2
Concepts
, functions and gateway design
UGW X-series
Concepts, functions and gateway design
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Client-server relationship in relation to data points
In a client-server relationship, a server provides data to connected clients. The server accepts
requests from clients, and then sends the requested data. This client-server relationship can be
transferred to the relationship of data points among one another.
Example:
A field device controls an actuator with feedback. An automation station is intended to set
the control variable and evaluate the feedback. The data points
control values
and
feedback
are
within the field device, which then acts as the server. Through reading and writing, the automation
station accesses these data points and thus acts as the client in this communication. Normally, all data
points of a device are client or server data points. For some protocols, both client and server data
points are in one device.
Actual value and set values as data points
Actual values are values that are measured or calculated by the server and whose values are
transferred to the client.
Set values are values that are meant to affect the behaviour of the server through the client. In the
case of set values, whether the value is transferred only by the client to the server or whether the
actual value of the set value must also be reported back to the client.
Example:
A typical actual value is the mapping of a temperature sensor (measured value).
A typical set value is a nominal room temperature set value in a room controller.
Analogue, binary, multi-level – more complex types as data points
Data points also differ as to which values are allowed. A differentiation is made between:
•
Analogue values (e.g. temperature sensor measured value)
•
Binary values (e.g. relay output)
•
Multi-level values
(e.g. status data point with the operating conditions Normal operation, Off, Economy mode
and Failure).
In some protocols there are more, sometimes complex data points.
Example:
Utilization times
Some of these values cannot be mapped or can only be mapped indirectly in the gateway. They include
attributes that can detect whether data points contain a valid value. With set values, there is an
automatic value which causes the server to take over control of the data point itself.
Abstract data points in the data point system
For the processing and forwarding of data points within the gateway, information exchangeable via
a protocol is shown in a generalized internal data point.
The properties of these internal data points allow the mapping of the most commonly used data
points in building automation. The linkage between different data points occurs via these internal
data points. Thanks to the decoupled internal data points, it is possible to add more protocols to the
gateway without needing to change the entire configuration.
Routing address
The communication driver of the gateway is selected with the routing address. The routing address
is specified for each communication driver when constructing the gateway according to a fixed
schematic. If a gateway has multiple connections of the same type, the routing address typically
increases by one.
Example:
If a gateway has two Modbus master connections, the routing addresses 80 and 81 are
used.
