Modbus RTU over Ethernet – OPC server reconditions?

[NJC123]

Basically I’ve got a Modbus RTU device (Nemo D4-L meter) with RS485 connections. I’ve connected to it over Ethernet using a RS485 to Ethernet bridge. At present I’m using Kepware OPC server to read back the data, some of the data is as expect but most is not. Can anyone recommend some software that is not as complicated to use as Kepware?

 

[JesperMP]

I would be suspicious about the ethernet-RS485 bridge device rather than the Kepware OPC server. I dont use Kepware, but I hear from others that it not particularly complicated in use compared to other OPC servers.

 

[danw]

How ironic, I just spent the morning messing with Kepware. I just installed KepserverEX 5.6, a recent download from their site.

With Kepware you have to be real careful in the choice of data formats:

Once you have the tag configured, you can edit it,
right click the tag, select properties:

Then you can select a data format from the drop down list in Data Type

If there's a comprehensive listing of all data types, I didn't find it in the Help, but I did find a partial listing for the driver I was using, and I imagine that their types are globabl throughout Kepserver:

I spent a couple hours figuring out the floating point format.

The Device's properties defines what the byte order format is for that slave device (Little Endian vs Big Endian, Intel vs Motorola, etc) I believe the standard Modbus format is this:

To navigate to the settings tab in device properties, right click the device, and select properties:

navigate to device properties, settings tab[/IMG]

Select the settings tab.
Here's selections for what my slave calls Big Endian:

Your mileage may vary with selections for byte order formats.

 

[diat150]

Basically I’ve got a Modbus RTU device (Nemo D4-L meter) with RS485 connections. I’ve connected to it over Ethernet using a RS485 to Ethernet bridge. At present I’m using Kepware OPC server to read back the data, some of the data is as expect but most is not. Can anyone recommend some software that is not as complicated to use as Kepware?

for testing I use a program called modbus poll to connect to devices and verify my data. works really well. it does not use opc though, I just use it for testing.

matrikon has a modbus opc server.

also wonderware sells a communications driver, Universal server. that does a very good job with all forms of modbus. I find it is much easier to customize than kepware. It can get expensive depending on how many devices you have, since it is licensed by number of devices. its a great product though.

 

[danw]

Modbus Poll, Modscan32 and Simply Modbus are great Modbus test tools to test connections and confirm formats.

Using an OPC server as a test tool requires some justification, since the cost of licensing is almost 10:1 over a Modbus master test program, like those above. I expect that most people use an OPC server because that's the connection to their HMI OPC client for permanent, on-line data collection.

I have Kepware installed to
a) use its test client to connect to other OPC servers.
b) prove that devices will in fact connect to an OPC server

and I find Kepware's licensing is effective for that, giving a run time of 2 hours, and a restart resets the time. There's no expiration.

The last time I looked, Matrikon had a 30 day trial, after which it won't run. That's of little value to someone using an OPC server as a test tool.

 

[Fred_Loveless]

Although Modbus is one of the most widely used protocols in automation it seems that every engineer that designs a device that supports Modbus feels that they can tweak the protocol to make it better. For that reason the Kepware Modbus drivers have 2 pages of configuration switches so that the device, in the server, can be configured to match what the device expects to see in read and write commands and how the responses are formatted.

The default configuration is for a Modicon/Telemechanique device.

When configuring a project to talk to a device that is not configured with the Concept Soft or Proworx ladder programs, form which the device addresses can be exported and imported into the server, the user has to manually configure the tags for the items they wish to see. If when creating the tags the default type is left then the tag will be generated with the default data type for that register are. For example the default time for holding registers is 'Word' or 'UINT16'. If looking at a bit within a holding register, for example address '400001.00' the default data type would be 'Boolean'. For all Kepware Drivers the driver help Address Descriptions section will show the default data types in bold as well as all supported data types for that register area. A list of the supported data types can be found in each help file under the Data Type Descriptions tab.

Unfortunately it is assumed that most people know the ranges of the different data types. This is perhaps something that should be changed in the help files.

 

[NJC123]

Danw,
Thanks, great advice. The problem was with the data encoding, for some unknown reason I had the first three tick boxes selected. Changed it to only “Modbus byte type” and now all the data makes sense.
I normally use Simply Modbus to for basic data checks. Never used Modbus Poll will give it a go when I get the chance.

Where possible I try to use the manufactures OPC server, most of the time I use Schneider kit and however lately it has been Beckhoff.
At the moment I’ve got a large project with lots of different kit on different protocol’s e.g. Modbus RTU, BACnet so I’m giving Kepware a go. Got to admit the 2hours trial period on Kepware is good for evaluation/development work, before getting the customer to pay up.

Thanks again