AB HMI to PLC dropped ethernet connection

roamex

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Join Date
Sep 2013
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St thomas
Posts
2
Hi Everyone,

I am new to the community and i would just like to first say hi. I will be posting alot of questions as i am newer to PLCs and will run into many issues.

My first issue i have run into is a connection issue between my PLC and HMI. I have a nicely programmed machine that was programmed by an engineer and now i need to make changes to it and am running into issues.

The engineer had the Ip address set to 192.168.0.1 for the plc and 192.168.0.2 for the hmi. In the HMI (PanelView Plus 600) settings it was set to detect the plc at this address. I have since expanded our lab and added multiple PLCs that are now all linked together to one computer for programming on the company network. I have set the AB PLC (Micrologix1400) to a static ip address of 10.20.202.3 and had my IT reserve this on their network. I set the HMI to DHCP and told it to point toward the 10.20.202.3 for the PLC connection.

Now here is the main symptoms. When I start up the machien everything works great. I push the start on my HMI and the machine runs. I can see the numbers returned on screen. I will leave the machine running and return in half an hour and the inputs all change to ERROR and i cant control the equipment through the HMI.

Looking for any and all suggestions. I will be sure to pay it forward if i can. Thanks.
 
Lost comms - Why did you set the HMI to DHCP if you know the static address of the PLC 10.20.202.3. Also check they are on the same gateway.
 
I have been tinkering with a PanelView+ recently.

Let us be clear I do not understand tcp/ip or why it does anything.

Like you I have had cause, either through experimentation or reason, to set my Panelview to use DHCP. I noticed it behaved unusually when I did this, in that it would powerup with an ip-address it got from (let's call it) "Source A" and after a short while it would revert to what I call a self assigned IP address (169.xxx.xxx.xxx). The time between these events wasn't half an hour, maybe it was more like 10 minutes.

When it did this, the PV would vanish from my isolated 192.168.1.xxx network of course.

Is it possible that through incorrect use of DHCP you are getting a similar effect?

As a result of what I found when tinkering, I opted for static set IP addresses in my devices because there will be no DHCP/BOOTP servers on this small isolated network. I did not get time delayed ethernet drop out once I had done this.

But like I say, all this is based on half memories of some things I did a few days ago using half truths and partial understandings, it's just the symptoms are similar.
 
Using DHCP within an HMI application "connected" to multiple CPUs on different subnets is quite an endeavor; I don't remember the last time I have seen a functional one.
Your IT department needs to be top-notch and their DHCP server properly configured in order to establish proper connectivity and routing.
I personally have never attempted this and probably never will; there are plenty of Static IP Addressing issues that could arise in a multiple CPU application; dynamically changing addresses is an exponential increase in the number and strength of the generated headaches...:D
 
Thank everyone. Seems like maybe i will need to give the HMI a static IP address after all. If you only knew the pain i have to go through in order to get the first static ip you would understand my hesitations. We have an insteresting IT department that doesnt even keep replacement computer parts on hand.

I would like to know more about this issue if anyone can ellabrote a bit. I only gave the PLC a static IP address becuase i was assuming that the HMI would always know where to find it. The IP address I gave the HMI itself was just a DHCP as nothing needs to know where the HMI is as longs as its able to pull information from the PLC I am happy.

Why does the HMI not work with DHCP?
 
Why does the HMI not work with DHCP?
It should. The ones I've been using both use DHCP just fine when I connect them to our giant office network. (In fact this is what I 'must' do with them out of the box to wake them up to the fact they are supposed to use ethernet at all.) When I use them on the DHCP giant office network they typically work just fine, all the time, no hiccups at all ever. In fact I find them more reliably attached to the network than my laptop usually is. I think with a robust DHCP server they most likely work extremely well with DHCP.

Hey, that's a point, is by some chance your network assigning an ip-address to your HMI with only a 30 minute lease time to use it? That would be pretty weird, but I'd make sure the lease on the ip-address is assigned for whatever is normal. 1440 minutes or something.


The ip-address dropouts on my local isolated network were *probably* or *possibly* related to me running a DHCP server on my laptop, also, BOOTP, also not having any real idea if I was using them right, but typing in IP-Addresses manually into a BOOTP server felt just wrong on all levels and I never expected it to work, sure enough, it didn't.
 

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