Method and system for performance testing of rotating machines

• US 6,591,200 B1
• Filed: 03/09/2001
• Issued: 07/08/2003
• Est. Priority Date: 06/16/1998
• Status: Expired due to Term

• Current Assignee: M.E.A. Motor Inspection Ltd.
• Original Assignee: M.E.A. Motor Inspection Ltd.
• Inventors: Cohen, Menachem, Cohen, Eyal
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): VO, HIEN XUAN
• Application Number:
  US09/719,780
• Time in Patent Office: 851 Days
• Field of Search: 702/38, 702/145, 702/43, 702/41, 731/173, 738/623.24, 738/623.25, 738/620.8, 738/620.9, 738/623.26, 731/16, 324/209, 324/163, 324/86, 324/162, 324/160
• US Class Current: 702/38
• CPC Class Codes: G01L 3/00 Measuring torque, work, mechanical power, or mechanical efficiency, in general
• CPC Class Codes: G01P 21/02 of speedometers
• CPC Class Codes: G01P 3/489 Digital circuits therefor
• CPC Class Codes: G01R 31/343 in operation

Abstract

A method and system for dynamic testing of loaded or unloaded electrical rotating electric motors, wherein a dynamic speed-time characteristic of the electric motor is determined during acceleration of the motor from standstill to steady-state speed or after the motor has reached steady-state speed, depending on the performance characteristic to be derived, and analyzed to derive a performance characteristic of the electric motor. Accurate measurement of the motor speed may be achieved by attaching to the shaft a digital rotary encoder which generates successive HIGH and LOW logic levels during respective successive time intervals. The shaft is rotated and the respective periods of each successive logic level are accumulated so as to allow derivation of the angular rotation or a function thereof of the shaft. Dynamic performance may be determined accurately as well as steady-state performance without slowing the electric motor'"'"'s speed of rotation by use of a flywheel.

Claims

1. A method for measuring an angular rotation of a rotating shaft, the method characterized by the steps of:

(a) attaching to the shaft a digital rotary encoder which successively generates opposing binary logic states such that any pair of sequential logic states corresponds to a known angular rotation of the shaft,

(b) rotating the shaft,

(c) separately measuring a respective time period associated with each successive logic state generated by the digital rotary encoder, and

(d) summing said respective time periods associated with each successive logic state so as to derive an accumulated elapsed time interval of successive pairs of logic states generated by the digital rotary encoder thereby allowing derivation of the angular rotation or a function thereof of the shaft.

2. A method for testing an electric motor or of a component thereof, the method characterized by the steps of:

(a) attaching an unloaded shaft of the electric motor to a digital rotary encoder which generates opposing binary logic states such that any pair of sequential logic states corresponds to a known angular rotation of the rotating electric motor,

(b) measuring an accumulated elapsed time period of successive pairs of logic states generated by the digital rotary encoder during rotation of the electric motor so as to allow derivation of a dynamic speed-time characteristic of the rotating electric motor or a function thereof, and

(c) using the dynamic speed-time characteristic of the unloaded rotating electric motor to derive static torque speed or dynamic torque speed or oscillating torque during steady state or speed and torque spectrum during steady state of the unloaded rotating electric motor.

4. The method according to claim 2, wherein step (c) includes:

(i) computing the time derivative of the dynamic speed-time characteristic, and

(ii) multiplying the time derivative obtained in (i) by a moment of inertia of the unloaded electric motor so as to derive a dynamic speed-torque characteristic of the unloaded electric motor.

5. The method according to claim 2 for determining oscillating torque during steady state of the electric motor after it has reached steady state speed, wherein step (c) includes:

(i) computing the time derivative of the dynamic speed-time characteristic during steady state of the electric motor, and

(ii) multiplying the time derivative obtained in (i) by a moment of inertia of the unloaded electric motor so as to derive a dynamic speed-torque characteristic of the unloaded electric motor in steady state.

6. The method according to claim 2, wherein step (c) includes:

(i) removing fluctuations on a transient part of the dynamic speed-time characteristic during acceleration of the electric motor until it reaches steady state speed so as to obtain a static speed-time characteristic,

(ii) computing the time derivative of the static speed-time characteristic, and

(iii) multiplying the time derivative obtained in (ii) by a moment of inertia of the unloaded electric motor so as to derive a static speed-torque characteristic of the unloaded electric motor.

8. The method according to claim 6, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) locking the shaft of the electric motor,

(2) monitoring the stator current of the electric motor, and

(3) releasing the shaft of the electric motor when the stator current achieves a steady state value.

9. The method according to claim 6 for use with a PSC type a.c. induction motor having a stator comprising a main coil and an auxiliary coil which may be switched in parallel with the main coil, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) feeding current initially to the main coil only at a known angle in the a.c. supply voltage cycle,

(2) monitoring the stator current in the main coil, and

(3) switching the auxiliary coil in circuit when the stator current in the main coil achieves a steady state value at the same known angle in the a.c. supply voltage cycle.

10. The method according to claim 6, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) rotating the shaft in an opposite direction to a normal rotation direction, and

(2) during the time that the rotating electric motor changes direction, commencing sampling of the speed-time characteristics.

11. The method according to claim 6, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) Fourier transforming the speed-time of the rotating electric motor during acceleration

(2) filtering the frequency spectrum so as to remove higher frequency components, and

(3) transforming the resulting spectrum back to the time domain.

12. The method according to claim 7, further including:

(iv) subtracting the combined static speed-torque characteristic of the rotating electric motor plus load from the speed-torque characteristic of the electric motor derived in claim 2 so as to derive the torque-speed characteristic of the load.

14. The method according to claim 2, for testing relative performance characteristics of stators for use in the electric motor, said method further comprising:

(d) providing a pre-calibrated rotor for said electric motor,

(e) providing successive stators and repeating steps (a) to (c) in respect of said stators so as to obtain respective stator-dependent characteristics of the motor.

15. The method according to claim 2, for testing relative performance characteristics of rotors for use in the electric motor, said method further comprising:

(d) providing a pre-calibrated stator for said electric motor,

(e) providing successive rotors and repeating steps (a) to (c) in respect of said stators so as to obtain respective rotor-dependent characteristics of the motor.

16. The method according to claim 2, further including:

(d) deriving a static torque-speed characteristic of the rotating electric motor with an inertial load having a known moment of inertia coupled to the motor shaft, and

(e) processing the respective torque-speed characteristics of the unloaded electric motor and of the electric motor plus inertial load so as to determine the moment of inertia of a rotor of the electric motor.

17. The method according to claim 4, wherein variations in speed or torque are used as a measure of electric motor noise.

18. The method according to claim 4, wherein variations in speed or torque are used as a measure of electric motor imbalance and vibration.

19. The method according to claim 2, further including:

(f) Fourier transforming the speed-time characteristic of the rotating electric motor or electric machine so as to derive a speed frequency spectrum, and

(g) analyzing the speed frequency spectrum of the electric motor or electric motor plus load for determining vibration, unbalance, air-noise, and oscillating torque of the electric motor or the electric motor plus load.

20. The method according to claim 2, further including:

(h) Fourier transforming the torque-time characteristic of the rotating electric motor or electric machine so as to derive a torque frequency spectrum, and

(i) analyzing the torque frequency spectrum of the electric motor or electric motor plus load for determining vibration, unbalance, air-noise, and oscillating torque of the electric motor or the electric motor plus load.

22. The method according to claim 2, including deriving an oscillating speed characteristic during a build-up to steady state speed of the rotating electric motor, comprising the steps of:

(d) coupling a high inertia flywheel to the rotating shaft so as deliberately to slow down the time to reach steady-state,

(e) deriving a steady-state speed-time characteristic of the rotating electric motor varying speed thereof subsequent to attainment of steady state performance, and

(f) zooming in on a desired range of speeds of the rotating electric motor so as to derive for a limited time frame the speed-time characteristics having superimposed thereon said oscillating speed characteristic.

23. The method according to claim 2 for deriving an oscillating torque characteristic at a steady state speed of the rotating electric motor, further comprising the step of:

(g) differentiating the speed-time curve with respect to time and multiplying by a moment of inertia of the rotating electric motor so as to derive varying torque as a function of time.

27. A method for displaying speed or torque characteristics of a rotating shaft derived according to claim 2, further including the steps of:

(g) sampling measured speed or torque at regular time intervals from a known initial sampling time,

(h) displaying at said regular time intervals said measured speed or torque samples versus time or frequency in an analogous way to using an oscilloscope or spectrum analyzer for voltage,

(i) controlling a first x-axis scale in respect of time or frequency while sampling the speed or torque in an analogous way to using an oscilloscope or spectrum analyzer for voltage, and

(j) controlling a second orthogonal y-axis scale in respect of torque or speed amplitude in an analogous way to using an oscilloscope or spectrum analyzer for voltage.

3. A method for testing an electric machine comprising an electric motor and attached load, the method characterized by the steps of:

(a) attaching a shaft of the electric motor plus load to a digital rotary encoder which generates opposing binary logic states such that any pair of sequential logic states corresponds to a known angular rotation of the rotating electric motor plus load,

(b) measuring an accumulated elapsed time interval of successive pairs of logic states generated by the digital rotary encoder during rotation of the electric motor plus load so as to allow derivation of a speed-time characteristic of the rotating electric motor plus load or a function thereof, and

(c) using the speed-time characteristic of the rotating electric motor plus load to derive a combined static torque-speed or a steady state combined oscillating torque-speed or steady state speed spectrum or steady state combined torque spectrum of the rotating electric motor plus load, where the combined torque of the electric motor plus load is equal to the torque of the electric motor minus the torque of the load.

7. The method according to claim 3, wherein step (c) includes:

(i) removing fluctuations on a transient part of the dynamic speed-time characteristic during acceleration of the electric motor plus load until it reaches steady state speed so as to obtain a static speed-time characteristic of the electric motor plus load,

(ii) computing the time derivative of the static speed-time characteristic of the electric motor plus load, and

(iii) multiplying the time derivative obtained in (ii) by a moment of inertia of the combined electric motor plus load so as to derive a combined static speed-torque characteristic of the electric motor plus load.

13. The method according to claim 7, further including:

(v) performing a GO-NOGO of the electric motor plus load as a function of the combined static speed-torque characteristic thereof.

21. The method according to claim 3 for determining oscillating torque during steady state of the electric motor plus load after it has reached steady state speed, wherein step (c) includes:

(i) computing the time derivative of the dynamic speed-time characteristic during steady state of the electric motor plus load, and

(ii) multiplying the time derivative obtained in (i) by a moment of inertia of the electric motor plus load so as to derive a dynamic speed-torque characteristic of the electric motor plus load in steady state.

24. Use of the method according to claim 3 for testing in real time steady state vibration, unbalance, noise or oscillating torque of a rotating electric motor plus load, including:

(i) maintaining said shaft coupled to the digital rotary encoder for a desired time duration,

(ii) constantly measuring in real time during said desired time duration said respective time periods of pulses generated by the digital rotary encoder during rotation of the electric motor plus load,

(iii) constantly deriving the steady state combined oscillating torque-speed or the steady state speed spectrum or the steady state combined torque spectrum of the rotating electric motor plus load, and

(iv) determining a departure in any of the characteristics derived in (iii) from a nominal rating thereof.

25. The method according to claim 3, for testing an operational performance of an air-conditioner, wherein the electric motor is coupled to a fan of the air-conditioner, and there are included the steps of:

(b) allowing the fan to reach steady-state speed,

(c) deriving the speed-time characteristic of the fan, and

(d) Fourier transforming the speed-time or torque-time characteristic of the rotating electric motor plus fan so as to derive a frequency speed spectrum or frequency torque spectrum for testing vibration, unbalance or air noise oscillating torque;

whereby a frequency harmonic in the speed or torque of the air conditioner having a high amplitude, indicative of low quality thereof, is highlighted.

26. The method according to claim 3, for testing an operational performance of an air-conditioner having an adjustable shutter for adjusting a direction of airflow, wherein the electric motor is coupled to a fan of the air-conditioner, and there are included the steps of:

(e) allowing the fan to reach steady-state speed, and

(f) repeatedly adjusting the shutter and deriving and displaying the speed-time characteristic of the fan for different shutter positions;

whereby sharp fluctuations in the speed of the fan, indicative of low quality performance thereof, are highlighted.

28. An apparatus for measuring an angular rotation of a rotating shaft, the apparatus comprising:

a coupling unit for attaching to the shaft a digital rotary encoder which generates opposing binary logic states for a known angular rotation of the shaft, such that any pair of sequential logic states corresponds to a known angular rotation of the shaft,

a pair of timers for measuring respective time periods of successive opposing binary logic states generated by the digital rotary encoder, and

a computer coupled to the timers for summing said respective time periods associated with each successive logic state so as to derive an accumulated elapsed time of successive pairs of logic states generated by the digital rotary encoder thereby allowing derivation of the angular rotation or a function thereof of the shaft.

29. An apparatus for testing a rotating electric motor or a component thereof, the apparatus comprising:

a coupling unit for attaching a shaft of the rotating electric motor to a digital rotary encoder, and

a power supply for supplying power to the rotating electric motor at a specified time;

characterized by;

the digital rotary encoder generating opposing binary logic states for a known angular rotation of the electric motor, such that any pair of sequential logic states corresponds to a known angular rotation of the electric motor,

a pair of timers for measuring a respective elapsed time period of successive pairs of logic states generated by the digital rotary encoder during rotation of the electric motor, and

a computer coupled to the timers for successively receiving a respective time period from a first one of the timers, computing an associated time period and initializing a second one of the timers, and accumulating respective time periods of the successive opposing binary logic states generated by the digital rotary encoder so as to allow derivation of a dynamic speed characteristic of the rotating electric motor and for using the dynamic speed-time characteristic of the unloaded rotating electric motor to derive static torque speed or dynamic torque speed or oscillating torque during steady state or speed and torque spectrum during steady state of the unloaded rotating electric motor.

31. The apparatus according to claim 29, further including a display device coupled to the computer for displaying graphically the characteristics computed thereby.

32. The apparatus according to claim 29 being adapted to remove transient effects so as to derive static torque-speed characteristics of the electric motor.

34. The apparatus according to claim 29 wherein the timers comprise:

an oscillator for producing high frequency clock pulses of known frequency at an output thereof, and

first and second counters each having a clock input (CLK) coupled to the output of the oscillator, each having an enable input (ENABLE) coupled to the shaft encoder and responsive to mutually opposing logic states thereof for feeding to a computer coupled thereto respective logic states of the shaft encoder so as to allow the computer to compute an accumulated time period of the opposing logic states, and each having a reset terminal (RST) responsively coupled to the computer so as to enable the first and seconds counters to be reset thereby.

35. The apparatus according to claim 29 for displaying speed or torque characteristics of a rotating shaft, further including:

a sampling unit for sampling measured speed or torque at regular time intervals from a known initial sampling time,

a display for displaying at said regular time intervals said measured speed or torque samples versus time or frequency in an analogous way to using an oscilloscope or spectrum analyzer for voltage, and

a control panel for controlling a first x-axis scale in respect of time or frequency and a second orthogonal y-axis scale in respect of torque or speed amplitude while sampling the speed or torque in an analogous way to using an oscilloscope or spectrum analyzer for voltage.

36. The apparatus according to claim 35, wherein the control panel includes a control for adjusting said time intervals.

37. The apparatus according to claim 35, wherein the control panel includes a control for adjusting the initial sampling time.

30. An apparatus for testing a rotating electric motor plus load comprising:

a coupling unit for attaching a shaft of the rotating electric motor plus load to a digital rotary encoder, and

a power supply for supplying power to the rotating electric motor at a specified time;

characterized by;

the digital rotary encoder generating opposing binary logic states for a known angular rotation of the electric motor, such that any pair of sequential logic states corresponds to a known angular rotation of the electric motor,

a pair of timers for measuring a respective elapsed time period of successive pairs of logic states generated by the digital rotary encoder during rotation of the electric motor plus load, and

a computer coupled to the timers for successively receiving a respective time period from a first one of the timers, computing an associated time period and initializing a second one of the timers, and accumulating respective time periods of the successive opposing binary logic states generated by the digital rotary encoder so as to allow derivation of a dynamic speed characteristic of the rotating electric motor plus load and for using the dynamic speed-time characteristic of the rotating electric motor plus load to derive combined static torque speed or a steady state combined oscillating torque-speed or steady state speed spectrum or steady state combined torque spectrum of the rotating electric motor plus load, where the combined torque of the electric motor plus load is equal to the torque of the electric motor minus the torque of the load.

33. The apparatus according to claim 30 being adapted to remove transient effects so as to derive combined static torque-speed characteristics of the rotating electric motor plus load.

38. A method for testing an electric motor or of a component thereof, the method characterized by the steps of:

(a) measuring a dynamic speed-time characteristic of the unloaded rotating electric motor, and

(b) using the dynamic speed-time characteristic of the unloaded rotating electric motor to derive static torque speed or dynamic torque speed or oscillating torque during steady state or speed and torque spectrum during steady state of the unloaded rotating electric motor.

40. The method according to claim 38, wherein step (b) includes:

(i) computing the time derivative of the dynamic speed-time characteristic, and

(ii) multiplying the time derivative obtained in (i) by a moment of inertia of the unloaded electric motor so as to derive a dynamic speed-torque characteristic of the unloaded electric motor.

41. The method according to claim 38 for determining oscillating torque during steady state of the electric motor after it has reached steady state speed, wherein step (b) includes:

(i) computing the time derivative of the dynamic speed-time characteristic during steady state of the electric motor, and

(ii) multiplying the time derivative obtained in (i) by a moment of inertia of the unloaded electric motor so as to derive a dynamic speed-torque characteristic of the unloaded electric motor in steady state.

42. The method according to claim 38, wherein step (b) includes:

(i) removing fluctuations on a transient part of the dynamic speed-time characteristic during acceleration of the electric motor until it reaches steady state speed so as to obtain a static speed-time characteristic,

(ii) computing the time derivative of the static speed-time characteristic, and

(iii) multiplying the time derivative obtained in (ii) by a moment of inertia of the unloaded electric motor so as to derive a static speed-torque characteristic of the unloaded electric motor.

44. The method according to claim 42, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) locking the shaft of the electric motor,

(2) monitoring the stator current of the electric motor, and

(3) releasing the shaft of the electric motor when the stator current achieves a steady state value.

45. The method according to claim 42 for use with a PSC type a.c. induction motor having a stator comprising a main coil and an auxiliary coil which may be switched in parallel with the main coil, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) feeding current initially to the main coil only at a known angle in the a.c. supply voltage cycle,

(2) monitoring the stator current in the main coil, and

(3) switching the auxiliary coil in circuit when the stator current in the main coil achieves a steady state value at the same known angle in the a.c. supply voltage cycle.

46. The method according to claim 42, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) rotating the shaft in an opposite direction to a normal rotation direction, and

(2) during the time that the rotating electric motor changes direction, commencing sampling of the speed-time characteristics.

47. The method according to claim 42, wherein step (i) of removing fluctuations on the transient effects during acceleration of the electric motor until it reaches steady state speed, includes:

(1) Fourier transforming the speed-time of the rotating electric motor during acceleration

(2) filtering the frequency spectrum so as to remove higher frequency components, and

(3) transforming the resulting spectrum back to the time domain.

50. The method according to claim 38, for testing relative performance characteristics of stators for use in the electric motor, said method further comprising:

(f) providing a pre-calibrated rotor for said electric motor,

(g) providing successive stators and repeating steps (a) to (c) in respect of said stators so as to obtain respective stator-dependent characteristics of the motor.

51. The method according to claim 38, for testing relative performance characteristics of rotors for use in the electric motor, said method further comprising:

(f) providing a pre-calibrated stator for said electric motor,

(g) providing successive rotors and repeating steps (a) to (c) in respect of said stators so as to obtain respective rotor-dependent characteristics of the motor.

52. The method according to claim 38, further including:

(j) deriving a static torque-speed characteristic of the rotating electric motor with an inertial load having a known moment of inertia coupled to the motor shaft, and

(k) processing the respective torque-speed characteristics of the unloaded electric motor and of the electric motor plus inertial load so as to determine the moment of inertia of a rotor of the electric motor.

53. The method according to claim 40, wherein variations in speed or torque are used as a measure of electric motor noise.

54. The method according to claim 40, wherein variations in speed or torque are used as a measure of electric motor imbalance and vibration.

55. The method according to claim 38, further including:

(l) Fourier transforming the speed-time characteristic of the rotating electric motor or electric motor plus load so as to derive a speed frequency spectrum, and

(m) analyzing the speed frequency spectrum of the electric motor or electric motor plus load for determining vibration, unbalance, air-noise, and oscillating torque of the electric motor or the electric motor plus load.

56. The method according to claim 38, further including:

(n) Fourier transforming the torque-time characteristic of the rotating electric motor or electric motor plus load so as to derive a torque frequency spectrum, and

(o) analyzing the torque frequency spectrum of the electric motor or electric motor plus load for determining vibration, unbalance, air-noise, and oscillating torque of the electric motor or the electric motor plus load.

58. The method according to claim 38, including deriving an oscillating speed characteristic during a build-up to steady state speed of the rotating electric motor, comprising the steps of:

(g) coupling a high inertia flywheel to the rotating shaft so as deliberately to slow down the time to reach steady-state,

(h) deriving a steady-state speed-time characteristic of the rotating electric motor varying speed thereof subsequent to attainment of steady state performance, and

(i) zooming in on a desired range of speeds of the rotating electric motor so as to derive for a limited time frame the speed-time characteristics having superimposed thereon said oscillating speed characteristic.

59. The method according to claim 38 for deriving an oscillating torque characteristic at a steady state speed of the rotating electric motor, further comprising the step of:

(h) differentiating the speed-time curve with respect to time and multiplying by a moment of inertia of the rotating electric motor so as to derive varying torque as a function of time.

63. A method for displaying speed or torque characteristics of a rotating shaft derived according to claim 38, further including the steps of:

(p) sampling measured speed or torque at regular time intervals from a known initial sampling time,

(q) displaying at said regular time intervals said measured speed or torque samples versus time or frequency in an analogous way to using an oscilloscope or spectrum analyzer for voltage,

(r) controlling a first x-axis scale in respect of time or frequency while sampling the speed or torque in an analogous way to using an oscilloscope or spectrum analyzer for voltage, and

(s) controlling a second orthogonal y-axis scale in respect of torque or speed amplitude in an analogous way to using an oscilloscope or spectrum analyzer for voltage.

39. A method for testing an electric machine comprising an electric motor and attached load, the method characterized by the steps of:

(a) measuring a speed-time characteristic of the rotating electric motor plus load, and

(b) using the speed-time characteristic of the rotating electric motor plus load to derive a combined static torque-speed or a steady state combined oscillating torque-speed or steady state speed spectrum or steady state combined torque spectrum of the rotating electric motor plus load, where the combined torque of the electric motor plus load is equal to the torque of the electric motor minus the torque of the load.

43. The method according to claim 39, wherein step (b) includes:

(i) removing fluctuations on a transient part of the dynamic speed-time characteristic during acceleration of the electric motor plus load until it reaches steady state speed so as to obtain a static speed-time characteristic of the electric motor plus load,

(ii) computing the time derivative of the static speed-time characteristic of the electric motor plus load, and

(iii) multiplying the time derivative obtained in (ii) by a moment of inertia of the combined electric motor plus load so as to derive a combined static speed-torque characteristic of the electric motor plus load.

48. The method according to claim 43, further including:

(vi) subtracting the combined static speed-torque characteristic of the rotating electric motor plus load from the speed-torque characteristic of the electric motor derived in claim 43 so as to derive the torque-speed characteristic of the load.

49. The method according to claim 43, further including:

(vii) performing a GO-NOGO of the electric motor plus load as a function of the combined static speed-torque characteristic thereof.

57. The method according to claim 39 for determining oscillating torque during steady state of the electric motor plus load after it has reached steady state speed, wherein step (b) includes:

(i) computing the time derivative of the dynamic speed-time characteristic during steady state of the electric motor plus load, and

(ii) multiplying the time derivative obtained in (i) by a moment of inertia of the electric motor plus load so as to derive a dynamic speed-torque characteristic of the electric motor plus load in steady state.

60. Use of the method according to claim 39 for testing in real time steady state vibration, unbalance, noise or oscillating torque of a rotating electric motor plus load, including:

(i) maintaining said shaft coupled to the digital rotary encoder for a desired time duration,

(ii) constantly measuring in real time during said desired time duration said respective time periods of pulses generated by the digital rotary encoder during rotation of the electric motor plus load,

(iii) constantly deriving the steady state combined oscillating torque-speed or the steady state speed spectrum or the steady state combined torque spectrum of the rotating electric motor plus load, and

(iv) determining a departure in any of the characteristics derived in (iii) from a nominal rating thereof.

61. The method according to claim 39, for testing an operational performance of an air-conditioner, wherein the electric motor is coupled to a fan of the air-conditioner, and there are included the steps of:

(k) allowing the fan to reach steady-state speed,

(l) deriving the speed-time characteristic of the fan, and

(m) Fourier transforming the speed-time or torque-time characteristic of the rotating electric motor plus fan so as to derive a frequency speed spectrum or frequency torque spectrum for testing vibration, unbalance or air noise oscillating torque;

whereby a frequency harmonic in the speed or torque of the air conditioner having a high amplitude, indicative of low quality thereof, is highlighted.

62. The method according to claim 39, for testing an operational performance of an air-conditioner having an adjustable shutter for adjusting a direction of airflow, wherein the electric motor is coupled to a fan of the air-conditioner, and there are included the steps of:

(n) allowing the fan to reach steady-state speed, and

(o) repeatedly adjusting the shutter and deriving and displaying the speed-time characteristic of the fan for different shutter positions;

whereby sharp fluctuations in the speed of the fan, indicative of low quality performance thereof, are highlighted.

64. An apparatus for measuring an angular rotation of a rotating electric motor or component thereof, the apparatus comprising:

a coupling unit for attaching a shaft of the electric motor to a digital rotary encoder for accurately measuring an angular rotation of the shaft,

a power supply for supplying power to the rotating electric motor at a specified time, and

a computer coupled to the digital rotary encoder for deriving a speed characteristic of the rotating electric motor;

characterized in that;

the computer measures a dynamic speed-time characteristic of the unloaded rotating electric motor, and uses the dynamic speed-time characteristic of the unloaded rotating electric motor to derive static torque speed or dynamic torque speed or oscillating torque during steady state or speed and torque spectrum during steady state of the unloaded rotating electric motor.

66. The apparatus according to claim 64, further including a display device coupled to the computer for displaying graphically the characteristics computed thereby.

67. The apparatus according to claim 64 being adapted to remove transient effects so as to derive static torque-speed characteristics of the electric motor.

69. The apparatus according to claim 64 for displaying speed or torque characteristics of a rotating shaft, further including:

a sampling unit for sampling measured speed or torque at regular time intervals from a known initial sampling time,

a display for displaying at said regular time intervals said measured speed or torque samples versus time or frequency in an analogous way to using an oscilloscope or spectrum analyzer for voltage, and

a control panel for controlling a first x-axis scale in respect of time or frequency and a second orthogonal y-axis scale in respect of torque or speed amplitude while sampling the speed or torque in an analogous way to using an oscilloscope or spectrum analyzer for voltage.

70. The apparatus according to claim 69, wherein the control panel includes a control for adjusting said time intervals.

71. The apparatus according to claim 69, wherein the control panel includes a control for adjusting the initial sampling time.

65. An apparatus for testing a rotating electric motor plus load comprising:

a coupling unit for attaching a shaft of the rotating electric motor plus load to a digital rotary encoder,

a power supply for supplying power to the rotating electric motor at a specified time, and

a computer coupled to the digital rotary encoder for deriving a speed characteristic of the rotating electric motor;

characterized in that;

the computer measures a dynamic speed characteristic of the rotating electric motor plus load and uses the dynamic speed-time characteristic of the rotating electric motor plus load to derive combined static torque speed or a steady state combined oscillating torque-speed or steady state speed spectrum or steady state combined torque spectrum of the rotating electric motor plus load, where the combined torque of the electric motor plus load is equal to the torque of the electric motor minus the torque of the load.

68. The apparatus according to claim 65 being adapted to remove transient effects so as to derive combined static torque-speed characteristics of the rotating electric motor plus load.