Setting Message Timeout for Modbus Client and Modbus Server

The message timeout that you set depends on the response time of the devices within your configuration. The information given here helps you to decide how to set the message timeout.

The message timeout defines the time-to-live of a Modbus request in the Panel Server. Any messages older than this setting will be dropped.

The message timeout for the Modbus TCP server is called Upstream timeout, set in ms (see Modbus TCP/IP Server Settings).

The message timeout for the Modbus client is called Downstream timeout, set in s (see Modbus TCP/IP Client Settings).

The following diagram illustrates a simple architecture between a Panel Server and connected devices (represented by a single device here). The response time (t) of the connected devices should be taken into consideration when calculating the message timeout of the Panel Server.

Set the Modbus client timeout (downstream timeout) as the response time (t) of the connected device plus an additional time as a margin (m).

Set the Modbus server timeout (upstream timeout) as the response time (t) of the connected device multiplied by 2.

For a parent child configuration with two Panel Server devices, for the child Panel Server use the recommendation above.

For the parent Panel Server, set timeouts as follows:

• Downstream timeout: child Panel Server upstream timeout plus an additional time as a margin (m)

• Upstream timeout: response time (t) of the child Panel Server connected device multiplied by 4

• SCADA timeout: response time (t) of the child Panel Server connected device multiplied by 4 plus an additional time as a margin (m)