CA2260695A1 - On-line diagnostic, shut-down and control system for machinery - Google Patents

Description

ON-LINE DIAGNOSTIC. SHUT-DOWN AND
CONTROL SYSTEM FOR MACHINERY
FIELD OF THE INVENTION
This invention relates to an electronic system for machinery, and in particular to an on-line diagnostic, shut-down and control system for machinery.
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 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 data 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 and performance condition of the machinery.
The mechanical condition refers to the fitness of mechanical parts that form parts of the machine to perform the function required by the machine. Example mechanical parts may be a bearing, a 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 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.
The examples provided in the above definitions are for purposes of illustration only and are not intended to limit the scope of the diagnostic, shutdown, or control functions of the single integrated unit.
System refers to the combination of electronic hardware which can read voltage and/or currents from sensors, can generate voltage and/or current outputs and contact open/close conditions 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 pumps used for pumping liquids, current electronic system are design to perfom a combination of these functions.
Shutdown and control are performed by existent systems, such as Programmable logic Controllers (PLC's). Many of these systems have the ability to perform control functions with hardware or software PID (proportional, integral, differential) functions. Such systems can acquire analog and digital signals and can generate analog and digital outputs. These systems are dedicated to the tasks of monitoring and control, following a ladder logic or flow diagram method of operation shown in Figure 1.
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 0.5 s, 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.).
Such systems do not have the capability to acquire and manipulate analog inputs at a data rate more than 10 to 100 times per second. As well, such systems do not have the computational capability to perform diagnostics beyond simple threshold alarms.
There are a number of systems available that perform monitoring capability 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. In the most advanced of these systems there have been some with 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 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. Normally these monitoring units have the capability for communications.
Because of the designs currently used for shutdown/control and monitoring/diagnostics each of them are not capable of adding the complementary capability.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an on-line diagnostic, shut-down and control system for machinery.

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.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
Reffering to Figures 1 A to 12, an electronic system for reciprocating equipment, combining the capabilities to perfom shutdown, control, monitoring and diagnostics in accordance with an embodiment of the invention is described.
In the following, an embodiment in accordance with the invention is referred by its commercial name "REMVue". Other embodiments in accordance with the invention ar referred to herein as the IMCS (Intelligent Monitoring and Control System) and the Condor.
The system can also have an integrated electronic communications capability that enables it to transmit and receive information electronically to and from other computers. This communications capability allows machine sensor readings to be collected from other electronic units and digital information to be sent to other machine control units. The communications capability also allows digital information to be transmitted to and received from other computer equipment. Communications capability includes RS232, RS485, RS422, Canbus, Fieldbus, Ethernet, Arcnet and similar communications standards.

A feature of the system software is the ability of the software to service the diagnostic, shutdown, control, and communications functions at the same time such that a minimum time response for critical control and shutdown operations can be guaranteed.
A second feature of the system software is the capability to remotely change the software functions operating on the system without affecting the capability to perform the diagnostic, shutdown, control and/or communications functions of the system.
This feature allows changes or improvements to the system software to be performed without shutting down the machine being diagnosed, monitored, or controlled.
Several parts of the diagnostic function of the system software are described below.
The input sensor electrical outputs can be converted to digital samples at speeds in excess of 20,000 per second. Examples where the high sampling speed is essential are dynamic pressure sensors, accelerometers (for vibration measurement), velocity type vibration sensors and electrical current sensors.
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 method 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.
The digital data from the sensor 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 (e.g.Fourier), 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.
In acordance with an embodiment of the invention, the capabilities to perform shutdown, control, monitoring, and diagnostics as well as communications, are combined in a single system for reciprocating equipment . The REMVue has the capability, by its design, to perform all of these tasks simultaneously. This is achieved by design of software, hardware and a real time operating system (RTOS).
Figure 1 B shows the basic components of the computing hardware tied together on a bus.
The hardware organization is shown in Figure 1 B. The serial, analog and digital cards are conventional and plug into a bus that is shared with the central processor (computer).
The computer also has access to both volatile and non-volatile memory.
The computer software developed by us is responsible for the ability to perform shutdown, control, monitoring, and diagnostics as well as communications tasks.
The multiple inputs and outputs are multiplexed and conditioned using conventional electronic circuits.
Figure 2 shows the top-level organization of the software on the REMVue. More detail is contained in the REMVue Software Design Description.
Other real-time software is capable of performing many tasks at the same time by scheduling techniques. The ability to obtain a long contiguous block of analog samples is achieved by performing the other tasks on a priority scheduling basis and using the direct memory access capability of the analog to digital hardware and clearing away the data before a buffer is full.

The ability to remotely change software functions by itself is advantageous for a system that performs the shutdown, control, monitoring, and diagnostics as well as communications functions on the same hardware platform. This is an important feature for the control and shutdown functions of the system, as the operation cannot be stopped while new software is installed. This is different from a system that performs only monitoring which can be interrupted (stopped) while new software modules are installed.
The ability to acquire a contiguous (uninterrupted) set of samples from an analog to digital convertor 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 (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 (0.5 s or less). The REMVue system allows the sample acquisition from the an analog to digital convertor 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 channels can be serviced without a significant time delay (in less than 1 second).
The method of acquiring correlated signals to indicate the exact rotational position of a shaft is described below.
Figure 3 shows the placement of the rotational pickup sensors.
Figure 4 shows the shaft causing a piston to reciprocate.
The vibration, pressure or other signal can originate from sensors fixed in place relative to the rotating or reciprocating parts.
The signals in Figure 6 show the N per Rev signal, the 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 signals) uced. Methods of combining the signals are as follows:
wiring the signals with three independent analog to digital converters (ADC) he N per rev and 1 per rev to deduce an angle of rotation.
~tronically adding the N per Rev and 1 per Rev signals and acquiring the ;nal and the sensor signal with 2 independant analog to digital converters and per rev and 1 per rev to deduce an angle of rotation.
uiring the three signals with a multiplexer leading to a single analog to digital converter and using the N per rev and 1 per rev to reduce an angle of rotation.
4. Electronically adding the N per Rev and 1 per Rev signals and acquiring the two 15 signals with a multiplexer leading to a single analog to digital and using the N per rev and 1 per rev to deduce an angle of rotation.
5. 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 20 sensor sample. Typically the two high order or low order bits are used as shown by the example 16 bit word below.
~0~0~1~0~1~0~1~1~0~0~1~0~1~0~1~1 1 er N per p Rev Rev 14 bit bit bit sample Which-ever method is used, the interleaving of the rotational position signals with the sensor signal enables the rotational position to be determined with considerable accuracy.
The above system 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 _g_ 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.
Some specialized and novel techniques can be applied to diagnostics for reciprocating machinery such as engines and compressors. These are described 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. The optimum 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. The optimum 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.

A further novel element of the diagnosis of machine faults in reciprocating machinery is the application of techniques including logic, fuzzy logic, probabilities, or rules implemented by software. Such 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 specific rules will vary according to the mechanical construction of the machinery, the sensor type, and the sensor placement.
The technique described in a) of using a vibration or equivalent sensor located in the crankcase area to determine looseness may be a novel idea - possibly the subject of a patent search.
Similarly, the idea described in b) of using a vibration or equivalent sensor lcoated in the crankcase area to determine detonation may be a novel idea - possibly the subject of a patent search.
The block diagram of the processes used is shown in Figure 7.
The vibration or equivalent sensor used to determine impact events is attached to a location near an engine crankshaft. The best orientation is such that the sensor is most sensitive to vibration in the direction of piston travel.
The following data acquisition steps are performed to determine if a looseness or detonation condition exists:
1. 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. The sample rate must be high enough that frequency components above 1000 Hz can be acquired.
2. Using the rotational timing data also acquired (see preceding section) the data set may be 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).

3. Using the TDCs determined fom the other cylinders from the timing diagram, determine the locations in the data set for the TDC of each cylinder.
4. Define a time window in the region of each TDC.
5. For each time window, determine the characteristics of the vibration data appropriate to a looseness condition or a detonation event. Such a characteristic may be vibration intensity.
6. Determine if the value of the characteristic determined above exceeds a threshold.
If a threshold is exceeds, record the cylinder number and for a 4 cycle engine, if the event is from a TDC at the power stroke or the free stroke.
1 S 7. At this point the alarm may be enunciated, additional data acquired (steps 1 to 6) to obtain confirmation, or a control action performed.
8. 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.
9. The data acquisition process is continued (steps 1 to 6) to determine if the control action was successful in reducing the detonation frequency and/or intensity.
The application of detecting looseness in double acting compressors is currently in commercial use where a vibration sensor placed near the cross-head of each cylinder is used to detect impact events. A possible innovation is the use of a single sensor in the compressor crankcase in a manner similar to that described for an engine.

Air-Fuel Control Air-fuel control is one of the features performed by the REMVue unit. For spark ignited natural gas engines this is 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.
Control of the air relative to the amount of fuel is normal.
REMVue calculates the amount of air according to fuel, engine RPM and air temperature. The addition of these other parameters results in more efficient operation over a wide range of speeds and air temperatures.
In addition, the control of fuel during a starting sequence results in more reliable starting 1 S and a reduced chance of "flooding" which is a condition of excess fuel relative to the air during a starting sequence.
The details of the air fuel control method currently used is contained in the document "Software Design Specification -Air Fuel Control "
According to an embodiment of this system, which performs the air-fuel control feature, 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.
Other documents attached describe in detail various embodiments of the system in accordance with the invention.
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.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electronic system for on-line control of machinery, said system comprising:
sensors for generating sensor signals signals indicative of conditions of the machinery;
monitoring means for monitoring the machinery by acquiring readings from the sensor signals and for performing at least one of:
displaying said readings;
storing said readings;
diagnostics means for performing diagnostics of the machinery in response to the sensor signals;
shutdown means for performing shutdown of the machinery in response to the sensor signals; and control means for performing control of the machinery by processingn the sensor signals into control signals.

2. The electronic system for on-line control of machinery as claimed in claim 1, the system further comprising means for acquiring contiguous blocks of data samples.

3. A method for determining a condition of a machinery provided with a rotating shaft, having a a sensor for a parameter relating to the condition to be determined, said method comprising the steps of:
generating a sensor signal with the sensor;
generating a rotational position signal indicative of the rotational position of the shaft;
correlating the sensor signal and the rotational position signal;

determining the condition in response to the correlation step.

4. A system for performing air-fuel control for an engine provided with an air-fuel mixing chamber and a rotational shaft, the system comprising:
means for determining the amount of fuel supplied to the chamber;
means for measuring the air temperature in the chamber;
means for measuring the rotational speed of the engine's shaft;
means for computing the amount of air supplied to the chamber based on the amount of fuel, the air temperature and the rotational speed.