Apparatus and method for measuring and displaying performance characteristics of reciprocating piston machines

• US 4,456,963 A
• Filed: 05/11/1981
• Issued: 06/26/1984
• Est. Priority Date: 05/11/1981
• Status: Expired due to Term

• Current Assignee: SA Instruments, Inc.
• Original Assignee: SA Instruments, Inc.
• Inventors: Wiggins, Gene D.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US06/262,761
• Time in Patent Office: 1,142 Days
• Field of Search: 364/511, 364/550, 364/551, 73/115, 73/116, 73/117.1, 73/117.2, 73/117.3
• US Class Current: 701/102
• CPC Class Codes: G01M 15/08 by monitoring pressure in cylinders

Abstract

Apparatus and method are disclosed for measuring and displaying predetermined characteristics of reciprocating piston machines. In the preferred embodiment, the predetermined characteristics comprise indicated horsepower, crankshaft angle and piston position. The apparatus comprises a central processing unit, memory devices, keyboard assembly, display controller, display unit, sweep generator, pressure data acquisition and scaling system, shaft encoder and pressure transducer operatively connected by an address bus and a data bus to measure and display the predetermined characteristics. A method is provided whereby an electrical signal is generated which is proportional to the instantaneous position of a designated piston in the reciprocating piston machine. A method is also provided whereby an electrical signal is generated which is proportional to the instantaneous angular position of the crankshaft with respect to a top-dead-center position of a piston in a predetermined cylinder of the reciprocating piston machine. Predetermined data is entered into the apparatus by the operator as well as from the pressure transducer and crank angle or shaft encoder attached to the engine/compressor which is to be analyzed. The sweep generator circuitry maintains an accurate sweep length for the display unit over the entire range of speeds from zero to the top speed of the engine or compressor being analyzed.

Claims

1. Apparatus for measuring and displaying indicated power of a reciprocating piston machine, said apparatus comprising:

a common data bus;

a common address bus;

a central processing unit operatively connected to said common data bus and said common address bus;

a decoder operatively connected to said address bus for providing enabling signals in response to predetermined addresses being placed on said address bus;

a read-only memory operatively connected to said common data bus and said common address bus and containing instructions for execution by the central processing unit, said read-only memory being capable of receiving enabling signals from said decoder;

a read/write memory operatively connected to said common data bus and said common address bus and being capable of temporary storage of data received from said data bus, said read/write memory being capable of receiving enabling signals from said decoder;

a keyboard assembly operatively connected to said common data bus and said common address bus and providing means for an operator to enter predetermined data onto the data bus for subsequent storage in said read/write memory, said predetermined data comprising connecting rod length, piston stroke and cylinder bore which are used in the calculation of a table of values proportional to the change in cylinder volume per degree of crankshaft rotation, said keyboard assembly being capable of receiving enabling signals from said decoder;

a display controller operatively connected to said common data bus and said common address bus and capable of providing controlling signals to a display device, said display controller being capable of receiving enabling signals from said decoder;

a display device operatively connected to receive said controlling signals from said display controller, said controlling signals being representative of predetermined display information including alphanumeric characters, curves and forms expressing physical or mathematical representations;

means for providing data that represent crankshaft angular position and angular velocity of said reciprocating piston machine to said central processing unit; and

means for providing data that represent cylinder pressure of said reciprocating piston machine to said central processing unit.

2. Apparatus according to claim 1 wherein said means for providing data that represent cylinder pressure comprises:

a pressure transducer means operatively coupled to said reciprocating piston machine and capable of providing an output signal proportional to the cylinder pressure of a predetermined cylinder of said reciprocating piston machine; and

a pressure data acquisition and scaling system operatively connected to said common data bus and said common address bus, said pressure data acquisition and scaling system being capable of receiving enabling signals from said decoder, said pressure data acquisition and scaling system including a pressure data acquisition means responsive to said output signal received from said pressure transducer and from said central processing unit to provide data in a form that can be operated on by said central processing unit in response to instructions located in the read only memory.

3. Apparatus according to claim 2 wherein said pressure data acquisition means includes self-calibration means;

said self-calibration means being responsive to control signals initiated by said central processing unit, a reference voltage signal and a ground reference signal to provide information that allows said pressure data acquisition means to read the output signal from the pressure transducer with a high degree of accuracy.

4. Apparatus according to claim 3 wherein said self calibration means comprises:

a signal source selection means that receives the pressure transducer signal, the reference voltage signal and the ground reference signal and in response to control signals received from the central processing unit, transmits a preselected one of the pressure transducer signal, the reference voltage signal or the ground reference signal to an instrumentation amplifier, said instrumentation amplifier being operatively connected to transmit said preselected signal, after amplification thereof, to means for instantaneously sampling and holding said preselected signal; and

an analog to digital converter operatively connected to receive said preselected signal which has been sampled and held and upon commands from the central processing unit, said sampled and held signal is converted from analog to digital form and is available for further manipulation by the central processing unit in response to instructions from the read-only memory;

whereby said preselected signal from said analog to digital converter is manipulated according to instructions from the central processing unit to determine the gain of the pressure data acquisition means.

5. Apparatus according to claim 2 wherein said pressure data acquisition and scaling system further includes scaling means for scaling the output of the pressure transducer, said scaling means comprises:

a signal source selection means which receives the pressure transducer signal; and

an instrumentation amplifier operatively connected to receive said pressure transducer signal from said signal source selection means and amplify said pressure transducer signal, whereby the amplified pressure transducer signal is capable of being displayed on an X-Y display device at a predetermined scale of pressure units per unit of vertical displacement of the X-Y display device.

6. Apparatus according to claim 1 wherein said means for providing data to said central processing unit which represents crankshaft angular position and angular velocity comprises:

first means operatively coupled for providing to the central processing unit an indication of when a one pulse per revolution signal occurs, said one pulse per revolution signal provides an indication that the piston of a reference cylinder is at a top-dead-center position; and

second means operatively coupled for providing to the central processing unit an indication of when a one pulse per degree signal occurs, said one pulse per degree signal provides an indication of each degree of crankshaft rotation of said reciprocating piston machine.

7. Apparatus according to claim 1 further including:

means for providing a top-dead-center setting input to the central processing unit from the keyboard assembly to provide an indication of the number of degrees between the top-dead-center position of a reference cylinder and the top-dead-center position of a predetermined cylinder other than the reference cylinder, said number of degrees being zero when the predetermined cylinder is the reference cylinder.

8. Apparatus according to claim 1 further including means for providing a predetermined number of inputs to the read/write memory from the keyboard assembly indicating the mechanical dimensions of connecting rod and crankshaft of the reciprocating piston machine;

and

means for using said mechanical dimensions to create in said read/write memory, a table of piston positions which define the distance of the piston from a top-dead-center position for each degree of crankshaft rotation.

9. Apparatus according to claim 1 further including

a first encoder means operatively coupled to said reciprocating piston machine, said first encoder means providing an output signal including a one pulse per degree signal;

a predetermined location in read/write memory being operatively coupled to said first encoder means for accumulating a count of the number of one pulse per degree signals received from said first encoder means;

means operatively coupled to said first encoder means and said read/write memory for incrementing the count in said predetermined location in said read/write memory from zero to 719 coincident with the occurrence of a one pulse per degree output signal from said first encoder means;

means for initiating the sampling of cylinder pressure when a predetermined top-dead-center setting, in degrees of crankshaft rotation, has elapsed after the sensing of a one pulse per revolution signal by the central processing unit, said one pulse per revolution signal being provided by a second encoder means.

10. Apparatus for providing and displaying crankshaft angle and piston position related events of a reciprocating piston machine for the purpose of indicating possible need for preventative maintenance of said reciprocating piston machine, said apparatus comprising:

a common data bus;

a common address bus;

a central processing unit operatively connected to said common data bus and said common address bus;

a decoder operatively connected to said address bus for providing enabling signals in response to predetermined addresses being placed on said address bus;

a read only memory operatively connected to said common data bus and said common address bus and containing instructions for execution by the central processing unit, said read only memory being capable of receiving enabling signals from said decoder;

a read/write memory operatively connected to said common data bus and said common address bus and being capable of temporary storage of data received from said data bus, said read/write memory being capable of receiving enabling signals from said decoder;

a keyboard assembly operatively connected to said common data bus and said common address bus and providing means for an operator to enter predetermined data onto the data bus for subsequent storage in said read/write memory, said keyboard assembly being capable of receiving enabling signals from said decoder;

a display controller operatively connected to said common data bus and said common address bus and capable of providing controlling signals to a display device, said display controller being capable of receiving enabling signals from said decoder;

a display device operatively connected to receive said controlling signals from said display controller, said controlling signals being representative of predetermined display information including alphanumeric characters, curves and forms expressing physical or mathematical representations;

means for providing data to be used in the calculation of piston position of said reciprocating piston machine to said processing unit;

means for providing data that represent crankshaft angular position and angular velocity of said reciprocating piston machine to said central processing unit;

means for providing data that represent cylinder pressure of said reciprocating piston machine to said central processing unit; and

a sweep generator system operatively connected to said common data bus and said common address bus and being responsive to a one pulse per degree signal received from an encoder means, a sweep reset signal received from the central processing unit and data generated by the central processing unit detailing piston position relative to top-dead-center to provide a first signal which is proportional to the position of the piston with respect to the top-dead-center position of the piston and a second signal which is proportional to the angular position of a crankshaft with respect to the position of the crankshaft when said piston is at its top-dead-center position, said sweep generator system being capable of receiving enabling signals from said decoder.

11. Apparatus according to claim 10 further including:

a pressure data acquisition and scaling system operatively connected to said common data bus and said common address bus, said pressure data acquisition and scaling system being capable of receiving enabling signals from said decoder, said pressure data acquisition and scaling system including a pressure data acquisition means responsive to signals received from a pressure transducer and from said central processing unit to provide data in a form that can be operated on by said central processing unit in response to instructions located in the read only memory.

12. Apparatus according to claim 11 wherein said pressure data acquisition means includes self-calibration means;

said self-calibration means being responsive to control signals initiated by said central processing unit, a reference voltage signal and a ground reference signal to provide information that allows said pressure data acquisition means to read the signal from the pressure transducer with a high degree of accuracy.

13. Apparatus according to claim 12 wherein said self calibration means comprises:

a signal source selection means that receives the pressure transducer signal, the reference voltage signal and the ground reference signal and in response to control signals received from the central processing unit, transmits a preselected one of the pressure transducer signal, the reference voltage signal or the ground reference signal to an instrumentation amplifier, said instrumentation amplifier being operatively connected to transmit said preselected signal, after amplification thereof, to means for instantaneously sampling and holding said preselected signal; and

an analog to digital converter operatively connected to receive said preselected signal which has been sampled and held and upon commands from the central processing unit, said sampled and held signal is converted from analog to digital form and is available for further manipulation by the central processing unit in response to instructions from the read-only memory;

whereby said preselected signal from said analog to digital converter is manipulated according to instructions from the central processing unit to determine the gain of the pressure data acquisition means.

14. Apparatus according to claim 11 wherein said pressure data acquisition and scaling system further includes means for cancelling the amount of offset signal received from the pressure transducer when zero pressure is applied to said transducer, said cancelling means comprising:

a signal source selector means which receives the pressure transducer offset signal;

an instrumentation amplifier operatively connected to receive said pressure transducer offset signal from said signal source selector means and amplify said pressure transducer offset signal;

means for reading the amplified pressure transducer offset signal received from said instrumentation amplifier;

means for changing the polarity of said amplified pressure transducer offset signal read from said instrumentation amplifier;

means for feeding a reversed polarity amplified pressure transducer offset signal from said polarity changing means to a reference terminal of said instrumentation amplifier such that the effect is to cancel the amplified pressure transducer offset signal value, said feeding means comprises a digital to analog converter, the output of which is controlled by the central processing unit.

15. Apparatus according to claim 14 wherein said means for reading the amplified pressure transducer offset signal comprises a sample and hold circuit operatively connected to a predetermined analog to digital converter.

16. Apparatus according to claim 11 wherein said pressure data acquisition and scaling system further includes scaling means for scaling the output of the pressure transducer, said scaling means comprises:

a signal source selection means which receives the pressure transducer signal;

an instrumentation amplifier operatively connected to receive said pressure transducer signal from said signal source selection means and amplify said pressure transducer signal;

means for attenuating said amplified pressure transducer signals received from said instrumentation amplifier by a factor determined by execution of instructions contained in read only memory by the central processing unit; and

means for applying a d-c bias voltage to said attenuated pressure transducer signal, the value of said d-c bias voltage being controlled by execution of instructions contained in the read only memory by the central processing unit.

17. Apparatus according to claim 16 wherein said means for attenuating comprises a multiplying digital to analog converter.

18. Apparatus according to claim 16 wherein said means for applying a d-c bias comprises means for summing the output of said multiplying digital to analog converter with the output of a predetermined digital to analog converter whose input value is controlled by the central processing unit.

19. Apparatus according to claim 18 wherein said means for summing comprises an operational amplifier.

20. Apparatus according to claim 10 wherein said means for providing data to said central processing unit which represents crankshaft angular position and angular velocity comprises:

first means operatively coupled for providing to the central processing unit an indication of when a one pulse per revolution signal occurs, said one pulse per revolution signal provides an indication that the piston of a reference cylinder is at a top-dead-center position; and

second means operatively coupled for providing to the central processing unit an indication of when a one pulse per degree signal occurs, said one pulse per degree signal provides an indication of each degree of crankshaft rotation of said reciprocating piston machine.

21. Apparatus according to claim 20 wherein said first means comprises a set/reset flip-flop which is capable of being set by the one pulse per revolution signal and whose output is capable of being read and reset by the central processing unit, said decoder enables said reading and resetting by said central processing unit.

22. Apparatus according to claim 20 wherein said second means comprises a set/reset flip flop which is capable of being set by the one pulse per degree signal and whose output is capable of being read and reset by the central processing unit, said decoder enables said reading and resetting by said central processing unit.

23. Apparatus according to claim 10 further including:

means for providing a top-dead-center setting input to the central processing unit from the keyboard assembly to provide an indication of the number of degrees between the top-dead-center position of a reference cylinder and the top-dead-center position of a predetermined cylinder other than the reference cylinder, said number of degrees being zero when the predetermined cylinder is the reference cylinder.

24. Apparatus according to claim 10 further including means for providing a predetermined number of inputs to the read/write memory from the keyboard assembly indicating the mechanical dimensions of connecting rod and crankshaft of the reciprocating piston machine;

and

means for using said mechanical dimensions to create in a predetermined read/write memory, a table of piston positions which defines the distance of the piston from a top-dead-center position for each degree of crankshaft rotation.

25. Apparatus according to claim 24 further including

means for incrementing a counter from zero to 719 coincident with the occurrence of a one pulse per degree signal input from an encoder means;

means for setting said counter to when a predetermined top-dead-center setting, in degrees of crankshaft rotation, has elapsed after the sensing of a one pulse per revolution signal by the central processing unit, said one pulse per revolution signal being provided by an encoder means; and

first switching means for directing the output of the counter to an address input of said predetermined read/write memory containing the table of piston positions such that the counter value addresses a corresponding memory location in said predetermined read/write memory and causes the data in said predetermined read/write memory location to appear on the input of a predetermined digital to analog converter, whereby an analog voltage proportional to the distance the predetermined piston is from top-dead-center position is output from said predetermined digital to analog converter.

26. Apparatus according to claim 25 wherein said sweep generator further comprises:

second switching means for directing the output of said counter to the input of said predetermined digital to analog converter, whereby the result is a linearly increasing voltage which is proportional to the angular displacement of the crankshaft from its position when said piston is at its top-dead-center position.

27. Apparatus according to claim 26 wherein said sweep generator further comprises:

means for attenuating the output of said predetermined digital to analog converter by a factor determined by the central processing unit upon execution of predetermined instructions in read only memory, whereby said output signal from said predetermined digital to analog converter is controlled such that any waveform generated by said sweep generator can be caused to have the same maximum amplitude without distorting the waveform.

28. Apparatus according to claim 27 wherein said means for attenuating comprises a multiplying digital to analog converter.

29. Apparatus according to claim 25 wherein said first switching means comprises a predetermined number of electronic gating circuits.

30. Apparatus according to claim 26 wherein said second switching means comprises a predetermined number of electronic gating circuits.

31. In apparatus for providing and displaying crank angle and piston position related events of a reciprocating piston machine for the purpose of indicating possible need for preventive maintenance of said reciprocating piston machine and including a common data bus, a common address bus, a decoder, a central processing unit, a read only memory, a read write memory, a keyboard assembly, a display device, a display controller, a sweep generator system, a pressure data acquisition and scaling system, set/reset flip flops and a timer,

an improved method of generating an electrical signal which is proportional to the instantaneous position of a piston in a predetermined cylinder with respect to the top-dead-center position in a cylinder, which signal can be used to present an accurate pictorial representation, on a display device, of the instantaneous piston position, comprising the steps of:

entering the values of predetermined mechanical dimensions of a connecting rod and a crankshaft of the reciprocating piston machine on the keyboard assembly and transferring the values to predetermined locations in the read/write memory;

calculating a table of piston position versus crank angle values and storing said values in predetermined locations in a read/write memory located in said sweep generator system;

entering a top-dead-center setting input to a predetermined location in read/write memory from the keyboard assembly, said top-dead-center setting represents the value of the number of degrees of crank angle rotation which occurs between the time when a piston in a reference cylinder is at top-dead-center and when a piston in said predetermined cylinder is at top-dead-center;

adjusting an encoder assembly opeatively positioned on said reciprocating piston machine such that a one pulse per revolution signal occurs when the piston in the reference cylinder is at top-dead-center;

waiting for the occurrence of the one pulse per revolution signal to be sensed by the central processing unit;

counting occurrences of a one pulse per degree signal which occurs after the sensing of the one pulse per revolution signal, said count being performed by the central processing unit under instructions from the read only memory;

outputting a signal from the central processing unit to clear a counter in said sweep generator system when the number of occurrences of the one pulse per degree signal equals the top-dead-center setting;

applying a one pulse per degree signal train to said counter to cause said counter to count one pulse per degree signals;

applying the output of said counter to address inputs of said read/write memory, said output of said counter having a value equal to the count of the one pulse per degree signals applied since said counter was cleared;

changing the output of said read/write memory in accordance with the changing value of the address inputs such that the output of said read/write memory is proportional to the position of the piston in said predetermined cylinder at the crank angle degree which said counter represents;

applying the output of said read/write memory to a digital to analog converter; and

changing the output signal from the digital to analog converter such that said output signal is proportional to the instantaneous position of the piston in a predetermined cylinder with respect to the top-dead-center position of said piston in said predetermined cylinder.

32. A method according to claim 31 further including the step of controlling the value of an output signal from a digital-to-analog converter such that all waveforms generated by said sweep generator system can be caused to have the same maximum amplitude without distorting the waveform.

33. In apparatus for providing and displaying crank angle and piston position related events of a reciprocating piston machine for the purpose of indicating possible need for preventive maintenane of said reciprocating piston machine and including a common data bus, a common address bus, a decoder, a central processing unit, a read only memory, a read write memory, a keyboard assembly, a display controller, a sweep generator system, a pressure data acquisition and scaling system, set/reset flip flops and a timer,

an improved method for generating an electrical signal which is proportional to the instantaneous angular position of the crankshaft with respect to a top-dead-center position of a piston in a predetermined cylinder, comprising the steps of:

entering a top-dead-center setting input to a predetermined location in read/write memory from the keyboard assembly, said top-dead-center setting represents the value of the number of degress of crank angle rotation which occurs between the time when a piston in a reference cylinder is at top dead center and when a piston in said predetermined cylinder is at top dead center;

adjusting an encoder assembly operatively positioned on said reciprocating piston machine such that a one pulse per revolution signal occurs when the piston in the reference cylinder is at top-dead-center;

waiting for the occurrence of the one pulse per revolution signal to be sensed by the central processing unit;

counting occurrences of a one pulse per degree signal which occurs after the sensing of the one pulse per revolution signal, said count being performed by the central processing unit under instructions from the read only memory;

outputting a signal from the central processing unit to clear a counter in said sweep generator system when the number of occurrences of the one pulse per degree signal equals the top-dead-center setting;

applying a one pulse per degree signal train to said counter to cause said counter to count one pulse per degree signals;

applying the output of said counter to a digital to analog converter, said output having a value equal to the count of the one pulse per degree signals applied since said counter was cleared.

changing the output signal from the digital to analog converter such that said output signal is proportional to the instantaneous angular position of the crankshaft with respect to the top-dead-center position of said piston in said predetermined cylinder.

34. A method according to claim 33 further including the step of controlling the value of an output signal from a digital-to-analog converter such that all waveforms generated by said sweep generator system can be caused to have the same maximum amplitude without distorting the waveform.