JimRowell

I think Panic Mode was trying to say 485 and typo-ed in 422 by mistake. Just so you are not confused....... 232 is the traditional pc serial port. It's good for short distances and reasonable speeds. Not so good at talking through noise. 422 uses differential pair signalling. Basically it is better at communicating in environments that are electrically noisy such as you'll find around machinery or over longer distances. It requires separate pairs for sending and receiving. 485 is similar to 422 in that it also uses differential pair signalling but it can use a common pair of wires for both sending and receiving data and also it allows multiple devices to share the same wires (called multi-drop). Originally it was a big deal to be able to use only 2 wires for all this. Less important now. Still nice to have the multi-drop capability. Google can give you a lot more info. Jim Rowell

No need to beat around the bush, Sleepy. Just say what's on your mind. <vbg>

Front page?

Have a look around the download and article sections of MrPLC. You'll find quite a bit of stuff.

This article may help. You may need a bit of previous knowledge but not much. Programming in List on a Mitsubishi PLC Jim Rowell

Jack, A one-shot is a term used in electronics to describe a timer that doesn't reset itself. When it's triggered, it begins timing. When the preset interval expires, it switches its output and then sits there forever until reset. The term has been hijacked by a couple of plc manufacturers to refer to similar things. AB has an instruction called OSR which stands for "One-Shot Rising". You use it to monitor the status of other devices. When the monitored device goes high, the OSR bit will go active for one program scan only. This way you know if something has "just now" changed. Similar to Mitsubishi's various pulse commands. As for timers and more specific help, you really should ask in the AB group (if that is in fact the plc brand you are interested in). Jim Rowell

Can you guys recommend a low-cost package for drawing ladder diagrams please. I need something I can recomend to others who are not prepared to buy (or learn) the full-blown cad packages. Something both for those wanting to learn and also for project contributors. Preferably something that is not limited to plc work but can also handle external items such as sensors, switches, etc. I own SmartDraw and I've tried Visio but they both fall way short in my opinion (too general, too many irritations). There must be some reasonable programs *dedicated* to ladder out there but darned if I can find them! Thanks, Jim Rowell

Well, I'm looking for something for people who don't have AutoCad and who won't put out several thousand dollars either so neither suggestion really fits. Something in the free to 100.00 range. I thought there would be dozens of these floating around. I have Cad but it's not for me I'm asking. Strangely enough, exactly what I'm looking for is the second serious program I ever tried to write (way back in the early eighties). Never did finish it. Wouldn't matter anyway since not too many of these people are using Vic 20's. :-p So I guess if one wants to have a go at relay or plc field logic design and isn't at the profesional level yet, the guy is stuck with a pencil? Sheesh. (Not that I don't have fond feelings for pencils, mind you). There's gotta be something.

Sleepy Wombat's suggestion of using a handheld tester probably makes the most sense but another possibility would be to tie cards together and make them test each other. Make an analogue output feed each analogue input. You could then programmatically vary the output from low to high and verify that the inputs agree with what the output is supposed to be. If all inputs claim the output is wrong, you know you have a bad output. If only one input disagrees, then you have a bad input. Something like that. I'll leave the details to you. Jim Rowell

Sam... VA is simply the voltage X the amperage. If you wish the secondary to be at 120 volts and you will be drawing 2 amps then your load will be 2 X 120 = 240 VA. Adding the K in front makes it one thousand times the VA (1,000VA is the same as 1 KVA). So, you need to have a rough idea of your total amperage requirements and then multiply by the voltage to get the VA. Divide that by 1000 to get KVA. You should then buy a transformer that is much bigger than that. The absolute limit for loading of transformers is 80% of their rating but 50% or less is better. The higher you load the transformer, the lower the output voltage will be. If you are talking about voltage sensitive loads such as motors, relays and solenoids, then it can be a real issue. Also, there are many different types of transformers. For example, "control" rated transformers have a low impedence to reduce the voltage drop on high load. In most cases you will need an "isolation" transformer as opposed to an "autotransformer" for both safety and performance issues. More to the point though.... what is it that you are doing? If you are modifying or designing a machine's control system, there are many, many pitfalls that await you. Sizing a transformer is a very basic skill. I don't mind explaining it in great detail for you. Always glad to help out, teach people, etc. But if you have to ask such a question, it makes me nervous about what you are taking onto your shoulders! Do you understand the basics of E-Stops, master contactors, mixing voltages, control isolation, proper supply grounding, etc, etc? I don't mean to offend. But I AM hoping to scare you a bit. Anyway, feel free to provide more detail. Jim Rowell

Actually, you can purchase the 32-bit version direct from Beijer. I asked about it a while back and they said no problem. I presume their agreements are just that they can not advertise it internationally. Just send an email to them if you're interested. It's not cheap though.

My personal standard is to use lights to indicate active conditions only. I never use a red light to indicate "running" or "power on" such as was traditionally done. Nor do I use lighted indicators that are lit when NOT active. The later was commonly seen in the old days. The thinking was that it helped locate a button quickly for a user in an emergency. If I have buttons that will be in a dark area and may not be obvious, then I provide general illumination for the panel. A big red palm-style e-stop doesn't need to be lit to be found quickly. Anyway, my synopsis is to only use lights to indicate an "active" condition meaning one of the following: Green light: ON, RUNNING, OK, SAFE, READY and similar positive, normal and "nice" things (green = "go"). Amber: CAUTION and similar warning type of things. Red light: EMERGENCY, DANGER, OVERLOAD, ERROR and similar negative or "nasty" things (red = "stop"). You can lessen the safety hazard/confusion caused by burnt-out lamps by using green for on and red for off but I tend to not use any indicator at all for off since too many lamps is sometimes just as big a problem and it also detracts from the impact of the colour red if people see it all the time. I like to save red for high impact messages. I also don't use incandescent lamps anymore - led's are just so much more reliable. It can be confusing to use green to indicate both "running" and "safe" (and dangerous) so I'll generally use an unusual colour for "safe". For instance, on punch presses, I use green for "running", red for "fault", blue for "safe". Safe is defined in this case as the main motor may be running but the cycle controls are locked out, ready for machine loading (with appropriate cautions on the part of the operator). Activating an e-stop kills all power and all lights go off. No illumination is allowed with the e-stop pressed because we don't want any power available that might be find a short path to the clutch solenoids, etc and create a hazard (possibly the very reason the e-stop was pressed in the first place). In other words, an e-stop is a complete power-down in this case. Jim Rowell

Anyone want to take a stab at deciphering what he is asking? I thought (and still think) that he is asking if anyone knows of a plc model or method that will overcome what, he feels, is possibly beyond the abilities of typical equipment (being that there is not enough cycle time to calculate and respond to the needs of the machine because of its speed). Or is he crowing that he succeeded where others couldn't? Any opinions on the intent and meaning?

As far as I know, any Mitsubishi plc package will work. I can at least verify that Melsec Medoc (Dos) and GX Developer will both work (both available from Mitsubishi).

Hi Proxy I'm curious as to what the 'SFC initialization code' is that you refer to. Can you give an example? Also, that version # you mention... is that Medoc Plus or Medoc 32-bit? By the way, I'm sure you've thought of it already but until the answer is found, you could send your code to the plc and then bring it back as IL, insert the instructions you wish (in IL), and then send it back to the plc (a lot of fooling around, I know). Jim Rowell

Here's one approach you could consider... (untested but it seems right) [Edited to remove rather large mistake] ;) Whenever you need to re-calculate a target (eg. the user changed the setting or a different spray head affects another one or whatever), you must store the current encoder count as a positive number. If its already positive, just store it. If its negative, convert it to a positive by just clearing the sign bit (the highest bit) and then store it. DON'T do a 2's compliment on it. You can clear the high bit by simply doing a "WAND H7fff" for 16-bit or DWAND H7fffffff" for 32-bit . Now add the appropriate number of pulses to this same positive number and store that as the target. Now get the carry flag which was affected by your addition and store it too. The carry flag will be set if your addition caused an overflow. That's telling you that your encoder should also overflow before it will be valid. Now on each subsequent scan you need to check to see if the target has been met. Note: "current count" in the following means current encoder count after clearing the sign bit. The target has been reached (or past) when: if the stored carry flag was low AND: (current count < stored count OR current count >= target) if the stored carry flag was high AND: (current count < stored) AND (current count >= target) You'll do all of this for each separate spray head. This may seem like a lot of work for the plc to do but each operation is fairly fast to execute. Its much better on the FX2n. It'll do this type of stuff like lightning. Regardless, it probably doesn't matter in your case if you miss a target by a scan or two. Jim Rowell

The inline comparison instructions of the Mitsubishi FX2n along with a MOV or two can do a lot in a short amount of time. Of course, this is slow compared to what can be done in hardware but its very quick compared to trying to use some of the so-called dedicated instructions that we used to have to rely on. You can do a move and inline compare MUCH faster than the older "high-speed", dedicated instructions. For instance, the HSZ (high speed zone compare) instruction takes 100.6 microseconds to execute versus only 1.84 microseconds for a 32-bit inline compare or MOV. That's just over twice the time of a basic instruction (ie fast). I just did a bending machine with an FX2n where I used quite a few different settings which were checked each scan against 2 different encoders with no problems at all. It was not the fastest machine around but the plc still had to keep up with quite a few counts per second while doing dozens of compare operations against them. At the same time it was doing a lot of other math and handling analogue outputs to a servo and a vsd. Jim Rowell

That's more like it, Panic. hehe For a minute there, you had me thinking that everything was wonderful and rosy in plc land. ;) I'm glad to hear you're not completely thrilled with the available software. I pretty much agree with everything you said. I think you would be amazed at how helpful the kind of debugging I'm talking about can be. You are very organized and careful by the sound of it and have a good aproach. But obviously, life still bites when it wants to. So if I can find another few thousand guys like you maybe I'll actually finish writing my Mitsi assembler/monitor.

Being a die-hard Medoc user, I have only a passing familiarity with GX. I see that it offers various debug options that don't exist in Medoc. Can anyone explain to me what the limits are with the FX series. I see more or less how the trace functions work. It looks to me that I can set up various locations to be recorded but I can NOT specify a STEP # when in FX mode. In other words, I can request the value of a location at the end of a scan but not at a particular step # (ie. BEFORE the value gets changed in a subsequent step). Is this correct? It also appears that I can not single step. Correct again? Thanks for your help. Jim Rowell

Ebay is used by a lot of people for selling control gear. Old plc's sell ok. Check it out. Jim

Sorry Panic Mode, I should have addressed your points a little more specifically. In general use, when referring to debugging, "Stepping" means to not run continuously but rather in "steps". The definition of a step's size is usually configurable in many different ways. On the other, Plc manufacturures have traditionally used the term "step" to mean a program memory location (nothing to do with debugging - I guess they just love to confuse the issue) and that's what I meant when I asked if I could specify a Step # when defining where the program should stop. In other words, can I tell it to "step" to a particular "step #". Boy is that confusing! As far as what I mean by complex programming... Hard to say. My programs are generally not that big by some standards. 2,000 to 4,000 "steps" in size usually. They tend to be following high speed events, do complex math, have lots of boolean, several modes of operation, tons of error trapping for users, recipes, etc. Often I will have to connect with both a display and a PC. I find the debugging process to be a major part of the process and I'm not very happy with the tools at my disposal. I also do a lot of programming in Delphi on the PC and its overrun with debugging tools (both built-in and 3rd party). For the plc, I have only what I build for myself. What do you use for debugging your programs? Jim

"Single Step" means to make the processor (PLC in this case) step through your code, 1 line at a time. It gives you the oportunity to view variables as they change, see what branches are taken, that sort of thing. There are variations on this that are offered by most modern programing editors. Things like run for x number of lines or run to a certain point or stop when a certain condition is met. Then there is "tracing"which is recording the last several moves that were made by a program including certain values you may wish to watch. Medoc offers none of this for the FX series. Zero. Nada. GX offers some limited tracing from what I can gather but not being very familiar with GX, I was hoping for someone to describe exactly what it will and will not do. I frequently will insert code that will catch values for me and/or skip parts of a program when I'm trying to debug and test. But this is very time consuming and often not very effective. Thoughts? Jim

Hmmm.... No takers, eh? Is that because nobody feels like typing or is it because nobody uses the debugging features? I was originally going to follow up by asking if anyone would be interested in a bit of commercial software that made debugging easier including single stepping on an FX and maybe graphing of values, table entry, etc. But I'm starting to think that I'm the only one that finds the current software limited. I can't be the only one writing difficult programs. You're getting me worried that I'm just really slow and make more errors than average. Jim Rowell

Quoting Macqiver: Apparently someone saw it. Jim