Customer Solutions

PXI-Based RF Component Testing System for Wireless Security Systems

Author(s):

Douglas Pete, B&B Technologies, an NTS Division

Industry:

Electronics

Product:

LabVIEW, Modular Instruments, PXI/CompactPCI

The Challenge:

Developing a system to test the power, frequency, and bit pattern transmitted from wireless security system components. The test system is used in the manufacturing plant by a production operator to test the various components and determine whether they receive a pass or fail rating. Thousands of tests may be performed each day.

The Solution:

Mounting an antenna to the NI PXI-5660 RF vector signal analyzer and the NI PXI-8186 P4 2.2 GHz controller housed in the NI PXI-1042 eight-slot chassis.

The PXI-1042 8-slot chassis was used for this wireless security application.

A client needed a test system to assist quality control in identifying defective radio frequency (RF) components for use in wireless security systems. Each component has to meet or exceed a specified minimum power level, be within a specified frequency range, and match a recognized bit pattern for it to be accepted. A production engineer enters the test parameters into the software and a production operator performs the testing. The operator starts the test from within the software and presses the button on the transmitter. A 400 MHz signal is received by the NI PXI-5660 vector signal analyzer then demodulated to determine the bit pattern. The bit pattern, measured power and measured frequency are compared to the test parameters entered by the engineer and a pass/fail indicator is displayed. The system is then ready for the next test. All data is saved in a test file along with the pass/fail statistics for the test.

We needed to test two types of RF components for each wireless security system. The first was a key chain remote, which arms and disarms the master alarm unit. It consists of two buttons (ARM and DISARM). When each button is pressed, a signal, which consists of two peaks, is transmitted. If both buttons are pressed simultaneously (PANIC mode), the alarm is activated on the master alarm unit. The peaks are expected to be centered around 400 MHz and be about 50 kHz apart from each other. The test system measures the peak positions and peak deviations. The demodulated data results in a communication packet consisting of 108 bits transmitted at 2 kbps. Multiple packets are transmitted each time a button is pressed to ensure a packet is received. The measured bit pattern is then compared to the expected bit pattern to determine if they match. The average power during the   transmission is also measured. Finally, the test system displays a PASS or FAIL indicator on the computer monitor depending on whether or not all measured values are within specification. If the component fails, a message is displayed with the failed parameter(s) and its value.

The second type of component is a motion detector. When motion is detected, a signal is transmitted and the receiver sets off the alarm. Each transmission is similar to that of the key chain remote. The same criteria are used for testing with the exception of using a different power specification. The reason for this testing is to eliminate components that are out of the specification even if they still communicate with the system. This reduces the chance of components failing in the future.

The manufacturer of the security system was looking for a compact, inexpensive test system, to operate at the plant within a two-week period. We selected an NI PXI-5660, which consists of a 2.7 GHz downconverter, and a 64MS/s high-spectral-purity digitizer, a PXI-8186 2.2 GHz Pentium 4 embedded controller and a PXI-1042, 8-slot chassis. An antenna was connected to the input of the downconverter using RG58 cable and a gold SMA connector. The antenna assembly was connected to an L-bracket that was mounted on a 2-slot wide blank faceplate on the front of the PXI chassis. By choosing this hardware, we acquired signals from the RF components within minutes using the LabVIEW RFSA and NI-SCOPE examples. In addition, the high measurement throughput of the PXI-5660 allowed us to keep the test time short so that thousands of tests can be performed each day.

As a newly hired system integrator and beginner LabVIEW programmer with no prior experience testing RF systems, I suspect that successful completion of the project within the specified timeframe would not be possible if we had not used LabVIEW. The large selection RFSA examples along with the Spectral Measurements and Modulation Toolkits allowed us to quickly develop the software.

Using LabVIEW 8.0, we developed a user interface that would be easy to operate in a production environment. We used large buttons that could be activated using keyboard shortcuts along with large indicators to simplify testing for the operator.

The first step for operating the RF component tester is to enter the test settings such as minimum power, acceptable frequency range, bit patterns, and test timeout.

The operator enters a filename, which describes the batch of components tested. The test results for that batch of components will be stored in this file.

A separate test window appears when the TEST button is pressed on the main panel. An indicator displays the batch name, and test number. When the operator is ready, testing can begin by clicking on the test button or pressing the space bar. The test timeout entered in the configuration step defines the maximum amount of time that the tester continuously looks for a signal. The test ends as soon as a signal with a recognizable bit pattern is detected. All measured values are displayed in the test window after each test. If a signal is not detected within the time allowed, the test fails and the operator can choose to retest to accept the failure. If a signal is detected with an acceptable bit pattern but does not meet the frequency or power specification, the operator again has the option to retest or accept.

The engineer or operator can analyze the test data by opening the data file. The file consists of a header with date, start time, type of component, and configuration settings. For each component tested all measured values are recorded along with the pass/fail result. The pass rate, total number of components tested and stop time are also written to the file.

We provided the client with a compact, inexpensive, flexible, and expandable system for testing its product in about two weeks. The test system is flexible enough to quickly make changes such as increasing resolution bandwidth and frequency span. After completion of the RF component tester, the manufacturer realized that about 25 percent of its components did not meet the specification even though they could arm, disarm, and alarm the master alarm unit. The manufacturer quickly resolved the problem before sending out security systems with a potential for failure.

For more information, contact:

Doug Pete

B&B Technologies, an NTS Division

Albuquerque, NM

Tel: (505) 345-9499

E-mail: dpete@bbtechno.com