Device Net Issue

Having problems with device net? Monitoring the signals been handled by the device net and randomly I see them blip off then back on for no reason. I have checked all the wring from the scanner card to the robot. Cable is individual screened pairs then the whole cable then has an outer screen jacket so well covered there. Each end is terminated as per AB instructions. Have checked all settings have tweaked the package send time but so far nothing has cured the above problem. Wondering if anybody else has had any experience of this?

What kind of controller are you using ? What kind of robot ?

What software package are you monitoring the data in ?

Does that scanner module indicate any problem with the network when the "blip" occurs ?

How long does the "blip" last ?

Common PLC-based scanners like the 1747-SDN and 1756-SDN do not change the input data table state when a slave device goes offline and back online with the network, so an input data state change is actually not necessarily an indicator of a network problem.

Ken

1. Control Logix CPU
2. Toshiba Robot (have used this robot many times with profibus and never had an issue). Toshiba use Anybus as there supplier for field bus communication devices. So installed in this robot is an Anybus device net card. All we have to do is tell the robot what type of field bus device is installed and the node address.
3. The scanner module displays no faults with the network at all.
4. The blip varies, max we think is about 1 sec.
5. We have also turned off all non essential power sources on the machine and still see the problem.

Hope this helps.

If this were a network connection failure the duration would probably be more like 2 or 3 seconds, as that's how long it takes the Scanner to re-establish a connection to a slave whose I/O connection has failed.

Build some logic on the ControlLogix to monitor the Device Failure bit for the 1756-DNB scanner module (Local:x:I.StatusRegister.DeviceFailure), or monitor the value for the I/O connection to the robot itself (Local:s:S.DeviceStatus[n], where s=slot # of the scanner and n=node number of the robot).

If the I/O connection is not failing, the problem is not on the DeviceNet network itself.

If I were diagnosing this, I might move into using a protocol analyzer to monitor the data coming across the network to verify that the change in state is being accurately produced by the robot and consumed by the ControlLogix. If the I/O connection remains unbroken and the data is correctly transported, you have to start looking at the robot-to-Anybus interface or at the robot I/O circuitry itself.

Ken

Got one question is it critical for the position of the scanner card in the plc rack?

The 1756-DNB can be in any slot of the ControlLogix chassis.

The tags mentioned above will, of course, differ by the "Slot" number wherever you put the 1756-DNB.

Ken

The scanner card is a 1769-SDN noticed you mentioned a 1756-SDN would that make any difference?

You mentioned ControlLogix, which would use the 1756-DNB.

CompactLogix uses the 1769-SDN.

The two scanner modules are not totally identical, obviously, but they are functionally very similar. You should see tags with nearly identical names in the Input and Status connections for the 1769-SDN.

Now, the slot number of the 1769-SDN can make a difference. Describe exactly which CompactLogix CPU, power supply, and I/O modules you are using.

I very much doubt that the CompactLogix I/O bus could fail and you wouldn't notice it, and indeed that should not cause input data to change state. Let's discuss your I/O configuration just for completeness.

SORRY!!!!

My fault yep the CPU is a
CompactLogix L35E

Current configuration is as follows

Slot 1 1769-IQ32/A Module
Slot 2 1769-IQ32/A Module
Slot 3 1769-OB16P/B Module
Slot 4 1769-OB16P/B Module
Slot 5 1769-OB16P/B Module
Slot 6 1769-OB16P/B Module
Slot 7 Universal Analogue Input card 8 channels
Slot 8 1769-SDN/A card

Where is the power supply located in that assembly ? Which power supply module is it, (1769-PA2, or -PA4?).

One thing I noticed right away is that the ordinary I/O modules have a power supply rating of 8, meaning they can be up to 8 modules away from the power supply.

The 1769-SDN and the 1769-L35E controller themselves, however, only have Power Supply Ratings of 4, because they draw a lot more 5V power.

I would assemble the system as follows:

1769-L35E CPU
1769-SDN
1769 Universal Analog
1769-PA2 or -PA4 Power Supply
1769-IQ32
1769-IQ32
1769-IQ32
1769-OB16P
1769-OB16P
1769-OB16P
1769-OB16P
1769-ECR End Cap

I would expect you to have bigger problems than an unusual Input data state change if the power supply was overloaded or could not supply the 1769-SDN over that long distance, and I'm assuming that your power supply was adjacent to the CPU. But it's something to be aware of, especially if you are not familiar with the CompactLogix Selection Guide and architecture guidelines.

Sorry for a bit of confusion above; I mentioned the "1756-SDN", when I meant the 1756-DNB DeviceNet Bridge for ControlLogix.

The 1769-SDN is the DeviceNet scanner for MicroLogix 1500 and CompactLogix.

The status bits and registers in the scanners will definitely prove whether or not there is a DeviceNet network problem. What you have to consider next is where else the "blip" in data could be coming from.

Ken,
Why would you layout you I/O like that? That is the way the oldtimers had shown me Communications, Analog In , Analog Out, DC in, DC out, AC in, AC out. I know you probably have a good answer not a "just cause it has always been that way"

JeffKiper said:

Ken,
Why would you layout you I/O like that? That is the way the oldtimers had shown me Communications, Analog In , Analog Out, DC in, DC out, AC in, AC out. I know you probably have a good answer not a "just cause it has always been that way"

Click to expand...

compact logix has restrictions on how far from the power supply you put you modules, as ken said a module with a 8 factor can go 8 slots from the supply,

Ken

That was the one answer I didn't want to hear! Just got a lot of program re-arranging to do. My question is why make a system that is dependant on how the system is layed out and not give you the ability to configue you own I/O addressing. I use Siemens quite a lot and with there 300 or 400 systems you can put modules where you like and then you can ether let the system configure your addressing or you can go in and configure the addressing yourself.

But never mind thanks for your help

In ControlLogix, the abstraction between I/O addresses and control program tags is called "Aliasing".

You don't have to use Aliasing, but it makes changing I/O assignments very easy and fast, and allows you to compile, download, and actually run a program with no I/O modules present at all.

In your case, I think you'll just have to use the Search/Replace function once for each module.

The base tags for I/O modules always refer to the slot, so you don't have to get into some kind of mapping function in software in order to physically correlate a wire to a controller tag.