System information

General Reference Guide eWON Configuration
RG-001-0-EN ver 1.5 eWON® - 20/03/2009 - ©ACT'L sa Page 67
3.4 Tag Setup
3.4.1 Tag definition: Introduction
The eWON Monitoring Web Interface features are based on:
• The configurable monitoring of Tags
• The execution of scripts
All the variables monitored by the eWON are defined as "Tags". A Tag is a Boolean or Float value changing with time and coming from a data-
source.
Typical data-sources are:
• eWON internal Inputs/Outputs
• Remote Inputs/Outputs (modbus, UnitelWay, ...)
• eWON memory Inputs/Outputs (updated by script)
The data source is called an "IO Server". An IO Server is the interface between the changing value and the eWON monitoring engine. It is a kind
of driver. Any variable from any data source must have a common representation for all IO Servers in order to define common interface in the
eWON.
The data-source representation in the eWON uses 3 fields for the definition of a Tag:
• The IO Server Name
• The Topic name
• The Item Name
A Tag’s data-source will be uniquely identified with these 3 parameters.
For example, the MODBUS IO Server needs to poll registers or coils from a slave, so it uses an item name representation to define the register
type, register address and slave address. (Example "40001,5" => Where 4 means read write register, 0001 is the register number and 5 is the
slave Modbus address).
A description of the different IO Server syntax is given in chapter “The eWON IO Servers” on page 85. Once a Tag is configured with its Server
Name, Topic Name and Item Name, it is given a Tag name that will be used everywhere in the eWON.
3.4.1.1 Tags are stored as Float
Internally, all the tags are stored in single precision FLOAT format (IEEE float representation).
This means that you can only expect a maximum precision of 7 decimal digits.
That’s why, the 32 bits Integer data read by an IOServer will be automatically converted in the nearest float number representation.
For a huge number, it will mean a truncation (ex: integer value 1600000015 will be stored as float 1600000000.0).
IO Server name
Is a kind of driver name. For each IO Server there is a specific Topic Name and Item Name
syntax. The following drivers are available: MODBUS, EWON, MEM, NETMPI, UNITE
(Unitelway), DF1, FINS, S7 3&400(MPI), S7 200(PPI) and S5-AS511.
Topic Name
Is used to group items inside an IO Server, for example the memory an IO Server uses the
blank topic ("") and the retentive topic ("ret"). All the Tags of the MEM IO Server defined in the
"ret" topic will have their value saved and restored when the eWON boots. All the IO servers
do not use Topic Name. In that case Topic Name must be empty.
Item Name
The item name is a string of characters; its syntax is specific to each IO Server. The Item
Name describes the physical variable to monitor using the IO Server.
Table 41: Tag’s data-source parameters