Automated Controller Integrity Testing Rig for a Nuclear Air System Compressor
Sector:
Energy & Nuclear
Type:
New Build - Control System, Software
Platform:
Siemens
Certification:
CE / UKCA
Summary
DelaControl designed, built and programmed a bespoke automated test rig to verify the integrity of a compressor controller destined for use in a nuclear facility clean air system. The project combined a Siemens S7-1500-based hardware enclosure with fully structured PLC software to exercise every input permutation of the controller under test, producing a fully auditable set of test results and a formal test report.
Challenge
A facilities engineering organisation required rigorous, structured testing of a third-party compressor controller — a Delcos XL SE7 unit — prior to its integration into a clean air system at a nuclear power station. The controller needed to be proven against a comprehensive test specification, covering all possible combinations of digital, analogue and temperature inputs, as well as fault injection across multiple operating modes.
The requirement was to demonstrate that no combination of inputs could produce an undesirable or unpredictable output from the controller, providing an auditable evidence trail suitable for a nuclear environment. No off-the-shelf test solution existed; a purpose-built rig with both hardware and software was needed.
Solution
DelaControl designed and built a dedicated test rig housed in a Rittal AX cabinet, powered from a 230 Vac mains supply. At its heart is a Siemens S7-1500 PLC with 32 digital inputs, 32 digital outputs, 16 analogue inputs and 16 analogue outputs. The rig accepts the Delcos controller as a free-issued item and interfaces to it across digital I/O, 4–20 mA analogue signals, a simulated PT1000 temperature input (via a bespoke resistor ladder circuit) and Modbus RTU communications. A temperature and humidity sensor was also integrated into the enclosure so that environmental conditions could be logged as part of the test dataset. The panel was built and pre-tested at DelaControl's Bristol facility, with a full drawing pack and inspection and test schedule produced as part of the documentation deliverable.
DelaControl then developed the test software in Siemens TIA Portal v19, implementing a three-phase test regime against the approved test specification. The first phase — initial testing — used simulated 4–20 mA and PT1000 inputs to characterise the controller's trip thresholds. The second phase — automated testing — cycled through every permutation of digital input to the Delcos while randomising analogue input values using the Siemens LGF_Random_DInt function, giving approximately 10,000 test points per four-hour test cycle across four rounds of automated testing. The third phase — fault injection — systematically injected defined fault conditions (including e-stop, motor fault, motor temperature trip, signal out-of-range conditions, high pressure and high temperature trips, start-up faults and a motor state fault) to prove the controller's tripping behaviour in all operating modes.
Prior to testing, a test sequence plan — comprising the PLC logic and a descriptive narrative — was submitted for review. All results were captured to CSV and accompanied by a timestamped video recording of the controller's screen throughout testing. On completion, DelaControl produced a formal test results report providing a full auditable trail. The scope was also extended during the project to incorporate five programmable inputs on the Delcos controller, expanding the automated test combinations accordingly. The customer was invited to witness testing at a Factory Acceptance Test.
Key Facts
• Siemens S7-1500 PLC with 32 digital inputs, 32 digital outputs, 16 analogue inputs and 16 analogue outputs
• Modbus RTU interface — 23 data points monitored between PLC and Delcos controller
• Bespoke resistor ladder circuit used to simulate PT1000 temperature input to the controller
• Five programmable inputs on the Delcos configured and incorporated into the automated test scope
• Approximately 10,000 test points per four-hour automated test cycle; four rounds of automated testing
• Fault injection testing covered eight any-time faults, two start-up faults and one motor state fault condition
• Deliverables included test sequence plan, raw results CSV and timestamped video, and a formal test results report
• Rittal AX enclosure; Weidmueller terminals; software developed in TIA Portal v19