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Choosing Components for a Stand-Alone NI CompactDAQ System

What Is Data Logging?

Data logging is a common measurement application. In its most basic form, data logging is the

measuring and recording of physical or electrical parameters over a period of time. The parameters can

be temperature, strain, displacement, vibration, pressure, voltage, current, resistance, power, and many

others. Many data-logging systems, however, require more than the acquisition and storage of data.

Inevitably, you need the ability to analyze and present the data to determine results and make

decisions. A complete data-logging application typically requires most, if not all, of the elements

illustrated in Figure 1.

Figure 1. Your data-logging system often requires more than just acquiring and logging.

Data-logging systems can typically be grouped into two categories: portable data-logging systems and

embedded monitoring systems.

Portable data-logging systems are designed to move from test to test. To achieve this, your system

needs to be compact and rugged while maintaining its ability to acquire, log, and process data. An

example where you could use portable data logging is during vehicle testing, often referred to as in-

vehicle data logging.

Embedded monitoring systems are usually embedded in harsh, industrial environments that are not

easily accessible. In addition to a compact and rugged solution, these conditions also require remote

access and/or stand-alone monitoring capabilities. If you are using advanced analysis, such as sound and

vibration analysis, your system should also have a powerful processor. An example of embedded

monitoring is using machine condition monitoring to supervise the health of machines and to even

predict failure.

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Key Components of an NI CompactDAQ Stand-Alone System

An NI CompactDAQ stand-alone system is composed of several different elements. These elements

include an electrical signal you want to measure, a module to measure and digitize the signal, a chassis

to synchronize signals and transfer data to the PC or controller, an OS and software to control the

chassis and modules, and a display to visualize the data. These elements can be integrated in multiple

ways to create a system that is optimal for your application.

1. Signal

2. Modules

3. PC/Chassis

4. OS

5. Software

6. Display

Signal

The first step in building a measurement system is to determine what physical or electrical phenomena

you want to measure. These phenomena could include light, vibration, sound, voltage, strain, current,

and more. If you need to measure a physical phenomenon, then you will also need to choose a sensor or

transducer that converts that phenomenon into either an analog or digital electrical signal. Table 1 lists a

few common phenomena and their transducers.

Phenomena Transducer/Sensor

Temperature Thermocouples Resistive temperature devices (RTDs) Thermistors

Strain Strain gages

Pressure Pressure sensors

Force Load cells

Vibration Accelerometer

Sound Microphone

Light Vacuum tube Photo sensors

Position and Displacement Potentiometers Linear voltage differential transformer Optical encoder

Fluid Head meters Rotational flow meters

pH pH electrodes

Table 1. NI CompactDAQ is compatible with more than 50 C Series modules for measuring a variety of sensors.

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Modules

Each NI C Series module is specifically designed for a particular electrical or sensor measurement and

contains the signal converter, connectivity, and conditioning circuitry in a single rugged package. Signal

conditioning, such as amplification, filtering, excitation, and isolation, is essential for acquiring accurate

sensor and electrical measurements. You can easily acquire signals from thermocouples, resistance

temperature detectors (RTDs), strain gages, load cells, accelerometers, microphones, controller area

network (CAN) buses, and many more devices using the appropriate C Series module. With other C

Series modules, you can generate analog and digital signals. You can use these signals to create

waveforms, communicate with instruments, or control your test.

Figure 2. You can mix and match C Series modules to create the optimal data-logging system.

When choosing a C Series module, it is important to consider measurement type, range, accuracy,

number of channels, sample rate, signal conditioning, and connectivity. C Series modules have a wide

range of connectors including BNC, spring terminal, screw terminal, RJ50, CAN, and D-Sub. To avoid

creating custom cables, make sure to verify that the sensor can connect to your module of choice.

Chassis and PC

The NI CompactDAQ chassis controls the timing, synchronization, and data transfer between an

embedded controller or host computer and up to eight C Series I/O modules. A single chassis can

manage multiple timing engines to run up to seven separate hardware-timed I/O tasks at different

sample rates in the same system. The NI CompactDAQ platform includes chassis with embedded

controllers that operate stand-alone, and lower cost chassis that are controlled by an external PC. When

choosing a chassis, you should take into account size, ruggedness, data transfer bandwidth, number of

slots, distance from the controlling PC, and the ability to be embedded.

The stand-alone NI CompactDAQ system with an embedded controller allows you to use your

measurement system in places that were previously inaccessible to most external PCs. This system

couples a rugged, fanless, and compact design with a high-power processor to be the ideal system for

applications that require remote or embedded measurements. This 8-slot system is available with either

an Intel i7 or Celeron processor to perform complex online and offline analysis.

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Figure 3. With the stand-alone NI CompactDAQ system you can embed your data-logging system almost anywhere.

If you prefer to use an existing PC, you can choose from USB, Ethernet, and wireless NI CompactDAQ

chassis that offer sizes of one, four, or eight slots.

Operating System

When choosing a stand-alone NI CompactDAQ system, you have the choice of two OSs: Windows

Embedded Standard 7 (WES7) and LabVIEW Real-Time. Each OS has a unique set of advantages and

challenges depending on your application. You should consider reliability, user interaction, database

connectivity, and the use of other Windows-supported software.

WES7 is a modified version of Windows 7 that has been optimized for industrial environments. It has

new features that make it a great choice for reliability. WES7 also makes available the extensive

Windows software ecosystem and the LabVIEW for Windows platform. Using WES7, you can take

advantage of functions found in .NET assemblies, ActiveX controls, and DLLs; or directly connect to a

remote database for logging with ease. Additionally, you can use the built-in VGA display output to

implement your user interface, which reduces system costs and maintenance requirements by

eliminating the need for a dedicated user interface computer.

LabVIEW Real-Time has been designed from the ground up to provide outstanding reliability. LabVIEW

Real-Time OS components have been reduced to the minimum required, which reduces the probability

of system failures. This OS also provides a virtually corruption-free file system and watchdog timers to

bring the system back to a known state quickly. User interaction and connectivity with databases can be

achieved with LabVIEW Real-Time, but it requires the use of another Windows-based PC to do so.

This OS is ideal for embedded monitoring where direct user interaction is limited.

Software

With NI LabVIEW system design software and NI-DAQmx driver software, you can develop custom

measurement systems faster. Within a single software environment, LabVIEW provides unparalleled

integration with NI data acquisition hardware, extensive signal processing libraries, and user interface

controls built for measurement data visualization. NI-DAQmx provides a single programming interface

for hundreds of data acquisition devices so you only have to learn the interface once. With NI-DAQmx,

you have access to low-level functions to create a powerful, flexible, and efficient measurement system.

Alternatively, you can choose the simple, easy-to-use DAQ Assistant to quickly configure your system

and collect data within minutes.

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Figure 4. With the NI-DAQmx API and LabVIEW, you can create flexible, powerful, and efficient data-logging software.

LabVIEW has emerged as a standard for developing virtual instrumentation test, measurement, and

control applications. However, NI-DAQmx also provides the same interface for other popular

programming languages, including Visual Studio .NET languages, ANSI C, and C++. If you want to use

text-based programming languages, you should choose WES7 for the best support and most flexibility.

Configuration-based tools built with LabVIEW and NI-DAQmx are also available through the LabVIEW

Tools Network. Each of these tools can benefit different applications, so it is important to consider

development time, flexibility, efficiency, and expandability when choosing your measurement software.

Figure 5. Using the configurable DAQ Assistant, you can be up and running in minutes.

Display

There are many ways for you to see the data that is being logged. These methods are highly dependent

on the OS that you select. Both OSs have methods for displaying data, so if this is not a critical piece to

your application, the OS should take precedence. Using a Windows system you can directly interact with

the system with a mouse, keyboard, and monitor, or you can use a touch screen. You can also broadcast

the data to the web or mobile devices using an Internet or network connection. Using LabVIEW Real-

Time, you can broadcast the data in the same way as a Windows system.

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Conclusion

When building a successful embedded measurement system, there are many elements that you should

consider. You can combine all of these elements to optimize your system for your application. If you

plan on using the same system for multiple applications, remember to give yourself the flexibility to add

channels and different measurement types when needed.