Filter
Top Products
Reference
WFM 601A, WFM 601E & WFM 601M User Manual
3–51
seconds that contained errors (errored seconds) is indicated. An elapsed time
indicator gives the total time since the error counter display was last reset. Use
the elapsed time to calculate statistics such as percentage errored seconds. Press
the RESET bezel button to set both the errored seconds readouts and the elapsed
time counter to zero.
Each ERR SEC readout has a STATUS field just below it. The status can be
either Valid, Invalid, or Missing. Valid means a transmitted CRC is available to
check for errors. Invalid means some EDH information is present, but the CRC
used to check for errors is not available. Missing means that no EDH information
is present. In this case, the EDH DET indicator is off. To check the error rate, the
EDH CRC being used – either FF (full field) or AP (active picture) – must be
Valid. Note that if a CRC becomes Invalid while the error rate is being deter-
mined, the ERR SEC readout will freeze. Errors are not detected while the CRC
is Invalid.
This measurement method is possible because the serial receiver under test
creates the reclocked serial output after it has equalized the input signal,
recovered the clock, and latched the data. Any detection errors affecting the
receiver also appear in the regenerated serial output and are detected by the
waveform monitor.
The ability to measure a receiver error rate by monitoring its regenerated output
is very useful in an operating system. Although many types of video equipment
do not include EDH error detection, most have regenerated (or reclocked) serial
outputs. This technique can bring error rate measurement capability to virtually
any point in a facility. Strategic placement of waveform monitors can help track
the performance of an operating video system. Similarly, you can use a single
EDH monitor to proof an entire digital chain by moving it from one regenerated
output to the next.
Error Rate Measurement with AP CRC. The waveform monitor calculates CRC
check-words for the active picture area of each video field. The two CRC values
are displayed on the SERIAL STATUS screen: one for field 1 (F1) and one for
field 2 (F2). With a fixed-pattern test signal, these CRCs should have constant
values. Hence, any change in the CRC indicates an error. By passing a static test
signal through system equipment, you can look for errors introduced by the
system equipment.
Connect the waveform monitor as shown in Figure 3–35. The source does not
need EDH, but it must be a fixed pattern signal (repeating every two fields).
Display the SERIAL STATUS screen. Press the RESET key and check that the
CHANGE SINCE RESET flag reads No. If an error occurs, a CRC value will
briefly change values then resume the fixed pattern value. Even a very brief
change sets the CHANGED SINCE RESET flag to Yes. The elapsed time
counter indicates the length of time since the flag was last reset to No. The flag
indicates only that one or more errors occurred.