Using modbus/TCP with USB ethernet adapters

I have a test stand where I have a handful of USB instruments and a single modbus/TCP slave. I'm considering adding a USB ethernet adapter to the stand so that there is a single USB cable connecting the computer to the hardware rather than both a USB and an ethernet connection. Does anybody out there have experience (good or bad) using USB ethernet adapters with modbus/TCP slaves?
The existing USB instruments all use ASCII/SCPI-style command sets. The Modbus/TCP slave is an Automation Direct EBC-100. Nothing high-bandwidth or low-latency. Basically, the computer issues no more than a handful or command or request (ether SCPI or Modbus/TCP) per minute.
Mark Moss
Electrical Validation Engineer
GHSP

Adam G wrote:
Hello Mark,
I was wondering what NI hardware you are going to be using in your application? Also are you going to be using LabVIEW for the programming? Have a great day!
Best Regards,
Adam G
The test software is written in LabVIEW, and the test stand uses M-Series cards for data acquisition.
Mark Moss

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Does OSD have a problem with USB ethernet adapters? It appears so....
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Juke Chou
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Problem communicating via Modbus TCP with Honeywell UDC3200

Hello:
I have to read the temperature of the Input 1 of this controllers. I've succesfully read the temperatures in the controllers. I'm using Modbus TCP/IP for the communication through the NI Modbus Library 1.1. I'm working on LabVIEW 8.5.1. However, sometimes when I open the connection, I get error 56 (timeout), despite that the controller responds to a ping. When I can initiate all the connections to the controllers, some hours after the monitoring has started, randomly, I get an error 66 (the connection was closed by the peer). This error interrupts the connection and the temperature readings stop. This is not acceptable.
Also, I've found out that if you don't request some data from the controllers in 5 seconds or more, also the error 66 appears. To solve this, I poll twice a second the controllers but the error 66 still shows up.
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In brief, I can communicate with the controllers but the communication is not reliable. Sometimes when I start the communication I get an Error 56 and sometimes after the communication starts I get Error 66. It cannot be predicted when this will happen.
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Hello:
Thanks for answering Pedro. I've read the document you told me to, but it refers to problems with VI Server, the application is not using VI server, so I guess the problem comes from somewhere else. I still haven't figured out why this is happening.
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USB Ethernet adapters?

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iMac? try asking over in the Discussion devoted to iMac G5
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Using Modbus TCP I/O Server with new DSC Shared Variables in LabVIEW 8.6

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Message Edited by utechle on 01-27-2009 11:12 PM

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I'm looking for examples/how to/lib/dll to build a communication to a Beckhoff BK9000(similar to Wago 750) which have a Ethernet - Modbus TCP Option.
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My Labview system needs to communicate with three Modbus slave units (motor drive controllers with Modbus TCP/IP option installed) to send commands (speed reference) and read drive status (actual speed, output voltage/current/power etc). The PC has a quad-port Ethernet adapter with three of the ports connected via standard Ethernet cable to the three controllers. The three Ethernet ports on the PC have been given static IP addresses (192.168.1.10, 192.168.1.11, 192.168.1.12). The three controllers have been configured to give the Modbus slave options static IP addresses as well (192.168.1.20, 192.168.1.21, 192.168.1.22). I have also downloaded the NI Modbus library (version 1.2) and would like to use its VIs to perform Modbus Master Query operations. To do this, it is first necessary to open TCP connections to the three slave units using the TCP Open Connection vi, and this is where my problem comes in. How do I bind TCP Open Connection to use a specific Ethernet port (one of the first three IP addresses) on the PC ? Thanks in advance for your help.
VRA
Solved!
Go to Solution.

Hello Mike:
Thanks for your response. I should have browsed this forum a little more before sending the message out. You are right; one way is to restrict each Modbus-dedicated Ethernet port on the PC to a range or even a single port number (using Advanced settings), and use that port number in the TCP Open Connection vi to ensure that this connection will go out of that port. The other way is to use subnet masks as pointed out more than once on this forum; instead of using a subnet mask of 255.255.255.0 for all three ports (which would put them all on the same subnet), I could use a subnet mask of 255.255.255.192 which would allow for four separate subnets, then give the three PC ports IP addresses in the range 192.168.1.(2-62), 192.168.1.(66-126), 192.168.1.(130-190), with gateways set to 192.168.1.1, 192.168.1.65 and 192.168.1.129. The Modbus slave units (motor drive controllers) would then have to be configured with static IP addresses in the respective subnet ranges, so that a TCP Open Connection to that IP address would automatically go out on that subnet.
Thanks again.
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USING AC ADAPTER WITH USB 2.0 PORT

I recently installed a new EA6500 wireless router (AC1750). I also bought some wireless AC USB adapters (WUSB6300). Will use of the AC USB adapters increase network speed if they have to be plugged into the USB 2.0 ports on my laptops?

The WUSB6300 utilizes the USB 3.0 standard. However, the adapter is backward compatible with USB 2.0 ports. The WUSB6300 could support up to 300 Mbps for 2.4 Ghz and upto 866.7 Mbps for 5 Ghz.
Key features of Linksys Wireless-N and Wireless-AC adapters

Can you determine link status with USB Ethernet adapter?

I'm wanting to replace an old G4 PowerBook with a 11" MacBookAir. I install networks, and I often need to determine link status of an Ethernet connection. With the built-in Ethernet port on most Macs, you can check the Network Status to see if there is link on an Ethernet connection (either the green or yellow status signs).
If I am using the Apple USB Ethernet adapter, do I get similar feedback from the Network preference panel? If not, perhaps a terminal command that would do the same?

Yes - the Network Panel under System Preferences works the same as with a regular Mac, showing USB Ethernet status (connected, disconnected, etc) and with the updated connected IP address, etc.

Problems using Modbus TCP accessed by NI OPC Server

Hi there,
i'm using NI OPC-Server to access a measurement module. The buildup is quite easy, my system with NI OPC, a modbus gate and there the module connected with RS485.
There's a thermocouple to provide me some sample data.
But there's the point. I know, my data is in the Holding Registers and I can access them, but every data type I'm trying doesn't bring my my data out, just any other (sometimes Huge with e34, sometimes very small like e-13...) sorts, i can't understand.
The type provided by the module should be single precision.
In Lookout the address used to be is 41000 in Labview it's just 999 and in the "target" OPC-Server I get some values at 401000 but not useful.
I also get the same results accessing 301000 in different types.
Read/Write or Read Only is equal.
I've tried to tell my OPC that the values are Strings, Floats, Words, BCD and all other possible ways OPC offers me, but nothing results in a usable temperature.
I hope I missed something and you could suggest it.
Cateros
Solved!
Go to Solution.

Thanks for your reply.
in LabVIEW I'm using the provided Modbus Libraries. If I unbundle the Holding registers, my value appears at Holding Register [0], I'm type casting it to single and get the sample temperature. (Address 999->unbundle->typecast->value)
In NI OPC, I'm reading ( [depends on zero based addressing] 300999/301000 equal to 400999/401000) an already typecasted Holding Register [1] compared to LabVIEW (and the value changes in the second or third digit behind the comma and they are changing at the same time). Data type in the tag is float.
Another disturbing thing is even if I change in the options "using zero-based addressing in registers" my value does not change.
If I'm reading two addresses close to each other (as you mentioned 401000-401001) I'm getting an unknown data type and no results. How do I read multiple addresses without such errors? And how do I specify a special register to read?
Scaling should not be the problem, I am having three ways to get my value (FTP-Server on the gate (just a *.dat file with correct type), software the the module manufacturer (while measuring and configuring the module) and LabVIEW(as can be seen above)) .
Sadly, I have not found any useable modbus documentation about the module (just it can use modbus, you have the registers, you could read/write and fine)
When I'm adding a second couple to the module, in LabVIEW Values in Holding Register [2] and Holding Register [3] appear and are changing.
Cateros

Compare transmission speed between thunderbolt gigabit and usb ethernet adapters

As the new MBA has an accessory (Thunderbolt ethernet adapter), will its transmission speed be significantly faster than using an old USB ethernet adapter in one of the new MBA's USB ports?

An emphatic yes. The new t-bolt adapter should be many times faster, provided all the other links in the chain support it. I mean, plugging a gigabit adapter into a 10/100 router port, or using a slow internet connection will at least partially negate the advantages.

Using modbus/TCP with USB ethernet adapters

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