The PC-based test industry has made great strides toward fast, efficient test, and continues to push the envelope by introducing more powerful computing technology. For example, PC microprocessors, such as the Intel Pentium™, dramatically improve the number-crunching capability of test systems.
The increased processor speed is the most important advancement for PC-based test, said Walter Maclay, president of Strawberry Tree. Other advancements such as the improved operation of the data bus and the enhanced parallel port allow thousands of data points per second to be processed. So, every time the processor speed increases, more applications become possible and existing ones work faster, he said.
Additional hardware features that improve the test functions of plug-in cards include the advancements of A/D and D/A technology, said Amar Patel, product manager at National Instruments. These converters make it possible to put stand-alone instrumentation circuitry on a PC board. Not only do you have the flexibility of various plug-in cards and the resources of a PC, but you also have the functionality of a benchtop instrumentation system based on industry-standard computers.
These newer boards no longer are dependent on the PC for its processing power, said Hadi Shavarini, sales and marketing manager at Geotest. Now you can combine a fast PC and a large amount of memory with an intelligent instrument, resulting in a powerful test machine that can surpass a traditional instrument.
The PCMCIA slot on the laptop computer is another advancement for PC-based test. It can be used to expand and enhance the laptop’s I/O functions as a portable test device, said Kevin Kline, sales engineer for Quatech. The slot accepts a wide variety of PCMCIA cards, which can accept an increased number of outside signals while providing access to powerful computing analysis.
ISA vs PCI Bus
Another part of the PC-based test hardware picture to consider is the movement of data across the PC bus. Until recently, there only was the industry-standard architecture (ISA). Now you must choose between the ISA and the peripheral component interconnect (PCI) bus. To help decide which is better for you, familiarize yourself with the advantages and disadvantages of each.
The ISA bus is an 8- or 16-bit bus used by the IBM AT-class computers to communicate with add-on cards. It is an asynchronous bus running at 8 MHz, providing a sustained data transfer of approximately 2 MB/s for the 16-bit version and 1 MB/s for the 8-bit type.
During the last decade, ISA bus technology has evolved from being just an instrument-control facility for other buses, such as the GPIB, to a multipurpose platform, said Mr. Shavarini. The advantages of using ISA-bus boards include a small size, high-speed operation, and low integration costs. Couple this with intelligent plug-in boards that have a digital signal processor (DSP), a microprocessor, and on-board memory, and the boards can outperform conventional instruments.
Like any technology, the ISA bus can be used for appropriate or inappropriate applications, said Stuart Streiff, product development manager for PC Instruments. Products such as DMMs, multiplexers, and function generators are good matches for the ISA bus because they do not need to transfer large blocks of data between the instrument and the PC.
Plug-in instruments that depend on the PC to perform waveform manipulations or analysis, such as spectrum analyzers, digital oscilloscopes, and arbitrary waveform generators are not good fits for the ISA bus because they may need a bus with a higher data rate than those cards that off-load the data manipulations. A well-designed ISA instrument does not rely on the PC for waveform manipulations. For example, digital oscilloscopes from PC Instruments have an on-board DSP that performs a waveform averaging function, which reduces the bus bandwidth requirement.
The ISA bus provides an open architecture, a huge installed base, and a low-cost platform that is easy to design applications for, added Ms. McCurry. Hundreds of suppliers offer inexpensive software. The ISA bus also supports a 20-slot backplane and expansion kits that double the backplane size.
The wide variety of data acquisition boards and the ease of writing custom drivers are two advantages of the ISA-based boards, said Leslie Logan, product marketing manager at Data Translation. It is significantly easier to write a board-level customer driver for the ISA bus than for the PCI bus.
For example, to write a custom driver routine for an ISA board, you need the register map. Then it typically is just a matter of reading and writing to the base address and adding the offset. The PCI bus, however, requires that you understand the PCI interface chip on the data acquisition board before you can communicate with the board, she said.
One significant drawback of the ISA bus is its insufficient support for DMA. It has only a single DMA controller that services all requests through software.
Other weaknesses of the ISA include limited speed compared to the PCI bus, unspecified timing for critical signals, no capability to handle multiple masters, and a memory map of only 16 MB. The maximum ISA bus data speed is 2.5 MB/s compared to 132 MB/s for the PCI bus. The ISA supports only 16-bit processor performance, and typically does not supply plug-and-play capability.
The PCI bus provides better plug-and-play capabilities than ISA, and even VXI, at a lower cost, said Mr. Shavarini. Currently, the PCI bus is missing a standardization of the trigger bus similar to the one available in the VXIbus architecture. Once manufacturers agree on a standard trigger mechanism, the PCI-based instruments will provide an excellent foundation, and be one of the best choices for next generation test systems.
Although the data acquisition boards operating on the PCI bus provide a higher data rate than ISA boards and support 32-bit processors, they still do not have a large software base, said Ron Gilbert of Keithley Instruments. However, the newest PCs equipped with more PCI slots will rectify this shortage. PCI-based boards also offer plug-and-play capability, a BIOS configurable board, and efficient operation under a multiprocessing operating system.
The most effective PCI boards will augment the bus capabilities with DSP chips, said Mr. Gilbert. New generations of PC boards will have programmable DSP chips that take over the processing and file-management chores to free the PC to perform higher-order functions.
Presently, PCI-based instruments are not as popular as ISA-based boards, said Mr. Shavarini. This mainly is due to the availability of ISA boards. On the other hand, the PCI bus provides the best path for extending the PC into new test applications that demand high-speed transfers between plug-in boards and system memory.
The PCI bus, with significantly faster transfer rates than the ISA bus introduces new applications for the PC, said Ms. Logan. They include operations that previously were the domain of VME, VXI or external instruments.
The new features allow higher-speed acquisition without large amounts of on-board memory. The number-one reason for buying PCI boards today is the limited availability of the ISA bus in the near future. Today, it is hard to buy a PC without PCI slots. Soon it will be hard to buy one with ISA slots, she continued.
The higher bus speed of PCI is not a drawing card for many test applications, said Mr. Maclay. Approximately half of our customers use the parallel port to interface to data acquisition equipment because it is readily available and shows no sign of becoming obsolete. The parallel port also has been enhanced to offer a data transfer rate of up to 800 kB/s.
The Software Impact
The migration to the Windows standard started with version 3.1 because it dramatically improved the run-time user interface for PC-based test systems, said John Hughes, director of sales and marketing at Signametrics. The Windows graphical user interface (GUI) made it possible to embed functionality in applications that were too complex for a text-based user interface.
Microsoft Windows is both a blessing and a curse for PC-based test, said George Scherma, product marketing manager at IOtech. On the positive side, it has unified the GUI, something not even available with DOS or stand-alone instruments. Graphical software like Visual Basic or Visual C helps you quickly develop test programs without the need for an extensive training manual.
Packages such as Visual Designer from Intelligent Instrumentation have a very short learning period, and supply an on-line help feature to support immediate application design. Most of the test and measurement functions you need are built into these packages, so all you do is select the desired function from a pull-down menu, said Rob Winkler, product marketing engineer at Intelligent Instrumentation. Each function block replaces hundreds of lines of code, reducing development time often by a factor of 40 or more.
On the downside, Windows is optimized for the business community not the test world, said Mr. Hughes. Some inherent operating-system latencies and interrupt handling practices that make no difference to an accountant can cause major difficulties for an engineer.
The OS Impact
The impact of the operating system on PC-based test, especially the multithreading and multitasking versions, must not be overlooked because it can dramatically speed up your operation. Windows NT 4.0 is the next step if you want to broaden the functionality of the operating system and the GUI.
It is the first multitasking GUI-based operating system that test engineers trust to be bulletproof, said Mr. Hughes. Windows NT 4.0 gives a platform on which to build applications with sophisticated user interfaces and complex test functions.
Windows NT is becoming the operating system of choice in many segments of the test industry, said Mr. Winkler. One of the primary reasons is the inherent security NT offers, preventing applications from causing other applications to crash. NT also supports total memory protection for 32-bit applications.
Although Windows NT provides a more stable environment for test applications, there are special considerations to keep in mind when contemplating a move from Windows 3.1 or 95 to NT 4.0, said Marty Rice, design engineer at PC Instruments. First is the potential incompatibility of existing software with NT. Software that was able to perform low-level interfacing to hardware under DOS, 3.1, or 95 via I/O mapped, memory-mapped, or interrupt-driven expansion cards must be rewritten. Windows NT does not allow programs to access the hardware directly.
Windows NT uses multilayered software drivers for data acquisition cards and other devices, said Ms. McCurry. It has a kernel driver and a corresponding user-level driver. Whenever the user-level driver or application program must access the hardware, it goes through the kernel driver. Each crossing from the user to kernel space runs a minimum of 300 µs. The same event under Windows 3.1 and 95 takes from 33 ns to <1 µs. To prevent this slowdown, manufacturers must write drivers specifically for the NT environment.
The move to NT 4.0 means that most developers must communicate with the application at a higher level, agreed Mr. Hughes. Polling is out, and block DMA transfers are in. Forget about the registers in the device interface and minimize interrupts, advised Mr. Hughes.
The changes needed to go from DOS and Windows 3.1 or 95 to Windows NT 4.0 will complicate your life until the bugs are worked out and the environment becomes more stable, observed Leslie Brooks, marketing manager at Alligator Technologies. But more importantly, the implementation of the NT operating system has required board manufacturers to write separate 32-bit drivers for Windows NT and 95 software programs. As a result, you must learn installation setups for each operating system.
PC-Based Test Products
PC Bus Expansion Kit Allows
On, Off Cycling of Chassis
The Model PTRC-AT is a two-card kit with cables for connecting a host PC-AT bus to an expansion chassis. It provides the capability to power-cycle and change cards in the expansion chassis without rebooting the host. The transmitter card plugs into the host, and the receiver board is installed in the expansion chassis. The kit supports DMA and interrupt operations and facilitates any I/O bus address range. Bus mastering from the expansion chassis is not supported. $590. Acces I/O Products, (800) 326-1649.
Programmable Filter System
Has Remote Signal Conditioning
The AT-SYS-1000 is a multichannel filter and amplifier system that provides remote signal conditioning via an RS-232 port. It consists of a rack-mount chassis with up to 12 plug-in filter and amplifier cards that feature software control of cutoff frequency, gain, and AC/DC coupling. Five 8-pole filters including Butterworth, Bessel, Cauer, high-speed Cauer, and high-speed linear phase are available. Cutoff frequencies are programmable from 2 Hz to 200 kHz, and channel gain can be set from 0.5 to 1,000. Starts at $8,995. Alligator Technologies, (714) 850-9984.
IEEE 488.2 Interface Converts
Data to PCI Bus Format
The PCI-GPIB IEEE 488 interface board converts any PCI bus PC into an instrumentation control and data acquisition system. Up to 14 instruments can be connected with IEEE 488 cables. The CB7210.2 state machine bus manager and a 1,024-word FIFO buffer transfer data over the GPIB at rates >1 MB/s. The board provides the circuitry and software to implement plug-and-play installation with no jumpers, and supports Windows 95, 3.1, and DOS. $299. ComputerBoards, (508) 261-1123.
Boundary Scan Controller
Has Network TCP/IP Support
The Net-1149.1™ Boundary Scan Controller provides an intelligent interface with memory-behind-the-pin architecture for support of TCP/IP protocol over a local area network. It has four test access ports with a programmable JTAG clock rate up to 35 MHz, and includes 16 individually controlled general-purpose I/O lines. A scan function library helps create test programs. A programmable delay accommodates propagation delay in long test cables. $5,950. Corelis, (310) 926-6727.
Multi-Function DAQ Board
Provides 1.25 MS/s Input Speed
The DT3010 Multi-Function Data Acquisition Board is a PCI-based instrument that provides 1.25 MS/s analog input speed with 12-bit resolution. It includes 32 single-ended or 16 differential analog inputs, 16 digital I/O channels, two high-speed digital and analog outputs, and four counter/timer channels. The board has a custom- designed chip for the PCI interface and another to provide the counter/timer capabilities. It supports ActiveX controls, interfaces to HP VEE™, LabVIEW™, and the programmers’ software development kits for Windows 3.1, 95, and NT. $1695. Data Translation, (800) 525-8528.
Measurement Board Includes
Control for Input Power Supply
The EL-467 Power Supply Measurement Board is used in conjunction with the company’s EL-465 Electronic Load Controller and electronic loads to form a power supply test system. The EL-467 combines analog measurement techniques with A/D converters to record the input and output values of the power supply under test. The EL-467/465 functions as a virtual instrument when used with the company’s POWERWIN™ software. Typical tests include line and load regulation, ripple, output noise spikes, and transient response. EL-467: $1,999; EL-465: $1,895; EL loads: $999. Eltest, (508) 339-8210.
A/D Board for PCI Bus
Has 500-MS/s Rate
The CompuScope 8500/PCI is a PCI bus-compatible 8-bit A/D card with a 500-MS/s rate. The signal-to-noise ratio is 45 dB with a bandwidth of DC to 250 MHz. Memory buffers of up to 2 million samples are available. With GageScope software, it operates like an oscilloscope without writing any programming code. $6,995. Gage Applied Sciences, (800) 567-GAGE.
RS-232 and RS-485 Functions
Added to System
The EDAS 1001E-1A and the EDAS-1002E-1A Ethernet Data Acquisition Systems now supply RS-232 and RS-485 ports and I/O capabilities. The systems provide remote interfacing and control of instruments, terminals, and machines; and use a built-in TCP/IP protocol stack to interface with other host platforms. The 1001E-1A provides 32 channels of TTL digital I/O in four 8-bit ports. The 1002E-1A supports 16 digital I/O channels, two 12-bit analog output channels, and 16 single-ended or eight differential analog input channels. Call company for price. Intelligent Instrumentation, (800) 685-9911.
High-Voltage Adapter Offered
For Data Acquisition System
The WBK61 Single-Channel High-Voltage Adapter option for the company’s WaveBook/512™ Data Acquisition System is used in applications such as measuring line voltages to 1,000-V peak. It contains cables with probe tips and alligator clips. The WaveBook/512 includes WaveView, an acquisition and display software package for configuring the system and streaming data to disk. WBK61: $295. IOtech, (216) 439-4091.
Data Acquisition System
Multiplexes 4,096 Channels
DAS-Scan is a rack-mounted data acquisition system that can multiplex up to 4,096 channels from analog and thermocouple measurement devices into a single PC expansion slot. It scans at a rate of 2,000 channels/s. Up to 256 channels can be sampled at speeds up to 100,000 channels/s. The system is used for life-cycle testing, quality testing, and process monitoring applications. The company’s ASO-SCAN software provides driver support under Windows 3.1 and 95. From $3,350. Keithley Instruments, (800) 552-1115.
CompactPCI Interface Offers
Control for Industrial Computer
The CPCI-GPIB provides an IEEE 488.2 interface for the CompactPCI bus standard for industrial computers running Windows NT or 95. It helps you integrate GPIB-based instruments into a CompactPCI computer. The CPCI-GPIB includes the multiplatform NI-488.2™ driver software to move GPIB applications to the CompactPCI-based computers without modifying or recompiling the applications. The transfer rates are 7.7 MB/s using the HS488™ protocol. It is compatible with the company’s instrumentation software. $495. National Instruments, (800) 258-7022.
PC Card Has Four
Tracking Converters
The 5718A001 PC/104 Card is a 16-bit module that incorporates four transformer-isolated synchro/resolver-to-digital tracking converters. The transformer isolation ensures galvanic separation from the equipment-under-test and protects against voltage spikes. The input voltage, frequency, and synchro or resolver format are individually specified for the converters. On-board self-test diagnostics include reference, signal, and tracking loss for each input. Call company for price. North Atlantic Instruments, (516) 567-1100.
Multiplexers Provide
DC to 200-MHz Switching
The PCI-702 and PCI-703 8-to-1 Multiplexers provide DC to 200-MHz signal switching in a half-size ISA card. The boards use stripline circuits and coaxial relays to provide 2.2-ns propagation delay and 200-ps channel-to-channel skew. The signal flow is bidirectional for both multiplexers. The PCI-702 supports an on, off, manual, and an auto-termination mode. The company’s BenchCom™ software package with 16-bit and 32-bit device link libraries, programmer libraries, and test control drivers is included. PCI-702: $995; PCI-703: $795. PC Instruments, (216) 963-0800.
PCMCIA Adapter Offers
Analog and Digital Channels
The DAQP-308 Type II PCMCIA Data Acquisition Card has four differential or eight single-ended 16-bit A/D input channels, two 12-bit analog output channels, and four digital I/O channels. It provides a sampling rate from 0.006 Hz to 100 kHz, an input range of ±10 V, and programmable gains of 1, 2, 4, and 8. The card contains a 2k data FIFO buffer and a 2,048-entry scan FIFO buffer. Scan speeds are selectable from 10 ms/channel to 40 ms/channel. Call company for price. Quatech, (800) 553-1170.
ISA- and PCI-Bus Cards
Sample at Rates to 55.8 kHz
The SI-DSP1600-ISA and SI-DSP1600-PCI are DSP-based data acquisition cards featuring four analog inputs simultaneously sampled at 16 bits with sampling rates from 39 Hz to 55.8 kHz. On-board timing circuitry provides programmable sampling rates with ±1-Hz precision. The ISA card handles transfer speeds up to 600 kB/s. The PCI card achieves transfers of 132 MB/s with bus mastering. Two analog outputs can update at rates up to 55.8 kHz with 16-bit resolution. Starts at $1,500. Sheldon Instruments, (800) SHELDON.
Calibration of 4-1/2-Digit DMM
Performed With PC Cover On
The SM-2010 Digital Multimeter has 4-1/2 digits of resolution and accuracy, and features autoranging operation. The board only needs a 2-minute monthly self-calibration and a yearly external source calibration, performed with the PC cover intact. All measurement modes are isolated and protected to 250 V. Driver software supports DOS-, Windows 3.1-, and Windows 95-based applications. $695. Signametrics, (206) 524-4074.
Portable System Connects
To Parallel Port
The DATAshuttle-Express family compliments the company’s DATAshuttle line of parallel-port data acquisition systems. It features acquisition speeds of up to 100 kHz, 16 differential analog inputs (12-bit), two analog outputs (12-bit), two counters/timers (16-bit), and a 24-line digital I/O parallel port interface. Each channel contains a switch for selecting voltage and current, and a test switch for simulating a transducer or sensor signal to the computer. $1,795. Strawberry Tree, (800) 736-8810.
PC-Based DSO Offers
Two Channels and 8-Bit ADCs
Four PC-based digital storage oscilloscopes ranging from 60 MHz to 100 MHz are ISA bus-compatible plug-in cards that operate under the Windows® 3.× operating system. The DSOs have two channels, one 8-bit analog-to-digital converter for each channel, and 32k storage memory, and perform 40 MS/s per channel. Test procedures can be set up and stored. $749 to $1,399. TC Instruments, (909) 622-2006.
Copyright 1997 Nelson Publishing Inc.
June 1997