Perhaps your task is to evaluate the performance of a spacecraft on the way to Mars or determine the suitability of a newly designed anti-lock braking system for next year’s cars. Or you must monitor the processes in a chemical plant, track the environmental control system in the local hospital, or examine greenhouse-gas emissions for conformance with an international agreement. If so, then the newest developments in recorders/dataloggers are of great interest to you.
The selection of a recorder/datalogger involves several factors that depend on the application. You may need to accept several types of measurements and condition each for proper handling. Data rates also may be a big factor. Encoding accuracy, including the dynamic range, might be significant. Reliability could be a big factor in your choice.
Depending on your application, the size, weight, and power consumption may be critical. On-site data readout, with or without some analysis, may be necessary. You can even have a powerful computer within the equipment if the on-site processing load is heavy.
The storage capacity always is a matter of concern. Will you be able to complete a collection sequence without memory overflow? And what is the cost of the storage medium in the capacity that you need?
The trend to paperless recording continues. There are several reasons for this, but perhaps the most significant ones are technological advances in solid-state memory and the ever-decreasing price-per-unit of storage capacity. The paper used on strip-chart recorders may be inexpensive, but chart analysis is labor-intensive, and there is no simple way to enter the data into a computer.
For several years, solid-state electronic memory devices similar to those used in computers were considered, but the cost was prohibitive in many applications. That no longer is the case.
Steve Lekas, vice president of IOtech, said, “With PC-Card memory approaching a gigabyte, paperless dataloggers and recorders not only collect and store data efficiently, but also provide data transfer to a computer. This service is not available in traditional chart recorders.” The PC Card, officially known as the PCMCIA technology, can archive data for electronic or physical transfer to the PC for analysis.
Stand-alone analysis capability now is offered to handle cases where the data collection site is in a sheltered location and a large amount of analysis is required. The typical arrangement includes a computer, a color graphic display, and a paper strip chart.
Many dataloggers now operate unattended, even in severe environments. With real-time connection to a central computer, you have access to all the data without the need to send an operator to the collection site. This is similar to the data acquisition function in the Supervisory Control And Data Acquisition (SCADA) systems that electric utility and other wide-area companies have used to monitor and control switching stations for many years.
Yet another trend is the use of small, lightweight, portable instruments for ad hoc data collection. Here, a technician responds to a trouble call and does some analysis on the spot while relaying all data to the central computer.
In reflecting on the uses of recorders/dataloggers, we see many cases where these instruments were not even considered a few years ago but now are deemed essential. For example, Mark Beasley, senior product manager at Endress + Hauser, observed “Companies continue to look for more ways to automate their data collection as manpower availability and budgets shrink.” He talked about a chemical company that transmitted measurements from their process recorders located in the production areas directly to the control room in real-time. This gives them real-time accuracy and speed in monitoring production.
A valuable feature in some applications is the capability to generate messages automatically in response to data content. Byron McIntire, president of Soltec, talked about his company’s unattended datalogger that sends a message to the engineer on duty when a problem is detected. The engineer can download the stored data via a modem and then rearm the equipment for normal operation. Alternatively, the datalogger can be programmed for automatic transmission by faxing a chart containing data collected before the trouble was detected.
A capability of interest on large testing systems is the synchronization of timing between two or more recorders to ensure time correlation on data playback. This is very helpful in establishing cause-and-effect relationships on multichannel data recording applications.
Jay Giles, vice president of sales at R.C. Electronics, reported that Boeing Rocketdyne uses multiple digital recorders to collect shock, vibration, and acoustic data during the test of large rocket engines. In this system, 168 channels are recorded and played back in synchronism. “A master controls all slave units, allowing simultaneous starting and stopping of measurements. All channels can be reviewed from the master unit. In addition, each slave unit can review the data that it collected,” explained Mr. Giles.
Several companies emphasize the capability to operate equipment in remote locations. Mark Cejer, manager of product marketing at Keithley Instruments, said, “Many applications do not require on-the-spot readouts. With an appropriate communications interface, a paperless recorder can send fully conditioned data anywhere it is needed, decreasing visits to the site.”
Another application of interest relates to cleaning up the environment as mandated by member nations in the Kyoto Agreement. Colin Nickerson, product manager HVAC, for ACR Systems, noted, “As a result of this international pact, greater fuel efficiencies will be demanded from the commercial, residential, and industrial sectors to reduce the consumption of energy. As such, dataloggers will be asked to perform multiple functions and to perform them faster.”
In the recorder/datalogger family, there is a wide variety of equipment from which to choose. The data collection site may be unattended and visited only in case of problems. Conversely, it may be a very busy location with high volumes of data to be collected for long periods of time. Data rates can be low, medium, or high. The environment could be friendly, or we might need equipment that withstands all the elements. Our data may be simple and easy to analyze or possibly require powerful analysis software on-site as well as at the central location. And budget constraints enter into the equation.
All recorder and datalogger applications fall into five general categories:
The unattended station could have a small, inexpensive scanner/datalogger with a real-time or a dial-up interface to a centrally located computer system.
A troubleshooting technician may carry a lightweight instrument to the remote station for on-site analysis even as data is sent directly to the main station.
The more permanent site might have a storage device with a display for on-the-spot troubleshooting, possibly even including a paper output plus a line to headquarters.
If large quantities of high-rate data are to be collected at a station, magnetic instrumentation tape may be needed. The line to a central computer is there as well.
For the highest intensity on-site analysis, a stand-alone computer system will be appropriate. This could include a graphic display and a chart paper output. Even with all this power, the station is connected to the main PC, the backup evaluation site.
Recorders and Dataloggers
The SmartReader Plus family of dataloggers measures temperature, resistance, or switch status at two to eight locations; stores the measurements internally; and sends them to a PC. Up to 10 loggers can be polled by the computer. On-board memory holds up to 1M readings. Software for Windows is provided to access, display, and analyze the data. Starts at $450. ACR Systems, (800) 663-7845.
Compact Display System
The Data-Vision.PC™ is a modular data acquisition and display system powered by a Pentium CPU. Up to 64 analog and 96 digital signals can be acquired, conditioned, stored, processed, and displayed. Resolution is 12 or 16 bits at conversion rates to 100 kS/s. It has Windows-based software, standard data acquisition development tools, and a graphics package. Starts at $995. ASC Systems, (313) 882-1133.
The Dash 16u Data Acquisition Recorder acquires 16 channels of DC-to-20-kHz analog data and digitizes at up to 200 kS/s per channel. It stores the measurements in 16-MB solid-state RAM, displays the data on a 10.4″ color screen, and prints an 8.5″ black-and-white chart. All data can be sent to a PC via Ethernet interface or by physical transfer of data on the 100-MB Zip disk. Call company for price. Astro-Med, (401) 828-4000.
Visual Data Manager
The Memo-Graph accepts and conditions eight or 16 analog inputs, digitizing each into a 14-bit word. The analog data and seven digital inputs are stored in a 450 kword memory. Selected measurements can be processed by the internal computer and displayed on a 5.7″ color graphic monitor. Data can be transferred to a PC via a 3.5″ disk or an RS-232-C interface for additional processing. Starts at $2,995. Endress + Hauser, (800) 428-4344.
The 4181G Videographic Recorder accepts up to 500 analog inputs and samples, encodes, and stores them in a 20-Mb memory. Selected data is processed on the internal computer and can be shown on the 10.4″ color graphic display or printed on a six-color printer. For additional processing on a separate PC, the unit has an RS-232-C interface. Eurotherm Chessell, (800) 801-5099.
The 2620T and 2635T Recording Thermometers accept 21 channels of thermocouple or RTD outputs or electrical signals such as ACV, DCV, frequency, resistance, and current. Data is stored on a removable PC Card. The 2620T can be tied to a PC for data analysis with Windows software; the 2635T data records are transferred physically on the PC Card. Starts at $3,490. Fluke, (800) 443-5853.
The DAstar Data Acquisition System has plug-in, programmable signal conditioners for up to 96 channels of data with a filter and 12-bit ADC for each input. The sample rate is up to 200 kS/s. Simultaneous sampling time-correlates data. Data is stored on a 2.1-GB hard drive. Options include a thermal writing chart recorder. From $8,000 to $10,000. Gould Instrument Systems, (216) 328-7000.
PC-Based Data Acquisition
The LogBook/360™ is a portable, PC-based, 16-bit data acquisition system that operates at 100 kS/s. It accommodates 16 single-ended or eight differential inputs, 24 general-purpose digital I/O and 16 dedicated digital inputs, four frequency/pulse counters, two frequency/pulse generator outputs, and four optional analog outputs. Data is sent to a PC via a 500-MB PC Card or through a modem interface. LogBook/360 operates on 9 V to 45 V DC or from a commercial AC source. Starts at $3,995. IOtech, (440) 439-4091.
The 2000-20 is a 6½-digit multimeter with a 20-channel scanner. As a multimeter, the instrument measures AC and DC voltage and current, resistance, frequency, period, decibel, and decibel referred to 1 milliwatt. The VDC measurement speed is 90 channels/s. The scanner handles up to 60 VDC or 30 VAC. The unit interfaces to a PC via an RS-232-C or an IEEE 488 interface. $1,595. Keithley Instruments, (800) 552-1115.
The EL-3-12BIT Dual-Channel Datalogger measures, digitizes, displays, and stores voltage, current, temperature, and humidity. Resolution is 12 bits. The memory holds 8,000 measurements. Up to eight dataloggers can be accessed by a PC, and data can be analyzed and displayed by the applications software on a Windows platform. The unit is battery powered. $356. Lascar Electronics, (912) 234-2048.
S-VHS Tape Recorder
The DTR-16 Analog Recorder/Reproducer operates as a single-channel, 16-MHz or dual-channel, 8-MHz recorder, storing data for 20 minutes on a commercial S-VHS tape cassette. With an accessory time-division multiplexer, it stores up to 16 analog channels plus time code and voice. It can be controlled from a PC via an RS-232-C or an IEEE 488 interface. $72,000 Metrum-Datatape, (303) 773-4700.
The 22-lb Vision Data Acquisition System has eight or 16 input channels, each with a 16-bit digitizer operating up to 100 kS/s. It stores data on a JAZ™ 2- GB removable disk or an 8-GB hard drive. The Pentium II processes information for a 10.4″ color display, which has real-time scrolling or XY formatting. Data is transferred to another computer system via 100Base T Ethernet or by physical transfer of a JAZ disk. Starts at $10,995. Nicolet Technologies, (608) 276-5600.
Small Tape System
The DataLite™ Portable Instrumentation System is a tape recorder and computer plus an Ethernet interface to a PC. The system has 16 input channels, each operating at DC to 40 kHz, with programmable signal conditioners and an ADC for each channel. The dynamic range is 90 dB. The Pentium computer has a graphic monitor, a detachable keyboard, a 6-GB disk, a CD-ROM, a floppy disk, and analysis software. Starts at $19,000. R.C. Electronics, (805) 685-7770.
The 1000 Series Squirrel Logger Systems accept eight to 96 measurements including voltage, current, and temperature. Each input is converted to a 12-bit reading and stored in a 260k measurement memory. Data can be displayed in engineering units as psi, % RH, and rpm. The systems interface to a PC for command and data transfer or store data on a PCMCIA card. Analysis and display software operates on Windows. Starts at $2,147. Science/Electronics, (937) 224-4444.
The TA220-3608 Digital Oscillographic Recorder conditions eight or 16 channels of analog data and digitizes the signals at 200 kS/s. It stores samples in a 2-Mword memory, processes selected channels, displays them on a 10.4″ color graphic monitor, and writes analog outputs on a thermal chart
recorder. Data can be stored on a PCMCIA card or sent to a PC via an RS-232-C, an IEEE 488, or a SCSI interface. Starts at <$10,000. Soltec, (818) 365-0800.
The WR1000 Portable Data Analyzer System collects data from 8, 16, 24, or 32 points at up to 1 MS/s. FFT capability includes 400-line frequency, auto- and cross-correlation, and waterfall analysis. Single- and double-integration and differentiation functions are provided for vibration studies, while the 256-kw/channel RAM and 9-GB hard disk are used for storage. Results can be viewed on a 10.4″ TFT color screen as Y-T, X-Y, or FFT plots. The 16-channel version is 16″ × 13″ × 5″. Starts at $10,800. Western Graphtec, (800) 854-8385.
Wideband Tape Recorder
The SIR-1000W Digital Data Recorder collects 160-kHz analog data plus voice, IRIG-B time code signals, and four channels of discrete data. It can record and play back from two to 32 channels of high-fidelity analog data. Tape speeds for both record and playback can be set at any of five ranges. The digital recording medium is a 25-GB helical-scan cassette tape. Playback data can be sent to a PC via an SCSI-II interface using Windows 95/98/NT. $35,000. Sony Precision Technology America, (949) 770-8400.
PCI Disk Recorder
The XLRWrite™ is a PCI card that interfaces with six to 18 IDE disk drives. Any PCI data or image acquisition card with bus-mastering capability can transfer data directly to this device at sustained rates to 100 MB/s. Data transfer capacity is more than 450 GB. Any application that interfaces to Windows DLLs can use this storage. Starts at $6,965. Boulder Instruments, (888) 497-7327.
Multimeter With Storage
The MetraHit 29S Precision Multimeter with its add-on memory operates in a stand-alone mode to measure V, A, dB, W , F, Hz, °C, W, VA, or PF. The memory holds 13,000 to 60,000 measurements which can be observed locally and sent to a PC via an RS-232-C interface. Windows processing software is offered. $824. GMC Instruments, (800) 462-4040.
The 7001 Starlog PRO Data Logger accepts 16 single-ended or eight differential analog signals plus four 20-kHz frequency-counter inputs. The memory holds 250k measurements that can be transferred to a PC through the RS-232-C port. A 64-character LCD is provided. Power is supplied from an external 12-V source or by an internal Ni-Cad battery. $846. Unidata America, (503) 697-3570.
Copyright 1999 Nelson Publishing Inc.