Modernizing Manufacturing Functional Test Systems for Uninterruptible Power Supplies

Author(s):
Larry Brown - MicroCraft Corporation

Industry:
Aerospace/Avionics

Products:
LabWindows/CVI

The Challenge:
Upgrading three automated test systems originally developed in 1994 for a leading manufacturer of uninterruptible power supplies

The Solution:
Using National Insturments software and hardware to increase the number of UPSs the manufactureer can test, improve teh established testing methods, decrease the overall test tiem, and reduce maintenance costs

Introduction
With continual requirements for improving accuracy, reliability, and speed in automated testing, manufacturers must upgrade automated test systems on a reocurring basis. Hardware improvements as minor as installing a CD-ROM or network card to improve data accessibility and transfer speed or as significant as refurbishing an entire system to replace outdated equipment are common in automated test applications. Software changes can expand the original test procedure, accommodate new hardware, or transform the existing test to work on a more modern operating system. Companies typically upgrade test systems to improve data accuracy, system reliability, speed, data analysis, data storage capacity, safety, and/or accessibility.

At MicroCraft Corp. (Raleigh, NC), we recently upgraded three automated test systems that we originally developed in 1994 for a leading manufacturer of uninterruptible power supplies (UPSs). Designed to supply constant AC and DC power, the UPSs provide 60 to 222 AAC nominal and 109 to 172 ADC maximum. With an inverter efficiency of 92 percent DC to AC, the UPSs also contain an onboard network of programmable boards that perform RS-232 communication for remote terminal monitoring, calibration, and emergency power-off.

The test systems measure voltages and current at various points in the UPS and communicates with the UPS via the onboard network to obtain data from an electrically erasable programmable read-only memory (EEPROM). By comparing the values measured by the test system to the EEPROM data, we can verify that the unit under test (UUT) is operating correctly and efficiently. The test systems can test each of the UPS models with independently formatted test sequences. In having the test systems refurbished, the manufacturer wanted to increase the number of UPS models they can test at one time, improve the established testing methods, decrease the overall test time, and reduce maintenance costs.

Hardware Changes Maximize Function and Minimize Cost and Time
Based on VXI modules controlled via GPIB with a 486/66 PC, the original test system could meet data accuracy and acquisition speed requirements only with the VXI platform. To lower replacement costs, shorten repair time, and increase system functionality, we replaced the original VXI modules with National Instruments measurement hardware and GPIB instrumentation. We also replaced the original relay matrix with two banks of 24-channel SSR backplanes housing a variety of solid-state relay modules controlled by a NI PCI-DIO-96 digital I/O board. We replaced the VXI-based digitizers with an NI 5102 digitizer and replaced the power meters with a Yokogawa WT1030 digital power meter. With a NI PCI-GPIB board, the user can configure the Yokogawa power meter to take a variety of measurements and calculations that the test system software previously had to calculate from several separate measurements. In addition to AC/DC voltage and current, the Yokogawa power meter calculates power, phase angle, frequency, power factor, and total harmonic displacement for voltage and current. We also increased the level of protection for the test equipment to protect components in the test system from current or voltage spikes when the UUT fails. We upgraded the PC to a 233 MHz Pentium II and increased the size of the hard drive for decreased repair cost and increased data storage, accuracy, reliability, and speed.

Software Upgrades Increase Compatibility and Networking
To begin the software changes, we replaced Windows 3.1 with Windows NT to make the test system more compatible with modern software applications, increased test system security, and integrated the test system into the manufacturer’s company-wide network. Additional software changes now control the new hardware components and accommodate the necessary changes in the driver-level software. We converted the test sequences in Microsoft Excel spreadsheets, to acquire the voltage, current, and calculated measurements directly from the Yokogawa power meter. Similarly, we converted the software modules to capture AC trip waveforms with the NI 5102 digitizer and to control relays with signals routed through the SSR backplanes. The software platform for the new test software is NI Measurement Studio upgraded from a previous version of LabWindows/CVI. With the integration of many departments using multiple programming languages, Measurement Studio provides the tools and flexibility to use the language best suited for each application and each programmer.

Conclusions
The UPS manufacturer has seen many benefits as a result of MicroCraft modernizing the test systems. Measurement accuracy improved from one to three digits of precision. The use of inline fuses to protect the system from power surges makes the system more robust. They can make more measurements with fewer steps, which decreases test time.

For more information, contact:

Larry Brown

Software Engineer

MicroCraft Corporation

3209-154 Gresham Lake Rd., Raleigh, NC 27615

Tel: (919) 872-2272

Fax: (919) 872-5822

E-mail: larry.brown@microcraftcorp.com

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