ASME PTC 19.22-2007 pdf download

ASME PTC 19.22-2007 pdf download.Data Acquisition Systems Performance Test Codes.
1-1 OBJECT The object of this Code is to provide guidance for design, selection, and application of the data acquisition systems used in ASME Code Performance Tests. This Code provides descriptions of the various data acquisi- tion system architectures and information on determin- ing system uncertainties and to assist in selecting and applying these data acquisition systems. The Code is intended to address data acquisition systems used for ASME Code Performance Testing but may also be used for guidance in selecting systems for any test applica- tion. These systems include systems specifically installed fora testand plantDistributedControl Systems (DCS) which also provide the ability to monitor sensors during a test. The Code is not intended to address long term Performance Monitoring but may provide guid- ance for such applications. 1-2 SCOPE The scope of this Code includes signal conditioning, signal multiplexing, analog-to-digital signal conversion,
and data processing. This Code addresses stand-alone data acquisition systems, typified by a sensor with an integral digital display, data acquisition systems that link multiple sensors to a common digital processor tied to a computer or printer, and systems that link multiple digital processors to one or more stand-alone or net- worked computers. This Code incorporatesinstrumentationpractices cov- ered by other Instruments and Apparatus Supplements (PTC 19 Series) as well as by the equipment Performance Test Codes. It also provides a means to determine the uncertainty associated with the data acquisition system, and its impact on the overall uncertainty of the perform- ance test. The Code does not directly address specific sensors or instruments used for ASME Performance Testing. These are addressed in other ASME Performance Test Codes.
The following definitions are provided to clarify the terms used in this document: accuracy: the closeness ofagreementbetweena measured value and the true value [1]. analog signal: a nominally continuous electrical signal that varies in some direct correlation with another signal impressed on a transducer [2]. analog-to-digital (A/D) converter: a device that converts an analog signal to a digital signal that represents equiv- alent information [2]. binary word: the maximum number of bits treated as a unit and capable of being stored in one location [3]. bit: a contraction of the words “binary” and “digit” [3]. calibration: the process of comparing the response of an instrument to a reference standard over some measure- ment range. channel: a single path through a transmission media intended to carry the signal of an instrument reading. Typically, it carries the raw electrical signal of the instru- ment, or the output of a multiplexing function. checksum bit (check bit): a bit, such as a parity bit, derived from and appended to a bit string for later use in error detection and possibly error correction [2]. contact resistance: the resistance between the closed con- tacts of a relay in a multiplexer. crosstalk: the undesired signal appearing in one signal path as a result of coupling from another signal path [3]. data acquisition system: any device or collection ofdevices capable of accepting information, converting this infor- mation to corresponding digital information, applying prescribed processes to the information, and supplying the results of the processes [3]. data compression: the method of filtering data, by excep- tion or other means, and storing it only if meeting speci- fied criteria.
filtering: electric, electronic, acoustic, optical, or software devices used to reject signals, vibrations, or radiations of certain frequencies while allowing others to pass [2]. full range (FR): the absolute value of the algebraic differ- ence between the minimum and maximum values for which the system is capable of measuring or generating. full scale: an instrument’s maximum reading or output for each of its ranges [4]. May have a higher numeric value than the range setting due to overrange capability. gain error(scale error): error in a signal due to nonlinearity in a device’s response. least significant bit (LSB): right most bit in a binary word whose value contributes the least to the overall value of the binary word and also represents the resolution of the digital word. multiplexer: a device that combines two or more informa- tion channels onto a common transmission medium [2]. noise: a disturbance that affects a signal and that may distort the information carried by the signal [2]. primary variables: those used in calculations of test results. They are further classified as: (a) Class 1: primary variables are those which have a relative sensitivity coefficient of 0.2 or greater (b) Class 2: primary variables are those which have a relative sensitivity coefficient of less than 0.2 [5].