Like the old gray mare, the recorder or datalogger “ain’t what she used to be.” Instead of low-speed data collection and pen-motor paper-chart generation or medium-speed operation using thermal graphic or light-beam galvanometer writing, you are more likely today to see high-speed data collection and storage with a variety of display options. Electronic recording and readout are the newest and most popular features.
Recorders and dataloggers can be categorized as laboratory or field systems, depending on their primary point of use. The laboratory equipment is a high-performance system, generally PC-based, in a climate-controlled area with commercial power. The storage capacity in the basic laboratory version is high, with optional memory expansion in many cases.
The field instrument may be mounted in a shelter with easy access and commercial power. Or, it could be protected from the weather and operate with commercial power but have limited accessibility. An even more challenging application is a harsh environment with no commercial electrical hookup.
There are systems for each of these environments, but the architectures and capabilities are extremely different. The common link is data storage in electronic form rather than on paper.
Trends
A major trend is toward the self-contained recorder or datalogger that collects, conditions, records, displays, reviews, analyzes, and prints data. Ideally, this is a relatively small, lightweight unit with high-performance characteristics.
“We see an increasing acceptance of digital signal processing (DSP) along with significantly improved capabilities in real-time statistical processing,” Paul Nylander, technical applications manager at Hi-Techniques, reported. “This doesn’t involve just closed-loop control but the whole realm of statistical operations using time, frequency, and probabilistic information. Also, as networking transceivers and interface circuitry have improved, a new type of data acquisition is viable.”
Now a user can have distributed collection capability, linking remotely located analog signals to a central location via a high-speed bus. This is the way for the everyday recorder or datalogger to maintain flexibility without the insecurity and frustration of physical data transfer.
There also is a trend to put more intelligence at the data source. “Using well-planned DSPs,” Ron Chapek, new business development manager at IOtech, noted, “you can collect tons of high-speed data, process it at the origin to reduce the volume to pounds or ounces, and transfer the information via a communications bus. There also is a strong move to incorporate commercial components and standard buses into the system. This holds the price down and creates an open architecture. In addition, slow buses such as RS-232 and IEEE 488 are being abandoned in favor of Ethernet with web access. Even wireless is growing in popularity.”
For low-cost storage, many users collect data at very high rates and stream it to a hard-drive disk via a high-speed bus. The Astro-Med Dash 18, for example, stores up to 250 MB on a zip disk at rates to 100 kS/s. Boulder Instruments uses two to 16 IDE disks in the StreamStor recorder. With the full configuration, it transfers up to 100 MB/s, and the storage capacity is 1,200 GB.
In some applications, it is unnecessary to sample data continually, filling the memory with redundant and meaningless words. TiePie Engineering has a better way. The company uses a ring memory to buffer data all the time, checking the characteristics of interest but recording nothing permanently. If a fault occurs, the recorder stores the time of day, the last 64k samples before the trouble occurred, and the next 64k samples following the event. When the law of averages works, all data of significance can be collected for hours or even days on a relatively small storage medium.
With all the glamour of high speed and large storage capacity, however, there still is a big market for the moderate-performance instrument. “Super-powered paperless recorders are not the answer to all data-collection requirements,” Mark Beasley, product manager for recorders at Endress+Hauser, has found. “Sure, they offer advantages to some users who need high-speed data collection, real-time or off-line display, and a dedicated computer. Some even have advanced math calculations and web-browser capability. However, these capabilities are of no use to many people, and generally, they come with greater operating complexity and higher prices than the simpler instrument.
“Users are concerned about how to verify that no data is lost and that the archived data has not been compromised,” Mr. Beasley continued. “Further, they want to be confident that they have performed the correct setup. We provide the basics of paperless recording and make data quality easy to check while holding the complexity and price at a reasonable level.”
The Role of the PC
Where space permits, you are likely to find a PC as part of the recorder system. There are good reasons for this.
“The PC is the data collector’s friend,” Anton Poelsma, design engineer at TiePie Engineering, said. “It has been proven in every conceivable way and has millions of dollars worth of software for the variety of data-analysis tasks. If there is a problem with this part of the system, a replacement is nearby. It has network connections, expandable memory, various monitors, and periodic upgrade capability.”
However, even though the computer is extremely capable of storage and manipulation, it is not suitable for the real-time tasks of data collection and conditioning. For this reason, the PC will not replace the data recorder. A data acquisition system must have dedicated front-end circuits for signal conditioning, encoding, formatting, and computer entry, and these roles are unique to the dedicated recorder or datalogger.
Applications
You’d be surprised to see the large number of applications for the recorder or datalogger. Some instrument suppliers shared with us a few of the cases where users need data for detailed analysis.
Emergency Power Unit
“Insurance companies need uninterrupted electrical power for their critical data systems,” noted David Kortick, product manager at Astro-Med. “One organization uses large, three-phase power generators for emergency backup and recorders to commission and test these systems. It chose a paperless recorder to collect critical measurements on a 4-GB hard drive. The color display allows the user to see data in real time or on playback, and interesting phenomena that signal potential problems can be transferred to a PC for further analysis.”
Outdoor Equipment
An important valve at a refinery was exposed to extreme weather conditions, and critical operations were in jeopardy because it was behaving erratically. To monitor operation for diagnostic purposes, a battery-operated recorder from GMC Instruments was wrapped in plastic and connected to the valve for a two-week period. Then the data was downloaded to a PC for detailed analysis, and the users were able to take corrective action and keep the refinery operating.
Power Shutdowns
“In a power-generation plant,” according to John Luchka of HIOKI USA, “a detailed analysis of each shutdown is needed to disclose any irregularities in the system. A recorder in such a plant captures the time of each shutdown, the voltage levels before and after the event, voltage and pressure fluctuations, strain and torque on the turbines, and the current being supplied.”
Components on a Truck
The manufacturer of a heavy vehicle was plagued with problems on critical components. To analyze the situation, engineers needed to accumulate data automatically over a period of several weeks. Since the activities were intermittent, there was no need to overload the recorder by collecting meaningless information during the idle times. HIOKI USA, working with the vehicle manufacturer, developed techniques for identifying and collecting important data that ignored the activities when the vehicle was running properly.
“First,” Mr. Luchka of HIOKI USA, recounted, “we used a special DSP algorithm for transitional recording, compressing the data stream by ignoring useless inputs. Second, we developed a sophisticated trigger scheme to start and stop the recorder and alter the sampling rate. With these developments, we compressed the data content by 200 to 1,000 times while recording all the information of interest.”
Rocket Motors
Each rocket motor for use on NASA’s space shuttle program must be monitored from the moment it is built until it lifts the vehicle into orbit. Surveillance is required during travel by rail as well as warehouse storage. For more than 10 years, a small, rugged, battery-powered datalogger from Instrumented Sensor Technology has kept these records for the supplier and the space agency.
Roller Coasters
In a more down-to-earth application, a major amusement park checks the quality of each roller coaster periodically, using a small, battery-operated recorder. Data is analyzed after a ride, and any occurrence that causes degradation of ride quality or an approaching safety hazard is detected.
Railroad Cargo
“Railroad companies are determined to maintain good quality in their freight transport services,” Daniel Burk, manager of applications engineering at Instrumented Sensor Technology, said. “One company uses our dataloggers to monitor the routine movement of cargo, logging the time and details of the event. This information enables transportation personnel to pinpoint problem areas and improve the quality of their delivery.”
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October 2001