Page 246 - Mechanical Engineers' Handbook (Volume 2)

9 Other Data Acquisition and Display Topics 235

lenges. One can consider the first piece of data collected about some object to be the
beginning of a chain of data and each successive data acquisition point in the manufacturing
process to be a link in that chain until the end of the chain, where the last piece of data
about a manufactured item is collected. Often, the steps of the manufacturing process may
proceed from raw material to some intermediate work-in-process unit, to some other step
that may be time based, then to some other step that may be finished-unit based. Many
varieties of the above exist. Each link can represent one of the following:
• Data collected from a start time to an end time
• A set of attributes about a particular manufacturing unit with an associated time of
processing

Often referred to as the genealogy, the steps can be linked together through:
• Some assumptions based on time stamp relationship of one link back to the previous
one
• Recording of units that entered or left the time-based portion of the process and the
beginning and ending of the entry time
• Some assumptions about the mixing of elements of the manufactured item

Using the techniques described above for combination of time-based and event data, a
set of data for the whole life cycle of a manufactured item can be created. Where mixing
occurs, the data will be less accurate but may provide clues as to the factors that went into
the final product, such as proportions of additives. As an example, Table 10 shows various
queries that can be combined to provide one picture of all data sources for a manufactured
unit.
Starting at the finished-good item, the batch ID of the previous step acts as a link into
the range of time data in the previous step. If the list of items broken down is retained from
the prior step, then those can be used to link back to the previous time frame.
Depending on the amount of mixing, the results will be more or less indicative of what
actually happened. The smaller the batch sizes, the easier the tracking back to source data
will be. Time lags between process steps can dramatically impact the ability to assume when
the raw materials for a particular item were processed.

9.2 Web Programs and Interfaces
Web interfaces have improved to the point that user interfaces can be written in Web browser
screens. This eliminates the effort and organization required to deploy code across a com-
pany. The application is written for a Web interface. When the user uses a Web browser to
access the page, functionality is downloaded to the user’s page or is executed in such a
fashion as to obtain the results of a query and transmit a data page to the user. The developer
does not have to get involved in the process of manually installing software on the user’s
machine. This reduces the demand on the desktop computer and allows the developer to
make a change and have it proliferated to all users when they next reference the Web.

9.3 Configuration versus Implementation
As a general rule of thumb, third-party data acquisition and storage systems provide config-
urable tools for acquisition and display. For simple applications which do not require great
flexibility in program functions, such as generating alarms, unusual graphics types, control
of the process, or integration into larger systems, it is appropriate to use these, often simple,