Take a quick look around; there are likely no fewer than half a dozen electronic devices that all have one thing in common. Three years ago they were probably twice the size or had half the capabilities, and in many cases both. Ideally, people want a personal assistant to hold everything including a camera, phone, wireless laptop, music player, clock, address book and more. In lieu of that personal assistant, the consumer electronics market is increasing functionality by integrating all of these devices of convenience into one package, hence the multitasking cell phone.
In pursuit of ultimate flexibility, the instrumentation market is not unlike the consumer electronics market. Companies and consultants constantly strive to get the most out of a limited amount of, usually expensive, measurement equipment. This drive has led to several evolutions in data acquisition.
Earlier data acquisition systems, or even the more simple data loggers, were one-hit wonders designed to measure a single, real-world phenomenon. A temperature data recorder did just that, and if more measurements needed to be taken, more equipment, space and money was required. One of the bigger evolutions came with the mass adoption of computer technology. Suddenly, the data acquisition system was separated into computational components and measurement hardware components. This movement to PC-based or virtual instrumentation brought great flexibility to the end user, because the processing and analysis capabilities were nearly endless with the power of the standard PC and programmable application software. For data acquisition hardware, multifunction devices became available for several PC buses including ISA, PCI, PCMCIA, PCIe and USB as well as a host of stand-alone and proprietary protocols. Data acquisition devices also began to measure several types of signals, including analog and digital, but even with multiple signal measurement types, these devices were still fully assembled by vendors, and customers were often left with extra channels, unneeded measurement types, or a limited expansion path when the project grew. And with that, another evolution of the data acquisition system, modular systems, was born.
Modular systems are a great approach for system construction because they allow for a reasonable amount of growth before having to reinvest in additional foundation components. Modular systems and platforms are designed and built by a variety of vendors on several standards, some of which are open such as PXI and VXI, while others are proprietary. The goal of modular I/O is to enable the end user to purchase only the channel count and signals needed and offer the ability to upgrade in the future without having to double the initial investment. Many of the benefits of a modular system are shared by the vendor and the customer. A customer can update, expand, or change a system with the purchase of new modules. A vendor can more rapidly enhance a data acquisition platform to meet the demand of the customer by adding new modules with new measurements or channel counts to their product lines.
A trend has developed stemming from a single instrument that did everything to having individual components broken out for the user to define and purchase separately at the discretion of the project needs. This trend has brought together the benefits of commercial off-the-shelf (COTS) quality, reliability and support with those of homegrown customization. As technology advances and the components used in instrumentation have gotten smaller, it has become easier to design smaller components for data acquisition systems. Modules that started as trays fitting into large card cages have evolved into smaller modules slightly larger than a deck of playing cards. In the ever-shrinking trend of hardware and modules, size has not sacrificed channel count, as some of these smaller modules offer more than 30 channels and may be placed in different chassis types for different configurations for various deployment options (Figure 1).
One-channel modules may or may not be an economical solution, but either way, the disaggregated module movement is ending. This begs the question “what is next?” The answer can be found by looking at some higher-level benefits of a modular platform. Modular systems have reduced the number of systems needed and components in a test department’s equipment library by using exchangeable modules in a single chassis or carrier. One of the remaining problems is that channel count and signal type are only two characteristics that can change. Self-contained measurement modules solve the problem of changing channel count and signal type, but the market demands more flexibility.
The next evolution of data acquisition systems is to exchange not only modules, but chassis for deployment as well. The test process, depending on the device, has many stages including design validation, controlled environment testing, subsystem component tests, hardware simulation tests, prototype tests, end-of-line manufacturing test and more. By creating a data acquisition system comprised of interchangeable modules and deployment options, test designers can further reduce their hardware needs and thus expenditures, storage space, vendor contacts and toolchain training for employees.
To fully harness the power of modular I/O, it is important to maximize reusability. Just as there are different modules for different measurements, the next evolution of modular data acquisition systems will have different deployment options for the same set of modules. Deployments will vary between industries, but will include options such as size, portability, PC-connectivity, ability to run in a stand-alone mode, ruggedness, reliability and so on. And, as with modules, no vendor will cover every possible use-case, but a family of modular, flexible hardware should be able cover a wide array of the aforementioned deployments.
To better illustrate this, consider a scenario where a fictional company deploys a single-vendor flexible deployment hardware platform.
Assume this company is a consultant-focused engineering house specializing in rotating equipment monitoring and maintenance in the machine condition monitoring (MCM) industry. This company uses accelerometers for vibration measurements. Accelerometer measurements are on the higher end of sensor measurements due to the high sample rate, resolution and bandwidth required. In addition, such integrated electronic piezo-electric (IEPE) sensors require current excitation to power the sensor. Anti-alias filters are a benefit to remove any traces of high-frequency noise in the system, and due to the speed of acquisition and nature of phenomena, simultaneous sampling ADCs are preferred to ensure signals are in phase. Using a modular platform, all of this signal conditioning and data acquisition circuitry must fit into one module.
Measurements performed by an MCM specialist are often from proximity sensors for shaft alignment, tachometers for shaft rotational speed, power load by the motors, and accelerometers for vibration analysis on bearing housings. These measurements are performed in different deployments. One application is the small, low-channel-count, portable unit that a consultant travels with for spot-checks on systems. These spot-checks can be done routinely or when a noise is heard by an operator and called in as a problem. Portable deployments require portable display, storage, reporting and easy setup. More complicated deployments involve a larger channel count for complete machine testing and mixed sensor types, since a complete machine check-up will have tachometers, proximity probes and accelerometers. This larger-scale monitoring system may have bigger storage and processing requirements due to the vast amounts of data involved. The system needs to be moveable, but not as portable as the spot-check system. With the temporary install location often in an industrial environment, the equipment must also be rugged. The final level of machine maintenance that this company offers is the permanently mounted monitoring system. These are online systems installed on rotating equipment to constantly monitor the health of the system and, when the limits are exceeded, notify managers of necessary repairs, or sound alarms or initiate emergency shutdown procedures in hazardous situations.
The company in this scenario is comprised of engineers and service technicians with significant industry experience in machine condition monitoring, but limited understanding of hardware design. In today’s market, the company must purchase several devices: a one-box solution originally designed a decade ago and is slightly large for full-system monitoring, a newer PC-based solution for the portable system that runs off of a laptop (Figure 2), and a more expensive, ruggedized brick-style system for the permanently mounted system. With these choices, the company must buy, learn and maintain a lot of different equipment, or try to find one vertical vendor that makes all three types of systems. But even with one vendor there may be a concession in quality or performance for a one-vendor solution. The other, preferable choice is to design and build their own systems. This ensures that the specs needed are met exactly and all functions are available. However, this company has more technical knowledge in collecting, reading and interpreting the results than hardware design.
The solution is to use a family of hardware with modular I/O and flexible deployment such as the C Series family of hardware from National Instruments. This collection of hardware offers more than 40 measurement modules that are a little larger than a deck of playing cards. These modules can be used in any one of several different chassis for multiple deployment options. In our example, an accelerometer module could be used in the single-module carrier with a rugged laptop for a portable vibration measurement system. For the full system monitoring, the same module could be inserted into an 8-slot chassis along with other modules for proximity probes and tachometers. For larger machines, multiple chassis can be linked together and synchronized for in-phase measurements.
Finally, the same set of modules can be inserted into an industrial computer chassis for a permanently mounted monitoring and alarming system. The CompactRIO chassis, for example, offers either four or eight slots and has a built-in storage and processing capability in an extremely rugged housing, and operates in environments ranging from -40° to 70°C and up to 50g shock.
Hardware is just half of the equation; software must still be considered. Functions such as FFT, order analysis, orbital analysis and waterfall plots are needed for a complete MCM system. This analysis and experience is where the consulting company’s expertise lies, and using software from the same vendor, NI LabVIEW, a company can write and reuse analysis code on all three application deployment platforms. With this one-vendor flexible solution, this consulting house can better manage the training and hardware needed for complete customer service. Should the company decide to resell the systems, the COTS benefits kick in again, because of the manufacturing resources of the selected big name vendor.