Hi,

I am trying to communicate to Omni Flow computer using Modbus protocol from Modicon Quantum PLC through BM85. But I am not able to communicate to the flow computer.

I am trying to read these registers:
7102 32 Bit Float
7103 32 Bit Float
7104 32 Bit Float
7105 32 Bit Float

But in standard Modbus, two registers are required for 32 bit float. I think Omni Modbus protocol is slightly different than Modicon Modbus protocol.

Can I use BM85C002 for this communication?

If no, can you suggest any other product that can communicate between Modicon PLC and Omni Flow computer?

Thanks in advance.

 

Hi,

What is the communication setting you had configured for that particular port? Is it Modicon compatible?

Else Omni would follow logical addressing and not the register addressing. Means one address 7101 (would bring 32bit information). I would suggest first you use Modscan or Modbus tester from Omni to test the communication, then you can try with PLC.

Write to me saralive @ gmail. com in case you could not get it done.

Regards,
saravanan

 

Hi,

The Omni Flow meter uses a different flavor of Modbus called Enron Modbus. Although many of the function codes are the same the address lengths are different. In Modbus a Float is defined as 2 16 bit registers. In Entron Modbus a Float is defined as 1 32 bit register. Unless the Modbus PLC you are using can speak Enron Modbus you will have to Read the data from the Omni Flow and then write it back down to the Modbus using Modbus drivers and bridging software.

Check out the Modbus Driver Suite from Kepware. The Modbus serial driver can be configured to talk to the Omni Flow both serially and via Modbus Ethernet. You can use the Modbus Slave, Ethernet or Plus drivers to provide your Modbus device a slave to connect to. Kepware LinkMaster can be used to read the data from the Omni and write it into the slave device configured in the server to be read by the other device. Writes can be passed to the OMNI the same way.

You can download a full functioning demo of the server and linkmaster from Kepware. Support can answer any additional questions you might have.

Fred Loveless
Application Engineer
Kepware Technologies
http://www.kepware.com

 

Hi,

From what I understand, when polling these registers the response will be 2 words, compared to standard Modbus registers that contain 1 word. I would guess that the Quantum PLC will have problems reading those types of registers.

There is a gateway that can be configured to poll one register and handle the 32 bit response.
On one side of the gateway, it will act as a standard Modbus RTU slave device and the other side can be programmed.

For more information, go to:
http://www.anybus.com/support/support.asp?PID=317&ProductType=Anybus Communicator

or send me an email at:
[email protected]

/Pat

 

Hola colegas:

I hope this tip will help you, with the issue you have.

A few years ago I did the same but using the Programmable version of the BM85.

In deed the Modbus from Modicon is the same for Omni computers. The real issue arise when you're trying to poll floating point data.

This is because the Bit order in the floating representation is different from each to other.

I need to did a swap in the bit order.

Best Regard.

Raymundo D. Balderas
ribyco_automation @ yahoo. com
Mexico D.F.

 

There is an option to set the serial port to use 'Modicon Compatible' which will return the expected number of registers - i.e request 2 registers for a floating point number. - Its all documented in chapter 3 of the manual, downloadable from www.omniflow.com

Don't forget that the modbus poll specifies the start register and the number of registers. The OMNI register map uses consecutive registers, so that if you are mapping OMNI registers to some internal registers inside your target device, the register map is going to double in size.

The OMNI modbus might have its quirks, but I've successfully done dozens of OMNI installations in the UK, talking to Allen Bradley PLC's, Prolinx Gateways, and PC's etc.

Carl Burgess
www.westwoodtec.co.uk

 

The Omni Flow Computer uses Enron Modbus, which defines the 7000 block as 32 bit registers in floating point format.

See http://www.simplymodbus.ca/Enron.htm for an explanation of Enron Modbus. Their test program also supports it.

 

Hi, the issue is this. In the OMNI if you request data from a floating point memory area the request that is sent has to be for a single holding register (2 bytes). The Omni will respond with 2 registers (4 bytes). Unless you are using a device or driver that supports enron Modbus you will get an error in the validation because the response contains more bytes than were expected.

Masters that are desinged for Enron Modbus Support will not have this problem

Fred Loveless
Application Engineer
Kepware Technologies
http://www.kepwar.com