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DVLD User Manual
algorithm detects a strike at a distance that is closer than about 40 km, it will output this number
to the Davicom unit for further action. Actually, the Davicom unit reads the data out of the DVLD
once every second. It is important to note that this averaging and distance estimation takes place
on a 17 minute cycle in the hardware. This means that once a strike has been detected (and the
information sent to the Davicom), the DVLD won’t send a return to normal reading until 17
minutes later (if no other lightning strikes are detected).
If the storm keeps approaching however, the DVLD will continue to update its output to the
Davicom with shorter and shorter distances.
This is where the “Distance Trigger” setting on the Davicom comes into play. Although the DVLD
is continuously monitoring and outputting any distances to approaching lightning activity, a user
can decide to ignore any strikes that occur too far away by setting the Davicom’s distance
threshold to a smaller distance. The closer this distance is to the site, the fewer nuisance alarms
will be caused by tangentially moving storms. On the other hand it is up to the user to decide
how comfortable he is with the risk that a fast-approaching storm could zoom-in to his site with
little or no forewarning. A display of 63 km indicates that no lightning has been detected.
6 Timeout delays
As explained in the paragraph above, the DVLD’s normal averaging period is 17 minutes, and
this period is fixed in the hardware. The Davicom unit however, has a “Trigger Timeout” period
that is added to the basic 17 minute timeout. Since the minimal time settable for the Trigger
Timeout in the Davicom is 1 minute, the total minimal timeout period is 18 minutes. The maximal
extra delay that can be added here is 99 minutes. The Davicom’s default Trigger value of 10
minutes will therefore produce a total timeout period of 27 minutes. The maximum extra delay
that can be added here is 99 minutes.
6.1 Noise rejection
In addition to the sophisticated averaging and distance estimation algorithm described above,
the DVLD also features an embedded man-made noise rejection algorithm. This feature reduces
false alarms that can be caused by electrical arcing, motor noises and other non-natural sources.
7 Using the DVLD
There are two suggested methods of using the DVLD to protect remote site equipment. One
method follows the lines of a “hands-off” philosophy and the other is more of a “hands-on”
method. You may obviously decide to adapt these suggestions to your particular operational
needs.
