ASME PTC 19.22:2007 pdf download Data Acquisition Systems Performance Test Codes
This Section discusses the fundamental elements to beconsidered when designing / selecting a data acquisitionsystem.
3-1CAPABILITY
Data acquisition systems are capable of improvingtesting in many ways.
(a) Data quality can be improved in basic data acquisi-tion systems through the use of digital displays thatreduce human error often incurred when recording datamanually.
(b)More sophisticated data acquisition systems canreduce human recording error by recording and storingdata digitally.
(c) Test personnel can be reduced by replacing manualdata collectors with automated data acquisition systemswhen sampling multiple data points.
(d) Automated data acquisition systems may have thecapability of online data reduction and results calcula-tions. wWith this feature, dissemination of data must beconsidered to accommodate validation of the data acqui-sition system.
(e)Test duration can be reduced by recording datamore frequently than manual methods, allowing for asufficient number of samples to be obtained in a shorterperiod of time.
(f) Data acquisition systems can be designed to allowfor remote, real time access of test data. The incorpora-tion of networked computers into data acquisition sys-tems permits transmission of test data to remotelocations.
3-2 TYPICAL DATA ACQUISITION sYSTEMS
To better understand the scope and types of dataacquisition systems, this subsection categorizes anddescribes the functions of each category.Three groupsare defined to differentiate among levels of complexity:basic, intermediate, and advanced data acquisition sys-tems. Figures 3-2-1 through 3-2-3 provide a representa-tion of these systems based on the individual functionsof the data acquisition systems.These figures do notnecessarily represent the components of the systemssince multiple functions may be contained in and per-formed by a single component. The order in which thesefunctions are executed may vary from one system tothe next.
3-2.1 Basic Data Acquisition System
The basic data acquisition system is characterized bythe following features that are the minimum requiredto be considered a data acquisition system:
(a) signal conditioning
(b) analog to digital conversion(c) multiplexing
(d) data logging (digital or hard output)
A schematic representation of a basic data acquisitionsystem is shown in Fig. 3-2-1.
The basic data acquisition system is appropriate fortests that require a minimal number of data points dueto the labor-intensive data reduction that is requiredwith this system. The basic data acquisition system typi-cally requires longer test periods so that a sufficientnumber of data samples can be recorded to meet therequired measurement uncertainty.Therefore, the basicsystem is ideal for tests with a small number of measure-ments that can be performed under steady conditionsfor a long period of time.
3-2.2 Intermediate Data Acquisition System
The intermediate data acquisition system is distin-guished from the basic system by digital data storagecapability. This is shown in Fig.3-2-2, illustrations (a)and (b).The features of the intermediate data acquisitionsystem include the basic data acquisition system andthe following capabilities:
(a)Elementary Calculations. This is an optional featurethat includes engineering unit conversion, scaling, andcalibration corrections.
(b) Digital data storage.(c) Digital data output.
Elementary calculations can be executed in variousstages of the intermediate data acquisition system. Forexample, calculations may be performed by a centralprocessor after the multiplexing component or beforethe multiplexing component in a transmitter.
The intermediate system is ideal for high frequencydata collection. Since this system records and stores datadigitally, the frequency of data collection is increasedsignificantly over the basic data acquisition system. Thismeans that a sufficient number of measurements can betaken in a shorter amount of time. Digital storage allowsthe possibility of transferring data directly into a sepa-rate computer application, which improves data reduc-tion time. Elementary calculations can further reducedata reduction time by performing unit conversions,
ASME PTC 19.22:2007 pdf download
