Colin Carpenter

From memory (mine that is, not the PLC or PC), say you want to insert a line: [F2] - to move to the ladder edit area Alt-O to go into online edit mode. [F3] then cusor up or down keys then [F3] to select a portion of the code you want to modify - (I always do it in instruction editor as you can see more of the code) Those lines should now change colour. Move cursor to the point (within the colour changed lines) where you want to insert the line [F5] - Insert mode, then insert line then [F5] or ESC to come out of insertion mode. [F7] - to write the changes you made to the PLC Pretty sure that then brings you out of ONLINE CHANGE mode, so repeat process for other changes. It works well and is less "buggy" than on line changes in IEC Developer V7.02 - which can still give me "out of memory" messages when checking a POU

Me too ... went to site the other day, uploaded and saved the programme, took a few hours to work out the mods, did them on line, messed up somehow (still not exactly sure how), had to hurriedly download the program that I had uploaded a few hours earlier (and saved for security) .... then had to sit there for hours manually finding and updating the important data table values (tank status etc) that had regressed to a point in time several hours earlier, even though the world and the plant had moved on during that time. Maybe copy and paste of individual rungs when in online mode is the best way (short of swapping it for a M*ts**is*i). < Exits, Stage Left, Ducking to avoid Missiles>

I've kinda tried that .... but not actually in a "live" mode. I opened two RSLogix windows and started a new project in one and an existing project in another, both projects having different names. I then tried to copy data tables from one project to the next, but found that it wouldn't work. Copying and pasting ladder files works well, but not data tables. Obviously these are different file names and RS Logix was not "online", so maybe it would work in that instance ....... still a bit of a "spooky" thing to have to do, though.

Just for info, I was looking into the possibility of hooking up a couple of Beijers E1510 terminals to a "three CPU SLC5/05 system", using ethernet comms and received a really good reply from tech support regarding the way SLC5/05 systems handle the comms. So if you want to speed up your comms, this might be worth knowing: >> When connecting more than one terminal or terminal/Scada/RSLinx at the same time the terminal can have a quite slow communication. The reason is that the SLC can only handle one request at the END of each scan cycle (this is the default setting), but there is a possibility to change the way the PLC process incoming requests. By changing the status bit S:2/15 from 1 --> 0 the PLC will process more than one request /scancycle. This will improve the performance of the terminal. A test made with a big customer project gave the following result: With S:2/15 = 1 : Online with PC (RS Linx) 1900ms. Offline with PC 1100ms. With S:2/15 = 0 : Online with PC 1200ms (RS Linx). Offline with PC 1100ms. To change the status bit is only useful if more nodes are accessing the CPU. The only disadvantage is that the scantime in the PLC will increase approx 5-10% <<

Have looked at this topic again, due to being closer to working on the PLCs, and thought that the protection mode might be the answer to the problem. Unfortunately, further investigation the AB web site revealed the following: >>> Check Constant if you want values in the data table file protected from all changes via communication ports or your ladder program. Choosing this option protects the datafile from being over written by a MSG write instruction coming in via the processor communication port. Also, constant protection protects the file from being over written by an instruction in the ladder such as a MOV instruction. NOTE:This does not protect files from being over-written during Download operation nor does it protect the file from being over written by a Load from EEPROM operation! Check Static to protect data table values from being altered by communication channels. (Again, this does not protect from Download or Load from EEPROM operations.) << Seems like nothing protects the data tables when downloading Surely there MUST be a way of doing this? ...... it causes so many problems.

Westermo make a seriously good but seriously expensive unit which converts "ethernet to RS232" and "ethernet to RS422/485". Seems like every laptop these days has an ethernet port, but no serial port. Strangely, the Westermo rep told me they they "just don't do USB" .... seems like it's not considered a "real" comms option. PS. Every Panasonic Toughbook has a real serial port .... it's what I ended up buying. Lotsa money, but quality kit.

Thanks for that. I thought it was just me that was missing some simple option in the software. It does cause problems. The other day, after an online editing problem, we had to reload a backup copy of the software to ensure that there were no other bugs that had happened without our knowledge. Problem was that the plant had "moved on" in those hours, and the back up software re-wrote data words, so that tanks that had been cleaned, were now showing product names etc., etc. The "snapshot" of the backup is not necessarily the true status of the plant now ..... spend another few hours changing bits and register values to enable the plant to carry on doing what it was doing, so that all the interlocks are satisfied. Would have thought it would be a pretty easy thing for Rockwell to sort out?

Hi, Can anyone tell me if there is a way of solving the following problem? I have been asked to look at a "complete" re-write of a system that consists of 3 SLC 5/05 CPUs, all linked to each other by ethernet comms. Each of the PLCs is pretty well full of IO, including remote IO racks. There are also two In Touch SCADA PCs communicating with all 3 of the PLCs. The system has become very unwieldy over the years, having been worked on by numerous PLC programmers and even more numerous SCADA programmers, to the point that the system is full of bugs and nobody truly understands it any more. Obviously it's a big job. Each of the CPUs is SLC 5/05 with 64 kb memory, with remaining instruction words being 6,593 on (1), 15,621 on (2) and 42,586 on (3), reflecting the PLCs that do the most work. One of the main problems with this system is that there are 3 software programmes running (one in each CPU), with a lot of "cross control", in other words, one cpu controlling IO physically attached to another CPU, leading to lots of confusion when attempting to debug problems. It would be good to have just the one CPU running most of the serious code, with the others just running mundane tasks such as controlling IO, handling comms, and running fault checking routines. Problem is, I have no way of knowing at this time whether 64 kb memory is enough on one CPU to hold all the code that will be needed. So, the questions are : Can I increase the memory on SLC 5/05 CPUs above the 64 kb limit? If not, is there a Control Logix option (more power, more memory) that will enable one CPU to use all the installed IO on the SLC 500 racks? I guess I could ask Allen Bradley, but you guys are at the "sharp end" and know the real score, from hard won experience. Thanks in advance

Absolutely, I totally agree ..... the code is incredibly overdone and complex for what is essentially a relatively simple system in "installed plant" terms. Having worked more with Mitsubishis,where the memory usage is calculated fairly simply as "steps of programme", (eg. 6142 steps out of 30,000) and I immediately know where I am, how is the memory usage calculated in an SLC? For example, the two CPUs which do most of the work show the following in RS Logix: 1) 20,442 instruction words used. 3,971 Data Table. 6,593 instruction words left. 2) 38,795 instruction words used. 9,311 Data Table. 15,621 instruction words left. Doesn't seem to add up ..... (2) has used more instruction words and more data tables yet has more instruction words left, but both have the same 64 kb memory?

Can I do that? Will a ControlLogix processor fit in an SLC rack and can it access SLC IO and comms? I've done Control Logix standalone systems and SLC standalone systems, but have never looked into merging the two into one system. Anyone know if it can be done?

Thanks, Ron. I'm going to incorporate all your text and diagrams on this subject into a PDF file and call it "Online Programming ... what it all means" and make sure that it's easily accessible on my laptop for future reference.

You're right, this is truly scary stuff! I must confess to not realising some of the implications of online editing, namely the exact meaning of the words "Accepted", "Tested" and "Inserted" and "Replaced". I had assumed that: "Accepted" - meant that the line being edited was now complete. "Tested" - meant that the line was being checked (verified) for syntax etc. by RS Logix "Inserted" - meant that the line was now, and only now, being inserted into the CPU. But, it seems like "Tested" means that the line is now "operational" in the CPU, but is waiting for you to confirm that you want it to stay in there. This is similar but very different to online editing using Mitsubishi's IEC Developer, but there are very big differences. With IEC, you select "Online Editing" mode, then you start to edit the rung. As soon as you move outside of that particular rung, then the software assumes that you have finished editing and starts to compile and check the code. If it compiles OK, then and only then do you get the choice of writing the code to the CPU. If it compiles incorrectly then it returns the rung to the original state unless you tell it to carry on. Sounds more restrictive, but maybe that's a good thing in the light of the problems that can arise with RS Logix and multiple edits all waiting to be actioned, maybe without your knowledge. Incidentally, we managed to insert those two rungs today without any further mishap. The re-loaded backup software (backed up just prior to the original mods) strangely didn't contain any pending edits when we went online. We had also assumed (wrongly) that you had to double click the rung below which you wanted to insert the new line, which kind of explains our "extra" tests etc, but then found out that all you have to do is drag a rung to anywhere you like in online mode. So I'm still slightly baffled about how that line managed to get deleted, but in a way, I'm glad that it did because, thanks to your time and patience, I've learned one heck of a lot about online editing in the past few days. Once again, many thanks ......

Wow .... thanks, Ron!! Reason I ask is that on Monday, I aim to have another go at adding those two pesky rungs, but this time, I'm gonna make 100% sure that those are the only lines that get modified. I'll use the above to search and find out what may still be lurking in the programme. For future use, is there a quick way to "CLEAR" ALL pending edits that others might have unwittingly left in as potential time bombs. This particular system (programmed by others) is so bug ridden that it has an RS Logix PC connected at all times and requires continuous fiddling with by maintenance electricians, some good, some not so good, so it's always open to this type of problem. Thanks again.

Ummm ..... one more thing ..... if edits do exist, is there a quick way of finding them? Can they be found when "offline" or does the PC have to be "online" to find them? Thanks again.

Yes, Thanks, that was really good...... now you mention it, it did seem that we had to "Test and Assemble" more often than the two rungs merited, but assumed that it was a function of inserting lines , which neither of us had done before in "Online" mode. Excellent, Thankyou ....

Thanks ..... goodness only knows how that line managed to become deleted, it's a complete and utter mystery as we never even went into that particular ladder. Very odd!!

Did you manage to get it to control OK in the end? Unfortunately, I still can't open the programme because I don't have the FX3U upgrade yet. What values did you end up with for the constants?

What are you trying to achieve with the Pot? The FX2N-4AD, as far as I am aware, can only be configured for A/D conversion of either mAmp inputs or 0-10 volt inputs. A potentiometer is a variable resistance, so are you using it to try and alter voltage or current? What have you got the channel configured as? mAmps or Voltage? Questions, questions, questions ......

Sounds to me like something's not quite right. With the values you have set, you should see some noticeable differences. Problem is that the FX3U is only just about to be launched over here (UK) and my GX Developer software doesn't yet recognise the FX3U, so I can't look at your code. For info, have attached some IEC developer screen shots of the PID on an FX2N .... probably won't help, but you necer know.

What exactly do you mean by >>I need to use the Limit Cycle method.<< Could you also tell me what you are physically trying to control with the Modutrol? Is it gas flow rate or water flow rate? If you have the proportional and integral constants set at reasonable values, then the MV can show 100% 0r 0%, but as the PID loop sees the PV approach the Set Point then you should see the MV start to alter. What happens to the MV when the PV get close to the SP ...... is it still acting like a switch? How quickly does the system show a significant reaction to a large change in MV ..... seconds, minutes, hours?

I was tuning PID loops on an FX2N a while ago, and presumably it's all very similar for the FX3U ..... have copied the post that I wrote back then if it's of any use. -------------------------------------------------------------- For what it's worth, this is what I've learnt this week. I had to tune a system that used a high spec pneumatic control valve to close againts a water flow generated by a centrifugal pump. The flow rate was monitored by a water meter giving a 4-20 ma output. This was the Process Variable. The Set Point was an operator specified flow rate. The valve took 10 secs to fully close (from 100% open), when working against the water flow pressure. The same valve took 5 secs to fully open (from fully closed) when working with the water flow pressure. Disabled the Derivative Constant and tried to set up the Proportional and Integral values from guesswork ..... no joy ..... just a wildly unstable system. Read the manual and tried the Autotune function ..... no joy, in fact I have't a clue how that's supposed to work, as it seems to hold the MV value constant. Anyone know? Spoke to a Guru, who said ... a) Set Proportion Constant to 100% b) Set Integral Value to 60% - 80% of the system response time (in other words how long it takes the valve to move from fully open to fully closed and vice versa) c) Disable the Derivative Constant. The Integral Value was then set to 6 secs (60 x 100 ms) and immediately the system got better. 100% on the Proportional was too much and resulted in much bigger changes than I needed .... ended up at 10% which gave me a slow, steady landing on the setpoint. Calibrated the flow rates against valve position bits, and use that value as the manual PID mv. After a few seconds, witch to auto and PID works like a charm. Fow what it's worth ......

Problem is that XP doesn't have a "true DOS" environment, so runs an emulator, as I understand it. I tried everything, then gave up and bought a copy of Microsoft's Virtual PC which let's me run a Windows 98 environment inside the XP operating system. Works fine for me. Files can also be transferred out of Virtual PC into the XP environment for backup if you want to. Suppose I could just use GX Developer, but I do just LOVE the old MEDOC 2.4 Other option might be to boot to a DOS operating system on a USB drive, but my laptop doesn't give me the option to do that.

Wonder if any knows a good way of doing the following? PLC is a Q2AS monitoring a density signal through an analogue input. It also receives a temperature signal via another analogue input. The product is cream at a certain fat percentage. By knowing the density at a certain temperature, I can theoretically determine the fat percentage from a "look up table", in other words, if it's this density at that temperature, then it must be this fat percentage. If I plot a graph of density (y axis) against temperature (x axis) and measure the density of a "known fat percentage cream" as it warms up (or cools down, for that matter), then I can plot a curve on the graph for that particular product. I need to do this for about 6 different creams over a range of 4 - 20 centigrade. It is almost certain that the plots will be curves, not straight lines, so it's going to be tough to come up with an equation for each curve, so a "look up" table seems to be the best bet. Hence the question ..... has anyone done anything similar? Are there dedicated commands? Should I get familiar with 2D arrays? Thanks in advance.

There are indeed numerous ways to do it. As stated, cheap 485 cards are good and very easy to set up, though limited if you want to transfer large numbers of data registers. If you do, then you would need to write multiplexing routines in the software to do so. Gotta feeling data registers are limited to 10 unless you get a bit smart with the software. CCLink modules aren't too dear, can transfer more data registers and work without problem in my experience. Not sure if E200s will accept ethernet expansion cards, but if they do, then you can set up an HMI ethernet network which works fine if wired correctly. PC or HMI? Depends on what you really, really want the monitoring system to do. Think very carefully ...... real time only, historical analysis, report writing capability, graphing functions etc. What do you *really* want it to do? For SCADA option, maybe check out www.tascomp.com for their Prodigy SCADA software. It's reasonably priced, excellent tech support, and works like a charm with Mitsubishis. (PS I have no connection with them ..... but a very good experience when installing their SCADA package)

Using IEC Developer and Mitsubishi FX2N PLCs' does anyone know of or can think of a truly foolproof way of protecting the code from prying eyes? I know that it can be password protected, but topics on the forum show that there are ways and means of overcoming this if you are determined. I have just written some software that I am *REALLY* keen to ensure that no-one else can get to use ........ what do you think?