TechArchive

Original article date: September 1997

National Instruments has announced the first six products in its DAQ instruments family of PCI, ISA and PCMCIA interfaces, designed to turn a PC into a measuring instrument. ED MCCONNELL, Data Acquisition Product Manager of National Instruments, explains the philosophy.

We have reached the point where plug-in boards have most of the same capabilities and functionality of stand-alone instruments such as scopes, DMMs, and arbitrary waveform generators. DAQ instruments bring instrumentation capability directly into the computer so that users of PC-based virtual instruments have more tools from which to build advanced and powerful solutions for test, measurement, monitoring, and control applications.

The DAQScope, DAQMeter and DAQArb are compatible with Windows NT/95/3.1. The deliver features said to be respectively comparable to standalone ocsilloscopes, digital multimeters (FDMMs) and function and arbitrary waveform generators.

Traditional instrumentation has evolved to provide increasing levels of performance, which centres around the instruments’ primary functionality. For example, digital scopes and function generators ran faster, and DMMs became more accurate. While providing important benefits, performance increases alone are only part of the requirements of new instrumentation. In order to reduce overall system costs, flexibility has become as important as performance. Along with performance, demands from today’s instrumentation users now include high-performance analysis, measurement automation, and real-time data access. This poses obstacles for traditional stand-alone instruments.

A shift in architecture from stand-alone instruments to PC-based instruments combines performance with flexibility. For example, National Instruments’ DAQScope combines oscilloscope circuitry with direct PCI, ISA, and PCMCIA bus interface. Analog triggering and digitisation rates of 20MHz capture signals while high-speed PCI bus circuitry transfers data directly, in real-time, into PC RAM.

The DAQArb generates waveforms at rates up to 40MHz and is directly controllable by the CPU. The DAQMeter is a PCMCIA-based DMM for measuring ohms, volts, and current. Because data is directly read in and out of computer RAM, it is instantly available for display, analysis, and control. This rapid data accessibility is the key to providing today’s requirements for flexibility.

By combining PCs and DAQ instruments, users can build oscilloscopes, DMMs, and arbitrary waveform generators that be connected to the internet.. Instruments can send e-mail and interface to standard desktop packages such as MS Word and Excel.

The PCI allows data to be transferred directly into computer RAM and can seamlessly integrate with existing DAQ boards. Windows NT provides the stability required of stand-alone instruments. This is due to the separation of user code and data from the operating system code. Optimising the transfer of data directly to RAM is critical. To accomplish this, National Instruments uses its custom MITE ASIC as a PCI bus master interface. The MITE frees the microprocessor and optimises the transfer of data: it is capable of 132Mbytes/s burst transfers and more than 80Mbytes/s sustained transfers.

Having the microprocessor completely free from the data transfer task gives it maximum efficiency for displaying and processing the data. Software then defines how the DAQ instrument will be used. Included with each DAQ instrument is the corresponding VirtualBench software instrument. This means the DAQ instrument will function like a stand-alone equivalent. The newly equipped desktop computer replaces a variety of benchtop instruments, and the laptop becomes a portable, instrument-grade measurement platform. For example, the DAQScope is quickly converted into a spectrum analyser, 1/3 octave analyser, or integrated into a temperature and vibration monitoring system. Importantly, programming DAQ instruments is the same as for all other National Instruments measurement-quality DAQ plug-in boards. Users have a familiar interface and a standard means for extending DAQ instruments or integrating them into bigger systems.

The DAQScope compared to standalone instruments

(source: National Instruments)

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• National Instruments
• Tel: 01635 572400
• Fax: 01635 524395
• Contact: Andy Penney

September 1997