Developing an Automated Test System for SCADA Radios

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"The NI PXI RF platform proved to be an excellent choice due to the suite of examples and ease of use to get the components up and going quickly. Engineers spent less time on understanding RF principles, so they could focus their efforts on developing an optimised and easy-to-use test sequencer application."

- Christopher Farmer, CPE Systems

The Challenge:
Designing and building a cost-effective test solution for a smart supervisory control and data acquisition (SCADA) radio that can accommodate large production yields and conduct a comprehensive set of device programming, testing, and RF calibration tasks, all with minimal operator intervention and in less than five minutes per unit.

The Solution:
Using National Instruments RF PXI technology, combined with powerful NI TestStand and NI LabVIEW software, for the basis of a reliable test system that provides the flexibility necessary to address the large suite of testing requirements.

Author(s):
Christopher Farmer - CPE Systems
Stephen Patterson -
Tim Streeter - CPE Systems

For more than 15 years, NI Silver Alliance Partner CPE Systems Pty Ltd (CPE) has worked with industry leaders to design and develop over 700 innovative solutions in test, vision, condition monitoring, and control for customers in the aerospace and defence, agricultural, power/energy/water, research, ICT, and biomedical industries..

4RF Communications develops point-to-multipoint long-range wireless link radio products. The Aprisa SR is a point-to-multipoint smart SCADA radio operating in the 400 MHz to 470 MHz licensed spectrum band, with a 12.5 kHz channel size and narrowband 9.6 kbit/s capacity. It is used by oil, gas, and utility companies for a wide range of monitoring and control applications. The IP-based design includes enhanced security and efficient handling of complex SCADA networks. The radio is configurable as a base station, remote station, or repeater and works with a large number of serial and Ethernet interfaces.

The new low-cost radio was designed to be used in the field and made in high volumes for the industrial market. This meant that 4RF Communications required a different test strategy to ensure low unit test costs, high throughput, and good test coverage for the product’s many features.

4RF Communications decided to outsource the test system development to NI Alliance Partner CPE Systems, a leader in test and measurement. CPE’s knowledge of the NI PXI RF platform and the NI TestStand and LabVIEW development environments complemented 4RF’s significant RF testing and calibration experience.

Test Development Process

The test targets for the system were as follows:

  • Test a board in five minutes
  • Be suitable for large-volume production
  • Run unmanned
  • Be operated by nontechnical staff
  • Access all test points by test probes on one side of the board
  • Include a debug facility
  • Allow for future expansion for other product variants (additional RF bands and bandwidths)

The tests were split into three main areas:

  • DC Testing—Used for testing component values, supply voltages, current consumption, and functional testing of the low-voltage shutdown, switch panel, and LED indication.
  • Built-In Self-Test (BIST)—Used for boot loader and software installation, testing of the RAM and Flash, and confirmation of Ethernet address allocation. These tests were programmed into the device and accessed through a command line interface.
  • RF Functional Testing and Calibration—Used to test and calibrate the transmitter, receiver, and system functions of the Aprisa SR board.

Challenges Faced in Developing the System

Because of the product development schedule, the test system was being developed in parallel with the product, which entailed multiple revisions of the board design. However, because of the way the test system was designed and specified with flexibility in mind, the printed circuit board (PCB) redesigns required only one change to test pin layout (otherwise known as the bed of nails). The use of NI hardware and software greatly enhanced CPE Systems’ ability to implement this concurrent development, which was further supported by effective communication between 4RF Communications and CPE Systems as well as efficient project and configuration management processes.

The inherent modular framework of NI TestStand permitted the development of test sequences, LabVIEW software drivers, and test fixture hardware to be easily distributed across several CPE Systems offices around Australia and New Zealand, allowing multiple developers to work on individual components remotely. The project was coordinated through the New Zealand office in Auckland, where the final system was integrated and tested prior to delivery to the client’s manufacturing facility in Christchurch.

One of the key constraints for the test system was test time, with an overall target of five minutes per board. This target required a significant amount of optimization of the RF calibration algorithms to ensure they operated efficiently. The speed and functionality of the selected PXI RF signal analyzer and PXI RF signal generator instruments supported this algorithm optimization process.

The Aprisa SR PCBA included RF transmission and reception circuits and had to be tested outside its enclosure. Therefore, the RF interference and screening had to be considered and included in the fixture design for both signal integrity and safety reasons. This was achieved using the CAD model of the product housing to machine an RF screening enclosure, which formed part of the top plate of the jig. This shielding gave results from the test fixture that were very close to those achieved with the board in its enclosure.

The Aprisa SR radio has internal data encryption that makes it impossible to generate simulated data streams to test receiver sensitivity. Using the NI vector signal analyzer, we were able to record and retransmit the radio signal. We were then able to use the NI vector signal generator at different levels to test receiver sensitivity with actual data. This methodology meant that the encryption process could change in the future without affecting the test system software.

Outcomes

RF test system development provided some interesting challenges both in terms of the management processes required to coordinate the project across multiple sites and in terms of the technical challenges involved in testing a complex RF product at high speeds with screening incorporated in the fixture.

CPE Systems rose to the challenge and developed a reliable test system that meets all the client’s requirements. It was delivered on time to meet a tight product release schedule. The outcome of the development was a custom yet affordable test system that tests and supports the manufacturing process of this new and innovative high-performance SCADA radio product.

The NI PXI RF platform proved to be an excellent choice due to the suite of examples and ease of use to get the components up and going quickly. Engineers spent less time on understanding RF principles, so they could focus their efforts on developing an optimised and easy-to-use test sequencer application.

A National Instruments Alliance Partner is a business entity independent from National Instruments and has no agency, partnership, or joint-venture relationship with National Instruments.

Author Information:
Christopher Farmer
CPE Systems
20a Harper Street
Abbotsford
Australia
Tel: +61 (0)3 9419 1499
info@cpesys.com.au

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