Note: Descriptions are shown in the official language in which they were submitted.
CA 02298060 2006-11-30
INTEGRATED MONITORING, CONTROL AND SHUT-DOWN SYSTEM
Field of the Invention
The present invention relates generally to monitoring and control systems, and
more specifically relates to an integrated monitoring, diagnostics, shut-down
and control
system.
Background of the Invention
Electronic systems of a machinery can perform various functions such as
monitoring, diagnostics, shutdown, and control.
Monitoring refers to the ability to acquire readings from electronic sensors
via
analog to digital conversion or open/closed contacts of sensors and to be able
to
display the numerical readings or status and/or to be able to store the result
by
electronic means.
Diagnostics refers to the ability to determine the mechanical condition and
performance of a machine from the sensors which are monitored. The diagnostic
results may be determined by alarm values of sensor data, or calculated values
derived
from the sensor data by various mathematical techniques or by means of logic,
fuzzy
logic, probabilities, and/or rules implemented by software. The mechanical
condition
refers to the fitness of mechanical parts that form parts of the machine to
perform the
function required by the machine. Examples of mechanical parts may be a
bearing, a
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=
valve, or a piston ring in an engine. The performance refers to the ability of
the
machine to perform its function such as turning a shaft at the desired speed,
or to
generate a flow of gas at the desired pressure and flow rate.
Shutdown refers to the ability to shutdown a machine that is operating in a
condition which is considered as unsafe or likely to cause the machine to
damage itself
or associated machinery. An example is the shutdown of an engine with a
abnormally
low oil level or low oil pressure. The shutdown function causes the machine to
stop
operating in response to a specified signal or a combination of electronic
signals from
analog and/or digital sensors that sense certain machine conditions. An
example is a
rotational speed sensor that generates a signal when the rotational speed of a
shaft
exceeds a pre-determined setting which in turn causes the shutdown system to
shut off
the fuel or source of energy to the device causing the shaft to rotate.
Control refers to the ability of an electronic system to read an electronic
analog
or digital sensor signal and generate an output analog or digital signal which
controls
an actuator to control an attribute of the machine. An example is the control
of coolant
temperature with the open/close position of a valve in the coolant flow line.
When the
coolant temperature rises causing a high reading on the temperature sensor,
the control
system changes an electronic output current or voltage to open the control
valve which
allows more cool water to flow.
System refers to the combination of electronic hardware which can read sensor
outputs, can generate control signals for actuators, contacts or switches for
the
purposes of control and/or enunciation, and software which causes the
electronic
hardware to respond in the desired manner.
In the case of machinery with reciprocating pistons, such as reciprocating
engines, reciprocating compressors used for compressing gases, and
reciprocating
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pumps used for pumping liquids, current electronic system are designed to
perform a
combination of the functions.
The performance of the functions of shutdown and control is currently
integrated
within control systems, such as systems using Programmable Logic Controllers
(PLC's).
Many of these control systems have the ability to perform these functions with
hardware
or software processes such as the proportional, integral, derivative(PID)
functions.
Such systems can acquire analog and digital signals and can generate analog
and
digital outputs. These systems are generally follow a ladder logic or flow
diagram
method of operation. Basically the loop is repeated while the system is
operating. The
key feature of these systems is the ability to ensure a response within a
guaranteed
time (such as 0.5s, 0.1 s). Some of the systems use a real time operating
system to
perform the tasks in addition to being able to perform electronic
communication with
other devices (RS232, RS485 etc.). However, such systems do not have the
ability to
acquire and manipulate analog inputs at a data rate higher than 10 to 100
times per
second. As well, such systems generally do not have the computational
capability to
perform diagnostics beyond simple threshold alarms.
There are a numberof systems available that perform monitoring using computer
technology with data sampling rates well above 1000 per second. Examples of
such
systems are the Beta-trap On-line made by Liberty Technology, the Model 6100
made
by Windrock systems, and the SCXI signal conditioning system made by National
Instruments. Normally these monitoring units have the capability for
communications.
Some of the most advanced of these systems have software diagnostic
capability. The
monitoring involves the acquisition of a contiguous stream of data followed by
the
processing of the data to either generate a numerical result or store the data
for later
processing. All of these monitoring systems cannot, by the nature of their
single tasking
design, perform the monitoring and shutdown capabilities at the same time as
the
monitoring.
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Because of the designs currently used for shutdown/control and
monitoring/diagnostics each of them are not capable of adding the
complementary
capability.
There is a need in the art for a system that integrates the functions of
shutdown
and/or control of a machinery with the functions of monitoring and/or
diagnostics of a
machinery.
Summary of the Invention
It is an object of the invention to provide a integrated monitoring,
diagnostics,
shut-down and control system for machinery.
In an embodiment of the invention, there is provided an integrated monitoring,
control and shut-down (IMCS) system for monitoring and controlling the
operation of a
machinery. The IMCS system includes: input ports for receiving input sensor
signals
indicative of conditions of the machinery that require monitoring and output
ports for
outputting control signals to actuators of the machinery that require control.
The IMCS
system also includes signal conversion means coupled to the input and output
ports,
for converting the input sensor signals into data samples and for converting
control
data into control signals. Furthermore, the IMCS system comprises memory
means,
said memory means storing at least a software application comprising a
communication
protocol. The IMCS system also includes a data processor for controlling
operation of
the signal conversion means, for processing the data samples into calculated
values,
for sending selected calculated values to be stored into the memory means, for
calculating control data, said data processor operating according to said
software
application. The IMCS further includes a communication bus coupling the data
processor, the signal conversion means, the memory means, according to said
communication protocol, and a power supply for providing power for the
operation of
the system.
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The invention can be used for monitoring, controlling, diagnosing and
determining the performance of machines used to develop mechanical energy such
as
reciprocating engines, machines driven by a rotating shaft such as electrical
generators,
rotating and reciprocating compressors, rotating and reciprocating pumps,
propellers
(air and water), water and gas turbines, and the like.
In one of its aspect, the invention also provides a data acquisition process
for
use in the monitoring and control of a rotating equipment comprising a shaft,
the
method comprising the steps of sampling a condition sensor output indicating a
condition of the rotating equipment that requires monitoring, for obtaining a
condition
signal; sampling a marker sensor indicating the rotational position of said
shaft, for
obtaining a rotation marker signal; and combining the condition signal and the
rotation
marker signal.
Brief Description of the Drawings
The present invention will now be explained, by way of example only, with
reference to certain embodiments and the attached Figures in which:
Figure 1 is a general overview of a system for monitoring and control of a
machinery;
Figure 2 is a block diagram of an integrated monitoring, control and shutdown
system according to a preferred embodiment of the invention;
Figure 3 is a block diagram of the hardware of a data collection and organizer
unit (CONDOR) of the IMCS system in Figure 2;
Figure 4 is a diagram of the software architecture of the CONDOR unit in
Figure
2;
Figure 5 is an example diagram showing the transparency of the network
incorporating the IMCS system of the preferred embodiment to software
processes and
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the ability of processes running in the IMCS system to communicate among each
other
and/or with processes on other systems connected in a network with the IMCS
system;
Figure 6 is a diagram showing an example in which a calculation block within
the
software of the CONDOR unit of Figure 2, is updated on-line;
Figure 7 is a diagram describing the data acquisition process performed by the
IMCS system, according to one embodiment of the invention;
Figure 8 is a diagram describing the data collection and storage process,
within
the CONDOR unit of Figure 2;
Figure 9 is an example of data evaluation conditions imposed within the IMCS
system, in one embodiment of the invention;
Figure 10 is a diagram depicting the data storage process in a Normal Mode of
operation of the CONDOR unit in Figure 2;
Figure 11 is a diagram depicting the data storage process in a Warning Mode of
operation of the CONDOR unit in Figure 2;
Figures 12A-12G are level-0, level-1 and level-2 data flow diagrams for the
monitoring and diagnostics processes performed by the IMCS system of the
preferred
embodiment of the invention, when used in conjunction with an engine or
compressor.
Figures 13A-13B are level-1 and level-2 data flow diagrams of the sequencing
logic performed by the IMCS system of the preferred embodiment of the
invention, for
achieving the functions of shut-down and control of an engine/compressor
Figure 14 is a diagram describing the data indexing process within the CONDOR
unit of Figure 2;
Figure 15 is a diagram showing a control loop performed within the IMCS system
for performing the control function, in one aspect of the invention,
Figure 16A-16G are level-0, level-1 and level-2 data flow diagrams forthe air-
fuel
control process performed by the IMCS system of the preferred embodiment.
Figure 17 is a diagram showing the signals acquired for a data acquisition
process according to one aspect of the invention;
Figure 18 is a diagram showing the parts of a general reciprocating system, on
which the process in Figure 17 ;
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Figure 19 is a diagram showing the parts of a general rotating system, on
which
the process in Figure 17 is applied;
Figure 20 is a diagram showing the correlation of signals in one embodiment of
the data acquisition process in Figure 17;
Figure 21 is a flow chart of a method of determining detonation in an
engine/compressor, according to another aspect of the invention.
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DETAILED DESCRIPTION OF THE INVENTION
In its broad aspect, the present invention provides an on-line monitoring and
control system that integrates the capabilities to perform monitoring,
diagnostics,
shutdown and control of a machinery. The communications capability is further
integrated in a further embodiment of the invention. This system, referred
herein as an
Integrated Monitoring, Control and Shutdown (IMCS) system, has the capability,
by its
design, to perform all of these tasks simultaneously. This is achieved by a
combination
of software, hardware and a real time operating system (RTOS), as it will be
further
described.
Figure 1 is a overview picture, meant to help in the understanding of the
operation of the IMCS system 1 according to one aspect of the invention. The
IMCS
system 1 in Figure 1 is an online diagnostic tool to be used in the monitoring
of
mechanical condition and performance characteristics of the engine/compressor
2 of
a machinery. In a broad aspect of the invention, the IMCS system 1 may be self
operated. Preferably, as shown in Figure 1, it provides an user I/O
capabilities 3 to alter
driver/load functions. Through tabulations of sensor data, the IMCS system I
can be
used as a tool not only to detect the symptoms of a mechanical problem, but
also to
evaluate the root cause. Through specialised sensors, the IMCS system 1 senses
abnormal sensor readings and provides productive maintenance recommendations
before problem situations arise. Should an emergency develop, the IMCS system
1
recognizes it and generates an electronic signal to cause a machine shutdown
or
provides advisory information indicating a shutdown situation.
The IMCS system 1 provides continual on-line monitoring information for
management of the machinery asset. One use of this monitoring/evaluation
process is
the implementation of a predictive maintenance scheme which extends the life
cycle of
consumable mechanical components. The benefit is seen in cost reduction, as
the use
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of a regular maintenance schedule often does not utilize the full operating
life of
consumable components.
Detailed Description of a Preferred Embodiment of the Invention
Referring to Figures 2 - 20, the invention is described in accordance with one
of
its preferred embodiments. The following description is not intended to be
limiting in
what concerns aspects that will be recognized by a person skilled in the art
as non-
essential. It will be understood that various technologies used in the
implementation of
the preferred embodiments may be substituted for equivalent alternatives,
currently
existent or as they emerge. Furthermore, the preferred embodiment of the
invention
applies to the control of a rotating engine/compressor 2, but it will be
appreciated that
it could be applied to any other similar machinery.
Referring to Figure 2, the IMCS system 1 comprises a Direct SensorArray (DSA)
coupled to a Collection and a Data Organiser Unit (CONDOR) 10. The DSA
comprises a High- speed Sensor Array (HSA) 22, a Low-speed Sensor Array (LSA)
24
and an Actuator Array (AA) 26. Optionally, the system may also comprise a
Digital
Acquisition and Control Unit (DA&C) 40 coupling an Indirect Sensor/Actuator
Array
20 (ISA) 30 to the CONDOR 10 . On-line interfaces with the CONDOR may be
provided
through one or more of a Data Manager (DM) 60, a Distributed Control System
(DCS)
50, and a Human Machine interface(HMI) 70. Such on-line interfacing may be
built
within the plant or it may be made manually and in absence of such interface,
the
CONDOR 10 would operate based on its established configuration. A
Configuration
Manager (CM) 80 may be used initially to specify sensors and actuators and to
specify
the monitoring, control, communications and diagnostic actions of the CONDOR
10.
All sensor and actuator arrays, DSA 22 and ISA 30, are coupled to the
machinery being monitored and controlled.
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The Direct Sensor Array (DSA) 20 includes all sensor signals that may be
sampled either at a low data rate (such as process temperatures) or sampled at
high
data rates, for example at periods of less than 1 ms, due to the rapid
variation of the
signals (vibration signals). The indirect sensor array is connected to a DA&C
40, which
can only sample or provide outputs at low data rates. Examples where the high
sampling speed is essential are dynamic pressure sensors, accelerometers (for
vibration measurement), velocity type vibration sensors and electrical current
sensors.
The HSA 22 and LSA 24 provide digital or analog signals from sensors, which
monitor
a Driver and a Load of the machinery. For the case of an engine/compressor 2,
examples of sensors to be included in the Direct Sensor Array 20 are listed in
the
following table.
Direct Sensor Array (DSA)
# of Sensors Sensor Class Sensor Type
20 Accelerometer Engine Cylinder Detonation
2 Accelerometer Engine Vibrational Crank Case Position
20 Piezo or Optical Diesel Engine Cylinder Fuel Pressure
20 Optical Engine Cylinder Pressure
16 Piezo or Optical Compressor Cylinder Pressure
8 Accelerometer Compressor Cylinder Distance Piece
1 Inductive 1/Rev (Engine Speed or Flywheel)
1 Inductive N/Rev
12 0 to 100 mV Thermocouples
6 4- 20 mA Manifold and fuel pressure
1 0 to 5V 02 in exhaust gases
1 Hall effect 1/2Rev
The HSA 22 and LSA 24 provide digital or analog signals from sensors, which
monitor a Driver and a Load of the machinery.
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The actuators, either comprised within the Actuator Array (AA) of the DSA 20
or
in the Indirect Sensor/Actuator Array (ISA) 30, provide signals to control
devices in
response to electrical signals from a controller. Examples of control devices
are devices
controlling a mechanical position like a valve position, or devices
controlling electrical
contacts like relays, or any equivalents thereof
In addition to actuators, the ISA 30 comprises other sensors that can be
sampled
at lower rates such as signals indicating state and process parameters, like
the
temperature, pressure etc., but they do not require a direct connection to the
CONDOR
10. The use of a DA&C 40 depends on site details and user needs. The CONDOR 10
receives sensor values from sensor of the ISA 30 and control actuators within
the ISA
30 through a DA&C 40.
The CONDOR 10 is responsible for one or more of the following functions:
a)performing sequential sampling of data from HSA 22 and LSA 24,
b)generating outputs for actuator array AA,
c)processing data samples (raw data) into calculated values corresponding to
properties of the Driver and Load parts,
d) storing calculated values and statistical information in a memory of CONDOR
10;
The storing operation may be done periodically and the information may be
stored for
a predetermined period. For example calculated values are typically stored
every hour,
and kept in the memory for 30 days or more;
e)calculating control outputs from set-point input(s) and input(s) derived
from a
measured value. A common control algorithm is the proportional, integral and
derivative (PID) function;
f) providing warning, alarm and shutdown conditions based on raw data
calculations,
normal operating limitations provided within the Driver/Load configuration.
The warning
conditions are stored in I/O registers that can be accessed by the HMI 70, DM
60 and
DCS 50;
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g) interpreting a user-defined sequence logic to automate a start-up/safety
shutdown
process.
The CONDOR 10 may have varying configurations depending on site requirements.
The DCS 50 is a control system, normally used for a large plant, which
controls
other systems within the plant. The DCS 50 is not essential for the external
control of
the IMCS system 1 and for smaller facilities its implementation is not
advantageous.
When the DCS 50 is present, it typically controls major items such as start,
stop,
revolutions per minute (RPM), while the IMCS system 1 controls local items
causing the
machinery to start in a desired manner, stop in a desired manner and operate
to
maintain a desired RPM.
The CM 80 defines sensor inputs for (HSA 22 and LSA 24), actuator outputs for
(AA), communications links, memory organisation, sequencing logic and other
parameters to enable the CONDOR 10 to perform its tasks.
The DM 60 performs at least one or more of the following:
a) uploads calculated and other values (historical or current data) from
CONDOR 10;
b) uploads contiguous high-speed sensor data;
c) performs advanced analysis and post-processing of data.
The HMI 70 is an optional interface unit or computer for the site technician
or
machine operator which may perform at least one or more of the following:
a) access specified data registers in CONDOR 10,
b) display CONDOR 10 information;
c) accept operator inputs to modify control actions of the CONDOR 10.
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The DA&C 40 is an optional electronic unit (data acquisition and/or control)
which
may also provide data to the CONDOR 10 or be controlled by the CONDOR 10. A
Programmable Logic Controller (PLC) may serve as a DA&C 40 for the CONDOR 10.
If present, the DM 60, CM 80and DCS 50 have user interfaces.
The general hardware organization of the CONDOR 10 is as shown in Figure 3.
Figure 3 shows the basic components of the hardware tied together on a bus
100.
Analog to digital (A/D) card 130 and Digital to Analog (D/A) card 150 are
plugged into
the bus 100 that is shared with the central processor or computer 120, which
has a
central-processing unit (CPU), as well as a Direct Memory Access (DMA) chip.
The
computer 120 has access to a memory block 110, comprising both volatile and
non-volatile memory. Input and output ports to are represented on the diagram
by a
multiple input/output block (I/O)140 couples the sensor and actuator-arrays to
the rest
of the CONDOR 10.The multiple inputs and outputs (I/O)140 may be multiplexed
and
conditioned using electronic circuits conventional in the art. Generally, a
signal
conditioning card 135 conditions the analog signals from the sensors before
sending
them to the A./D card 130. A digital I/O card 160 is also linked to the
central bus 100,
in the preferred embodiment. A serial communication unit 170 is tied on the
bus 100 for
allowing communication among devices. The serial communication unit 170 may
comprise conventional hardware, complying with standards such as RS232, RS485,
Ethernet, Canbus, Fieldbus, Arcnet and others. A modem may be included either
connected to the bus 100 or connected to a serial communication unit (SCC)
135. A
power supply 180 to provide the necessary power for the operation of the
CONDOR 10
is present. Power requirements criteria would be obvious to a person skilled
in the art
and they will not be described here. An external watchdog timer circuit 190 is
connected
to the computer and will de-energize a relay if it does not receive a trigger
pulse from
the computer within a defined time period. The watchdog timer 190 thus
verifies the
operation of the system software.
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The CONDOR 10 is responsible for data sampling, A/D & D/A conversion,
multiplex control, data collection, data & communication conversion and
operational
control. The CONDOR 10 hardware sequentially monitors the Direct Sensor Array
20
based upon software criteria and, possibly, a Driver/Load shaft rotation
marker signal,
as it will be described later on. Provisions can be made such that cycling of
power will
return the CONDOR 10 unit to a data acquisition state and resume data
collection (i.e.,
Cold Start). The CONDOR 10 hardware of the preferred embodiment has a well
developed real-time operating system (RTOS) such as QNX, I/O Device Drivers
for
RTOS and Basic Input Output System (BIOS) capability for cold start of the
CONDOR
10 software.
Memory 110 is upwards expandable dependent on installation requirements. The
CONDOR 10 has sufficient Non-Volatile (NV) storage memory to support the RTOS
SW, CONDOR 10 software and Configuration information. The CONDOR 10 also has
sufficient RAM to store a set of sensor data and the calculated values for a 1
hour
period of time (or any other predetermined period of time). Furthermore, the
CONDOR
10 has sufficient NV memory to store 30 days (or any other predetermined
period of
time) of summary calculated data. The DM 60 has sufficient hard-disk to store
an
appreciable amount of CONDOR 10 uploaded data summaries.
The signal conditioning card (SCC) 135 acquires / conditions the sensor
signals.
Each sensor line has protection and associated input buffering and/or
amplification, as
required. Data lines are be grouped into sensor sets according to sensor class
(i.e.,
Vibrational, Cylinder pressure) and signal type (i.e., Engine Cylinder
Detonation). In
this way, a sensor set can utilize the same conditioning module. The signal
conditioning
card (SCC) 135 comprises one or more conventional conditioning modules and a
multiplexer. The numberof sensorsets determines the numberof conditioning
modules,
which, in turn, specifies the number of the signal conditioning card analog
outputs. The
multiplexer on the SCC 135 then selects the appropriate sensor signal /
conditioning
module pair to be used during data acquisition. A conditioning module may
provide
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translation/gain, isolation barrier, filtering and any other safety or signal
manipulation
that may be required. Test points can be incorporated into the HW design such
that
sensor signals can be monitored at critical stages (i.e., after input
protection,
before/after signal conditioning). These test points may be accessed only if
the circuit
board assembly is exposed.
The A/D card 130 converts the conditioned analog signals to digital and buffer
the sampled signal values. When the microcontroller is ready, the buffered
samples are
transferred to RAM. The A/D should preferably be selected for a reasonable
number
of input channels such that a pre-multiplexing of conditioning card output
signals is not
required. For example, A/D may be 8 or 16 channels with an onboard
multiplexer. An
embodiment in which several A/D cards 130 operate at the same time to achieve
both
sequential and simultaneous data acquisition is contemplated. For example, if
4 A/D
cards 130 operate in conjunction with the LSA 24 and the HSA 22 at the same
time,
several channels can be acquired simultaneously from these arrays.
The D/A card 150 converts generated digital control signals to analog control
signals, which are to be fed to the actuators.
The SCC 135, the A/D cards 130 and the D/A cards 150 are collectively referred
herein as signal conversion means. It will be understood by a person skilled
in the art
that the signal conversion means may comprise alternative hardware elements
achieving equivalent functions, as well as other components that act upon the
input or
output signals.
Provisions can be made to have Digital I/O capabilities 160 for the following
signals: Input: Remote/Local and Output: Warning On/ Warning OF or others. A
Remote/Local toggle may originate, for example, from a hard switch mounted on
a user
interface connected to CONDOR 10.
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Referring back to Figure 2, existent DA&Cs 40, if any, have suitable analog
and
digital I/O for sensor sampling and CONDOR communication. In addition,
existent
DA&Cs 40 may have sufficient processing power to be a controller for
Driver/Load
parameters.
Figure 4 illustrates generallythe software architecture of the IMCS system 1.
The
IMCS system 1 software is built on the top of a real-time operation system
(RTOS),
preferably POSIX 1.004 compliant, such as QNX. Some processes may communicate
with the hardware directly, as needed.
In the preferred embodiment, the processes are built using a standard
interprocess communication protocol (IPC) such as QNX IPC (message passing).
This
allows processes running on different units connected by a network to
communicate
among each other, as shown in Figure 5. Also, the network is totally
transparent from
the software processes. This is accomplished by special low-level protocols of
the
RTOS, such as "fleet" in QNX. This feature makes the system software very easy
to
expand without rewriting any code.
In the preferred embodiment, the IMCS system 1 software is built so that any
process can be updated on-line. Figure 6 illustrates this feature, by way of
example:
suppose one of the calculations is wrong. The developer fixes the
corresponding
process and uploads it to the system. Then the new process can be restarted
without
resetting the whole system.
Since some of the processes can be updated on-line, the calculation can be
customized for different applications. The preferred embodiment includes one
or more
of the following calculations: peak value, indicated power, efficiency, rod
load, flow,
valve loss, signal smoothing, vibration statistics and others.
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Referring back to Figure 2, the operating system and communication standards
of the preferred embodiment are described next. The DM 60 may operate on a 32
bit
platform such as Win 95, Win NT. The CONDOR 10 may operate on a QNX RTOS
platform. The Digital Control System (DCS) 50 communicates with the CONDOR 10
using a communication protocol such as Modbus. The CONDOR 10 will respond to
queries from the DCS 50 providing information and control as required. Remote
queries
will be run in the background during normal operation. The DM 60 communicates
with
the CONDOR 10 using a communication protocol such as TCP/IP using a RS232,
Ethernet/10BT, or modem/RJ11 connection. Preferably, the communication
protocol
between the DM 60 and the CONDOR 10 adheres to a standard such as TCP/IP. The
DM 60 sends and retrieves configuration files to and from the CONDOR 10. In
addition,
the DM 60 retrieves either historical or current calculated data from the
CONDOR 10.
Remote queries will also be run in the background so as not to disturb normal
operational functions. The CONDOR 10 has the capability to communicate with at
least
1 external Data Acquisition and Control Units (DA&C) 40 using a communication
protocol such as second Modbus or TCP/IP connection. The CONDOR 10 acquires
Indirect sensor data from a DA&C 40 and sends output or set point values to a
DA&C
40 for control of actuator(s). The DA&C 40 may be in the form of an Engine
Controller.
The CONDOR 10 provides display information to a set of I/O registers, which
are to be
accessed through the HMI 70. The CONDOR 10 and the HMI 70 may communicate via
a third ModBus connection. The CONDOR 10 may have provisions for a modem
connection. In this way, a DM 60 can remotely connect to a CONDOR 10 and be
provided with I/O capability 3. The HMI 70 obtains information from a
specified set of
CONDOR 10 registers and presents this information to the user. The user will
be able
to alter CONDOR 10 set point values and configuration limits via the HMI 70.
If there
is no HMI 70 present, then the site DCS 50 will provide the user with I/O
capability 3.
Fail safe features of the preferred embodiment of the invention are next
described, with reference to Figure 2. A power passive on protocol is
implemented in
the CONDOR 10. Specifically, all I/O ports remain dormant until the CONDOR 10
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system has initialized itself and is ready to enter normal operating mode. The
CONDOR
self starts its RTOS and executes the CONDOR SW. The CONDOR SW
initializes/checks communication with all Modbus devices. All inputs may
remain active
during CONDOR 10 self start, but data will not be recognized until sensor
power has
5 been reinstated. If necessary, the CONDOR 10 may control sensors' ramp to
their
normal operating conditions. The CONDOR 10 waits until sensors have stabilized
to
provide valid data samples. If necessary, the CONDOR 10 undergoes a test
sequence
to determine data availability. All control lines are held in a closed state,
i.e. assert
power-on state, until required otherwise. Output lines are held in a closed
state until
10 required otherwise. All output relay lines are energized after the CONDOR
10 has
reached a stable state.
The CONDOR 10 operates on a time window storage scheme. Therefore, once
data for a time window has been collected, it will be summarized and stored to
NV
memory. Prior to storing the current dataset, the CONDOR 10 checks to see if
the last
data set was stored completely. In either case, the current data set is stored
following
the last complete data set. Preferably, a new file containing the current
dataset is
generated rather than appending the current dataset to a file containing the
last
complete dataset, so that the old dataset can never get corrupt. Also held in
NV
memory is the RTOS, CONDOR 10 SW and configuration information. Thus, a power
failure only loses the current time window of data. Summary data of all
previously
sampled time windows would have already been stored to NV memory and will not
be
lost. Similarly, the CONDOR SW and configuration information reside in NV
memory
and are be available upon re-instatement of power to the unit. The shut-down
(SD)
software updates the CONDOR's watchdog timer 190; if the timer 190 is not
updated
within a preset time (e.g loss of power to the CONDOR or processor failure),
an
external relay will be de-energized. This normally causes an emergency shut-
down.
The following table shows possible types of hardware communications failures
that may take place within the IMCS system 10 of Figure 2.
18
CA 02298060 2000-02-04
Failure Solution
DCS Communication Failure SW Watchdog timer
DAU Communication Failure Detected by CONDOR
I nition Communication Failure Detected by CONDOR
Direct Sensor Failure Detected by CONDOR
ir/Fuel Control Failure Detected by CONDOR
Internal CONDOR Failure External Watchdog circuit
In the preferred embodiment, the CONDOR 10 detects most of the
communication errors automatically. When an internal error occurs, the CONDOR
10
itself will not be able to recover and will not generate the signal expected
by the
external watchdog circuit 190. The external watchdog circuit 190 will de-
energize a
relay, which will cause an external alarm or machine shutdown. The CONDOR 10
also
has a software watchdog timer. The DCS 50 has to triggerthe predefined CONDOR
coil
within a given interval. If the DCS 50 this does not occur, the communication
failure
alarm for DCS 50 will turn on.
All the communication alarms can be accessed through the sequencing logic.
The CONDOR 10 can be programmed such that it will perform different actions on
different communication failures. If the communication to the DCS 50 fails,
the
CONDOR 10 can use the last received set point values and continue to run as
before,
or it can go to the local control. If the communication with a DA&C unit 40 or
direct
sensors is not healthy, then, based on how critical the data is, the CONDOR 10
can
choose either ignore the failure, generate an alarm or cause a machine
shutdown.
The sensor data processing, as it occurs in the preferred embodiment of the
invention is next described. Specifically, data algorithms required for data
acquisition,
calculation, reduction, compression, and storage are described.
As previously mentioned, data acquisition occurs by two methods: Direct and
Indirect. Direct data acquisition has the sensor data lines being input
directly to the
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CA 02298060 2000-02-04
CONDOR 10, through the DSA 20. The CONDOR 10 provides the necessary
multiplexing, signal conditioning, A/D conversion, and signal filtering of the
sensor
signals such that useful data can be obtained. During Direct data acquisition
the
sensors are sequentially sampled (i.e., one sensor will be sampled at a time).
The DM
configuration software obtains sampling information from the user which will
specify
parameters such as channel type, sensor type, filter choice, sample rate,
sensitivity,
location, etc.. In addition, the configuration software may provide a userwith
the option
of altering the sensor sampling sequence should the order of data acquisition
be
important.
The Indirect Sensor Array (ISA) 30 is sampled by one or more DA&Cs 40. The
CONDOR 10 queries the DA&Cs' 40 Modbus for Indirect sensor data. Figure 7
illustrates a scenario in which the gathering of Direct and Indirect data is
interleaved.
The CONDOR 10 acquires subsets of Indirect data through multiple polls of a
DA&C
40. The Direct data is acquired sequentially sensor by sensor, storing the
information
into RAM. Not all sensor data is acquired at once. The contiguous data
acquired from
the HSA 22 is acquired at the same time as data from the LSA 24 and the
indirect
sensors via the DA&C 40.
Data filtering techniques may be implemented upon raw sensor data to maximize
the signal to noise ratio (SNR). Furtherfiltering may be used to remove excess
data and
focus on regions of interest, thereby reducing the complexity of
characteristic value
calculations.
Figure 8 illustrates a data collection, calculation and storage process
technique
implemented in the preferred embodiment of the invention. For an engine or a
compressor, pressure sensors generally require at least 720 samples/rev to
perform
power calculations and vibrational sensors should preferably acquire data at
their
maximum sampling rate. A current embodiment of the invention achieves the
maximum
sampling rate of 25000 samples/sec. For vibrational and pressure Direct
sensors, an
CA 02298060 2000-02-04
initial calculation for a desired parameter is performed after each sampling
period. For
the case when the resultant parameters are the only numbers of importance, the
data
buffer is free to be overwritten by the next acquired sensor sample set. Final
calculations are performed after all relevant sensors have been polled and
interim
parameters calculated. These final calculations are tabulated, time stamped
and
posted to output registers. In this way, final calculated values are made
available to the
HMI 70 display. The tabulated data has an associated Avg / Max / Min / St.
Dev.
appropriate to the characteristic calculation. Only these summary values will
be
forwarded to the software for storage.
Figure 9 illustrates data evaluation conditions in the preferred embodiment of
the invention. Data and/or calculated values have a user configurable warning
message
alert/no alert for the user configurable max/min warning boundary conditions.
If the
values do not fall within the normal operational range then a warning message
may be
issued to all devices connected to the system. Furthermore, data and/or
calculated
values have user configurable alarm max/min boundary conditions. If the values
exceed the alarm level, messages are issued to devices indicating that the
system has
not been able to correct the warning and that an alarm condition has
developed.
Moreover, data and/or calculated values have user configurable shut-down
max/min
boundary conditions. If the values exceed the shut-down level, messages are
issued
to devices indicating that the system has not been able to correct the alarm
and that a
shut-down condition has developed. The CONDOR 10 can either generate a shut
down digital output signal or set the Watchdog signal to indicate such a
condition.
In the preferred embodiment of the invention, data storage occurs in two modes
of operation: Normal and Warning. Both of these modes of operation have RAM
and
NV storage requirements. Figure 10 illustrates the Normal Mode operation. For
the
engine/compressor 2 case, Normal Mode is defined to be the state of data
acquisition
where the engine speed _crank speed. The CONDOR 10 only acquires data and
stores
the summary information to RAM if Normal engine speed level is achieved. Data
to be
21
CA 02298060 2000-02-04
stored in Normal Mode only includes user defined Indirect and Calculated
values with
associated time stamps, as opposed to Warning Mode in which all Indirect and
Calculated values are stored. If a SD / restart is encountered prior to 1 hour
(or any
other predetermined time period) of continuous runtime being achieved, the
CONDOR
10 appends the current data to the previously acquired data noting when the SD
occurred. Figure 11 illustrates the Warning Mode operation. The Warning Mode
is
defined to be the state of operation in which a user defined data and/or
calculated value
has exceeded the max/min warning limits. Data stored in Warning Mode includes
all
Indirect and Calculated values with associated time stamps. The CONDOR has an
additional warning buffer which contains 2 complete sets of values. When a
warning
is encountered a "snap-shot" of the data set is stored in RAM containing the
warning
message number, the warning value, the warning limit and the previous data
set. A
single data set is then periodically acquired until the warning is cleared. If
the warning
is cleared before the warning memory is filled, then only the "snap-shot"is
stored to NV
memory. Otherwise, both the " snap-shot" and the periodic samples are stored
to NV
memory. The CONDOR 10 continues to store periodic samples until the warning is
cleared. If the NV memory becomes full, then data is overwritten. Warning data
may
always be uploaded, however, to clear the warning NV memory the user may set a
password protected flag to assist in data management. If the warning becomes
an
alarm, then the CONDOR 10 continues to store data in this mode. If the alarm
becomes
a shut-down, then the CONDOR 10 stores all collected information to NV memory
and
awaits for engine restart.
Figures 12A through 12G illustrate the data flow for the software processes
implemented in the preferred embodiment, for performing Engine/Compressor
monitoring and diagnostic functions. Figure 12A is a level 0 diagram, showing
the main
data category exchange by the CONDOR 10 with systems external to the CONDOR
10,
such as Direct sensors, users, Configuration and Data Managers, a database,
Alarm
registers, Registers for calculated results, and an external Modbus Device,
for
exchanging data with a DA&C 40. Figure 12B is a level-1 diagram detailing the
data
22
CA 02298060 2000-02-04
flow processes shown in Figure 12 A. Figures 12C through 12G are Ievel-2
diagrams
detailing the processes shown in Figure 12B. Specifically, Figure 12 C
illustrates the
data flow for the configuration process, taking place between CM 80, DM 60,
users and
the CONDOR 10. Figure 12D details the data flow in the communication process.
Figure 12E details the data flow in the calculation processes. Figure 12F
details the
data flow in the alarm process. Figure 12G details the data flow in the 'fast
acquisition'
process of acquiring raw data from direct sensors that require sampling at
high-rates.
The input sensor data can be combined in logical and or mathematical means
to perform a desired action such as controlling an output. Sequencing logic is
used to
set the conditions for a machinery shut down or start-up or the initiation of
a warning
message. As well, mathematical calculations can be defined for control outputs
or user
information. This is an activity that performs the same action as a PLC. The
implementation is by ladder logic or by similar means such as flow diagrams or
a
software language. The sequence logic is implemented from start to finish and
repeated
so long as the system software is operating. Figures 13 A and 13 B illustrate
level- 0
and level-1 data flow diagrams for the sequencing logic for the shutdown and
control
processes in the preferred embodiment of the invention.
The preferred embodiment also features a process referred to as'status', which
monitors the status of other processes. If a process is not working properly,
the 'status'
process can restart the process. The 'status' process can also show the
current status
of other processes.
In the preferred embodiment, data can be accessed in different ways. It can be
obtained through Modbus, in which case data is indexed by the Modbus device
address
and the Modbus register. Data directly from the sensor channels may also
require
accessing. In this case, data is indexed by the mux number and the channel
number.
Furthermore, data to be accessed could also be a calculated result and stored
in the
memory.
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CA 02298060 2000-02-04
To simplify the data accessing, in the preferred embodiment data is indexed by
location, i.e. Modbus, channel or memory, signal type and calculation for
which it is
required. Data transfer, data readings and other processing requiring data
access, are
considered to be calculations, for the purpose of describing the data indexing
process.
Figure 14 illustrates the data indexing process. For each data, after the
signal type and
location are specified, all possible calculations in which that data may be
required,
based on the known location and signal type are determined, and a final
indices are
assigned to the data. Thus, when a specific calculation is required, the
system has
immediate access to all necessary data. For external data communication, data
is still
indexed by the Modbus address. This mode of indexing data automates the data
accessing process, by comparison to traditional data acquisition systems in
which
individual calculation blocks are set-up forevery channel configuration and
the similarity
in functionality of various calculation blocks, regardless of signal type and
location is not
explored.
The primary communication protocol in the preferred embodiment is Modbus.
The blocks communicating by Modbus can act as both Modbus master and Modbus
slave. Modbus communication becomes a bottleneck of the system. To optimize
the
communication, three special designs are added to the preferred embodiment:
a)Shared memory
There is a special trunk of memory to be shared by all processes. Any process
can access the data using an internal fast indexing.
b)Common register
Two data with the same signal type, location and calculation will share the
same
internal memory location, although they can have different Modbus addresses.
If two data with the same signal type, location and calculation with one
Modbus
slave address and one Modbus master address, they share the same memory
location. In this case, the data from the slave will "immediately" go to the
master
when the slave data is obtained. There is no copying involved. However, in the
24
CA 02298060 2000-02-04
user point of view, the data is similarly coming from the slave device and
copying
to the master.
c)lmage process
There is a module mainly taking care of the Modbus register (shared memory).
When this module is running, another copy will be created and executed. One
of the copies will reply the request the Modbus master device, and the other
copy will acquire the data from the slave constantly. Since the system
software
is running in a multi-tasking environment, when one of the copies is waiting
for
the serial port, the other copy can use this time period to reply the message
to
the serial port.
A secondary communication protocol of the preferred embodiment is TCP/IP. For
example, a personal computer with TCP/IP can be connected to the IMCS system
1.
The basic functions involve FTP and Telnet. There is also a module that
provides a
socket for TCP/IP communication. Commands can be sent to this module, called a
command interpreter. The command interpreter interprets commands sentthrough
FTP.
When a command file exist, the command interpreter will execute the commands
in the
file. Once it finishes, it will remove the file so that it will not execute it
again. Most of the
commands generally require other process to update the configuration without
restarting the whole system.
The ability to acquire a contiguous (uninterrupted) set of samples from an
analog
to digital converter at rates at or above 20,000 samples per second or more is
not done
by control systems such as PLCs. A typical contiguous sample period might be
as long
as 2 seconds, which could be the equivalent of more than 40,000 samples. This
is
incompatible with a control or shutdown system which must loop through the
ladder
logic or flow diagram within the required time period, such as 0.5 s or less.
The IMCS
system 1 allows the sample acquisition from the an analog to digital converter
to
proceed in an uninterrupted fashion while still performing the ladder logic
and control
loops at more than 20 times per second. In addition, the serial communications
CA 02298060 2000-02-04
channels can be serviced without a significant time delay (in less than 1
second).
Since the whole data set contains the dynamic information of the machine, many
different calculation and analysis can be applied on it. To acquire the data
in high
frequency, DMA transfer and interrupts are used as follows. The whole dynamic
data
acquisition is done through DMA transfer in background. This lets the main
processor,
CPU, to have more time to do other processes. The DMA buffer has limited size.
The
CPU uses interrupts to change the DMA buffer when the buffer has been filled
up. In
each acquisition cycle, only two signals are acquired: data signal and encoder
signal.
The data signal contains the data and the encoder signal contains the timing
information. The system SW uses the timing information to extract the useful
part of the
data signal. Data from HSA and LSA is acquired independently such that the
high-
speed acquisition process does not affect the control/shutdown parts of
CONDOR. The
dynamic (fast) channel(s) may be acquired in Round-Robin fashion. This means
the
performance of the dynamic acquisition is independent on the number of
channels of
the IMCS system 1.
In the preferred embodiment, all calculations have 20 alarm limits (both lower
and upper limits), which can be specified. They are grouped by ranks. In other
words,
there are 20 different ranks of alarms. If a calculation is outside the
limits, the
corresponding alarm will be activated. The system will turn into the
corresponding rank
if there is no other higher rank being activated. On the other hand, the
system disables
the alarm if there is no other higher rank being activated.
In addition to acquiring data for monitoring, diagnostics and shutdown
function,
the CONDOR 10 also calculates control algorithm set-points and outputs for
controlling
the machinery. A number of control loops are be defined in the software of the
preferred
embodiment of the IMCS system 1. Each control loop may run independently and
at a
different speed, i.e may be recalculated more or less often. Figure 15
illustrates the
inputs and outputs of a control loop. Generally, the control inputs and
outputs are very
26
CA 02298060 2000-02-04
important to a user, therefore in the preferred embodiment these signals are
also
displayed on user interfaces, in addition to being used in the control
process. The
CONDOR 10 has the ability to use several independent PID (proportional,
integral and
derivative) algorithms for the control functions.
For an improved diagnosis of machine faults, automated diagnosis techniques
can be implemented by using the results of calculations, sensor signal values,
and
combination of conditions characteristic of known mechanical faults. The
digital data
from the sensors can either be stored for transmission to another computer, or
can be
processed using a range of data processing techniques to extract numerical
information
that relates either to the performance of the machinery or to a specific
condition. The
resulting numerical information can be stored or further reduced using
standard
database, electronic file, data compression, or averaging techniques. Example
data
processing techniques include frequency analysis with frequency transforms
such as
Fourier transforms, vector dot or array product, vector mathematical
processes, matrix
mathematics, digital filtering, peak value determination, threshold
determination, rate
of change (first derivative), multiple derivative, integration, averaging etc.
It would be
appreciated by a person skilled in the art that specific rules would vary
according to the
mechanical construction of the machinery, the sensor type, and the sensor
placement.
Air-Fuel Control
Air-fuel control is one of the features performed by the IMCS system 1 when
used to control an engine's performance. For spark ignited natural gas engines
the air-
fuel control is generally achieved by controlling the pressure of the air in
the intake
manifold relative to the amount of fuel or the amount of air supplied to an
air-fuel mixing
chamber.
In one aspect of the invention, the air fuel control is a real-time portion of
the
IMCS system 1, which does the air fuel ratio control. Figure 16A to 16G
illustrate the
27
CA 02298060 2000-02-04
data flow in the air-fuel control process as it occurs in the preferred
embodiment of the
invention.
Figure 16A is a level-0 data flow diagram for the air-fuel control process.
The
CONDOR 1 acquires Data from a Direct Sensor, it acquires parameters from a
touch
panel of a user interfaces such of an HMI 70, the DCS 50 or the DM 60. The
CONDOR
also stores statistical data in a data storage unit, and sends control signals
to an
analog output. Figure 16B is a level -1 data flow diagram detailing the
processes
illustrated in Figure 16A. The airfuel-control is done through a PID control
loop. Figures
10 16C to 16G are level-2 data flow diagrams for the air-fuel control process.
They detail
respectively: a) the data input subprocess; b) the subprocess of providing the
required
parameters to the PID loop, from the user interface and from a configuration
unit, such
as the CM 80, DM 60 or DCS 50 c) the subprocess of outputting results from the
PID
loop to the user interface and to the analog control device; and d) the data
flow in the
PID loop.
The air-fuel control system requires that PID loop controls are updated by a
timer
interrupt. For example, the timer interrupt may be set to be 10ms. However,
the PID
loop only updates itself in the multiple of 50ms. Since the system comprises a
real-time
operating system, it will guarantee that the PID loop process will get the
interrupt in
each 10ms. During the idle time of the PID loop processes, the RTOS will
schedule the
task to do another process, such as serial communication.
Traditionally, the air fuel control is done by controlling the amount of air
relative
to the amount of fuel is normal. In the preferred embodiment, the IMCS system
1
calculates the amount of air according to fuel, as well as engine RPM and air
temperature. The addition of these two other parameters other parameters
results in
more efficient operation over a wide range of speeds and air temperatures. In
addition,
in the preferred embodiment of the IMCS system 1, the air-fuel control is
performed
during a starting sequence. This results in more reliable starting and a
reduced chance
28
CA 02298060 2000-02-04
of "flooding" which is a condition of excess fuel relative to the air during a
starting
sequence. In the preferred embodiment, linear equations of the form y = mx + b
where
m is a slope, b is an offset, x is proportional to fuel, and y is proportional
to the air
pressure, are used in the air-fuel control process.
Combining sensor signals with a marker signal from a rotation shaft
In one embodiment of the invention, in the data acquisition process, the
sampled
sensor signals are acquired in combination with a marker signal from a
rotation shaft.
By sampling a machine sensor output and a sensor showing the rotational
position of
a shaft either at the same time or by interleaved samples, the sensor signal
can be
accurately correlated to the rotation position of the shaft or the position of
any
reciprocating or rotating components which are connected to the shaft whose
position
is being monitored. This allows determination of a more accurate rotational
position
than is possible by using a signal generated once per revolution and deducing
the
rotational position by interpolation.
A method of acquiring correlated signals to indicate the exact rotational
position
of a shaft is described below, with reference to Figure 17 through 20. Figure
17 shows
the placement of the rotational pickup sensors. The vibration, pressure or
other signal
can originate from sensors fixed in place relative to the rotating or
reciprocating parts.
Figure 18 shows the shaft causing a piston to reciprocate. Figure 19 shows a
side view
of a general assembly of pulley and gear, shaft support and bearing and the
placement
of a vibrational sensor with respect to these rotating parts. Figure 20 shows
the
correlation of a N per Rev signal, a 1 per rev signal and the signal from the
sensor. An
additional signal required for 4 cycle engines is a 1 per 2 Rev signal. By
combining all
of the above signals, the exact rotational position of the sensor signal(s)
can be
deduced. Combining the signals comprises the following steps:
a) Acquiring the signals with analog to digital converters and using the N per
rev and
1 per rev to deduce an angle of rotation.
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CA 02298060 2000-02-04
b) Electronically adding the N per Rev and 1 per Rev signals and acquiring the
resulting
signal and the sensor signal with analog to digital converters and using the N
per rev
and 1 per rev to deduce an angle of rotation.
c) Acquiring the three signals with a multiplexer leading to an analog to
digital
converter and using the N per rev and 1 per rev to reduce an angle of
rotation.
d) Electronically adding the N per Rev and 1 per Rev signals and acquiring the
two
signals with a multiplexer leading to an analog to digital converter and using
the N per
rev and 1 per rev to deduce an angle of rotation.
e) Acquiring the vibration signal with an analog to digital converter and
using the N per
rev and the 1 per rev signals as two of the bits of the digital word making up
a sensor
sample. Typically the two high order or low order bits are used as shown by
the
following example 16 bit word: '0123456789abcdef . In this 16 bit word where
each bit
location is shown by the digits 0 to 9 and the letters a to f inclusive, the 1
per rev and
N per rev status (high = 1, low = 0) can be superimposed on the digital word
representing the value of the analog signal.
According to the above, the interleaving of the rotational position signals
with the
sensor signal enables the rotational position to be determined with
considerable
accuracy.
The IMCS system 1 can be applied to any machinery for one or more of
monitoring, diagnostics, shutdown, control and communications. The classes of
machinery include the groups of rotating and reciprocating machine types.
Rotating
machines include pumps, compressors, propellers, generators, turbines
(turbochargers,
turbofans, rotary compressors), and rotary engines. Reciprocating machines
include
reciprocating engines (2 and 4 cycle), reciprocating compressors, and
reciprocating
pumps.
Several techniques which can be applied with the IMCS system 1 to fulfill the
diagnostics of reciprocating machinery such as engines and compressors are
described
CA 02298060 2000-02-04
below.
a) For 4 cycle engines, vibration sensors can be used to detect looseness in
the
connecting rod bearing or bushing, wrist pin bearing or bushing, and the main
crankshaft bearings by the detection of a signal when the piston is in the
vicinity of the
top dead center between the exhaust and intake strokes. By looking for a
signal only
when the piston is at this position, the problem can be attributed to such
looseness.
This capability is possible due to the acquisition of a rotational position
signal at the
same time as the sensor signal. A preferred sensor location is near to the
crankshaft,
but the sensor can be located at other physical locations on the engine to
achieve
similar results.
b) For most reciprocating engines with natural gas fuel and spark ignition a
vibration
sensor located in the crankcase region can be used to detect uncontrolled
combustion
known as detonation. By looking for a vibration signal during the crank
position in the
combustion region, detonation can be detected. A preferred sensor location is
near to
the crankshaft, but the sensor can be located at other physical locations on
the engine
to achieve similar results.
c) For double acting compressors used for compressing gas, a vibration sensor
can be
used in the region of the cross-head to detect looseness in the cross-head,
the
connecting rod bearings, and the piston attached to the rod. By looking for a
vibration
signal during the crank position when the force acting along a line connecting
the axis
of the piston and the center line of the crankshaft reverses direction, a
mechanical
problem due to looseness can be detected.
The block diagram of the processes used is shown in Figure 21. The vibration
or equivalent sensor used to determine impact events is attached to a location
near an
engine crankshaft. A preferred orientation is such that the sensor is most
sensitive to
vibration in the direction of piston travel.
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CA 02298060 2000-02-04
Figure 21 is a flow chart illustrating the data acquisition process performed
to
determine if a looseness or detonation condition exists: A contiguous
vibration data set
covering a minimum of 2 revolutions for a 2 cycle engine and three revolutions
for a 4
cycle engine is acquired at step 210. The sample rate must be high enough that
frequency components above 1000 Hz can be acquired. Next, at step 220, using a
rotational signal or timing data also acquired, the data set is truncated such
that the
data set starts at the Power top dead center (TDC) of the reference cylinder
(typically
1, 1 L or 1 R). At step 230, using the TDCs determined from the other
cylinders from the
timing diagram, the locations in the data set for the TDC of each cylinder is
determined.
At step 240, a time window in the region of each TDC is defined. At step 250,
for each
time window, the characteristics of the vibration data appropriate to a
looseness
condition or a detonation event are determined. Such a characteristic may be
vibration
intensity. At step 260, it is determined if the value of the characteristic
determined
above exceeds a threshold. If a threshold is exceeded, the cylinder number is
determined and if the event is from the power stroke or the free stroke (4
cycle engine
only). At this point the alarm may be enunciated, at step 270, or additional
data may
acquired by repeating steps 210 through 260, to verify the alarm. At 290 , a
control
action is performed. For detonation the normal control actions are fuel
reduction to the
cylinder in question, reduction of the engine load, or retarding of the
ignition, either for
the whole engine or for the cylinder showing detonation. At 300, the data
acquisition
process is continued by performing steps 210 through 260 to determine if the
control
action was successful in reducing the detonation frequency and/or intensity.
For the application of detecting looseness in double acting compressors the
use
of a single sensor in the compressor crankcase in a manner similar to that
described
for an engine may be advantageous by comparison to current systems where a
vibration sensor placed near the cross-head of each cylinder is used to detect
impact
events.
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CA 02298060 2000-02-04
Numerous modifications, variations and adaptations may be made to the
particular embodiments of the invention described in the documents attached
herein,
without departing from the scope of the invention, which is defined in the
claims.
33
