Automated testing using NI software

Designing and developing a test system that has component and unpowered testing, device programming, radio signal analysis and calibration, and no operator intervention for production testing of a point-to-multipoint radio product used for remote supervisory control and data acquisition network applications, is the challenge.

The solution was creating a test system based on the National Instruments PXI platform and LabVIEW, TestStand and Switch Executive software to connect to the unit under test using a pneumatic test fixture, including custom RF screening for the RF sections to provide a high-performance RF test solution.

In 2008, 4RF Communications started developing a new range of radio products to augment its existing point-to-point long-range wireless link product. Used by oil, gas, and utility companies for monitoring and control applications, the Aprisa SR is a point-to-multipoint Smart SCADA radio operating in the 400 to 470 MHz band with a 12.5 kHz channel size and narrowband 9.6 kbps capacity.

The Aprisa SR is designed to address the key concerns facing the industry such as the need for enhanced security, the need to efficiently handle the increasing complexity of SCADA networks and the evolution to an IP-based and smart grid infrastructure.

The radio platform’s features enable a variety of monitoring and control applications that address current and future requirements. The radio is configurable as a basestation, remote station or repeater for integration into any network topology (Figure 1). It supports a large number of serial and ethernet interfaces in a single box and has built-in security features.

4RF required a different test strategy to ensure low unit test costs, high throughput and good test coverage for the new product features so the company turned to CPE Systems to design and develop a test system for cost-effective production testing of the radio.

The requirements included component and unpowered testing, device programming, radio signal analysis and calibration and no operator intervention.

The outsourcing was due to its limited experience with medium- to high-volume test fixtures and limited internal engineering resources and development was contracted to CPE which selected the National Instruments PXI platform coupled with LabVIEW and TestStand software to provide the most cost-effective and flexible test.

The system has to be capable of: testing a board in five minutes; suitability for a volume of 3000 products a month; no operator attendance during the test; being operated by non-technical staff; accessing all test points by test probes on one side of the board; including a debug facility; expanding for future product variants such as other RF bands and bandwidths.

The tests were split into three main areas:

• DC testing: Used for testing component values, supply voltages and current consumption and functional testing of the low-voltage shutdown, switch panel and LED indication;
• Built-in self test: 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.

Due to the product development schedule, the test system was developed in parallel with the product, which entailed five re-spins of the board design. However, due to how the test system was designed and specified with flexibility in mind, these PCB redesigns required only one change to the jig.

Using National Instruments’ hardware and software greatly enhanced the ability to carry out concurrent development, which was further supported by good communication between 4RF Communications and CPE and good project and configuration management processes.

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 optimisation in the RF calibration algorithms to ensure they operated efficiently.

The speed and functionality of the PXIe-5663 vector signal analyser and PXIe-5673 vector signal generator supported this algorithm process.

The Aprisa SR printed circuit board assembly included RF transmission and reception circuits and had to be tested out of its enclosure. As such, consideration had to be given to RF interference and screening in the jig design.

This was achieved using the CAD model of the product housing to machine an RF screening enclosure that formed part of the top plate of the jig. This shielding produced results from the test fixture that were close to those achieved with the board in its enclosure.

The radio has internal data encryption, which makes it impossible to generate simulated data streams to test the receiver sensitivity. Using the PXIe-5663 VNA, the radio signal recorded and retransmitted using the PXIe-5673 VSG at different levels to test the receiver sensitivity with actual data.

This meant that the encryption process could change in the future without affecting the test system software.

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

NI hardware and software platforms provided the capability and flexibility to support this development by helping to efficiently develop a highly reliable test system that met all client requirements and was delivered in time to meet 4RF’s tight product release schedule.