Virtual Instrumentation

With more than 6 million new measurement channels sold last year, National Instruments is a worldwide leader in virtual instrumentation. Engineers have used virtual instrumentation for more than 25 years to bring the power of flexible software and PC technology to test, control, and design applications making accurate analog and digital measurements from DC to 2.7 GHz. This document discusses both the compatibility and differences between virtual instrumentation and traditional instruments.

Table of Contents

1. What is a virtual instrument and how is it different from a traditional instrument?
2. How do virtual instrumentation hardware capabilities compare to traditional instrumentation?
3. Are virtual instruments and traditional instruments compatible?
4. How are virtual instruments and synthetic instruments different?

What is a virtual instrument and how is it different from a traditional instrument?

Virtual instruments are defined by the user while traditional instruments have fixed, vendor-defined functionality.

1. What is a virtual instrument and how is it different from a traditional instrument?

Virtual instruments are defined by the user while traditional instruments have fixed, vendor-defined functionality.


Figure 1. Traditional instruments (left) and software based virtual instruments (right) largely share the same architectural components, but radically different philosophies.


Every virtual instrument consists of two parts – software and hardware. A virtual instrument typically has a sticker price comparable to and many times less than a similar traditional instrument for the current measurement task. However, the savings compound over time, because virtual instruments are much more flexible when changing measurement tasks.

By not using vendor-defined, prepackaged software and hardware, engineers and scientists get maximum user-defined flexibility. A traditional instrument provides them with all software and measurement circuitry packaged into a product with a finite list of fixed-functionality using the instrument front panel. A virtual instrument provides all the software and hardware needed to accomplish the measurement or control task. In addition, with a virtual instrument, engineers and scientists can customize the acquisit ion, analysis, storage, sharing, and presentation functionality using productive, powerful software.

Here are some examples of this flexibility in practice:
1. One Application -- Different Devices
For this particular example, an engineer is developing an application using LabVIEW and an M Series DAQ board on a desktop computer PCI bus in his lab to create a DC voltage and temperature measurement application. After completing the system, he needs to deploy the application to a PXI system on the manufacturing floor to perform the test on new product. Alternatively, he may need the application to be portable, and so he selects NI USB DAQ products for the task. In this example, r egardless of the choice, he can use virtual instrumentation in a single program in all three cases with no code change needed.

Figure 2. Upgrading hardware is easy when using the same application for many devices.

2. Many Applications, One Device
Consider another engineer, who has just completed a project using her new M Series DAQ device and quadrature encoders to measure motor positi on. Her next project is to monitor and log the power drawn by the same motor. She can reuse the s ame M Series DAQ device even though the task is significantly different. All she has to do is develop the new application using virtual instrumentation software. Additionally, both projects could be combined into a single application and run on a single M Series DAQ device, if needed.

Figure 3. Reduce costs by reusing hardware for many applications.

How do virtual instrumentation hardware capabilities compare to traditional instrumentation?

An important concept of virtual instrumentation is the strategy that powers the actual virtual instrumentation software and hardware device acceleration. National Instruments focuses on adapting or using high-investment technologies of companies such as Microsoft, Intel, Analog Devices, Xilinx, and others. With software, National Instruments uses the tremendous Microsoft investment in OSs and development tools. For hardware, National Instruments builds on the Analog Devices investment in A/D converters.

Fundamentally, because virtual instrumentation is software-based, if you can digitize it, you can measure it. Therefore, measurement hardware can be viewed on two axes, resolutions (bits) and frequency. Refer to the figure below to see how m easurement capabilities of virtual instrumentation hardware compare to traditional instrumentation. The goal for National Instruments is to push the curve out in frequency and resolution and to innovate within the curve.

Figure 4. Compare virtual instrumentation hardware over time to traditional instrumentation.

Are virtual instruments and traditional instruments compatible?

Many engineers and scientists have a combination of both virtual and traditional instruments in their labs. In addition, some traditional instruments provide a specialized measurement which the engineer or scientist would prefer to have the vendor define rather than actually defining it themselves. This begs the question, “Are virtual i nstruments and traditional instruments compatible?”

Virtual instruments are compatible with traditional instruments almost without exception. Virtual instrumentation software typically provides libraries for interfacing with common ordinary instrument buses such as GPIB, serial, or Ethernet.

How are virtual instruments and synthetic instruments different?

A fundamental trend in the automated test industry is a heavy shift toward software-based test systems. For example, the United States Department of Defense (DoD) is one of the world’s largest customers of automated test equipment ( ATE). In order to reduce the cost of ownership of test systems and increase reuse, the DoD, through the Navy’s NxTest program, has specified that future ATE use an architecture built on modular hardware and reconfigurable software called synthetic instrumentation. The adoption of synthetic instrumentation represents a significant development in the specification of future Military ATE systems, and reflects a fundamental shift as reconfigurable software takes center-stage in future systems. Successful implementation of software-based test systems , such as synthetic instrumentation, requires an understanding of the hardware platforms and software tools in the market, as well as an understanding of the distinction between system-leve l architectures and instrument-level architectures.

The Synthetic Instrument Working Group defines synthetic instruments as “a reconfigurable system that links a series of elemental hardware and software components with standardized interfaces to generate signals or make measurements using numeric processing techniques”. This shares many properties with virtual instrumentation, which is “a software-defined system, where software based on user requirement s defines the functionality of generic measurement hardware”. Both definitions share the common properties of software-defined instrumentation running on commercial hardware. By moving the measurement functionality into user-accessible reconfigurable hardware, those adopt ing such architectures benefit by achieving greater flexibility and reconfigurability of systems, which in turn increases performance capabilities while reducing cost.