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A Data Acquisition System in LabVIEW 5.0 Remotely Controlled Via Network
For the Emissions Test Lab of the Chrysler Tech Center
Products Used:
LabVIEW 5.0
DAQ, SCXI
The challenge:
To develop a data acquisition system which is remotely controlled by a host computer, an IBM RS6000 workstation, via a Local Area Network (LAN). The host computer sends commands to the data acquisition system. All of the data is acquired from more than 150 channels and must be transmitted to the host computer at a high speed
(up to 20 Hz). Data from the analog input channels is taken at different sampling speeds, combined, and then transferred to the host computer.
The Solution:
National Instruments LabVIEW 5.0 was used to develop the data acquisition software. An Intergraph Pentium II PC, a PCI-MIO-16XE-10 data acquisition card, 5B modules, and SCXI modules collect data from 64 analog and
32 digital input channels. The system also includes 18 analog output channels and 32 digital output channels. The built-in networking functions of LabVIEW 5.0 were used to build a TCP/IP server and a UDP client. The TCP/IP server receives commands sent from a host computer. The UDP client transfers acquired data to the host computer at a high speed. The TCP/IP server and the UDP client run concurrently with the data acquisition and display. Full advantage is taken of the multithreading capability of LabVIEW 5.0 in order to allow the CPU-intensive Virtual Instruments (VIs) to run smoothly.
Abstract
V I Engineering has developed a LabVIEW based data acquisition system for the Emissions Test Lab of the Chrysler Tech Center in Auburn Hills, Michigan. An SCXI chassis, 5B modules and a PCI data acquisition card are used to acquire signals from multiple analog and digital channels from the vehicle emissions test cell. The system also controls dynamometers and other equipment in the test cell. The operation of the data acquisition system is remotely controlled by commands from a host computer, an IBM RS6000 workstation, through a 100 base-T using TCP/IP protocol. All acquired data is sent back to the workstation at a frequency of 20 Hz using UDP protocol. A diagnosis and maintenance mode allows users to locally operate the data acquisition system.
Introduction
The Chrysler Tech Center is building a new generation vehicle emission test laboratory to test vehicle models for compliance with the emission standard set by US Environmental Protection Agency (EPA). A data acquisition system is needed to collect data from the test cell and control other equipment such as dynamometers and test benches. A central host computer controls the operation of the data acquisition system as well as other systems in the test cell. Chrysler selected V I Engineering, Inc., a Premier National Instruments Alliance Member, to develop this system. LabVIEW 5.0 was used to develop the software for the data acquisition system. Combining LabVIEWs renown easy and fast developing advantages and V I Engineering's expertise, the system was developed for Chrysler with minimum cost and time. This system is robust and flexible for future modifications and expansions.
Networking Controlled Data Acquisition
The data acquisition system communicates with a host computer through a 100Base-T Ethernet. All test operations are controlled by commands from the host computer. Because TCP/IP protocol is a connection based, reliable communication protocol, a TCP/IP server was setup to receive control commands from the host computer. On the side of the host computer, a TCP/IP socket, which connects to the TCP/IP server, acts like a TCP/IP client. After receiving test commands, the TCP/IP server directs the data acquisition operation, and then sends back a response message which includes the requested test result and/or the error/event information. All of the acquired data, which is received from over 150 digital and analog channels, is sent to the host computer at the rate of up to 20 Hz. The UDP protocol is used to perform this action because of the faster speed capability of UDP comparing to TCP/IP.
Command Interpreter
Chrysler engineers designed the commands for the data acquisition operations. By sending commands, the host computer obtains the test system's status information, analog and digital input data, and error/event information. The host computer can also acquire the reading of an individual channel or any combination of input channels. The host computer can set the output of an individual channel or any combination of output, as well as control the operation of the data acquisition and data transferring.
A command interpreter has been developed to read and parse the commands and perform the actions according to the commands. The command interpreter checks the syntax of the commands as well. If it detects any syntax error in the received command, it will report the error to the host computer immediately.
Error/Event Handling
A robust error/event handling mechanism has been developed for the test. During the test, all of the errors and events are saved into an error/event queue and are reported to the host computer through TCP/IP channel upon request. Errors include command errors, data acquisition errors or file I/O errors, and more. Events represent some operational activities of the test. The errors and events are saved into a log file, which allows users to view the error/event history and perform clean-up in the future.
Data Acquisition
A PCI-MIO-16XE-10 data acquisition card and SCXI modules are used to acquire the analog and digital signals.
5B modules perform the signal conditioning together with the SCXI modules. Two SCXI 1100 modules acquire
32 thermocouple inputs and 32 other analog inputs. Three SCXI 1124 modules are used to provide 18 channels of analog output signals. An SCXI 1163R and an SCXI 1162HV are used to provide 32 digital inputs and 32 digital outputs. Most of the signals change slowly. Data is acquired at the base rate of 20 Hz. For some channels, however, signals change quickly, and need to be monitored closely. As requested by the customer, the software has been developed for some of the analog input channels to acquire and transfer at high rates while the rest of the analog inputs acquire at a base rate of 20 Hz. Users can easily select the rates and the channels to run at the higher rates. Since the data blocks are transferred at a fixed rate of 20 Hz, a special code has been developed for multiple data points of the high speed channels to be inserted into the data stream and transferred to the host computer.
Multithreading
The application has four operations running concurrently. They are a Data Acquisition VI, a TCP/IP VI, a UDP VI and a Display VI. The Data Acquisition VI and the UDP VI are computing resource intensive. However, they are also time critical and cannot have any delay because the other instruments in the test cell rely on the test data to be acquired and transferred in real time. By taking advantage of the multithreading capability of LabVIEW 5.0, these separate VIs are assigned to different threads. The time and CPU resource critical operations (DAQ and UDP) are therefore insured to run smoothly.
Manual Mode Test
Although the test is completely controlled by the test commands received from the remote host computer, users need the ability to manually run the test for maintenance and diagnosis purposes on the local data acquisition computer. The software provides the capability for users to fully run the test system manually in the local data acquisition system as well as to change the test setup parameters and preferences. The software also provides a networking diagnostic console which allows users to test the network connection and the header information in the command messages.
Security
The software provides multi-levels of user access privileges. Users with different access privileges can have different controls of the test in the local data acquisition system. A password is required in order to access a specific level. A user-friendly User Access Manager has been developed to allow the administrator to edit the user names and passwords.
Conclusion
V I Engineering has developed a data acquisition system to test vehicle models for compliance with emission standards set by the US Environmental Protection Agency (EPA) using LabVIEW 5.0, a PCI data acquisition card, and SCXI modules. The data acquisition operations are completely controlled by a remote host computer through the LAN. By using LabVIEW, the system has been developed with minimum time and cost to Chrysler Corporation. The system is robust and easy to revise when future modifications are required.
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