M251 - Modbus Serial (RTU) Slave : A module reports an error

[FaresMuhammad]

M251 - Modbus Serial (RTU) Slave: A module reports an error

I have an M251 connected to an EGX, which interfaces with four slave devices. The data is sent to the PLC through the EGX. I've noticed that the data monitoring process is quite slow, leading to data loss, especially when energizing an incomer associated with one of the slave devices. Sometimes, I experience significant delays in data updates or the data might not be updated at all, and I have observed this warning in Machine Expert. Could this warning be related to the issues I'm facing? How can I address the data delay or loss problem overall?

I have to mention that when I use any MODBUS scanner to read the data directly from the EGX sometimes I get a timeout error

 

[FaresMuhammad]

I have an M251 connected to an EGX, which interfaces with four slave devices. The data is sent to the PLC through the EGX. I've noticed that the data monitoring process is quite slow, leading to data loss, especially when energizing an incomer associated with one of the slave devices. Sometimes, I experience significant delays in data updates or the data might not be updated at all, and I have observed this warning in Machine Expert. Could this warning be related to the issues I'm facing? How can I address the data delay or loss problem overall?

I have to mention that when I use any MODBUS scanner to read the data directly from the EGX sometimes I get a timeout error

 

[FernandoRodrigues]

Hello @FaresMuhammad 
The gateway (in this case EGX, but any gateway) represents a bottleneck on this communication. The gateway needs to convert requests coming from Ethernet side and send it to the Serial, wait for device's reply and forward it back.
Normally, IO scanning is too aggressive for this application, flooding the gateway and leading to data loss.
I'd suggest you to move to READ_VAR  / WRITE_VAR, where you can manage it on a better way (not easier, but better).

This won't make it faster, but reliable.

Also, number of requests for each device must be reduced to the minimum. E.g.: Better to read in 1 shot a larger length and bring unnecessary data in between than create 2 reading requests (not all devices allow it though, specially power meters..)

By experience, I'd say 100-200ms for each request (meaning 400-600ms for a complete round on those four devices IF one request is done by device, otherwise it will increase drastically) is feasible to reach and matches what serial can provide.

If you have several request for each device, this can goes easily to 1000ms or more to complete one round.

To increase performance, you might need to add extra EGX or to move to an Ethernet based fieldbus.