3.0 Sequence Testing
Sequence testing, as its name implies, involves the sending of a sequence of test signals
for the complete and automatic evaluation of a system. Sequence testing on the LA100 is
completely self contained and requires no programming effort, yet it is powerful and
flexible, and designed to fully test any circuit or equipment which operates in the audio
band in about one minute. The test results can be displayed on the LA102’s LCD, printed
directly to a printer and downloaded to a PC.
Frequency shift keying Limit testing
A key feature is the use of test segments; standard ‘building blocks’ from which the
sequences are assembled. Each test segment (identified by a letter A-Z or a-z) consists of
a short sequence of tones or a frequency sweep, preceded by an FSK (Frequency Shift
Keyed) header code lasting around 200ms. The header acts as the synchronising trigger
for the LA102, as well as identifying the segment code: the LA102 then makes the
necessary measurements at the right time. Segments can be sent in almost any
combination over any audio path, or recorded and replayed, and any LA102 will still
make correct measurements without any programming. The use of short segments brings
many advantages over a single long test sequence. Speed errors on tape replay, which
could put a long sequence out of synchronism, are well tolerated as each segment is
retimed from its own FSK header. ‘Breaking-in’ on a continuous repeating sequence is
also possible, as the LA102 waits and responds to the next FSK header. Perhaps most
important, though, is the way in which segmented sequences combine flexibility with
standardisation. A relatively small number of segments can be put together to form an
almost unlimited number of test sequences, and yet every one will be recognised
automatically by any LA102 because the segments are standardised.
Up to 5 sets of results can be stored in the LA102’s non-volatile memory to be examined,
printed or transferred to a computer later. Tolerance limit tests can be applied to the
sequence results and up to 10 sets of user tolerances can be entered allowing limits to be
specified for every measurement providing pass/fail testing which is ideal for production
testing, or routine checking of equipment. A source identification message can be entered
into the LA101 (for all sequences, or for each sequence separately) and this is transmitted
to the LA102 as FSK. The heading and the date can be entered into the LA102, to be
printed at the top of the page. All sequences, results, tolerances and messages are
preserved in non-volatile memory when the unit is turned off so complex definitions need
only be entered once (they can also be entered from a remote computer via the serial port
- see chapter 9).
New users should read sections 3.1 to 3.4 which explain the basics of sequence testing.
They may then proceed to chapters 4, 5 or 8 for details on modifying the test sequences,
pass/fail tolerance testing or results printing respectively.
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