Next Generation Switching: Density, Price, and SPECS

The ATE Challenge

For design engineers, the ultimate goal of development is a superior product, unmatched in innovation. For test or automated test equipment (ATE) engineers, the development of that same product might have very different ramifications – more often than not, innovation is required to test innovation. Luckily, the test and measurement industry has supplied highly accurate and responsive instrumentation for years, allowing the necessary verification checks to be made. There are many different platforms on which these measurements can be taken, and thus begins a significant amount of comparison shopping to meet the design needs of the test systems.

Once the ideal measurement equipment has been chosen and a suitable software package selected, there is still a missing piece of the puzzle. Some form of switching or signal routing is almost always required to expand the channel counts of the instruments or provide the necessary flexibility of measurements for optimal equipment usage and test throughput. Even more than measurement devices, switching has become heavily commoditized, yielding a plethora of vendors and integrators able to offer solutions. However, the choice for switching, unlike most instruments, does not focus on resolution and frequency – a switching system is often chosen or eliminated based on channel count and price per channel. Switch vendors must meet these two criteria, or they have little chance of competing.

It’s often said that switching hardware and development time can account for up to half the cost of an automated test system. With such time and money at stake, it’s important to add value to the process in ways other than just relay density and price per channel. National Instruments has focused on five additional elements to improve the development time and modularity of test systems. These features can be summarized in the acronym SPECS:

· Superior software support
· Predictable switch lifetime
· Ensured quality and reliability
· Compliance and safety
· Scanning support

Each of these points adds value to the test development process, from software integration to safety factors. Make no mistake about it – density and price per channel rule today. NI offers high-density matrix, multiplexer, general-purpose, RF, and relay drive modules in both the PXI and SCXI platforms at an affordable price. But, the elements of SPECS can make the difference in maintainability and time-to-market, ruling tomorrow. Let’s take a look at each of them individually to understand how they fit into ATE design.

Superior Software Support

In order to tie every facet of a test system together, an efficient and intuitive software environment is necessary. Many software packages are on the market today that enable rapid development and deployment of test code (most notably NI LabVIEW 7 Express and NI TestStand 3.0) allowing test engineers with varying backgrounds to develop sophisticated test systems. NI recognizes the importance of software integration with the hardware platform of your choice.

Every NI switch module has been designed specifically for integration with the industry-standard application software tools. For example, the NI-SWITCH driver application programming interface (API) offers native LabVIEW I/O controls to identify NI switch modules and simplifies error checking with LabVIEW 7 Express’s new error handling. Also, all NI-SWITCH examples are searchable in the NI Example Finder, giving you easy access to a well-established example program database from within all NI software environments.

The NI-SWITCH driver also supports improved debugging through NI Spy, LabWindows/CVI user protection, and a number of other features for application development environment integration. As an IVI-compliant driver, it exports the complete functionality of NI switches through an easy-to-use interface, whether programming in C++, Visual Basic, LabWindows/CVI, or LabVIEW.

In addition to traditional programming environments and test executives, switch-specific software packages are beginning to emerge. NI Switch Executive, named one of EDN's Top 100 Products of 2002, is an intelligent switch management and routing application. With NI Switch Executive, you gain increased development productivity by interactively configuring and naming switch modules, external connections, and signal routes. You also increase test code reuse and system performance with switch programming in conjunction with TestStand, LabVIEW, LabWindows/CVI, and Measurement Studio.


(For more information on NI Switch Executive, visit www.ni.com/switchexecutive)

Predictable Switch Lifetime

Relay lifetime is a commonly listed specification of switch modules. This is usually on the order of hundreds of thousands or millions of cycles and will depend on the type of relay found in the switch module. National Instruments offers electromechanical, reed, and solid-state relays that have considerably different lifetimes associated with them.

From a maintenance perspective, however, it is a challenge not only to keep track of modules and corresponding relay types, but also how many times each relay has been actuated. It can be a difficult question to answer without paying very close attention to your test system.

To simplify this process, all new NI switch modules track and store the number of relay cycles onboard the module. Engineers can use the relay count information to help predict when a switch module is near the end of its life. With this capability, you can perform preventative maintenance and help avoid costly downtime.

As Figure 2 shows, the relay count information is easily accessible through the NI-SWITCH API in LabVIEW.


Similar function calls are also available in text-based languages (LabWindows/CVI, C++, or Visual Basic).

Ensured Quality and Reliability

Switching systems are often used in manufacturing environments, where harsh conditions exist on a daily basis. Therefore, it’s important to use equipment that is durable enough to resist any temperature, vibration, or power fluctuations that may occur. With weak equipment, a large investment can quickly evaporate.

All NI switch modules go through HALT (Highly Accelerated Life Testing) to ensure reliability and quality standards are being met. HALT is an R&D process that stresses a product well beyond normal shipping, storage, and in-use levels to determine (and correct) product weaknesses. Examples of the typical stresses to the module include temperature variations, power cycling, and 6-axis random vibration. With these processes occurring in the development phase, defects are less likely to be exposed in the manufacturing (or production) phase.

Compliance and Safety

Before any NI switch module is released to manufacturing, it must first be recognized by the appropriate certification bodies. Depending on the country, state, or principality, certifications can be necessary for use inside the region. For some certifications, like CE, this can be done in-house. For many modules, however, we require additional compliance testing from a third-party certifications body.

All NI modules that have a voltage rating greater than 60VDC or 30VAC and 42.2Vp are considered high-voltage modules. These modules are certified by UL (and VDE or Demko, when necessary), to ensure they meet all safety regulations. Specifically, the following standards are always met on high-voltage modules:

Safety
IEC 61010-1, EN 61010-1
UL 3111-1, UL 61010B-1
CAN/CSA C22.2 No. 1010.1

Electromagnetic Compatibility
Emissions ........................... EN 55011 Class A at 10 m FCC Part 15A above 1 GHz
Immunity............................. EN 61326:1997 + A2:2001, Table 1
EMC/EMI........................... CE, C-Tick, and FCC Part 15 (Class A) Compliant

CE Compliance
Low-Voltage Directive (safety) .................................................73/23/EEC
Electromagnetic Compatibility Directive (EMC) ......................89/336/EEC

Scanning Support

Maximizing throughput is a common requirement in automated test applications. To improve system throughput, many NI switch modules support scanning. Scanning improves throughput by downloading a list of connections to the switch modules and cycling through the list using an event (trigger) without any interruption from the host processor.

The most efficient method of scanning is hardware-timed handshaking because it uses two-way communication between a switch module and an instrument. For example, if the instrument is a digital multimeter (DMM), it will issue a digital pulse after each measurement that triggers the switch to close its next connection in the scan list. After each scan list connection, the switch will issue a pulse that will trigger the DMM to take its next measurement. This process ensures optimal throughput because the entire measurement sequence is hardware-timed and has no additional software delays.
Testing innovative products requires innovative test systems that deliver more than just density and price. ATE engineers can benefit greatly from looking at other factors as they configure test systems. The SPECS acronym outlays a list of features provided by NI switch modules designed to reduce frustration, increase maintainability, and improve time-to-market in product development cycles.

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