AlThePal

Guys, Thanks for your help. I finally managed to work out how to do this using 'state' variables to track which bit of code I should be running (I'd simplified things a bit for the example). I had no sooner done this than the thought of Bubba phoning at 3am prompted me to do it the simple way! As Alaric and panic mode both suggested, I'm going to set bits for the results of each check in a DINT and look for a known value at the end of the checks. This also lets me use these bits as alarms to an HMI. I've done a reasonable amount of PLC coding before, but this is the first time I have produced the specification in a flowchart format. I have to say that I thought it would be easier to translate from flowchart to ladder, but it seems not. Any help with uploading images so I can display them in posts?

I have produced the specification for part of a job using a flowchart which I've attached as a pdf. I now have to convert this to ladder logic (in a ControlLogix) and am suffering brain fade! Any pointers? (As an aside, can anyone tell me how to upload images so I can embed the flowchart in this post?) Flow_chart.pdf

This suggests that this is the standard way of doing things. My problem now is finding how I can use the COP command to fill the structures with I/O data in the order I want (i.e. potentially a bit at a time).

Hi, I have an application with a ControlLogix L61 processor, a number of local 32-way input and output cards and an ENBT Ethernet module, which connects to a network of 16 Point IO racks. The local IO connects to 4 identical devices, with the Point IO modules in 16 identical devices. From the point of view of the PLC code, it makes most sense to store the IO data in arrays of structures, so the same code can be run multiple times on data from each device. After a bit of head-scratching (this is our first CLX installation) it turns out you cannot alias array members directly to IO points - you have to copy the data in through code. When I try to use the COP command to copy the data, it doesn't seem to be happy unless I copy the whole of an input card to a structure. However, each 32-bit input card handles data from 2 devices. Is there any way I can use the copy command at the bit level, so I can copy the first 16 bits from an input card into one structure and the second 16 bits into another structure?

I want to swap information between 2 devices using Modbus/TCP. The 2 devices are on different Ethernet subnets, so I believe I need a router or Layer 3 switch to enable the data from one device to get to the other device and vice versa. Has anyone installed a similar setup? What networking hardware did you use?

One option may be to use the IE Tab add-on for Firefox. I use this for IE-only sites - it allows you to open a page inside Firefox, but using the IE rendering engine. I don't know whether this will still trigger the behaviour you have been seeing, but it may be worth a try.

I've used the smaller G308 as an HMI for a Mitsubishi FX2N running a 1MW hydro station. I was very impressed by its flexibility - its programming software is both free and very intuitive. We're just about to install one in a system reading data from a ControlLogix PLC, with a bidirectional link to a Siemens control system using Modbus. I reckon this will be easier to set up than using the ProSoft Modbus card in the ControlLogix. I think TWControls is correct when he says it doesn't support DH+, but DH485 and DF1 are both available (as is Native Tag Addressing over Ethernet). The one issue I did have was failing to get Ethernet comms working to my laptop. I was trying to puzzle this out when someone closed the cabinet door on the wire and pulled it tight - comms started immediately! It turns out the Ethernet port used a cheap connector and some of the contacts had been squashed flat.

Hi, I'm only just starting out with CLX so I may be wide of the mark here, but I think you would do this with User-Defined types and arrays. Say you created a User-Defined type with name 'Recipe' and members 'Length' and 'Weight'. You can then define a new variable of type 'Recipe' - call this 'Object' for example. At this point you can also choose whether to make it an array. If you set Dimension 0 to greater than 0, you would then have a number of independent data structures which you could fill with data using the same code, just by changing the offset value i.e. Object[0].Length, Object[1].Length etc. The following document explains this in depth: 1756-PM001I-EN-P page 2-44. Hope this helps.

That's a good point Gerry - I didn't think of the effect of traffic on each of the Point I/O Ethernet adapters. I guess that if the switches had IGMP snooping, they would funnel all multicast traffic to the central PLC, leaving the Point I/O adapters unbothered. Then again, do the Point I/O adapters have to spend any processing power rejecting the data, or do they just ignore it, waiting for an opportunity to send their data? If another adapter is sending data to the central PLC, they will not be able to send anyway, as both the fibre backbone and the link between the PLC and its switch is occupied. Do you have any answer to the problem of multicast data from Point I/O colliding when trying to reach the central PLC? I can't see a way round this, but don't know if it a problem in the real world.

Thanks for all your input. To reply to some points raised by paulengr: Most multi mode products give their maximum distance as 2km. The Moxa switches state 4-5km depending on the fibre used. I've used Moxa equipment for a number of years and have always found it to be excellent, and substantially cheaper than European alternatives. As you point out, I only have one master, so as far as I can work out IGMP (which would keep broadcast traffic to one part of the network) won't have any great effect. You mentioned about full duplex Ethernet being deterministic - this point has always confused me. Switches work by connecting one Ethernet device directly to another. However, if you have a network where basically you have one master (generally with one Ethernet port) and many slaves, only one slave can talk to the master at one time. Ethernet/IP uses multicast to send the data to the consumer(s) without the consumers having to ask for it - quite different to the classic serial command/response model. This means that slaves could be trying to send to the master at the same time, and so continually colliding and backing off - if effect you have a situation that is no different to using hubs instead of switches (although you still need intelligent switches to cope with a ring configuration). Is this correct or does anyone know better?

The whole network is dedicated to this task. Anyway, it is only planned to use the system for closing the breakers - they are opened by the main control system or by protection. I'll be interested to see how reliable Ethernet/IP is - Rockwell are certainly pushing it hard at the moment.

I've been asked to design a system to monitor and control wind turbine circuit breakers (x16) spread over approximately 8km. As there doesn't need to be any local intelligence (no comms, no control), I've opted for a 1756-L61 ControlLogix processor with a 1756-ENBT Ethernet adapter, connecting to Point I/O modules connected to 1734-AENT Ethernet adapters. The Ethernet network will consist of 17 switches connected in a ring with Multi mode fibre. Being new to ControlLogix and Ethernet/IP I have a number of questions for you learned folks out there: 1. Does Ethernet/IP need switches with IGMP when used in a ring configuration? 2. Does anyone have any experience using Point I/O in a similar setup? 3. We also have the option of using ControlNet, but I thought Ethernet was an easier (and cheaper!) option - any comments? 4. Anyone have any experience with Moxa managed Ethernet switches?