Using Virtual Instruments to Reduce Measurement Costs

Like most engineers, you have probably tried to find ways to reduce the cost of your automated test or measurement application. This document will show you how National Instruments can help engineers accomplish this task. The document begins with an overview of the five major cost sources in the process of developing a measurement system (see the cost column in Table 1 below). You will learn how to apply virtual instrumentation technology to reduce individual costs and thus reduce the overall measurement cost.

Table 1: Cost sources and corresponding cost control solutions for developing measurement systems

Cost of measuring application systems

Please try to recall the time you spent on the previous measurement system. You may have spent most of the project time on setting up hardware configuration and developing applications. If you carefully examine the development process of such a measurement system, you will find that the cost mainly comes from five places (see Figure 1 below). The source of the data in Figure 1 is a survey of 37 engineers from different industries and countries on the costs they spent on their recently developed test or measurement systems. You can find that on average, they believe that the price of hardware and software is the largest single cost source, while the time cost of other items combined accounts for the vast majority of the overall cost. (Note: Time cost is calculated at $100 per hour)

Figure 1: Five sources of cost in developing measurement applications

For the past 26 years, National Instruments has been committed to using virtual instrumentation to reduce your overall measurement costs. Virtual instrumentation combines software with off-the-shelf hardware technology and takes advantage of the high performance and flexibility of today's personal computers to effectively reduce each cost. "National Instruments' system can effectively reduce costs and save time while taking into account the repeatability of results and system life." said Wolfram Koerver of SEA Datentechnik GmbH.

Decrease the time it takes to specify your system

Deciding on the measurements you want to make and the types of advanced analysis you want to perform can be time consuming. Once you’ve made your selections, you then have to decide how to build the measurement system. To reduce the time it takes to specify your system, National Instrument offers a wealth of online resources. DAQ Designer (available for trial at ni.com/advisor or a free CD at ni.com/taiwan) walks you through the steps required to specify your system; it guides you through selecting the right sensor or signal type, sampling frequency, number of channels, and other parameters, and then it lists the hardware and software solutions that best meet your needs.

Consulting services from third-party vendors, also available on ni.com, recommend products to complement your hardware and software choices, such as sensors and PCs that can operate in harsh environments. These tools can help save time by quickly identifying the products that best fit your application.

Figure 2: DAQ Designer CD-ROM and Online Edition can help you save time on developing a DAQ system

Reducing the cost of hardware and software

The most significant cost in a data acquisition system (DAQ system) is, of course, the price of the hardware and software. Most people try to reduce costs in this area, but they don't consider whether the overall development cost is also reduced. Figure 1 shows that the price of hardware and software only accounts for 36% of the total cost, while the time and money spent on other aspects account for the vast majority of the total cost.

Virtual instrumentation not only reduces time costs, but also minimizes the cost of hardware and software. To understand why, please refer to the price and performance trends of the off-the-shelf technology used by National Instruments in its data acquisition devices: Figure 3 shows the price trend of 12-bit and 16-bit analog-to-digital converters over the past few years; please note that the cost of purchasing a 12-bit converter in the early 1990s can purchase a 16-bit converter today! Trends like this allow National Instruments to continuously provide better data acquisition performance at comparable or lower prices. There is a similar trend in the personal computer industry - the famous Moore's Law (see Figure 4); under this law, processor performance continues to increase while prices continue to fall. This trend is also beneficial to users of virtual instrumentation, because they can get higher software performance by simply upgrading their computers.

Figure 3: Price and performance trends of DACs and NI data acquisition devices

Figure 4: Moore's Law - Intel processor performance improvement trend since 1970


In general, NI has been continuously improving the engineering cost structure to reduce the data acquisition cost for customers. In 2002, NI released the NI6013 and NI6014 multifunction data acquisition devices, setting a new low price for 16-bit data acquisition technology. In 2004, NI added new low-cost digital interface products and analog output products to the product line, which reduced the cost per channel by 30% and 70% respectively compared with earlier similar devices.

Reduce the time cost of setting up configuration

Once the specifications are established and the measurement hardware is purchased, the real work begins. You must first install the hardware and software, set all the necessary configurations, and confirm that every part of the system is working properly. This stage also includes all necessary hardware installation, such as sensor connection, wiring, and preparation of the device under test. As you can see from Figure 1, this step alone can account for 23% of the total cost of a typical system, so saving this time can save a significant amount of the total cost.

Many NI data acquisition devices use the latest external computer bus specifications, such as USB, FireWire, and PCMCIA, which eliminates the trouble of shutting down and opening the case. In addition, NI-DAQ software can automatically detect newly installed devices, which can save a lot of installation time, especially if you plan to use the same hardware in different locations.

NI-DAQ also includes other configuration software that can reduce time. NI MAX (Measurement and Automation Explorer) can automatically detect and configure all data acquisition devices, GPIB devices, FieldPoint devices, PXI devices, and VXI devices at once. You can also perform self-diagnostic tests to ensure that all devices are working properly. You can quickly view the signals of each channel on the data acquisition device through the test panel.

To further simplify the installation and connection process, NI is currently participating in the development of the IEEE P1451.4 standard for transducer electronic data sheets (TEDS). Basically, TEDS is a small memory chip integrated into the sensor that provides the computer with information about the sensor in digital form, allowing the computer to convert the sensor's voltage or current data into appropriate engineering units, such as "℃" or "kg". You can imagine that TEDS will help you save a lot of configuration time, especially when it comes to multi-channel sensor applications. For those "legacy" sensors that do not include TEDS, NI also provides a virtual TEDS database where you can search and download the sensor's TEDS data, so that even if you do not have a real TEDS sensor, you can still enjoy the benefits of TEDS.

Reduce the time cost of developing applications

Developing the code for measurement applications usually accounts for 30% of the total cost. If you can use time-saving application development tools, you can greatly reduce this stage of cost. National Instruments' data acquisition software is tightly integrated with the NI LabVIEW development environment, saving customers a lot of costs.

NI-DAQ can help you save considerable time during the software development phase. The DAQ Assistant allows users to configure data acquisition in an interactive way, including timing, triggering, and sensor unit conversion. The whole process only requires three simple steps:

1. Select your DAQ "task" type (such as thermal coupling input or digital output)

2. Select one or more physical channels to be used on the DAQ device, associate them with the "task" and enter the relevant information for voltage or sensor unit conversion so that the data can be displayed in the appropriate units later.

3. Set the timing, triggering and sampling related items (such as continuous waveform input, 1kS/s sampling frequency, and start the operation with a digital trigger signal) With

the DAQ Assistant (Figure 6), there is no need to set up a large number of data acquisition functions, which can help you quickly build a test system. If necessary, you can even go back and easily modify some parameters without having to reconfigure the entire system. DAQ Assistant is integrated with LabVIEW's spectrum measurement, histogram and other analysis tools. The captured data can be directly sent to these analysis tools without any pre-processing or additional programming.

Figure 6: DAQ Assistant allows users to interactively create data acquisition tasks and is tightly integrated with the Express Analysis VIs in LabVIEW

For more complex data acquisition applications, you can use DAQ Assistant to automatically generate modifiable NI-DAQmx code for use in LabVIEW, C, or Measurement Studio.NET. Using this code as a starting point, you can build from code that has been proven to work correctly (rather than writing it from scratch), saving you time that would otherwise be spent reading manuals and trying to configure your DAQ device.

NI-DAQmx also includes a technology called "virtual channels." Each virtual channel corresponds to a physical channel and contains related voltage, sensor, or custom unit conversion information that the user can enter through an interactive menu. Because virtual channels can be used in LabVIEW or any other NI development environment, you can save time setting up unit conversion options individually. Comparing the two LabVIEW block diagrams in Figure 7 below, you can see that without virtual channels, you would have to spend a lot of time just to convert "thermal coupling voltage" to "℃". In contrast, virtual channels allow you to focus on other parts of the measurement application.

Figure 7: In this thermocouple measurement, virtual channels can reduce your development time by reducing the necessary settings to convert data to "℃".

Another way to reduce development time is to develop based on a sample program. The NI-DAQ driver will install a variety of sample programs to your platform, and you can find more than 3,000 sample programs on the ni.com website. Some examples are general-purpose, while others focus on specific applications. With such a large database, you can find an example that is very close to your application needs, and the example will clearly point out all aspects of the application system that need to be considered, from data acquisition to analysis to data display.

Reduce the time cost of system verification and hardware calibration

. Virtual instrumentation relies heavily on software to improve productivity and provide flexibility. For example, during the verification and calibration phase, NI data acquisition devices can be calibrated entirely in software. You don’t have to manually adjust the voltmeter or remove any hardware from the computer. Instead, you call a simple function, either through program code or from MAX (see Figure 8), and the rest of the calibration process is handled by the software.

Figure 8: The interactive auto-calibration feature in MAX allows you to calibrate your DAQ device in the software.

To get more accurate results, you may want to perform a system calibration of your entire hardware system. For this purpose, NI also provides system calibration software for you to download online (NI Developer Zone) to save some time. These VIs are developed for thermal coupling systems, but you can modify them to suit any type of application.

Thorough debugging and testing of your measurement application system can also be time-consuming, and you may not get useful error reports. NI-DAQ 7 takes a new approach to reporting errors: reporting the root cause of the error and possible solutions, rather than just reporting a set of error codes for the user to read in the application manual. Figure 9 below compares the error reporting method of NI-DAQmx with the error reporting method of a certain vendor.

Figure 9: NI-DAQmx's incorrect reporting method and a vendor's incorrect reporting method.

Summary Looking

at the five major cost sources for developing measurement applications, you can see that the total cost includes not only hardware and software expenses, but also "hidden" time costs. We provide data acquisition software to increase your productivity, we provide online tools to help you make decisions and get started quickly, and we provide accurate and reliable hardware at reasonable prices to help you reduce your overall costs.

These cost reductions will gradually help you shorten your time to market and promote more competitive pricing. To confirm this more clearly, you can examine Table 2 below. This table uses a sample system with a hardware and software cost of $50,000. The time cost is calculated based on the ratio in Figure 1. It can be seen that the overall system cost savings by using virtual instrumentation can be as low as 10% and as high as 40%.

Table 2: Cost savings from using virtual instrumentation for a sample application system with hardware and software costs of $50,000