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A Data Acquisition
System, 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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