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modbus tcp timeout

Im using Lookout 6.7.1, CalAmp Viper Radio Modem, and Schneider Electric SCADAPack32 PLCs (Formerly Control Microsystems). Using the modbus tcp driver in Lookout, Im getting com fails after one bad response even though the number of retries is set to 7.

 

The communication log is attached.

Brian T. Kinard
President - SCADA and Security Division
2110 Nance Street
Newberry, SC 29108
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Message 1 of 28
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Any idea why this is happening?

Brian T. Kinard
President - SCADA and Security Division
2110 Nance Street
Newberry, SC 29108
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Message 2 of 28
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I am going to see if I can test this on my setup, but have not noticed it on my deplyed systems (6.7.1 as well).

 

 

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Forshock - Consult.Develop.Solve.
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Message 3 of 28
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Just to confirm, Modbus TCP right?  Not RTU/Serial?

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Forshock - Consult.Develop.Solve.
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Message 4 of 28
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That is correct. Modbus TCP.

 

One thing to note is that I have two ethernet ports. One is hooked to the internet and the other is for the SCADA system only. The internet uses the 192.168.1.XXX scheme with 255.255.255.0 subnet mask. The SCADA system uses 192.168.10.XXX and 255.255.0.0. I changed the ethernet port to 10Mbps Half Duplex and started using a sequencer to poll the sites. My theory was that the sites were trying to poll similtaniously but even with those changes, I still get com fails on each site after one bad response. An additional note is that the bad poll does not matter if it is "response too short" or "no response". Still get the red X's if not a valid response. This happens on multiple sites even though I only sent the log for one site.

Brian T. Kinard
President - SCADA and Security Division
2110 Nance Street
Newberry, SC 29108
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Message 5 of 28
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So I can confirm this on Lookout 6.2 and 6.7.1 as well.

 

Set modbus object for 10 retries, 1500ms timeout.  

After first poll, items get "No response from socket" and comm fails (red x).

Seems to ignore the retries.

 

When running in Modbus RTU, retries happen as is expected.

 

 

EDIT:  Also, no multiple networks on the test bench.  192.168.2.x / 255.255.255.0

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Forshock - Consult.Develop.Solve.
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Message 6 of 28
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So you are getting the same thing using modbus TCP? Red X's after one com fail even though retries are set to 10?

 

Note: I originally had SCADA on the same network. I assumed that was the reason I was having the issue so I changed networks. Obviously that did not help. Same issue with Lookout ignoring the # of retries using Modbus TCP

Brian T. Kinard
President - SCADA and Security Division
2110 Nance Street
Newberry, SC 29108
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Message 7 of 28
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Correct.

 

Have the following on the bench:

  • AutomationDIrect DL-06 with ECOM100 card (192.168.2.108/255.255.255.0, ID 1)
  • Windows 7 (x64), all updates as of this week (192.168.2.100/255.255.255.0) (Lookout 6.2, 6.7.1)
  • Windows XP, all updates (192.168.2.101/255.255.255.0) (Lookout 5.1 & 6.0)

On all versions of Lookout I created a new process with single Modbus Driver.  Set for Modbus Ethernet.

Poll rate = 00:01

Retry attempts = 10

Receive Timeout = 1500

 

Allow system to poll data register 400001 (Timer) for 10 seconds at 100% receive.

Disconnect LAN cable from PLC, after ~2 seconds the site goes Comm Fail and Red X (bad quality).

Reconnect cable and sites comes back in.

 

Happens in all version I have on hand:

  • 5.1
  • 6.0.2
  • 6.2
  • 6.7.1
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Forshock - Consult.Develop.Solve.
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Message 8 of 28
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Never really noticed this before, but most of our Ethernet based systems are using more traditional ethernet connectivity (Hardwired, Unlicensed and Licensed 5Ghz and 900Mhz) over short distances (<2 miles).

 

Perhaps with the latency of sending full TCP packets accross your licensed radios you get it more often?  We just started testing ourselves with GEMDS SD4 Packet mode but have not deployed in field.

 

 

 

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Forshock - Consult.Develop.Solve.
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Message 9 of 28
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The radio units that I am using are licensed UHF. Even with the delay, it doesnt seem to me that the Lookout should ignore the retries. If it fails, should it not retry for for the set number of retry attempts before giving me red X's? 

 

On the very next poll it will see the site again. I figured it would work like the serial port does.

Brian T. Kinard
President - SCADA and Security Division
2110 Nance Street
Newberry, SC 29108
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Message 10 of 28
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