Remote Data Acquisition
[ Ethernet Data Acquisition An Independent Evaluation ]
[ Ethernet Data Acquisition Improves Measurement Accuracy in Race Car Testing ]

Inizio

Ethernet Data Acquisition An Independent Evaluation by: James W. McGregor and Ed C. Baroth, Ph.D. Measurement Technology Center, Jet Propulsion Laboratory, California Institute of Technology and John Burns, Software Research Reprinted from Evaluation Engineering Magazine, January 1999

  With all the interest in the Ethernet port on today's computers, it only seems natural for someone to ask "Why not use it for data acquisition?" Well, several companies now produce data acquisition units to accommodate Ethernet data transfer. For example, Keithley offers the Smartlink line, and Intelligent Instrumentation has the EDAS-1000 Series.

  We became interested in the EDAS-1002E-2A and obtained a starter kit with everything needed for an evaluation. It consisted of the EDAS-1002E-2A Ethernet Data Acquisition System, a termination panel, a power adapter, cables, documentation, and software. It is small, compact, and portable - 9" x 5" x 1" and 21 oz (Figure 1). It could be easily stashed in a briefcase or laptop case and taken on the road. This was done several times during the course of our evaluation.

Figure 1. EDAS System With EDAS, Power Supply, Null Modem Cable,    10Base-T Cable and Crossover, and Terminal Board.

  The EDAS-1000 Series includes the EDAS-1001E-2A with 32 programmable digital I/O channels and the EDAS-1002E-2A, a multifunctional Ethernet data acquisition system with 16 single-ended or eight differential, 12-bit resolution analog input channels, two 12-bit analog outputs, eight digital inputs, eight digital outputs, a programmable 16-bit counter, an RS-232 port, an RS-485 port, and a 10Base-T Ethernet port (Figure 2).

Figure 2. System Block Diagram

  The analog inputs can be configured through software control as 16 single-ended or eight differential input channels with gains of 1, 10, and 100 and voltage ranges of 0 to 10 V and +/- 10 V. A rate generator allows analog input rates from 0.001 Hz to 100 kHz. The analog outputs have a range of +/- 10 V.

  The digital I/Os are TTL-compatible and programmable in two 8-bit ports, one input and one output. The inputs can be used to read digital status, detect state changes, and count events up to 250 Hz. The outputs can be operated in an on/off state or programmed with delay times and on/off times for controlling and timing applications.

  The high-speed, 16-bit counter is used with any one of the digital input lines. It can count TTL level signals up to 250 kHz or make direct frequency measurements.

  The RS-232 port has two functions. It is used locally to configure the EDAS Ethernet parameters. It also can control and monitor RS-232 instruments or devices. The RS-485 port can be used for controlling and monitoring RS-485 devices.

Figure 3. LAN Diagram

The Approach
  We decided to concentrate the initial evaluation on the use of the EDAS with Ethernet rather than on its available data acquisition features. Even so, most of its capabilities were examined.

  First, the EDAS was used locally with an AMS Tech laptop computer with Windows 98. Then, it was connected through an Ethernet hub to a local area network that had both 10Base-T and 10Base-2 nets and an internet connection (Figure 3). It was used with Windows 95 and 98 as well as Windows NT. EDAS also supports DOS and Windows 3.1, but these modes of operation were not tried.

  The EDAS has support libraries for both Intelligent Instrumentation's Visual Designer™ and National Instruments' LabVIEW®. Both of these were used with the EDAS. Also provided was a C/C++ library, which was not included in the evaluation.

Configuring the System
  The EDAS-1002E was connected to a 233-MHz AMS Tech Pentium laptop with Windows 98 via the RS-232 port and the null modem cable. The serial port was set to the EDAS default of 9,600 baud, eight data bits, one stop bit, no parity, and no handshake.

  The SYSCHECK program was installed and run on the laptop. The program was simple and easy to understand. Only occasional references were made to the documentation, and the EDAS was quickly configured. The Internet Protocol (IP) addresses were set to 192.168.100.1 for the EDAS and 192.168.100.0 for a fictitious gateway.

  These addresses were chosen from the Internet Assigned Numbers Authority (IANA) list of reserved IP addresses for private networks. These addresses are filtered by internet routers and do not have to be globally unique.

  A system check was performed over the RS-232, and everything seemed to work as it should. The laptop was given an address of 192.168.100.111, also from the IANA list, and connected to the EDAS via a 10Base-T cable and a crossover adapter. To our surprise, no Ethernet connection could be established.

  After much experimenting, it was discovered that the laptop computer, which had no gateway address assigned, had to be given the same gateway address as the EDAS even though the gateway was fictitious and didn't really exist. The reason for this was not pursued further.

  Once network communications were established, testing continued. All of the EDAS functions were tested using SYSCHECK over the Ethernet connection, and everything worked.

Visual Designer Library
  Included in the evaluation package was a demonstration CD ROM version of Intelligent Instrumentation's Visual Designer. Visual Designer is a graphical programming language in which icons that represent functions blocks, such as analog input, are inserted into a diagram using drag and drop. Then the data paths are inserted from one icon to another.

  Once the diagram is complete, it is executed by clicking on the run button of the tool bar. The application development process is easily learned with little reference to the documentation.

  The evaluation program included in the kit was a complete 32-bit version of Visual Designer that could be used for developing data acquisition applications.

**** "It would make a worthwhile addition to any group
contemplating data acquisition or control using Ethernet." ****
  These applications, however, would only execute for three minutes at a time. Then they would have to be restarted with the run button of the tool bar. This was only slightly inconvenient and did not cause any major problems with the evaluation.

  The nine EDAS Visual Designer icons were multifunctional. Each had to be configured, not only for which series of EDAS it represented, but also for the many parameters that it needed.

  For example, if the digital input icon were chosen, you would have to double-click on the icon to bring up the parameters dialog box. Then the correct EDAS series would be chosen and the IP address entered. This had to be done each time an icon was inserted and was somewhat annoying. When the icon was wired to another icon, additional parameters had to be given.

  Example application diagrams for the EDAS were included in the EDAS Visual Designer Support Library Manual. All of these easily understood examples were entered and executed to test some of the functions of the EDAS.

  Additional programs were developed to check many other capabilities of EDAS. The analog inputs were checked with a function generator using sine, square, and sawtooth waves of various amplitudes. DC voltage levels, as well as various voltage patterns and waves, were generated and measured from the analog output channels. Everything worked perfectly.

  The RS-232 serial port of the EDAS was connected to an ADAM-4018M thermocouple unit connected to an ADAM-4520 RS-422-to-RS-232 converter. A Visual Designer program was created, and temperatures were measured, plotted, and logged. This entire operation took less than 15 minutes to accomplish.

Virtual Instrument Support Library for LabVIEW
  The EDAS Support Library for LabVIEW 4.0 or higher contained a configuration utility, nine example programs, and 45 low-level virtual-instrument (VI) icons. The installation from a 3-inch floppy disk was typical of all Windows installations and easily done without problems.

  You must have already installed LabVIEW on the computer before installing the Support Library. A WINSOCK.DLL had to be in the path, and TCP/IP had to be functionally active so the EDAS block would load and function properly.

  The configuration utility looked very much like SYSCHECK, except that there were no built-in routines for checking out the various system functions (Figure 4). It was executed from LabVIEW and used to configure the IP addresses of the EDAS and the gateway and set the subnet address.

Figure 4. LabVIEW Configuration Utility for EDAS

  There was only one drawback. When we exited the program, we also exited from LabVIEW - so we had to enter LabVIEW again. All of the EDAS capabilities were covered in the nine example programs:

• Alarm Sample.vi - demonstrates the various alarm modes of the EDAS.
  
• Analog Input Sample.vi - demonstrates how to acquire data from multiple analog input channels.
• Analog Output Sample.vi - demonstrates how to write data to analog output channels.
• High-Speed Analog Input Sample.vi - demonstrates how to perform multiple channel high-speed analog inputs.
• Digital Input Bit Sample.vi - demonstrates how to use digital input port bits: normal (unlatched), falling edge latched, rising edge latched, up counter, down counter, event counter, frequency counter, and change-of-state latch.
  
• Digital Output Bit Sample.vi - demonstrates how to use digital output port bits: normal, pulse low, pulse high, delay low, delay high, and square wave.
• Digital I/O Sample.vi - demonstrates how to read and write digital I/O data.
• Serial I/O Sample.vi - demonstrates how to send and receive data via the RS-232 or RS-485 serial ports.
• Thermocouple Sample.vi - demonstrates how to make temperature measurements using Type J, K, or T thermocouples.

  Most of the example programs were multifunctional in nature. This led to some confusion at first because there were so many parameters to set. Some parameters were used only for one function, and others were only used for another function.

  All of the example programs were executed with only minor difficulty. The troubles actually were misunderstandings easily overcome by examining the program's diagram or reading the documentation.

  Most of the 45 functional VIs had multiple inputs and outputs, making programming with LabVIEW more involved and complicated than with Visual Designer. As can be seen in Table 1 (below), there are 16 categories of VIs. Each VI had on-line help available by right-clicking on its icon and selecting On-line Help from the menu.

System Inquire Functions	Firmware Inquire Functions
nSYSinquire.vi	nVERinquire.vi
Trigger Functions	I/O Locking Functions
nTRIGConfigure.vi	nIOLock.vi
Synchronization Functions
nSYNCConfigure.vi
Initialization Functions	Network Command Functions
nSWinit.vi	nSessionBegin.vi
nSWDeinit.vi	nSessionEnd.vi
Analog Input Functions	Analog Output Functions
nAIConfigureList.vi	nAOConfigureList.vi
nAIRead.vi	nAOWrite.vi
Rate Generator Functions
nRGConfigure.vi
nRGEnable.vi
Digital I/O Port Functions	Serial I/O Functions
nDIOConfigureList.vi	nSERIALConfigure.vi
nDIORead.vi	nSERIALReceive.vi
nDIOWrite.vi	nSERIALSend.vi
Alarm Functions	High-Speed Analog Input Functions
nALARMConfigure.vi	nAIHSConfigureList.vi
nALARMEnable.vi	nAIHSEnable.vi
nALARMFree.vi	nAIHSRead.vi
nALARMStatus.vi	nAIHSStatus.vi
nALARMTransferOptions.vi	nAIHSTransferOptions.vi
Utility Functions	Digital I/O Functions
nCountsToTemperature.vi	nDIOBITConfigureList.vi
nCountsToTemperatureA.vi	nDIOBITEnable.vi
nCountsToVolts.vi	nDIOBITMeasure.vi
nCountsToVoltsA.vi	nDIOBITRead.vi
nFrequencyToRGCounts.vi	nDIOBITReadCount.vi
nVoltsToCounts.vi	nDIOBITReadLatch.vi
nVoltsToCountsA.vi	nDIOBITReadNormal.vi
	nDIOBITWrite.vi

Table 1. VI Function Categories
  The four functions in the Initialization Functions and the Network Command Functions categories must be included in each program, regardless of the data acquisition or I/O performed. Partial diagrams of the required initialization and de-initialization process are given in the documentation. It was easy to implement these diagrams and copy them into each program written.

EDAS Documentation
  The EDAS documentation was very complete. It consisted of two booklets and four manuals.

  The first booklet, Factory View-Real-Time Interactive Data Access Solutions, was an overview of all Intelligent Instrumentation's hardware and software products. It also contained a CD ROM with even more detailed information about the company's products and the evaluation version of Visual Designer. The other booklet described all of the EDAS modules, their specifications, capabilities, software support, and accessories.

  The EDAS User Manual had documentation for all of the EDAS systems. It explained how to install, configure, and use each system and contained example programs using Visual Designer.

  "Appendix C, TCP/IP Reference Information" was especially helpful. Even with no knowledge of TCP/IP and networking, you could configure EDAS and your PC and have them communicating in very little time. This appendix also contained a useful list of web sites for additional information and help.

  The Net Link Software Libraries Reference Manual documents the high-level language support for the EDAS series. Net Link is a run-time library that provides client functions for EDAS systems. It can be linked with Windows, or UNIX application programs written in C/C++ and Microsoft Visual Basic under Windows.

  The Win32 version of the Net Link Software Library supports Borland C++, Microsoft Visual C++, and Visual Basic. As stated earlier, this library and its manual were not evaluated.

  The EDAS Visual Designer Support Library Reference Manual is a detailed reference for all Visual Designer function blocks for EDAS. It covers the software library installation and the use of its nine function blocks. It contains the same four examples that are in the EDAS User Manual plus an additional one.

  The EDAS Virtual Instrument (VI) Support Library for National Instruments LabVIEW Software User and Reference Manual gives a complete description of the 45 VIs used with the EDAS. The EDAS Support Library provides VI functions for EDAS for LabVIEW 4.0 and higher running under Windows 95, Windows 98, or Windows NT.

  It would have been nice to have a description of the example programs included with the libraries. The on-line help was more useful than the reference manual.

  All of the manuals were well written and easy to understand. Each had a table of contents and an index. All except the Visual Designer reference manual had appendices. In reading the manuals, no errors were noted. The Visual Designer and the LabVIEW reference manuals would have benefited from the use of color, especially in the wiring diagrams.

Conclusions
  The EDAS-1002E-2A is well designed and constructed, although the cantilevered terminal board was worrisome. It was easy to configure and use, especially with Visual Designer. It performed every task attempted. Multiple users could access data via Ethernet, or the EDAS could be told to lock out other users.

  The documentation was well written. The software support was excellent. User support was prompt both by phone and e-mail. It would make a worthwhile addition to any group contemplating data acquisition or control using Ethernet.

Disclaimer
  This article was written by the authors as private individuals and not in conjunction with JPL.

About the Authors
  James W. McGregor is the technical group supervisor of the Measurement Systems Group at the Jet Propulsion Laboratory (JPL). Mr. McGregor graduated from Mississippi State University with a B.S. in science and mathematics. He received an M.S. in physics from the University of Mississippi and was a Shell Merit Fellow in Physics at Leland Stanford Jr. University.

  Ed C. Baroth is the technical manager of the Measurement Technology Center at JPL. He holds a bachelor's degree in mechanical engineering from City College of New York and master's and doctorate degrees in mechanical engineering from University of California, Berkeley.

Jet Propulsion Laboratory, California Institute of Technology
4800 Oak Grove Dr.
Pasadena, CA 91109
Phone: 818-354-8339
Email: ebaroth@jpl.nasa.gov
  John Burns is the owner and operator of Software Research, a company that specializes in custom computer-system integration. He also is a consultant to JPL.

Software Research
1150 E. Lancaster Blvd.
Lancaster, CA 93535
Phone: 805-945-1133

Inizio

Ethernet Data Acquisition Improves Measurement Accuracy in Race Car Testing by: Robert M. Winkler, Intelligent Instrumentation Reproduced with permission, Evaluation Engineering Magazine, September 1998

If you keep your ear to the ground for the latest trends these days, you probably hear much discussion about the use of Ethernet as an I/O network.   Visit any of the large automation trade shows,and you'll find the topic to be the most hotly debated.   For the last 12 months, Ethernet has been widely discussed as a major contender in the fieldbus wars, for plant floor and sensor applications as well as for industrial controls. The driving forces for this trend really are a matter of both economies of scale and the market's tendency to gravitate toward open systems and standards.

  Ethernet's rise to popularity is based on the same market forces that have resulted in the dominance of PC's and Windows over other computing platforms and operating systems in nearly every industry. With such a huge installed base and so many forces lining up to endorse its use in new industries and application areas, Ethernet will continue to gain in popularity and market share.

Benefits
  What kinds of benefits can tou realize from incorporating Ethernet into their data acquisition applications? One that comes immediately to mind is the capability to easily acquire data from remote locations. Since most facilities already have Ethernet networks installed, data acquired from one location in a facility can easily be fed to other PCs located elsewhere in the facility. It is no longer necessary to dedicate a PC to data acquisition in every location where you want to acquire data.

  Ethernet also can reduce unwanted noise incurred when signals are transmitted over long sensor wires. It is not uncommon to take measurements from signal sources located 20 to 50 feet away from the PC.

  Data typically is transmitted using 4-to 20-mA signals which are susceptible to noise. By placing an Ethernet Data Acquisition System next to the signal source instead of using a data acquisition board plugged into a PC, the level of noise induced on the desired signals is greatly diminished. This is because the desired signals are digitized right next to the source, before they've had a chance to incur unwanted noise.
These digitized signals are relatively immune to the effects of noise due to their discrete nature. The digital signals then are passed over low-cost unshielded twisted pair cable which, by its very nature, protects the integrity of the signals through common-mode rejection.

Race Car Manufacturing   A classic example of how Ethernet can help in data acquisition can be seen at Dan Gurney's All American Racers (AAR). AAR was founded in 1965 by former race car driver Dan Gurney. Today,the company builds Indy-style open-wheeled race cars for their own racing teams as well as customers. Throughout their history, AAR has built more than 150 race cars.   The company fields two racing teams which compete nationally in CART (Championship Auto Racing Teams) competition. Over the years, AAR teams have won eight championships, gathering 78 victories, including the 'Indy 500', and 82 pole positions.   A critical element of the race car manufacturing process is the company's wind-tunnel testing facility, where aerodynamicists subject 40% scale model race cars to tests that simulate extermely high-speed driving conditions. PC-based data acquisition systems have been in place for many years to monitor and control wind tunnel conditions and acquire data from the race car models under test. Recently, the company found that Ethernet data acquisition yields dramatically more accurate results in this facility.

Data Acquisition in the Wind Tunnel
  Previously, AAR monitored race car and wind tunnel conditions using data acquisition boards which plugged into a PC's ISA slots. Since the PCs must be located outside of the wind tunnel, the data acquisition boards interfaced with the sensors and wind tunnel controls using long signal wires. And since the inside of a wind tunnel is naturally a very noisy environment, the measurements being taken incurred a significant amount of error due to inductive and capacitive coupling. A solution that digitizes the measured signals at or near the signal source would allow AAR to eliminate the undesired effects of noise on their measurements.

  AAR recently undertook a project to improve the accuracy of the data from their wind tunnel testing. To accomplish this goal, they selected several EDAS Multifunction Ethernet Data Acquisition Systems from Intelligent Instrumentation and an Ethernet-ready pressure scanning system from Scanivalve. Each EDAS-1002E system incorporates a high-speed analog-digital converter and monitors up to 16 analog inputs from a variety of sources. The systems also feature 16 TTL-level digital I/O channels.

  The ZOC-33 Pressure Scanning Module from Scanivalve measures up to 128 pressure inputs. The inputs then are digitized and converted to Ethernet packets using the company's DSM-3001 Compact Digital Service Module.

  Both the Intelligent Instrumentation and the Scanivalve systems use built-in TCP/IP protocol stacks to provide seamless communication with a variety of host platforms as well as Internet and Internet resources. Once digitized, measurements are sent from the wind tunnel via Ethernet to a PC located outside the tunnel. The PC runs National Instruments' LabVIEW software to process the data. The PC operating system is Windows 95.

Measuring the Car Under Test
  When subjecting race cars to wind tunnel testing, the most pertinent information is the side force, lift and drag caused by the effects of the wind. AAR obtains this data from several six-component balances. Designed for wind-tunnel applications, these sensors measure force in pounds in all three axes using three-axis load cells.

  The six-component balance also measures the moment (in inch-pounds) around each of the three axes. The balance provides six +/-20-mV outputs which are interfaced through standard 5B-style strain gage signal conditioning modules to the data acquisition system mounted on the roof of the model car.

  The pitch and roll that the car sustains from the effects of high-speed driving are other important aspects in the design of the race car body. These phenomena are measured by a two-axis inclinometer mounted inside the model car that outputs a +/-5-V signal for each axis. These also are measured by the data acquisition system through 5B signal-conditioning modules.

  One other closely monitored condition is the air pressure in front of and behind the radiator inside the hood compartment of the model car. These parameters help characterize the airflow quality through the radiator, which is a very important consideration in designing high-performance race cars. AAR uses the pressure scanning system to perform this portion of the test.

Wind Tunnel Monitoring and Control

AAR also uses the data acquisition system to monitor and control wind-tunnel conditions. This subsystem is centered around several huge fans and what is known as a moving ground. The moving ground is a large conveyor that simulates the effect of the road passing beneath the car.   First, AAR monitors a number of sensors to ensure that the "health" of the wind-tunnel and the moving ground are maintained. These include an absolute gage to monitor barometric pressure, several high-accuracy differential pressure gages, and an off-the-shelf temperature and humidity sensor kit. These sensors all output 0 to 5 V and interface to the data acquisition system through 5B signal-conditioning modules.   Meanwhile, a number of sensors are monitoring the conditions of the moving ground. Particularly, a large platinum plate across which the moving ground is pulled must be monitored to ensure that it is being properly cooled. Without this monitoring, the friction of the moving ground can cause the plate to become so hot that it will warp. Six RTDs are placed on various locations under the plate to warn an operator if the temperature is exceeding the allowable limit.

  This platinum plate has several holes drilled through it to create a vacuum beneath the moving ground. This keeps the model car from pulling the moving ground off of the table. The vacuum is controlled by a pump situated under the platinum plate and monitored by 10 pressure gages connected to the data acquisition system through the 5B signal-conditioning modules. The pressure measurements are used to control the vacuum pumps through thresholds defined in a software program running on the Windows 95 PC.

  Another group of sensors monitors the car's wheel speeds to ensure that slippage caused by the moving ground does not exceed 10% and invalidate the test data. Four infrared speed sensors are positioned on the outside wall of the tunnel, one corresponding to each wheel. These monitor revolutions per minute (rpm) of each wheel, using pieces of reflective tape placed on the wheels.

  Each of these infrared sensors produces a TTL pulse output (maximum 60Hz) which corresponds to rpm. The pulse outputs are monitored directly by software counters built into each of the 16 digital I/O channels on the data acquisition system.

The Results
  The addition of Ethernet data acquisition to their wind-tunnel test system has allowed AAR to dramatically improve measurement accuracy without significantly increasing the overall system cost. Critical force measurements have improved by a factor of nearly eight, from a resolution of +/-150 lb before the enhancements to a resolution of +/-20 lb with the new system. A significant portion of this improvement can be attributed to the fact that AAR shortened the length of their signal wires by almost 70%.

  With the capability to take more accurate measurements, AAR expects to design race car bodies that are more aerodynamic. Improved wind-tunnel monitoring and control will provide added protection for the moving ground and the race car models.

Conclusion
  As Ethernet becomes ubiquitous in all sorts of computing environments, from the corporate office to the manufacturing floor to the test lab, more and more useful applications for this network will come to light. While the idea of using Ethernet to solve AAR's problem is a relatively new concept, it already is being duplicated in test facilities all over the world.

About the Author
  Robert M. Winkler worked as a Product Marketing Engineer at Intelligent Instrumentation. Before joining the company in 1994, he served three years as a Network Communications Officer in the U.S. Army Information Systems Engineering Command at Fort Huachuca, AZ. Mr. Winkler graduated from Lehigh University with a degree in electrical engineering.

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