Planning the Global Data (Publish/Subscribe) System
Original instructions
About us
Overview
Global Data service is a real-time publisher/subscriber mechanism that provides the most efficient data exchange for PLC application coordination.
Devices that support Global Data are arranged in a distribution group for the purpose of application variable exchange and synchronization. Each Global Data device can publish up to one network (application) variable and subscribe to up to 64 network (application) variables.
The Quantum NOE’s embedded Global Data Configuration Web page provides a configuration screen to determine which and how many application variables are exchanged with this service. After configuration, exchanges between all stations belonging to the same distribution group are done automatically.
The Global Data service uses %MW (4x registers) or unlocated variables for Global Data exchanges.
Key Features of Global Data
The main features for Global Data are:
Global Data has an advantage over client/server services when more than one subscriber is receiving the same data since only one transaction is necessary for all subscribers to receive the data. There are two benefits:
Planning Your System Configuration
The Global Data (publish/subscribe) utility is a powerful function incorporated into the NOE product line. Implementing Global Data requires a configuration that spans many PLCs throughout the system. Therefore, we recommend pre-planning your installation before implementation. Pre-planning saves time and money by:
Go to paper before computer.
We offer the following table to assist in system planning. The Global Data Planning Spreadsheet below is a graphic representation of a recommended configuration table for system planning. You can create your own table using the format below or you can download a Microsoft ExcelTM spreadsheet template, which is available on the Schneider public Web site.
Here is the graphic representation of the Global Data Planning Spreadsheet:
Parameter Checking
Variable ID
Symbol*
Length (Registers)
Device Number
Variable Public. Status
1
2
...
3
1
VALVE_STATUS
20
PUB
SUB
NONE
OK
2
VALVE_CONTROL
10
SUB
NONE
PUB
OK
...
64
PUMP_CONTROL
50
SUB
PUB
NONE
OK
Device Publication Status:
OK
OK
OK
Total Publication Size per Node:
20
50
10
Total Subscription Size per Node:
60
20
0
Group IP Address
239.255.255.0
Multicast Filtering Enabled
OFF
Default %MW Address for Health
%MW100
Distribution Period
10
Health Timeout
1000
Data Zone
%MW200
*Entries or changes to the symbol (description) do NOT affect or change a variable or the system. The symbol used in the Quantum product line has no relation to the Concept/Control Expert product line symbol(s).
Table of Global Data Limits:
Parameter
Limit
Maximum number of publish variables per device
1
Maximum size for the publish variable
512 registers = 512 Words (16 bits) = 1024 bytes
Maximum number of subscription variables per device
64 (63 if this device is publishing)
Maximum size for the subscribe variables per device
2048 registers = 2048 Words (16 bits) = 4096 bytes
NOTE: We recommend that you consider the following when planning.
  • Allow for a 10 to 20 % increase in growth of any variable.
  • Add variables at the end of the configuration where they do not affect the existing application address. Therefore, you avoid changing the existing addresses in your configuration, which can be a time consuming process.
Table of Global Data Planning Spreadsheet
Parameter
Description
Parameter Checking
Reserved
Variable Id
Represents the Data ID on the NOE’s Global Data Configuration Web page
Symbol
Symbolic name for Global Data exchange.
Length Words (Registers)
Length of Global Data information. Number of %MW words (4x registers) or unlocated variables.
Device Number
Number of devices (up to 64) for the Global Data network.
Variable Public. Status
Automatic information of the correct publication status of the Global Data network. Only by using the Microsoft ExcelTM spreadsheet. Information per symbol.
Device Publication Status
Automatic information of the correct publication status of the Global Data network. Only by using the Microsoft ExcelTM spreadsheet. Information per device.
Total Publication Size per Node
Publication size for the specific node. The maximum publication size is 512 words (registers) per node
Total Subscription Size per Node
Subscription size for the specific node. The maximum subscription size is 2048 words (registers) per node
Group IP Address Enabled
IP address for multicast networking. Identifies the stations distribution group. The address range is from 224.0.0.0 to 239.255.255.255
Multicast Filtering Enabled
A check box for Ethernet switches that support multicast filtering.
Default Address for Health%MW (4x register)
%MW (4x register) address for the Health bits. This is the memory area where the Health bits are stored. It has the size of 4 words (registers).
Distribution Period
Is the minimum number of controller scan times before an update will occur.
Health Timeout
Is the maximum time between received subscriptions before a subscription is declared unhealthy (faulty). The value is measured in milliseconds and can be set from 50 to 15000 ms in 50 ms increments.
Data Zone
The starting address for the data. This are the registers where the data information are stored.