TCP driver, missing messages and loss of connection

Update: I seem to be mistaken about the UDP connection. It’s TCP. Post edited.

My Ignition reading of a checkweigher is missing transmissions.
Skip to the end for the actual questions. Come back to here for the details.

The details

I have several checkweighers serving on port 9000 a weigh reading every 3 s or so, when running. The message is in the form:

“?Date=2011-05-11,TIME=9:47:31,MachineID=1234567,Product=Yum Yum Chocolate CM,SKU=YYC001,Weight=216.35,TO=228.37,Target=216.37,TU=204.37,Length=183,Speed=35.0,TradeCount=997,Total=1000,BatchNum=RUN3 30 MIN?”

I have a TCP driver setup with

  • IP address:
  • port 9000
  • Inactivity timeout = 0
  • Message delimiter type: PacketBased
  • Message delimiter: [blank]
  • Field count: 0
  • Field delimiter: [blank]

Tag configuration:

  • Data type: String
  • Enabled: Yes
  • Access Rights: Read only
  • OPC Item Path: ns=1;s=[{OpcDevice}]9000/Message
  • Source data type: Automatic
  • Scan class: Default

I am able to parse the messages and assign the values to the tags in my UDT.

Maybe relevant:

  • OS: Windows 10.
  • Ignition 7.8.
  • Checkweigher is behind a multi-NAT router connected to the same LAN as the Ignition server.


  1. The Tag Browser alternates between connected and not connected.
  2. I’m not catching all the messages. I pop them into a database with the transaction manager and I can see that the ‘Total’ field increments one at a time sometimes and then skips one, two or three records. I can see this in the Ignition Web OPC Client too.
  3. I’m monitoring the Total value in my _UdpDataString valueChanged event and it intermittently drops from the current count (e.g., 2637) to 1 and then resumes the count. (Ignore the fact that it’s not UDP.)

valueChanged event code:

Check that the datastring starts and ends with ‘?’. If not exit.

if not currentValue.quality.isGood():
cv = currentValue.value
if (cv[0:1] + cv[-3:-2]) != ‘??’:
cv = cv[1:-3]

Create a dictionary by splitting on ‘,’ and then on ‘=’.

d = dict(x.split(’=’) for x in cv.split(’,’))

system.tag.write("[.]DebugString", str(d[‘Total’]))
system.tag.write("[.]BatchNum", d[‘BatchNum’])
system.tag.write("[.]Length", d[‘Length’])
system.tag.write("[.]MachineID", d[‘MachineID’])
system.tag.write("[.]Product", d[‘Product’])
system.tag.write("[.]SKU", d[‘SKU’])
system.tag.write("[.]Speed", d[‘Speed’])
system.tag.write("[.]Target", d[‘Target’])
system.tag.write("[.]TradeCount", d[‘TradeCount’])
system.tag.write("[.]TU", d[‘TU’])
system.tag.write("[.]Weight", d[‘Weight’])

Write the total last as this will trigger the Transaction Group and we want the others ready first.

system.tag.write("[.]Total", d[‘Total’])


  1. Can anyone suggest a way to prevent the ‘not connected’ status?
  2. Is my TCP setup correct for my application?
  3. Am I using the correct scan class or should I create a dedicated one?
  4. What would cause my count to drop to 1 intermittently? (I have the transaction group paused so it shouldn’t be that.)

Many thanks.

Hi there,

Not an expert on Ignition’s TCP/UDP driver, but I’m interested in learning the solution to this issue. So I’m here to bump and subscribe.

Just so I’m not totally useless, though, here are some questions/comments that come to mind after reading your post:

  • Are you sure about the default behavior of the driver with Inactivity Timeout set to 0? I mean, if it’s set to zero, does that mean that it will never disconnect and reconnect, or is there some other situation that could cause it to do that?

  • I don’t expect that the scan class makes a difference, since you’ve disabled the disconnect timeout. I expect that it would just give you the most recent value. But is it possible that it’s trying to poll the checkweighers on scan and expecting a response in a short time? Also, you might want to check on the timeout for stale quality to make sure that it won’t go stale before you’ve had a chance to get a new value from the UDP driver.

Good luck!