Modbus communication in hot standby

S

Thread Starter

Sachin

Hi

I am using Hot Standby configuration of quantum system. can we use modbus and modbus plus port in hot standby.

how we can do the wiring as inbuilt module has 232 port

please suggest

waiting for reply
sachinrmishra [at] rediffmail.com
 
R

Robert Willis

You will need to convert the RS232 port to multi drop RS485. The Modbus Address of the Standby Controller is equal to the following:

Standby Modbus Address = Primary Modbus Address + 127

Depending on the Modicon Quantum Controller you have it may have a RS232 / RS485 serial port. These are the 140CPU6xx series controllers.
 
Yes, you can use Modbus Serial or Modbus Plus or Modbus TCP/IP to communicate to the HSBY controlers. The addressing between the primary and standby is offset and automatically switched on failover. For RS232 you have a problem, this is a point to point communications (master-slave) and not multidrop. So you will have to make or locate a Y cable to ensure that the serial port signals do not conflict (google RS232 Y cable).
 
Dear

Thanx for the info provided

Any special programming is required or directly by using Y Cable we can achieve redundancy

at any given time how polling will be done whether both primary and secondary will poll the data at same time or one will poll and other will b in standby
 
No special programming required. The Y cable ensures that the signal lines do not conflict (contains diodes). The "host" is always communicating with the Modbus address of the primary. The address switches on failover.

If you are polling #1 then the standby is offset by 128( standby i at #129) and will not reply.
 
Dear Brian

Thanx for the info provided

Is this solution proven i.e- is it used somewhere means hot standby is achieved by using Y Cable

Let me know is this the only solution or some other solution is also possible

Sachin Mishra
 
Quantum HSBY modbus serial port, alternative solutions...

1. Put a RS232/485 converter on each controller serial port. No issue with multidrops of RS485.

2. Don't use the serial port for comms. Use Modbus Plus or Modbus TCPIP.
or...

3. Look at moving to the Quantum Unity HSBY. Faster, easy to configure (no configuration), transfer all program every scan and the serial ports can be configured RS232 or RS485. Concept projects can be migrated by the user into Unity. No converter required. Proven design provides for I/O module configurations without stopping the controller.

 
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