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Increasing timing accuracy in a high electrical power test controller with CompactRIO and LabVIEW

The challenge posed was to replace an obsolete high electrical power test controller with a solution that offers easier maintenance, more features, and greater flexibility. The solution devel oped used NI CompactRIO, LabVIEW and digital I/O to coordinate test sequencing for superior timing accuracy combined with the ability to interface with existing hardware.

The existing program controllers at the client site were in-house manufac tured timing units that coordinated test sequence events required for high-power testing procedures of electric utility distribution equipment. The systems consisted of custom-designed hardware controlled by a DOS computer that became increasingly difficult to service.

The client hoped to increase the timing accuracy over the existing system and run the system software on a Windows OS computer for easier main tenance. The most critical specifications included timing accuracy for contact events (±10 µs) and accuracy of the zero crossing detection (at ±10 µs) of the 240 Vac reference signal. The development team ruled out using PCI data acquisi tion cards because Windows does not permit submillisecond software timing. Instead, the team selected CompactRIO hardware programmed using the LabVIEW FPGA Module that commu nicates with LabVIEW on a Windows computer. The development team programmed the CompactRIO hard ware with the LabVIEW FPGA and LabVIEW Real-Time modules. Using LabVIEW, the team designed, programmed, and customised the CompactRIO embedded system without having to use complex VHDL language. The timing event program controller system consists of:

o LabVIEW on a Windows PC

o A test sequence timing engine soft ware program in LabVIEW FPGA

o An analogue input module to read test input voltage (divided down)

o A digital input module to detect user- initiated contact closures

o A digital output module to generate pulsed output voltage to control power switch contact closure

o A digital output module that opens or closes the corresponding contacts for each of the required events

The LabVIEW program initialises the software and hardware and loads the most recently used test specification. It also configures a desired test specifica tion of a specific contact event sequence for the corresponding channel in the 11- channel make-or-break contact unit and displays all programmed timing events, including: Selecting appropriate contact event name; Determining whether contact event has normal or inverted polarity; Entering start time and dura tion (one or two pulses) for each contact event; Setting switches to temporarily enable or disable a particular contact event, gives the operator flexibility to make small sequence modifications without creating a new test sequence.

LabVIEW allowed the development team to implement scalable architectures in the test system, which makes future modifications easier. Also, LabVIEW provided easy implementation of multi loop program structures, deployment of event-based programming, and creation of unique and easy-to-use software inter faces. Using NI hardware ensured the solution satisfies the client’s timing accu racy requirements (±10 µs).

The resulting system provides the customer with an improved high elec trical power test controller that replicates the look and feel of the user interface of the previous system while improving the readability of the graphical display. It reproduces existing functionality and increases timing accuracy.

[Stephen Boronkay of Balaton Technologies is a Certified LabVIEW Developer.]

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