ASME PTC 19.7
Part 7: Measurement of Shaft Power Instruments and Apparatus
|Publication Date:||1 January 1980|
OBJECT AND SCOPE
The object of this Supplement is to describe the function, characteristics, advantages, disadvantages, and accuracy of equipment and techniques currently available for the measurement of shaft power of rotating machines.
The scope of the Supplement is limited to descriptive material which will enable a user to select an appropriate system or procedure for his application. It includes criteria for the operating conditions of the equipment whose power is being measured, and instructions for the calibration of apparatus.
Two direct methods of shaft power measurement are described. The reaction torque method utilizes a dynamometer which may supply or absorb shaft power. The other method utilizes a torquemeter which measures torque transmitted between a prime mover and a driven machine.
When direct means of shaft power measurement are impractical, certain indirect methods may be used. Indirect methods measure the power by electrical means or by thermodynamic analysis.
For each method presented, this Supplement describes, insofar as appropriate:
Apparatus and required facilities.
Operating principles and characteristics.
Range and limits.
Sources of error;
Advantages and disadvantages.
Table 1 provides guidance on the range of application of the various torque and power measurement systems.
Some of the procedures and equipment measure shaft torque, and require concurrent determination of rotational speed to provide a value for shaft power.
There are three general methods available for measurement of rotational speed:
(a) Devices which display, indicate, or record a number of revolutions within a known time interval.
(b) Devices which display, indicate, or record time-averaged rotational speed.
(c) Devices which continuously record instantaneous angular velocity.
Reference 12 (Appendix D) contains a complete description of types, methods, and classification of rotational speed measuring devices.
The scope does not include operating instructions for specific measurement apparatus.
It is expected that the main equipment Performance Test Codes will contain instructions concerning the frequency of calibrations, number of observations, limitations on time variations, etc., which are appropriate for the purpose of the equipment tests.
Specific instructions about the statistical treatment of test data should be found in the main equipment Performance Test Codes.