Figure 1. An industrial PC populated with data-acq cards from United Electronic Industries forms the heart of the PSTN21 test stand from Genesys IBS Ltd. This rack of equipment allows users to check a wide variety of telecomm-related parameters and characteristics and thereby meet the exploding demand for test equipment arising from the European Community's R&TTE Directive.

As a result of this dramatic shift in policy, the demand for inexpensive, flexible telecomm testers is about to mushroom as manufacturers look for ways to check their latest systems at all phases of the development process. In addition, testing labs will be looking for equipment that allows them to not only conduct tests quickly but also to change over to test different types of devices. To fill this market gap, Genesys IBS Ltd (Monmouth, S Wales, UK) has developed the PSTN21 Test System (Fig. 1), a PC-based test stand that relies heavily on PCI-bus data-acq cards from United Electronic Industries (Watertown, MA, www.powerdaq.com). The system can test for a wide variety of telecomm-related parameters and characteristics. Among them are insulation resistance, ring signal characteristics, impedance unbalance about earth, resistance to earth, equipment-under-test transient performance, DC characteristics, sending-level limitations, spectral analysis, dial tone and call-progress tone recognition, DMTF dialing, loop disconnect (pulse) dialing, automatic calling and repeat attempts, and series connection. The system comes with ISO 9001 calibration certificate. As an added bonus, an international "call progress tone database" comes preloaded with more than 400 supervisory tones, and users also get a preloaded "ring signal database." Besides taking single samples, the test stand can calculate measurement uncertainty information for each test, and a report generator saves test summaries and data in Microsoft Office format.

Need for flexibility

From this rather lengthy list of test types, it's easy to see that this system requires extreme flexibility. Thus the designers chose a PC platform along with general-purpose data-acquisition cards. On top of a 748-mm high 19" free-standing rack sits a color monitor and keyboard. The rack incorporates an industrial-grade PC chassis along with specialized telecomm test equipment such as a serially controlled matrix switch. When tests are running, though, a UEI card, the PD2-MF-16-1M, handles most of the heavy lifting. The system multiplexes at most two of the 12-bit analog inputs, which run at an aggregate rate of 1.2 MHz. This capability meets the test stand's requirement of sampling at 550 kHz/channel, which allows it to perform frequency analysis at ranges to 200 kHz. To handle the unusual conditions of the telecomm industry such as high-voltage ac and dc circuits, Genesys designed its own signal-conditioning front ends.

The firm selected the UEI card, explains managing director Nick Evans, because it was the only one at the time that combined the required number of high-speed analog inputs along with analog outputs and some digital I/O. Meanwhile, the number of digital I/O points the system requires has grown to exceeds 70, more than the 16 inputs and 16 outputs on the PowerDAQ II card, so the designers have had to turn to an auxiliary board for that capability.

Figure 2. A graphical user interface that controls the underlying HP VEE program makes it easy for test technicians to run existing tests, and being based on VEE also allows design engineers to set up new tests with considerable ease and efficiency.

The software that controls the test stand is written in HP VEE. Genesys chose that application-development environment for several reasons. First, the engineers felt that it gave them more productivity and the ability to write programs faster than other test-program environments. It's also easy and fast to take a program written to address tests based on standards in one country and adapt that program to test against standards in other countries. Second, it allows them to write menu driven applications that are necessary because the end users are oftentimes not familiar with the details of running telecomm tests (Fig. 2). The system must be extremely easy to use because, thanks to the R&TTE Directive, people are getting into telephony without understanding everything that's going on in a piece of user equipment.

Genesys' development team did have to ask UEI to supply the source code for the HP VEE drivers, which the card supplier was happy to do. The compiled versions, says Evans, placed too many restrictions on changing the card's sampling rate programmatically. But when given the full source code, the engineers were able to quickly find a way to achieve the sample-rate flexibility the test stand needs.