elements (e.g., debounce timers, filters, custom logics).
- Remove all obsolete or unused I/O from the code.
- Improve the industrial network architecture in the new project where possible (e.g., implement redundant PROFINET).
- Validate that all analog scaling is correctly normalized and scaled (e.g., NORM_X and SCALE_X for Siemens, SCL for Rockwell, and AINPUTGP for Schneider).
- Test as much as possible during the workshop and FAT, including I/O checks, network communication (PROFINET/PROFIBUS, DP-DP or PN-PN couplers), simulation, HMI trends, and alarms.
- Review PID parameters, scan times, and control settings. Monitor process behavior and be prepared to fine-tune the PID loops.
- Ensure set-point values are retained or saved in the new PLC. Implement a first-scan routine to initialize them as needed.
- Configure correct starting values for all set-points and parameters.
- Review filtering logic in the software (e.g., moving averages for analog inputs). Add filtering if necessary, especially since new hardware typically updates and processes data faster than older systems.
- Create a comprehensive Watch Table for all I/O. Pay close attention to signals that operate with inverted logic, such as fail-open valves.
- Confirm the type of each variable-frequency motor application (e.g., pump, fan) to ensure correct control logic.
- Perform a full cross-reference of all I/O to ensure every signal is used correctly and none were overlooked during implementation.
- Add a ramp to smooth and improve some processes, such as a large motor when reaching target speed or to smooth the output of a sensitive PID control loop, such as a compressor.
- Check the PLC’s cycle time, CPU and memory loads.
- Check the SCADA's CPU and memory loads.
- Configure Windows's autologin as Operator user in the SCADA Client PCs.
- Verify correct PID operation. Use Greg McMillan's recommended initial tuning parameters listed below as a starting point if required.
Electrical:
- Review the existing power supplies and upgrade or redesign them if necessary. If multiple power supplies are used, ensure their voltages and reference points are aligned. If possible, consolidate them into a single supply.
- Verify compatibility between existing field wiring/termination and the new I/O hardware.
- Ensure all relevant electrical and control drawings are available and up to date.
- Confirm that output cards meet the required current specifications, especially relay output modules.
- Ensure all power supplies, racks, and backplanes are properly earthed.
- Verify the presence of proper shielding and shield termination bars for all analog-related cables (e.g., analog inputs, Telefast blocks, RTDs, analog outputs).
- If the system communicates with multiple SCADA platforms, confirm that communication with each SCADA system is functional and stable.
- Assess whether hardwired communication between PLCs (via multicore cables and relays) may be simpler or more reliable than network-based communication for certain signals, particularly when dealing with obsolete systems.
- Check the polarity of all analog output signals.
- Use a 500 Ω resistor to convert 4–20 mA signals to 0–10 V during tests that require a current source meter.
- Confirm that no unintended or incorrect power supply has been introduced into the existing instrumentation or field wiring.
- Identify all resistors used for current-to-voltage conversion (e.g., 500 Ω resistors for 4–20 mA to 0–10 V). These may exist in terminal blocks or inside I/O modules. Ensure they are not removed or bypassed incorrectly during the changeover.
- Use a network tester to verify the integrity of all Ethernet connections and cables. The tester should show correct sequencing across all 8 conductors plus the ground (1 to 8 + Ground (G)).
- Configure electronic fuses to the appropriate current rating (e.g., 1 A for 16-channel digital inputs and 2 A for digital outputs). Leaving them at default high settings (i.e., 6 A) will prevent them from tripping correctly during faults.
- Configure motor over-load protection to trip at the appropriate current rating (e.g.,
if SF >= 1.15 THEN OL = FLA x 1.25
else OL = FLA x 1.15).
- Review DC drive settings and reduce the minimum speed if required by the application.
Process:
- Talk to operators and process engineers who work with the equipment daily to gain a solid understanding of how the process functions and what the key success factors are.
- Use the migration as an opportunity to correct simple existing issues, such as undersized alarm pages or trend display problems.
- Take photos of all HMI screens and faceplates before starting the migration.
- Take detailed photos of all electrical cabinets during operation, including gauges, rotary switches and VFD displays showing their actual operating frequency.
- Pay close attention to run-away or unstable processes, such as exothermic reactions, oxidation processes, or pH-sensitive operations.
- Understand the expected behavior of the process during start-up and shutdown sequences.
- Develop awareness of discrepancy timers for valves and motors, and be prepared to increase timer values for sticky or slow-reacting processes.
Project:
- Take a phased approach to minimize risk during the migration or commissioning process.
- Identify all potential risks in advance and prepare alternative action plans for each scenario.
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