modbus-scada

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Thread Starter

Remi Van Damme

is it possible in a modbus network to have a SCADA system which polls for data from the slaves and another SCADA system which also collects data from the same slaves?
 
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Darrin Hansen

You can't do it on the same subnet, as a Modbus subnet can have only one master. But the ICC XLTR-1000 gateway (http://www.iccdesigns.com/products/millennium/xltr-1000.html) will let you do this as it supports a Modbus sniffer driver. With this driver, a separate Modbus master can non-intrusively capture data from an existing Modbus network.

Of course, using a sniffer driver like this means that the secondary device can only read values from the existing network: write data cannot be injected back onto the network being sniffed. But this configuration is commonly used when (for example) a PLC is controlling some slaves (read/write), and it is then desired to add a separate HMI to display network status data or capture historical values (read only).
 
If you use a Modbus TCP gateway in front of the Modbus RTU line it is possible.

If you can only use Modbus RTU it is different.
But if you introduce a small embedded device with 3 serial interfaces it is possible. In that case you could implement a "router".
Using a modbus library like the one that is supplied with our http://pvbrowser.org you can easily code such a Modbus RTU router.
We proofed the concept using a Raspberry Pi.
 
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We have 2 solutions for your application. In order to avoid having 2 masters in your PC, you will need a Gateway like the previous responder said.

First solution: Via "virtual" com port connection. The TDS-715 will allow you to connect multiple PC's via Ethernet to the same RTU slave(s) connected via RS-485. Each PC will have a driver installed to add a virtual com port to the PC through an Ethernet connection. This method is key in situations that the software can only open Com port(Modbus RTU) connections to communicate.

http://www.icpdas-usa.com/tds_715.html

Second solution: Modbus TCP Gateway
The TGW-715 is slightly easier to configure if your software can accept Modbus TCP connections to your devices. The TGW will be assigned an IP address and will convert the Modbus TCP commands from your multiple PC's to Modbus RTU and allow for transparent communication. It will be as if you are connected to a Modbus TCP slave device.

http://www.icpdas-usa.com/tgw_715.html
 
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