Communication protocols

>This is a pretty vague example. What kind of shared library
>change are you talking about? When linux libraries are changed,
>they are to add new API's, or fix broken API's that don't work as
>documented. If you are talking about the switch from libc5 to
>libc6, you are also spreading misinformation. You can still use
>libc5 and libc6 at the same time.

My original statement was about the change in the library format. It has been a while when it happened. Back when I used Linux regularly the shared library format itself was changed. I can't
remember what the type formats were. I think one of them was similar to how Sun did theirs. The point is that just as Microsoft changes their software platform so can "open" source. The change between different versions of libraries is also a maintenance problem. Yes, you can run multiple versions of the same shared library, but it is a maintenance issue. My point is that change can happen on any platform. People blame proprietary software companies like Microsoft, Sun, HP, IBM, SGI and others for making changes in their operating system that cause problems for
them down the road. Well, the same thing can happen with any operating system. If Linux is not in vogue in 5 years then someone can end up in a situation like the example where the computer
hardware is obsolete, but the OS can't handle the new hardware. In either case you will have write your own driver. What's the difference?

>This is wrong. Open source does not mean inexpensive source
>at all. Open source means you have the source. The source
>may be free, or it may come with a purchase price. You may
>have a license to make changes, you might not.
>
>Open source may not be well developed, but at least you have the
>opportunity to look at the code and make that decision before you
>run it, instead of needing to run it to find out if its bad.
>
>Closed source programs are always well documented either, and
>since you don't have the source its much more difficult to figure it
>out on your own, or find someone that can.
>
>But getting back to the message that you responded too, to bring
>things back into context, open source doesn't make new
>hardware work automatically, if you have the source (and license
>to change it), it is still posible for you to get your system to run
>again even if the vender won't, or won't do it for a reasonable price.

Wrong for you maybe. I don't see the benefit of having source to the operating system. I believe that you should minimize the software that you develop and it is hard for me to see a good business reason for fiddling with operating system source or anything else that I can get commercially. If I didn't think NT or OPC was going to perform then I wouldn't use them. I wouldn't use software because I have source to it. I use Samba, but I do that because it is the best software for the job, not because I can get to the source.
 
M

Michael Griffin

<clip>
>SOAP, XML and the like are for computer program to computer
>program communications. I hope nobody is seriously going to
>use this to acquire data from field devices. If so, then we
>are going to see a lot of people with shot off feet.
<clip>

From what admittedly little I know about XML, I can think of a few very good applications which could use it today. These would involve
integration of production equipment into larger overall systems, not addressing of field devices.

For example, you can now buy "web server" cards for PLCs. The idea seems to be that you can install these cards in your PLC racks and create a
very simple system for monitoring the current status of your equipment using an ordinary web browser. The web page can access registers inside the PLC CPU representing whatever it is you want.

This sounds good if you have a dozen or two machines. You can look at each machine every morning and get the current cycle time, production
counts, etc. Now suppose you have not a dozen machines, but rather 200 machines. If you spent 3 minutes per machine to examine a dozen machines,
this would take slightly more than half an hour. The same amount of time spent on each of 200 machines would take more than 10 hours. This idea is obviously no longer practical on this scale.

However, suppose you had a special software program which could go out and examine each web page for you and tell you which ones need
attention. If the PLC "web card" were also an "XML card", this would be possible. Each PLC register you are interested in would have an XML "tag" associated with it by the PLC programmer.

You could of course accomplish the same thing by defining machine register addresses for each value, but this is a lot of work and potentially quite error prone (although this is exactly what I am working on at the moment). However, if you could simply ask the machine for "Cycle Time", regardless of the type of controller used, then this becomes much easier.


**********************
Michael Griffin
London, Ont. Canada
[email protected]
**********************
 
R
Somehow my question turned into a discussion about the relative merits of open source operating systems vs. Windows NT. This is not really what my question was trying to get at. Specifically, my point was that if I use a PLC then my customer can get a machine running again after a hardware failure with no help from me. If I use a PC, then this is not the case, unless the hardware is 100% compatible with that with which the machine shipped. Once we start talking about recompiling, etc., then my engineers are
required.

My question was, how have other OEMs dealt with this situation?

Randy DeMars
 
A

Anthony Kerstens

Sounds like a situation that most of us are in.
IE. customers that don't always give us perfect
information, and hence things don't always work
out and we have to scramble.

Anthony Kerstens P.Eng.
 
C

compu-weigh-jvp

I think this problem only exists on PC's if using Windows based software.

However if you are really honest then you will admit that if a breakdown occurs on a PLC installation 5 years after the install, the chances are that that model of PLC is no longer available and the replacement needs address changes or is mounted different or,,,,,

We have been installing PC based batch weighing systems for nearly 12 years now, and have never had the problem where an upgrade would not run on the hardware. In the early days we had to recompile without the 286 switch to run on a 8088 but that was the only change.

We do encourage customers to upgrade their hardware as the years go on. For example the Y2K fiasco. From booting machines on Floppies, we have progressed to RomDisk's, then to Disk On Chip. The same 48 bit I/O boards now plug into ISA backplanes instead of Motherboards. We have put intelligence on our I/O boards , but they still work on 8088's.

I am afraid I am a control freak, I won't allow somebody at Microsoft to decide my workload for the next 12 months. OK so the screen's dont look as fancy, but the machine works perfectly to the customer's satisfaction.

However now I am at cross-roads.
Some of my customers want their reporting info downloaded to their windows box.
(What version, 3.1? 95 ?, 98?, 2000?)
Maybe I just provide them with a floppy.???

Regards,

Jan van de Poll
Technical Manager
Compu-Weigh Pty. Ltd.
[email protected]
 
D
>> hardware issues and we can restore the machines in like 6 minutes. <<
>
>But, you never have to do that. <

Nice line, I must apologize, while on vacation I talked to my partner at work and he informed me that he had to restore one of our MMI machines the other day (Monday)......I was wrong he did then have to "re-boot" it....................

Oh by the way, a water pipe had broken feeding an air conditioner and water went into the power supply when the Operator noticed the leak. (Hey its a tough world out there) I guess there is a need for our salary, he had it running in 31 minutes. Put out a spare and ghosted it across the nework. We do have a second MMI running.

The only time we have rebooted our MMI machines on the plant floor, 24/7 in the past year is maybe and I am going out on a limb here, maybe once or twice. Usually the product of a power spike or power outage during a down day or "planned" maintenance gone bad. Other than that we have the occasional hard drive and like one
power supply in last 3 years. The other thing is monitors every few years. Other than that they just keep going and going................

Sorry for not having more trouble with Windows.............Must have gotten the CD made on a Wednesday instead of the Friday version............

Dave Ferguson
Blandin Paper Company
UPM-Kymmene
DAVCO Automation
 
C
Hi Dave

I have no trouble at all with Windows now :^) You mentioned you were having a terrible time at work, I was just telling you how I fixed that.
Probably 70% less trouble for all involved by simply upgrading to Linux. I spend my time on planned work instead of platform management. Try it, you'll like it. You don't realize how much extra hassle you're going through until it stops.

Regards

cww
 
D

Dave Ferguson

I am not having a terrible time at work. If you read the entire thread you would have recognized cheap, selfless sarcasm. I have little to no trouble with my Windows machines. Does that mean that I will close my mind to all other technology like most "specialists" NO. (No flames needed)

As I also pointed out if you know what you are doing, then it should all be planned work. If you do not then it is all unplanned.......

Dave
 
G

Gilles Heinrich

To interface your load cells, you could just use a momentum weighing module and a Modbus TCP/IP tophat... Makes your life simplier!
 
Top