L-VIS User Manual
177
LOYTEC
Version 6.2
LOYTEC electronics GmbH
Binary
: A
binary
data point contains a Boolean value. Meta-data for binary data
points includes human-readable labels for the Boolean states (i.e., active and
inactive texts).
Multi-state
: A
multi-state
data point represents a discrete set of states. The
associated data type is a signed integer machine variable. Each state is identified
by an integer value, the
state ID
. State IDs need not be consecutive. Meta-data of
a multi-state data point includes human-readable descriptions for the individual
states (state texts) and the number of available states.
String
: A
string
data point contains a variable-length string. The associated data
type is a character string, encoded in UTF-8 for international language support. A
string data point does not include any other meta-data.
User
: A
user
data points contains un-interpreted, user-defined data. The data is
stored as a byte array. A user data point does not include any other meta-data.
This type of data point also serves as a container for otherwise structured data
points and represents the entirety of the structure.
10.1.2 Timing Parameters
Apart from the meta-data, data points can be configured with a number of timing
parameters. The following properties are available to input or output data points,
respectively:
Pollcycle
(input): The value is given in seconds, which specifies that this data
point periodically polls data from the source. This is referred to as static polling.
Receive Timeout
(input): This is a variation on the poll cycle. When receive
timeout is enabled, the data point actively polls the source unless it receives an
update. For example, if poll cycle is set to 10 seconds and an update is received
every 5 seconds, no extra polls are sent. The receive timeout setting cannot be
used for feedback data points.
Poll-on-startup
(input): If this flag is set, the data point polls the value from the
source when the system starts up. Once the value has been read, no further polls
are sent unless a poll cycle has been defined.
Minimum Send Time
(output): This is the minimum time that elapses between
two consecutive updates. If updates are requested more often, they are postponed
and the last value is eventually transmitted after the minimum send time. Use this
setting to limit the update rate.
Maximum Send Time
(output): This is the maximum time without sending an
update. If no updates are requested, the last value is transmitted again after the
maximum send time. Use this setting to enable a heart-beat feature.
Dynamic polling is an option that some network technologies offer. With static polling the
poll cycle is used to permanently poll values over the network. This is required for data
points that require constant value updates a fixed poll cycle (for example to trend the data).
For other data points that do not need permanent value updates, so-called dynamic polling
is activated, as soon as the values are needed. When the data is not needed, polling stops
and no longer puts a burden on the network. The advantage is that a few data points can be
refreshed at a higher rate at a time compared to static polling, where all data points must
permanently share the available network bandwidth.
10.1.3 Default Values
Default values can be defined for data points when needed. The value of a data point will
be set to the defined default value, if no other value source initializes the data point. Default
values are beneficial, if certain input data points are not used by the network and need a
pre-defined value, e.g., for calculations. Default values are overridden by persistent values
or values determined by poll-on-startup.
