9492600990 19-17
DECS-150 BESTlogic™Plus
When true, this element opens the normally-
open watchdog output and closes the
normally-closed watchdog output.
Logic Schemes
A logic scheme is a group of logic variables written in equation form that defines the operation of a DECS-
150 Digital Excitation System. Each logic scheme is given a unique name. This gives you the ability to
select a specific scheme and be confident that the selected scheme is in operation. One logic scheme is
configured for a typical protection and control application of a synchronous machine and is the default
active logic scheme. Only one logic scheme can be active at a given time. In most applications,
preprogrammed logic schemes eliminate the need for custom programming. Preprogrammed logic
schemes may provide more inputs, outputs, or features than are needed for a particular application. This
is because a preprogrammed scheme is designed for a large number of applications with no special
programming required. Unneeded logic block outputs may be left open to disable a function or a function
block can be disabled through operating settings.
When a custom logic scheme is required, programming time is reduced by modifying the default logic
scheme.
The Active Logic Scheme
The DECS-150 must have an active logic scheme in order to function. All DECS-150 controllers are
delivered with a default, active logic scheme preloaded in memory. The logic scheme is tailored for a
system with the PSS option disabled or enabled depending on the PSS option selected in the system
style number. The functionality of this logic scheme is similar to the functionality of a DECS-100. If the
function block configuration and output logic of the default logic scheme meet the requirements of your
application, then only the operating settings (system parameters and threshold settings) need to be
adjusted before placing the DECS-150 in service.
Sending and Retrieving Logic Schemes
Retrieve a Logic Scheme from the DECS-150
To retrieve settings from the DECS-150, the DECS-150 must be connected to a computer through a
communications port. Once the necessary connections are made, settings can be downloaded from the
DECS-150 by selecting Download Settings and Logic on the Communication pull-down menu.
Send a Logic Scheme to the DECS-150
To send settings to the DECS-150, the DECS-150 must be connected to a computer through a
communications port. Once the necessary connections are made, settings can be uploaded to the DECS-
150 by selecting Upload Settings and Logic on the Communication pull-down menu.
Always remove the DECS-150 from service prior to changing or
modifying the active logic scheme. Attempting to modify a logic
scheme while the DECS-150 is in service could generate unexpected
or unwanted outputs.
Modifying a logic scheme in BESTCOMSPlus does not automatically
make that scheme active in the DECS-150. The modified scheme
must be uploaded into the DECS-150. See the paragraphs on Sending
and Retrieving Logic Schemes above.
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