Connect many devices in a Modbus Protocol

A

Thread Starter

Alex

Hi,

In the plant I work at, there are four electric rooms with devices, they can communicate by modbus protocol (currently only have 4-20 mA). How can communicate all devices in one bus? Can the master be a PC? Is Simatic PDM capable to configure and calibrate the Modbus devices?

Regards
 
Yes, you are right. If you are using PC, then your PC becomes the Modbus master. You can use SCADA to monitor your signal.
 
C
1) In answer to your question about communicating to all devices on one bus, if the devices have native (built-in) Modbus [slave] capability, then using an HMI program that is a Modbus master could manage communications with devices.

2) >Can the Master be a PC?

Yes, with an appropriate HMI program that accomplishes the tasks you need to perform and which is a Modbus master.

Most HMI panels can operate as Modbus masters. A custom programmed HMI panel could handle configuration taskso over Modbus.

3) Siemens Simatic PDM is designed as an asset manager for field instruments primarily using HART as its comm protocol.

I believe that PDM has Modbus drivers specifically for several Siemens-Milltronics ultrasonics products, but I am unaware of any generic Modbus master capabilities that would allow you to communicate to Modbus RTU devices using PDM.

PDM is unlikely to do what you seem to be asking it to do.

Carl Ellis
 
P
4-20 ma is generally limited to point-to-point connections. Modbus can be used with devices connected in a bus configuration, and is generally implemented with an RS-485 physical connection. So, in your application, you would need to convert your devices to RS-485.

Another option may be Ethernet, using a Modbus gateway, which can connect RS-232/422/485 serial devices to Ethernet, and convert between ASCII or RTU and the TCP protocols.

Yes, a PC can be the master, whether you use serial (RS-485) or Ethernet (Modbus/TCP).

Paul...
 
Thanks for the replies. Here is my problem, the instrumentation have HART protocol option, so I need to communicate this two protocols in one maintenance station. Maybe a OPC solution?

Alex
 
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