Value objects can be seen as virtual data points which are defined in the BACnet standard and have the same functions as the I/O blocks.
- Analog value block
- Binary value block
- Multistate value block
The only difference, in the case of value blocks, is that it is not possible to define physical connections to sub-components or components (e.g., to I/O modules) in the plant. The value objects BVAL, AVAL and MVAL are used in the program whenever BACnet-defined functions, such as commands, alarm generation and runtime totalizing are required, or when a value is to be modified via an operator unit. Value blocks look like all other blocks, and can be connected with other blocks.
Typical applications
Value objects are used typically in aggregates as command control links (PWR_CTL or CMD_CTL). The command control mechanism passes the commands to the value object and derives the status from the BACnet referencing system.
Furthermore, the value objects can be used for alarm monitoring (reference values or high/low limit value), or to determine and monitor operating hours. The value objects designed specially for operation via BACnet client can be used, e.g., as a simple way of enabling the user to operate setpoints and switch commands.
Analog Value (AVAL)
The analog value block provides access to the dataflow, that is, to signals and pins with a Real number as the data type. The value objects can be inserted into the program structure and interconnected in any configuration.
This block is used when, e.g.:
- An alarm is to be created within the CFC chart as a commandable interface of an aggregate (e.g., limit monitoring of an output value of an aggregate).
- Access from the operator unit is required, in order to modify a value
The following functions are integrated into the block:
- Evaluation of the priority array [PrioArr]
- Interruption of the output signal [OoServ]
- Limit value monitoring (OFFNORMAL alarm)
- Deviation monitoring
- Reliability monitoring [Rlb] (FAULT alarm)
- Change of state messages (events / system events)
- Process monitoring [StaFlg]
Binary Value (BVAL)
The binary value block provides access to the dataflow, that is, to signals and pins with a Boolean number as the data type. The value objects can be inserted into the program structure and interconnected in any configuration.
This block is used when, e.g.:
- An alarm is to be generated as the commandable interface of an aggregate (e.g., monitoring of logic operations)
- The hours run are to be totalized after a logic operation
- Access from the operator unit is required, in order to modify a value
- Configurable switch types (normal, switch, pushbutton with delay)
The following functions are integrated into the block:
- Evaluation of the priority array [PrioArr]
- Interruption of the output signal [OoServ]
- Process value monitoring (OFFNORMAL alarm)
- Reliability monitoring [Rlb] (FAULT alarm)
- Change of state messages (events / system events)
- Configurable switch types (normal, switch, pushbutton with delay)
- Runtimes and monitoring periods
- Switch-command delays
- Process monitoring [StaFlg]
- Runtime totalization and maintenance messages
Multistate Value (MVAL)
The multistate value block provides access to the dataflow, that is, to signals and pins with a Multistate number as the data type. The value objects can be inserted into the program structure and interconnected in any configuration.
This block is used when, e.g.:
- An alarm is to be generated as the commandable interface of an aggregate (e.g., for limit monitoring)
- Access from the operator unit is required, in order to modify a value
- Hours run are to be totalized
The following functions are integrated in the block:
- Evaluation of the priority array [PrioArr]
- Interruption of the output signal [OoServ]
- Process value monitoring (OFFNORMAL alarm)
- Reliability monitoring [Rlb] (FAULT alarm)
- Change of state messages (events / system events)
- Runtimes and monitoring periods
- Runtime totalization and maintenance messages
- Process monitoring [StaFlg]