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13-32 Standards and Practices

Database Documentation

As facilities expand in size and complexity, a set of conventions will longer answer all of the
questions. At some point, a wire leaves an equipment rack and its destination is no longer obvi-
ous. Likewise, equipment will often require written documentation as to its configuration and
purpose, especially if it is utilized in an uncharacteristic way.

Database documentation records the locations of both ends of a given circuit. For this, each

cable must be identified individually. There are two common systems for numbering cables:
ascension numbers, and from-to coding. In ascension numbering schemes, each wire or cable is
numbered in increasing order, one, two, three, and so on. In from-to coding, the numbers on each
cable represent the source location, the destination location, and normally some identification as
to purpose and/or a unique identifier. For example, a cable labeled 31-35-B6 might indicated that
cable went from a piece of equipment in rack 31 to another unit in rack 35 and carries black, it is
also the sixth cable to follow the same route and carry the same class of signal.

Each method has its benefits. Ascension numbering is easier to assign, and commonly avail-

able preprinted wire labels can be used. On the other hand, ascension numbers contain no hints
as to wire purpose or path, and for that reason “purpose codes” are often added to the markings.

From-to codes can contain a great deal more information without relying on the printed docu-

mentation records, but often space does not permit a full delineation on the tag itself. Here again,
supplemental information may still be required in a separate document or database.

Whatever numbering system is used, a complete listing must be kept in a database of some

type. In smaller installations, this might simply be a spiral notebook that contains a complete list
of all cables, their source, destination, any demarcations, and signal parameters.

Because all cabling can be considered as a transmission line, all cabling involves issues of ter-

mination. In some data and analog video applications, it is common for a signal to “loop-
through” several pieces of equipment. Breaking or tapping into the signal path often has conse-
quences elsewhere, resulting in unterminated or double terminated lines. While more forgiving,
analog audio has similar concerns. Therefore, documentation must include information on such
termination.

Analog audio and balanced lines used in instrumentation have special concerns of their own.

It is seldom desirable to ground both ends of a shielded cable. Again, the documentation must
reflect which end(s) of a given shield is grounded.

In many cases, signal velocity is such that the length of the lines and the resulting propagation

delay is critical. In such circumstances, this is significant information that should be retained. In
cases where differing signal levels or configurations are used (typical in data and control sys-
tems), it is the documentor’s obligation to record those circumstances as well.

However or wherever the database documentation is retained, it represents the basic informa-

tion that defines the facility interconnections and must be available for updating and duplication
as required. 

Graphic Documentation

Electronics is largely a graphical language. Schematics and flow charts are more understandable
than net lists or cable interconnection lists. Drawings, either by hand—done with the aid of draft-
ing machines and tools—or accomplished on CAD (computer aided design) programs are highly
useful in conveying overall facility design quickly and clearly. Normally, the wire numbering

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Engineering Documentation 13-33

scheme will follow that used in the database documentation, so that the graphic and text docu-
mentation can be used together.

CAD drawings are easy to update and reprint. For this reason, documentation via CAD is

becoming more popular, even in smaller installations. Because modern CAD programs not only
draw but also store information, they can effectively serve as an electronic file cabinet for docu-
mentation. While there have been attempts to provide electronic/telecommunications engineer-
ing documentation “templates” and corresponding technical graphics packages for CAD
programs, most of the work in this area has been done by engineers working independently to
develop their own systems. Obviously, the enormous scope of electronic equipment and telecom-
munications systems make it impractical for a “standard” CAD package to suit every user.

13.2.2c

Update Procedures

Because documentation is a dynamic tool, as the facility changes, so too must the documenta-
tion. It is common for a technician to “improve” conditions by reworking a circuit or two. Most
often this fixes a problem that should be corrected as a maintenance item. But sometimes, it
plants a “time bomb” wherein a future change, based on missing or incomplete documentation of
the previous work, will cause problems.

It is essential that there be a means of consistently updating the documentation. The most

common way of accomplishing this is the mandatory “change sheet.” Here, whenever a techni-
cian makes a change it is reported back to those who keep the documentation. If the changes are
extensive, the use of the “red-line” drawing and “edit sheet” come into play; the original drawing
and database, respectively, are printed and corrected with a “red pen.” This document then is
used to update the original documentation.

In some cases, the updating process can be tied to the engineering reports or discrepancy pro-

cess. Most facilities use some form of “trouble ticket” to track equipment and system perfor-
mance and to report and track maintenance. This same form may be used to report changes
required of the documentation or errors in existing documentation.

13.2.2d

Equipment Documentation

Plant documentation does not end when all of the circuit paths in the facility are defined. Each
circuit begins and ends at a piece of equipment, which can be modified, reconfigured, or
removed from service. Keep in mind that unless the lead technician lives forever, never changes
jobs, and never takes a day off, someone unfamiliar with the equipment will eventually be asked
to return it to service. For this reason, a documentation file for each piece of equipment must be
maintained.

Equipment documentation contains these key elements:

•

The equipment manual

•

Modification record

•

Configuration information

•

Maintenance record

The equipment manual is the manufacturer’s original documentation. As mentioned previ-

ously, the manuals must be organized in such a manner that they can be easily located. Typically,

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13-34 Standards and Practices

the manuals are kept at the site where the equipment is installed (if practical). Remember that
equipment with two “ends” such as STLs, RPUs, or remote control systems need manuals at
each location!

Of course, if a piece of equipment is of custom construction, there must be particular atten-

tion paid to creating a manual. For this reason, a copy of the key schematics and documentation
is often attached directly to the equipment. This “built-in manual” may be the only documenta-
tion to survive over the years.

Many pieces of equipment, over time, will require modification. Typically, the modification is

recorded in three ways. First, internally to the equipment. A simple note glued into the chassis
may be suitable, or a marker pen is used to write on a printed circuit board or other component.
Second, the changes can be recorded in the manual, either inside the cover, or on the schematic
or relevant pages. If the manual serves several machines, this may not be appropriate. If this is
the case, a third option is to keep the modification information in a separate equipment file.

Equipment files are typically kept in standard file folders, and may be filed with the pertinent

equipment manuals. Ideally, the equipment file is started when the equipment is purchased, and
should contain purchase date, serial number, all modifications, equipment location(s), and a
record of service.

The equipment file is the proper place to keep the configuration information. An increasingly

large amount of equipment is microprocessor based or otherwise configurable for a specific
mode of operation. Having a record of the machine’s default configuration is extremely helpful
when a power glitch (or an operator) reconfigures a machine unexpectedly. 

Equipment files should also contain repair records. With most equipment, documenting fail-

ures, major part replacements, operating time, and other service-related events serves a valuable
purpose. Nothing is more useful in troubleshooting than a record of previous failures, configura-
tion, modifications, and—of course—a copy of the original manual.

13.2.2e

Operator/User Documentation

User documentation provides, at its most basic level, instructions on how to use a system. While
most equipment manufacturers provide reasonably good instruction and operations manuals for
their products, when those products are integrated into a system another level of documentation
may be required. Complex equipment may require interface components that need to be adjusted
from time to time, or various machines may be incompatible in some data transmission modes—
all of which is essential to the proper operation of the system.

Such information often resides only in the heads of certain key users and is passed on by word

of mouth. This level of informality can be dangerous, especially when changes take place in the
users or maintenance staff, resulting in differing interpretations between operators and mainte-
nance people about how the system normally operates. Maintenance personnel will then spend
considerable time tracking hypothetical errors reported by misinformed users.

A good solution is to have the operators write an operating manual, providing a copy to the

maintenance department. Such documentation will go a long way toward improving inter-depart-
mental communications and should result in more efficient maintenance as well.

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13.2.2f

The True Cost of Documentation

There is no question that documentation is expensive—in some cases it can equal the cost of
installation. Still, both installation and documentation expenses pale in comparison to the cost of
equipment and potential revenue losses resulting from system down-time.

Documentation must be seen as a management and personnel issue of the highest order. Any

lapse in the documentation updating process can result in disaster. Procrastination and the result-
ing lack of follow through will destroy any documentation system and ultimately result in plant
failures, extend down-time, and premature rebuilding of the facility.

Making a business case for documentation is similar to making any business case. Gather

together all the costs in time, hardware, and software on one side of the equation, and balance
this against the savings in time and lost revenue on the other side. Engineering managers are
expected to project costs accurately, and the allocation of sufficient resources for documentation
and its requisite updating is an essential part of that responsibility.

13.2.3 Bibliography

Baumgartner, Fred, and Terrence Baun: “Broadcast Engineering Documentation,” in NAB Engi-

neering Handbook, 9

th

 ed., Jerry C. Whitaker (ed.), National Association of Broadcasters,

Washington, D.C., 1999.

Baumgartner, Fred, and Terrence Baun: “Engineering Documentation,” in The Electronics Hand-

book, Jerry C. Whitaker (ed.), CRC Press, Boca Raton, Fla., 1996.

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