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Claims  |
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What is claimed is:
1. An apparatus for conducting an automated test on a generator set in
accordance with prescribed test criteria, and further for automatically
analyzing a result of the test in accordance with prescribed analysis
criteria, the generator set having generator set output signals indicative
of generator set output characteristics, the apparatus comprising:
an automated load bank coupled to the generator set for imposing upon the
generator set an electrical load which is dependent upon load bank control
signals; and
automated testing means comprising:
a load bank control package coupled to said automated load bank for
generating said load bank control signals in dependence on load bank
command signals,
output measurement means coupled to said generator set for receiving the
generator set output signals and further for generating processing signals
which are indicative of the generator set output signals, and
a controller coupled to said load bank control package and to said output
measurement means, said controller for receiving said processing signals
and for generating test result signals indicative of the result of the
test in dependence on said processing signals and in accordance with the
prescribed analysis criteria, and further for generating said load bank
command signals in accordance with the prescribed test criteria.
2. The apparatus of claim 1 wherein said output measurement means
substantially simultaneously receives output signals indicative of a first
generator set output characteristic and output signals indicative of a
second generator set output characteristic, and further substantially
simultaneously generates a first set of processing signals indicative of
said first generator set output characteristic and a second set of
processing signals indicative of said second generator set output
characteristic.
3. The apparatus of claim 2 wherein said first generator set output
characteristic is generator set voltage and said second generator set
output characteristic is generator set frequency.
4. The apparatus of claim 1 further comprising:
a file server for providing to said automated testing means signals
indicative of the prescribed test criteria and signals indicative of the
prescribed analysis criteria, and further for receiving from said
automated testing means said test result signals, and further for storing
said test result signals.
5. The apparatus of claim 1 wherein said automated load bank comprises:
load bank means comprising a load element which is selectable between a
first state and a second state, wherein said load bank imposes a first
electrical load when said load element is in a first state, and imposes a
second electrical load when said load element is in a second state, and
load bank control means comprising a load bank control switch circuit for
selecting said load element state in dependence on said load bank control
signals.
6. The apparatus of claim 5 wherein said load bank control package
comprises a plurality of output channels, wherein each output channel of
said plurality of output channels generates a prescribed subset of said
load bank control signals in dependence upon a prescribed subset of said
load bank command signals, and wherein said load bank control switch
circuit selects said load element state in dependence on a prescribed
subset of said load bank control signals which are generated by an output
channel of said plurality of output channels.
7. The apparatus of claim 1 wherein said output measurement means
comprises:
signal conditioning means coupled to said generator set for receiving said
output signals from said generator set, and further for generating
measurement signals indicative of said output signals, said signal
conditioning means comprising a plurality of transducer means, wherein
each transducer means of said plurality of transducer means receives a
prescribed subset of said output signals indicative of a prescribed
generator set output characteristic and generates a prescribed subset of
said measurement signals indicative of said prescribed generator set
output characteristic; and
data acquisition means coupled to said signal conditioning means for
receiving said measurement signals from said signal conditioning means,
and further for generating said processing signals in dependence
thereupon.
8. The apparatus of claim 7 wherein said data acquisition means comprises a
plurality of channels, wherein each channel of said plurality of channels
receives a prescribed subset of said measurement signals and generates a
prescribed subset of said processing signals.
9. An apparatus for conducting a plurality of automated tests on a
plurality of generator sets in accordance with prescribed test criteria,
and further for automatically analyzing results of said tests in
accordance with prescribed analysis criteria, each said generator set of
the plurality of generator sets having generator set output signals
indicative of generator set output characteristics, said apparatus
comprising:
a plurality of automated test stations, each automated test station of said
plurality of automated test stations comprising:
an automated load bank coupled to a generator set of the plurality of
generator sets for imposing upon the generator set an electrical load
which is dependent upon load bank control signals;
a load bank control package coupled to said automated load bank for
generating said load bank control signals in dependence on load bank
command signals,
output measurement means coupled to said generator set for receiving the
generator set output signals and further for generating processing signals
which are indicative of the generator set output signals, and
a controller coupled to said load bank control package and to said output
measurement means, said controller for receiving said processing signals
and for generating test result signals indicative of the result of the
test in dependence on said processing signals and in accordance with the
prescribed analysis criteria, and further for generating said load bank
command signals in accordance with the prescribed test criteria; and
a file server coupled to said plurality of automated test stations for
providing signals indicative of the prescribed test criteria and signals
indicative of the prescribed analysis criteria to each of said plurality
of automated test stations, and further for receiving from said plurality
of automated test stations said test result signals and for storing said
test result signals.
10. The apparatus of claim 9 wherein each of said plurality of automated
test stations conducts a different one of the plurality of tests on the
plurality of generator sets.
11. An automated testing apparatus for conducting an automated test on a
generator set in accordance with prescribed test criteria, and further for
automatically analyzing a result of the test in accordance with prescribed
analysis criteria, the generator set having generator set output signals
indicative of generator set output characteristics, the generator set
coupled to an automated load bank which imposes upon the generator set an
electrical load which is dependent upon received load bank control
signals, the apparatus comprising:
a load bank control package coupled to the automated load bank for
generating said load bank control signals in dependence on load bank
command signals,
output measurement means coupled to said generator set for receiving the
generator set output signals and further for generating processing signals
which are indicative of the generator set output signals, and
a controller coupled to said load bank control package and to said output
measurement means, said controller for receiving said processing signals
and for generating test result signals indicative of the result of the
test in dependence on said processing signals and in accordance with the
prescribed analysis criteria, and further for generating said load bank
command signals in accordance with the prescribed test criteria.
12. The apparatus of claim 11 wherein said output measurement means
comprises:
signal conditioning means coupled to said generator set for receiving said
output signals from said generator set, and further for generating
measurement signals indicative of said output signals, said signal
conditioning means comprising a plurality of transducer means, wherein
each transducer means of said plurality of transducer means receives a
prescribed subset of said output signals and generates a prescribed subset
of said measurement signals indicative of said prescribed generator set
output characteristic; and
data acquisition means coupled to said signal conditioning means for
receiving said measurement signals from said signal conditioning means,
and further for generating said processing signals in dependence
thereupon.
13. The apparatus of claim 12 wherein said data acquisition means comprises
a plurality of channels, wherein each channel of said plurality of
channels receives a prescribed subset of said measurement signals and
generates a prescribed subset of said processing signals.
14. A method for conducting an automated test on a generator set in
accordance with prescribed test criteria, and further for automatically
analyzing a result of the test in accordance with prescribed analysis
criteria, the generator set having generator set output signals indicative
of generator set output characteristics, the method comprising the steps
of:
imposing upon the generator set an electrical load in accordance with the
prescribed test criteria;
generating processing signals which are indicative of the generator set
output signals; and
generating test result signals indicative of results of the test in
dependence on said processing signals and in accordance with the
prescribed analysis criteria.
15. The method of claim 14, wherein said step of generating processing
signals comprises the steps of:
substantially simultaneously receiving output signals indicative of a first
generator set output characteristic and output signals indicative of a
second generator set output characteristic; and
substantially simultaneously generating a first set of processing signals
indicative of said first generator set output characteristic and a second
set of processing signals indicative of said second generator set output
characteristic.
16. The method of claim 14, further comprising the steps of:
receiving from a file server signals indicative of the prescribed test
criteria and signals indicative of the prescribed analysis criteria;
presenting said file server with said test result signals; and
storing said test result signals on said file server. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates to generator set testing and more
specifically to generator set testing and analyzing the results of
generator set tests.
BACKGROUND OF THE INVENTION
Instruments which test generator sets are known in the art. As is also
known in the art, such instruments evaluate generator set performance by
analyzing prescribed output signals indicative of generator set output
characteristics such as output voltage, frequency, current and power
quality while the generator set is under a variety of electrical load
conditions. An example of an instrument which tests generator sets is
disclosed by U.S. Pat. No. 5,144,232, incorporated herein by reference.
Disclosed therein is a device which measures the operating speed and
voltage output of a generator set, thereby allowing a user to verify if
the generator set operates properly. The device includes an analog AC volt
meter and a digital frequency display which respectively provide a visual
reading of generator set voltage and frequency. U.S. Pat. No. 5,144,232 is
exemplary of known generator set testing systems, which systems comprise
instruments for recording prescribed generator set outputs, such as
voltmeters, ammeters, oscilloscopes and strip charts. Each such instrument
is capable of recording a single prescribed output at a time.
Generator sets which are to be sold to certain military entities must
comply with the test procedures set forth in MIL-STD-705C, "Military
Standard, generator sets, Engine Driven, Method of Tests and
Instructions", incorporated herein by reference. MIL-STD-705C explains,
establishes and standardizes specific methods for measurements associated
with the evaluation of generator sets. Those who sell generator sets to
purchasers who require compliance with MIL-STD-705C are contractually
obligated to assure that generator sets conform to MIL-STD-705C
requirements. Before the purchaser accepts a batch, or lot, of generator
sets, each generator set in the lot is subjected to MIL-STD-705C specified
tests. A generator set which fails to meet any of a number of prescribed
requirements during any test is considered defective, causing rejection of
the entire lot. Furthermore, rejection is grounds for the purchaser to
refuse further acceptance of generator sets from the seller until the
seller implements purchaser-approved corrective action at the seller's
expense.
In light of the above, those who sell generator sets invest significant
resources in testing generator sets for compliance with MIL-STD-705C. In
conventional generator set testing systems, a technician configures a
generator set and test equipment in accordance with the requirements for a
test. The test equipment generally includes a device known in the art as a
load bank. A load bank imposes a prescribed electrical load upon a
generator set to which the load bank is coupled. The characteristics of
the load which is imposed upon the generator set is determined in
accordance with load bank controls such as toggle switches and mechanical
dials which are coupled to the load bank and operated by a technician.
The technician conducts the test on the generator set and records the test
results by observing outputs of devices which measure test specific
parameters such as generator set voltage, frequency, current and power. To
conduct a test and to record test results typically requires forty eight
hours. A trained analyst analyzes the recorded test results in accordance
with prescribed analysis criteria, thus determining whether the generator
set has passed the test. The test results typically require twenty hours
to analyze.
A drawback of known generator set testing systems is that it requires
several hours to conduct a single test and analyze the test results. It
would be advantageous to have a generator set testing system which can
automatically conduct tests and quickly analyze test results. It would be
especially advantageous to have a generator set testing system which
automatically conducts tests in accordance with MIL-STD-705C.
Another drawback of known generator set testing systems lies in the large
amount of time spent by the technician and the analyst. The technician
must continually record test data as the test is in process, and therefore
cannot perform more than a single test at a time. Similarly, an analyst
can analyze the results of only a single test at a time, The technician
and analyst thereby act as a bottleneck in testing generator sets and
analyzing test results. Furthermore, since the analyst can analyze the
results of only a single test at a time, the technician must decide
whether to await the outcome of the analysis before initiating another
test or to immediately initiate another test. If the technician
immediately initiates another test, he risks wasting valuable time and
resources testing a generator set which the analysis will show to be
defective. On the other hand, if the technician awaits the outcome of the
analysis before initiating another test, he tests generator sets much more
slowly, seriously reducing generator set testing throughput. It would be
advantageous to have a system for testing generator sets in which several
generator sets are tested simultaneously by a single individual.
Still another drawback of known generator set testing systems is that they
depend on highly trained technicians to conduct the tests and to record
test results. Similarly, such generator set testing systems require
trained analysts to analyze test results. It would be advantageous to have
a system for testing generator sets which does not require a highly
trained technician nor a highly trained analyst.
Another drawback of known generator set testing systems is that the trained
technician who records test results often introduces errors into the
recorded test results by rounding a test result to an integer value or
even by incorrectly transcribing a test result. It would be advantageous
to have a system for testing generator sets which accurately records test
results.
Another drawback of known generator set testing systems is that they do not
automate the administration of the procedures set forth in MIL-STD-705C.
Known generator set testing systems must be tailored to implement the
MIL-STD-705C procedures. It would be advantageous to have a system for
testing generator sets which automates the procedures set forth in
MIL-STD-705C.
A generator set has output, characteristics, such as voltage and frequency,
which generally depend on a load imposed upon the generator set. Ideally,
the generator set voltage and generator set frequency remain at
substantially constant values. Typically, the voltage and frequency do not
remain constant, but slightly deviate from a mean voltage value and a mean
frequency value, respectively. Minor deviations of the voltage from a mean
voltage value, that is, deviations wherein the voltage lies within a
desirable voltage range, or band, are deemed to be acceptable voltage
values. Similarly, minor deviations of the frequency from a mean frequency
value, that is, deviations wherein the frequency lies within a desirable
frequency range, or band, are deemed to be acceptable frequency values.
Unfortunately, a frequency value or a voltage value of a generator set may
continually and periodically fluctuate outside of the desirable range. The
periodic fluctuation of a generator set output characteristic outside of a
desirable range is known as a "hunting condition", and generally indicates
a generator set which does not meet specifications. In known generator set
testing systems, a technician or other individual detects a hunting
condition by listening to sounds emitted by the generator set. The
technician, based on his experience, ascertains whether a hunting
condition exists if the sounds emitted are repetitive tones of prescribed
frequencies. It would be advantageous to have a system for testing
generator sets which automatically detects hunting conditions.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a generator set testing
system which conducts a test and analyzes test results in a substantially
shorter time than conventional generator set testing systems.
Another object of the present invention is to provide a generator set
testing system in which several generator sets are tested simultaneously
by a single individual, thereby providing high generator set testing
throughput.
Still another object of the present invention is to provide a generator set
testing system which does not require a highly skilled technician to
conduct tests and record test results, and further does not require a
trained analyst to analyze the test results.
Another object of the present invention is to provide a system which
accurately records test results.
Another object of the present invention is to provide a system which
acquires, stores, analyzes, and reports generator set test results
pursuant to satisfying contractually specified tests set forth in
MIL-STD-705C, "Military Standard, generator sets, Engine Driven, Method of
Tests and Instructions".
Still another object of the present invention is to provide a system which
can perform prescribed sets of tests on a first generator set, and
simultaneously perform another prescribed set of tests on a second
generator set.
Another object of the present invention is to provide a system which
automatically detects hunting conditions.
Still another object of the present invention is to provide a system which
eliminates the need for expensive and complicated test equipment.
Another object of the present invention is to provide a system which can
readily and easily be adapted to perform new tests.
According to the present invention, an apparatus for conducting a test on a
generator set in accordance with prescribed test criteria, and further for
analyzing results of the test in accordance with prescribed analysis
criteria, wherein the generator set has generator set output signals,
comprises an automated load bank coupled to the generator set for imposing
upon the generator set an electrical load which is dependent upon received
load bank control signals, and an automated testing unit comprising a load
bank control package for generating the load bank control signals in
dependence on load bank command signals, an output measurement apparatus
for receiving the generator set output signals and further for generating
processing signals in dependence on the generator set output signals, and
a controller coupled to the load bank control package and to the output
measurement apparatus. The controller receives the processing signals and
generates test result signals in dependence on the processing signals and
in dependence on the prescribed analysis criteria, and further generates
the load bank command signals in dependence on the prescribed test
criteria.
According to another aspect of the present invention, the hereinabove
described apparatus for conducting a test on a generator set in accordance
with prescribed test criteria, and further for analyzing results of the
test in accordance with prescribed analysis criteria, includes an output
measurement apparatus comprising a signal conditioning box and a data
acquisition board. The signal conditioning box is coupled to the generator
set and receives the output signals from the generator set, as well as
generates measurement signals in dependence on the output signals. The
signal conditioning box comprises a plurality of transducers, wherein each
transducer receives a prescribed subset of the output signals and
generates a prescribed subset of the measurement signals. The data
acquisition board is coupled to the signal conditioning box, and receives
the measurement signals from the signal conditioning box, as well as
generates the processing signals in dependence thereupon.
According to another aspect of the present invention, an apparatus for
conducting tests on a plurality of generator sets in accordance with
prescribed test criteria, and further for analyzing results of the tests
in accordance with prescribed analysis criteria, wherein the generator
sets have generator set output signals, comprises a plurality of automated
test stations and a file server coupled thereto. The automated test
stations are for conducting the tests on the generator sets and for
receiving the generator set output signals, and for generating signals
indicative of test results in dependence on the generator set output
signals and in dependence on signals indicative of the prescribed analysis
criteria. The file server is coupled to the automated test stations, and
provides signals indicative of the prescribed test criteria and signals
indicative of the prescribed analysis criteria to the automated test
stations, and further receives from the automated test stations the test
result signals and stores the test result signals.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a generator set testing system
provided in accordance with the present invention.
FIG. 2 is a schematic illustration of the generator set testing system of
FIG. 1 in greater detail.
FIG. 3 is a schematic illustration of the generator set testing system of
FIG. 1 shown in a testing facility.
FIG. 4 is a schematic illustration of a network of testing stations.
FIG. 5 is a flow chart which illustrates a process by which file server
software directs the operations of a file server.
FIG. 6 is a flow chart which illustrates a process by which testing
software directs the operations of an automated test station.
FIG. 7 is a schematic illustration of a load bank control package of FIG.
2.
FIG. 8 is a schematic illustration of a network of different types of
testing stations.
FIG. 9 is a graph of an output signal of a generator set over time.
FIG. 10 is a flow chart which illustrates a process by which an automated
test station determines the existence of a hunting condition in a
generator set.
FIG. 11 is a chart which illustrates a use of bins in detecting a hunting
condition.
DESCRIPTION OF PREFERRED EMBODIMENT
The present invention performs the functions previously allocated to
various individuals by determining tests to perform, performing the tests
and analyzing test results. The present invention permits a nominally
trained test technician to test a plurality of generator sets
simultaneously. The technician who operates the generator set testing
system requires only basic computer skills which allow him to follow
computer displayed instructions. Furthermore, a trained analyst is not
required to analyze test results, since the present invention performs the
analysis without the need for human intervention.
Referring now to FIG. 1, there is shown in simplified schematic form an
automated test station 12. The automated test station 12 comprises a
generator set 10, an automated load bank 14 and an automated test unit 16.
Each of the components 10, 14 and 16 of the automated test station 12 is
coupled to the other, as shown by FIG. 1. In the preferred embodiment, the
automated test station 12 provided in accordance with the present
invention is not limited to a specific type of generator set, but instead
is suitable for testing generator sets of a variety of sizes and speeds
which are enumerated hereinafter. Adaptation of the present invention to
generator sets of sizes and speeds different than those enumerated
hereinafter requires those skilled in the art to make minimal
modifications to the design presented herein, and does not depart from the
scope of the present invention.
The automated load bank 14 imposes on the generatorset 10 an electrical
load. As is known in the art, the load bank 14 imposes an electrical load
when current from the generatorset 10 passes through the load bank 14. The
characteristics of the imposed load are determined by load bank control
signals sent on line 15 from the automated test unit 16 to the automated
load bank 14. The load bank control signals configure the automated load
bank 14 in accordance with prescribed test methods, and the automated load
bank 14 thereby imposes a desired electrical load condition in a manner
described hereinafter.
The automated test unit 16 receives from the generatorset 10 output signals
on line 18. The output signals are indicative of output characteristics of
the generatorset 10 while the generator set is under a load imposed by the
automated load bank 14. Typical output signals are indicative of such
generator set output characteristics as voltage, current, power and
frequency. Thus, the automated test unit 16 performs a variety of tests
upon the generatorset 10 by configuring a desired electrical load
condition on the generatorset 10 through the automated load bank 14, and
receiving the output signals from the generatorset 10 on line 18. As is
known in the art, some output characteristics of the generator set are
constant, while other output characteristics vary with time. Accordingly,
a prescribed subset of the output signals are constant, and another
prescribed subset of the output signals are time-varying.
FIG. 2 shows the automated test unit 16 of FIG. 1 in greater detail. Unlike
conventional generator set testing systems which require dedicated
equipment, the embodiment of the automated test unit 16 which is described
herein is sufficiently flexible to permit its adaptation to a wide variety
of tests with very minor modifications.
In the preferred embodiment, a load bank 11 is a commercially available
load bank, such as Model K675A Permanent Resistive and Reactive Load Bank
from Avtron Manufacturing, Inc. As described hereinafter, the commercially
available load bank is controlled by load bank controls 13, which are
modified so that they are responsive to the load bank control signals sent
on line 15 from the automated test unit 16. As is known in the art, a load
bank comprises motor driven adjustable ratio transformers (not shown),
called variable autotransformers, load elements (not shown), such as
resistive elements and reactive elements, contactors(not shown) to
selectively engage the load elements, and a fan (not shown). Variable
autotransformers allow control of the imposed load conditions, and the fan
cools the load bank when the load elements heat due to excessive power
consumption. The Model K675A load bank is especially suitable for testing
5 Kilowatt and 10 Kilowatt generator sets at 120/208 Volt, 3 phase, 4 wire
at 60 or 400 Hz. The Model K675A is also capable of connection and
operation at 120 Volt, 1 phase, 2 wire and 120/240 Volt, 1 phase, 3 wire
configurations. The Model K675A is rated at 15 kW/25 Kilovars at 120/208
Volt, 3 phase, 4 wire, 60 and 400 Hz.
Multiple commercially available load banks can also be cascaded together to
function as a single load bank. For example, the Avtron Manufacturing,
Inc. Model K575 provides resistive loading, while the Avtron Model K341
provides reactive loading. Using both the K575 and the K341 simultaneously
to load a generator set is preferred for testing 15 Kilowatt, 30 Kilowatt
and 60 Kilowatt generator sets at 120/208 Volts and 240/416 Volts, 3
phase, 4 wire at 60 or 400 Hz. Those skilled in the art can substitute
other load banks or combinations of load banks to serve as the load bank
11 without departing from the scope of the present invention.
As is known in the art, in conventional generator set testing systems load
bank controls which configure a load imposed by the load bank 11 are
typically manually operated mechanical devices such as push buttons or
toggle switches. Manually operating the mechanical load bank controls,
such as pushing a button or toggling a switch, closes or opens an
electrical circuit contact, thereby engaging or disengaging different
components of the load bank and imposing a load on the generator set 10.
To facilitate control of the automated load bank 14 by the automated test
unit 16, the load bank controls 13 comprise controls of a commercially
available load bank which are modified to accept load bank control signals
on line 15. Relays (not shown in FIG. 2) which are coupled to each
mechanical load bank control are responsive to the load bank control
signals, and close and open in accordance with the load bank control
signals sent from the automated test unit 16. As described hereinafter, in
the preferred embodiment, the relays coupled to the mechanical load bank
controls are normally open AC solenoids. Thus, the automated test unit 12
duplicates conventional operations of the mechanical load bank controls by
sending load bank control signals to the load bank control.
A signal conditioning box 20 receives the output signals from the generator
set 10 on line 18. The signal conditioning box 20 generates measurement
signals in dependence on the received output, signals. The signal
conditioning box 20 comprises a power supply 19 and a plurality of
transducers 21 powered thereby. Each transducer in the plurality of
transducers 21 accepts a subset of the output signals and generates a
subset of the measurement signals in dependence thereupon. In the
preferred embodiment, the measurement signals generated by the plurality
of transducers 21 are analog voltage signals between 0 Volts and 10 Volts.
In another embodiment, the measurement signals generated by the set of
transducers 21 are analog voltage signals between -5 Volts and 5 Volts. In
still another embodiment, some of the measurement signals are analog
voltage signals between -5 Volts and 5 Volts, and the remaining
measurement signals are analog voltage signals between 0 Volts and 10
Volts.
Also in the preferred embodiment, the following types of transducers, known
to those skilled in the art, are provided in the signal conditioning box
to permit measurements prescribed by MIL-STD-705C: High Speed Current
Transducer, High Speed Voltage Transducer, RMS Current Transducer, RMS
Voltage Transducer, Power Transducer, Pressure Transducer, Thermocouple
Transducer, Multi-tap Current Transformer and Frequency Transducer. As
discussed hereinafter, the signal conditioning boxes of other automated
test units may comprise different types of transducers. Table 1 enumerates
transducers used in the preferred embodiment, as well as their Ohio
Semitronics, Inc. respective part numbers.
TABLE 1
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Part Numbers of Preferred Transducers
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FTA-4567 0-500 Hz Frequency Transducer
CT7-015D 0-10 Amps Current Transducer
PC20-002DX1337
Volt/Watt/Amp Transducer
VTR-001DX1358
0-150 V Transducer True RMS
VTR-002DX1358
0-300 V Transducer True RMS
VT7-009D 0-500 V Transducer DC to 10 kHz
2000G-1G5-A 135 PSI, Pressure Transducer
CT7-017DX1047
0-20 Amps Current Transducer
VT7-003DX1047
0-50 V Transducer DC to 10 kHz
VT7-005D 0-150 V, DC to 10 kHz, Generator set Field
Voltage
CT7-015DX1047
0-10 Amps Current Transducer
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A data acquisition board 22, preferably a 7875 PC Multifunction Board by
Virtech, Inc., receives the measurement signals from the signal
conditioning box 20 and generates processing signals in dependence
thereon. The signal conditioning box 20 and the data acquisition board 22
together comprise an output measurement apparatus which receives the
output signals from the generatorset 10 and generates processing signals
in dependence thereupon. Whereas the measurement signals are analog
signals, the processing signals are digital signals, preferably twelve-bit
digital signals, which are indicative of the measurement signals. The
processing signals can comprise any number of bits, and it is known in the
art that a greater number of bits provides greater resolution of the
measurement signals. For example, twelve-bit digital signals provide a
resolution of 2 12, or 4,096 different values.
The data acquisition board 22 periodically samples the measurement signals
as described hereinafter. As is known in the art, sampling a signal
consists of determining and storing the value of the signal at prescribed
instants which are fixed time intervals apart, for example, every
millisecond or every sixteen microseconds. As is also known in the art,
the rate at which sampling occurs must be at least twice as fast as the
highest frequency component in the time-varying signal. For example, if
the time-varying signal has a maximum frequency of 100 Hz, then the
sampling rate must be 200 Hz or faster to avoid sampling errors. In the
preferred embodiment, the sampling rate is at least 25% higher than twice
the highest frequency component in the measurement signals.
The data acquisition board 22 samples at one of a number of possible
sampling rates, depending on the test to perform and expected
characteristics of the measurement signals which are known to those
skilled in the art of generator set testing. For example, during method
608.1b, "Frequency and Voltage Regulation, Stability and Transient
Response Test (Short-Term)" of MIL-STD-705C, the sampling rate is 100 Hz,
or one hundred samples per second, in the preferred embodiment. For other
tests, such as method 655.1a, in which MIL-STD-705C specifies that test
results are to be displayed on an oscilloscope and photographed, the
sampling rate in the preferred embodiment is 40 kHz, or 40,000 samples per
second.
The data acquisition board 22 preferably has a dedicated microprocessor,
thereby allowing the board 22 to accurately sample the measurement signals
at a desired sampling rate without interruption. If the board 22 does not
have a microprocessor which is dedicated to sampling the measurement
signals, the board 22 may not be able to sample at each of the prescribed
instants and will miss samples of the measurement signals.
The data acquisition board 22 comprises a plurality of channels (not
shown). A channel receives a subset | | |
