L-Gate User Manual 61 LOYTEC
Version 3.2 LOYTEC electronics GmbH
through a client mapping. Data points of other technologies and the min/max/avg
algorithms cannot be trended in this firmware version.
BACnet trend logs are limited to interval and COV logs. The trigger mode is not supported
in BACnet. The setting linear and ring-buffer logging is mapped to the Stop_When_Full
property of the underlying BACnet trend log object. This setting in the Configurator
software is a default and can be overridden by writing to the Stop_When_Full property by
the OWS.
If an enable data point is configured by the Configurator software, the Log_Enable
property is written with the value of that data point. If no enable data point is configured,
the Log_Enable is TRUE as a default and can be modified over the network.
The fill-level action is mapped to generating a buffer event notification in the BACnet
trend log object. The fill-level trigger can still be used for e-mails even if no notification
class is configured in the BACnet trend log object. The fill-level percentage maps to the
Notification_Threshold property. The percentage setting in the Configurator software is a
default and can be changed by the OWS over the network.
5.7 Automatic Generation of Connections
When generating matching counter parts to NVs, there are two types of NVs to be
considered: Simple NVs that hold only one value (scalar or enumeration), and structured
NVs, that consist of a number of fields. For simple NVs only one BACnet object per NV is
generated. For structured NVs, one BACnet object is generated for each structure member.
Which type of BACnet object is created depends on the type of the simple NV or of the
structure member. For scalar types, analog objects are created. The scaling factors are
applied to the NV to get the resulting scalar value for the Present_Value property. Other
properties of analog objects are derived from the SNVT, including the engineering units,
min and max present value. Multi-state objects are created for NV enumeration types. The
CEA-709 state IDs are sorted and renumbered to start at ‘1’ in BACnet (i.e., a ‘-1’ of
MOTOR_NUL in CEA-709 maps to a ‘1’ of MOTOR_NUL in BACnet). This is necessary
as the SNVT states ‘-1’ and ‘0’ cannot be represented in BACnet as a raw value, because
allowed BACnet multi-states start at 1. Which state IDs exist is documented in the BACnet
multi-state texts array. Optionally, binary objects are created for enumerated NVs with
three states, excluding the ‘-1’ state.
In BACnet commandable objects can be written with values at a certain priority. The value
with the highest priority is in effect. When revoking a written value, the NULL value is
written. This takes back the value. When all written values are withdrawn, the
Relinquish_Default value is in effect. In CEA-709 there is no notion of taking a value back.
To model this behavior, a distinctive invalid value can be written to an NV. Most SNVTs
have such an invalid value. For those that do not an invalid value, it can be specified when
editing the data point. To make a BACnet object convey that invalid value to the CEA-709
side, enable the property “Relinquish to Invalid”.
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