Data Acquisition Application Brief
PMTI uses DADiSP
, the graphic display and data management software from
DSP Development Corporation
, as well as DADiSP/Filters
Shepherd, Department Head of Marine Engineering, uses these tools to
teach students the essentials of data acquisition and analysis for
computer-assisted engineering. DADiSP is employed as part of a diesel
engine monitoring system that the students are exposed to during their
three-year engineering apprentice program.
Monitoring Diesel Engine Parameters
PMTI's computer system, built around a personal computer, was designed
by students and faculty in a cooperative effort. Its primary functions
are to produce an automated heat balance in an animated bar chart form,
and to display cylinder pressure diagrams on screen to process cylinder
pressure data. The diesel engine being monitored is a four-cylinder
Perkins 4.108 developing 41 kW at 4000 rpm and driving a Froude
hydraulic dynamometer. It incorporates an analysis system, which
includes cylinder and fuel pressure sensors, an injector lift
transducer, and thermocouples that sense temperature transients.
Magnetic pick-up proximity sensors sense speed and crank angle and are
used to synchronize other sensors to engine speed. An oscilloscope is
used to monitor combustion-related phenomena.
Plotting Engine Functions
In a typical project, students run an engine up to temperature and
monitor cylinder pressure conditions over a variety of loads. The data
are continuously acquired by the software acquisition system at a
sampling rate of either 13250 Hz or 300 Hz, depending upon the
application: the high speed is necessary for monitoring the internal
cylinder conditions; the low speed is used for thermocouple readings
for heat balance computations. Data are continuously downloaded to the
PC's hard disk for processing with DADiSP. Plots are generated of the
engine functions being monitored - for instance, cylinder pressure vs.
crank angle and its derivative.
DADiSP, an Integral Part of Student Understanding
Mr. Shepherd, Department Head of Marine Engineering, states that using
DADiSP in this way "gives students a window" into the engine cylinder.
DADiSP allows them to study combustion-related phenomena in greater
detail than would otherwise be possible. According to his article on
the system for Marine Engineering Digest, PMTI's apprentice-ship
program is designed to teach students through application of computers,
that their function is "to make conclusions on the acquired data and
leave the ponderous activity of collecting data to the computers." He
mentions that, in addition to working with DADiSP, students are
required to perform all calculations and draw plots by hand, so they'll
know what to do if they get caught at sea without a functional
computer. Shepherd reports that PMTI plans to expand their computer
system to include a database system for spare parts inventory, planned
maintenance, condition monitoring systems and simulation - always
keeping DADiSP as an integral part.