zanker99
Lifetime Supporting Member
Protocol: Modbus RTU
PLC: AB/Rockwell Micro850 as master
The PLC is able to read and write holding registers from 20 devices. I want to understand what is the sampling rate of each device if I have 50 holding registers per device. Can someone help me go through this calculation and point out if I am making any mistakes here?
Data from/to each device = 50 registers * 2 bytes * 8 bits = 800 bits + overhead ~ 1000 bits
Baud rate of Modbus RTU connection = 38400 bits/sec
Time taken for the data to reach a device = 1000 / 38400 sec = 26 millisec
Time taken for processing ~ 48 millisec ( assuming for calculation )
Time taken for data to get back after processing = 26 millisec
Total time per device = 26 + 48 + 26 = say 100 millisec
Does that mean that I will be able to get information from one of my 20 devices only once in every ( 20 * 100 millisec = 2 sec )?
Is it going to be that slow a sampling rate from each device? Is there any way to improve this, given the setup ?
Your comments and suggestions are much appreciated.
Thank you!!
PLC: AB/Rockwell Micro850 as master
The PLC is able to read and write holding registers from 20 devices. I want to understand what is the sampling rate of each device if I have 50 holding registers per device. Can someone help me go through this calculation and point out if I am making any mistakes here?
Data from/to each device = 50 registers * 2 bytes * 8 bits = 800 bits + overhead ~ 1000 bits
Baud rate of Modbus RTU connection = 38400 bits/sec
Time taken for the data to reach a device = 1000 / 38400 sec = 26 millisec
Time taken for processing ~ 48 millisec ( assuming for calculation )
Time taken for data to get back after processing = 26 millisec
Total time per device = 26 + 48 + 26 = say 100 millisec
Does that mean that I will be able to get information from one of my 20 devices only once in every ( 20 * 100 millisec = 2 sec )?
Is it going to be that slow a sampling rate from each device? Is there any way to improve this, given the setup ?
Your comments and suggestions are much appreciated.
Thank you!!
