Opinions Please

C

Thread Starter

Curt Wuollet

I have a question or two for you folks who use PLC's. First a little background.I am designing a drop in replacement for typical PLC's that will run PC compatible software. Since this project does not have to generate revenue, I can consider
each facet carefully for value, utility, and cost. I asked what kind of connectors are preferred a while ago ( "http://www.control.com/1014311117/index_html":http://www.control.com/1014311117/index_html ) and got some very good input. I have a couple more things I'm looking at and I thought I'd get some more input from users.

How important is packaging? I've noticed that PLC's are beginning to look more like consumer products than industrial products. They've even gotten curves and styling that have nothing to do with function. Packaging is extremely expensive to do in small quantities and has to be considered very critically. Almost every PLC I've seen is mounted in some sort of enclosure along
with the wiring, terminal strips, contactors, etc. This in my mind sort of defeats the purpose of the fancy styling as it's dark in there once
you close the door. Would an open card rack product be acceptable? Is it necessary to hire european designers to grace the inside of a Hoffman enclosure? What is actually needed? Is money spent on beauty money well spent?

On the subject of power. Bulk power is much less expensive that the dedicated supplies that plug into a rack. Almost any collection of automation hardware is going to have a 24VDC supply there anyway. Would 9-30 VDC power only be acceptable? If not, why not? I have seen enclosures that had 6 or 8 separate power supplies in them from wall
warts to very spendy din mounts, all providing 24 VDC.

Your opinions are appreciated. All offlist responses will be kept strictly confidential.

Regards

cww

Curt Wuollet
<[email protected]>
 
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Steve Myres, PE

I have noticed the shift toward consumerish looking hardware as well, and I find it esthetically offensive. Something industrial should look industrial, not like an answering machine. It's ugly, and I think it makes it too easy for customers to trivialize our task in their minds as well. I don't like the open card idea, as I believe the enclosed card cage gives some protection from contamination, shavings, etc. Connectors MUST be removable. As far as asthetics are concerned, think Siemens S7 GOOD -- AB ControlLogix BAD. ;-)
 
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Nicholas J. Baranyk

First off, I am "delighted" that you, Mr. Myres, likes working his behind off programming S7 PLCs. At Penn State, we were always taught that we would be paid by our Employers for achieving meaningful results -------- not, punching-out reams of cryptic STL Code!! Perhaps at your Plant, up-time is a needless luxury, but at my
Plant, up-time translates into revenue.

Now that I have gotten that off my chest, good, solid connection terminations are very important, and for the same reason -------- up-time. Bulk Power Supplies are also a smart move, not only from a cost-savings standpoint, but also from a
space-saving standpoint. Plant Floors are becoming tighter and tighter, so Real Estate continues to be a premium.

Insofar as astethetics are concerned, it might be nice to look at something that looks neat, but I'll swap that for good, solid functionality any day. The critical issue -------- ruggedness. People who usually are in a hurry to get thinks back up will be servicing these solutions, so they must be able to withstand repeated insertions and removals.

One last comment:

Siemens PLCs, Drives, Servos, etc., are in fact, very good equipment. We use Siemens, and it is both flexible and reliable. But, the only reason why the S5 and S7 Architectures are, "flexible", extensible, and powerful is because the Programming Language isn't a whole lot different than Assembly Language. Say what you want, but I think that there is something wrong when one has to "build" a stinking one-shot Function. You might not need to do that with an S7 Platform, but
you do with even a S5-135. That wastes my valuable time, and that typifies the basis behind the S5 Architecture -------- European austerity. They don't use this Structure because it's superior -------- they use it because it's cheap!!
 
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Bob Peterson

Curt Wuollet wrote:
> I have a question or two for you folks who use PLC's. First a
> little background.I am designing a drop in replacement for
> typical PLC's that will run PC compatible software. Since
> this project does not have to generate revenue, I can consider
> each facet carefully for value, utility, and cost. I asked what
> kind of connectors are preferred a while ago and got some very
> good input. I have a couple more things I'm looking at and I
> thought I'd get some more input from users.
>
> How important is packaging? I've noticed that PLC's are beginning to
> look more like consumer products than industrial products. They've even
> gotten curves and styling that have nothing to do with function.
> Packaging is extremely expensive to do in small quantities and has to
> be considered very critically.
> Almost every PLC I've seen is mounted in some sort of enclosure along
> with the wiring, terminal strips, contactors, etc. This in my mind sort
> of defeats the purpose of the fancy styling as it's dark in there once
> you close the door. Would an open card rack product be acceptable? Is
> it necessary to hire european designers to grace the inside of a
> Hoffman enclosure? What is actually needed? Is money spent on beauty
> money well spent?

I think the trend towards making the stuff out of cheap looking plastic is not esthethically pleasing (at least to me), but looks really don't
matter much. If its functional, who cares? And for the market you are looking at (home brew PLC replacer) no one is going to care. If the end
user accepts the idea of using the device in the first place, its not going to matter much to them what it looks like.

I am not a huge fan of open card racks, but, if the tiny market niche you are trying to fill accepts it, what difference does it make?

> On the subject of power. Bulk power is much less expensive that the
> dedicated supplies that plug into a rack. Almost any collection of
> automation hardware is going to have a 24VDC supply there anyway. Would
> 9-30 VDC power only be acceptable? If not, why not? I have seen
> enclosures that had 6 or 8 separate power supplies in them from wall
> warts to very spendy din mounts, all providing 24 VDC.

I'd prefer 24V input power. More flexibility that way - you can use a generic power supply rather then an expensive model sold only by one
manufacturer. Isn't most of the logic level stuff going to be 5VDC anyway? You can make that onboard pretty cheap (if somewhat
inefficiently) from the external 24V supply. Reverse polarity protection is a real good idea.

Bob Peterson
 
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Hi Curt

You're right, there are some extremely expensively designed bits of plastic wrapped around PLCs these days!

I don't use PLCs much but the Siemens parts I've seen recently seem to have so many little doors and flaps and windows that they'd be just as at home on the "Transformers" shelf at Toys'r'Us!!

The irony is that it costs less to make enclosures in metal for low volumes than in plastic.

I also agree that it seems a little crazy to put the electronics into some expensively designed box (the shape of which has been psychometrically designed to compliment your corporate identity) only to put the finished product inside a plain, rectangular, grey box.

Our products are "PLC-like" ie they sit next to one another along a DIN rail, I/O wires in along the top and bottom edges, they require a local power supply.

We've opted for a custom built enclosure in powder coated mild steel, 500mm long, 200mm high and 100mm deep, with a two point lockable lid on the front hinged along the bottom edge.

The enclosure is divided into three full length horizontal compartments by means of two "comb" shaped pieces of mild steel (also powder coated)
welded in place. A length of DIN rail screws down onto bushes down the length of the middle compartment (onto which our components clip) and the top and bottom compartments provide all the necessary cable management.

Cable entry is acheived by glanding into the top or bottom of the box (knock outs provided for easy installation).

Our product's component parts are mounted in Phoenix DIN rail mounting bases and have 0.5mm thick stainless steel covers (custom made) which
clip into the PCB to protect the electronics whilst leaving the terminals (along the top and bottom edge of the board) exposed.

The covers of the individual components are silk screened with wiring instructions and we usually attach additional documentation to the inside of the lid so that it's all visible with the lid open.

We make a couple of variants of power supplies (all the same PCB, just populated differently depending on output voltage and power) and select
which to fit depending on what's going into the box. Again the PSUs are DIN rail mounting and fit into the middle compartment of the enclosure at one end where we can keep the mains power seperate from the low voltage.

The result is quite a nice looking (very distinctive) enclosure that does exactly the right job for us (its IP55 which is good enough for us) at a very reasonable price.

We used to mount the components onto chassis plates fitted with DIN rail and mounted inside Sarel or Rittal lockable enclosures but this worked out very expensive, very heavy (expensive to ship), required lots of parts (DIN rail, slotted trunking, lots of fasteners etc) and was pretty labour intensive to put together.

The new enclosure is quick and simple to assemble, does exactly the job it was designed for and is distinctive.

Regards

Geoff
====================================
Straight Forward Solutions Ltd
Maynooth Road, Prosperous,
Naas, Co.Kildare, Ireland
Phone : +353 (0)45 892739
Fax : +353 (0)45 893880
Mobile : +353 (0)86 8179683
email : [email protected]
====================================
 
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Gabriele Corrieri

I think that seriously plc or softplc need a good enclosure for each card or module, or rack mount for cards, than I hope that have his power supply, from main control voltage,unless you have a pc such as a softplc, that have his power supply. Generally separate power supply give an advantage because the plc or pc supply doesn't go out to control box, and it cannot be disturbed by
external events ...

Best Regards

Gabriele Corrieri
 
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Michael Griffin

On April 30, 2002 04:01 pm, Curt Wuollet wrote:
<clip>
> How important is packaging? I've noticed that PLC's are beginning
> to look more like consumer products than industrial products. They've
> even gotten curves and styling that have nothing to do with function.
> Packaging is extremely expensive to do in small quantities and has to be
> considered very critically.

The packaging serves several purposes. It protects the innards physically when the device is being installed, or when service is being done in the panel. It also protects the device from electrical shorts due to trimmed wire strands, shavings from knock-outs, etc. (although ventilation slots defeat this to some degree). It also provides a place for labels identifying the
device and its various terminals LEDS, switches, etc.
You might wish to look at electronic packaging from Phoenix, Entrelec, various enclosure manufacturers, etc. I don't know what your target market is, but "it would be nice" if the design could come as either an enclosed version or as an open "OEM" version.

<clip>
> On the subject of power. Bulk power is much less expensive that the
> dedicated supplies that plug into a rack. Almost any collection of
> automation hardware is going to have a 24VDC supply there anyway.
> Would 9-30 VDC power only be acceptable? If not, why not? I have seen
> enclosures that had 6 or 8 separate power supplies in them from wall
> warts to very spendy din mounts, all providing 24 VDC.
<clip>

From my own view point, accepting 24VDC (or rather 9-30VDC) would be *better* than requiring 120VAC. There are lots of approved 24VDC power supplies on the market, the user can select whatever is convenient for them. In the area where I work, the fewer 120VAC devices there are in the panel, the fewer things there are for the electrical inspector to look at and object to. When given a choice between two low power devices where one uses 120VAC and the other uses 24VDC, we would normally pick the 24VDC version.
Make sure the 24VDC input is well filtered and protected, since a lot of small machines are built with a single power supply running everything (PLC, OP, valves, sensors, etc.).

************************
Michael Griffin
London, Ont. Canada
************************
 
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Hi Curt;
DIN rail mounted modules and power supplies
would to be the way to go if cost is not a big issue. Just have funtional modules without a lot of glitter but enclose the modules.

[email protected]
 
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Curt Wuollet

Hi Bob

It's good to hear from you despite the snide remarks and incidental disparagement because you represent the market I'm targeting. The hobbyist experimenter market doesn't interest me much because they are quite capable of producing their owm solution and very little will change by addressing that market. Your strong if glancing
objections are exactly those which I intend to overcome through engineering and responding to those needs. What I am really asking through these sets of questions is how to produce a platform that matches your needs better than the commercial solutions available. So far, the only requirement that can't be reasonably met or
surpassed is that it come from a megacorporation that fills magazines with glossy ads.

(more comments below)

> -------- Forwarded Message --------
> From: [email protected]
>
> Curt Wuollet wrote:
> > I have a question or two for you folks who use PLC's. First a
> > little background.I am designing a drop in replacement for
> > typical PLC's that will run PC compatible software. Since
> > this project does not have to generate revenue, I can consider
> > each facet carefully for value, utility, and cost. I asked what
> > kind of connectors are preferred a while ago and got some very
> > good input. I have a couple more things I'm looking at and I
> > thought I'd get some more input from users.
> >
> > How important is packaging? I've noticed that PLC's are beginning to
> > look more like consumer products than industrial products. They've even
> > gotten curves and styling that have nothing to do with function.
> > Packaging is extremely expensive to do in small quantities and has to
> > be considered very critically.
> > Almost every PLC I've seen is mounted in some sort of enclosure along
> > with the wiring, terminal strips, contactors, etc. This in my mind sort
> > of defeats the purpose of the fancy styling as it's dark in there once
> > you close the door. Would an open card rack product be acceptable? Is
> > it necessary to hire european designers to grace the inside of a
> > Hoffman enclosure? What is actually needed? Is money spent on beauty
> > money well spent?
>
> I think the trend towards making the stuff out of cheap looking plastic
> is not esthethically pleasing (at least to me), but looks really don't
> matter much. If its functional, who cares? And for the market you are
> looking at (home brew PLC replacer) no one is going to care. If the end
> user accepts the idea of using the device in the first place, its not
> going to matter much to them what it looks like.

The reason I'm asking the question is that I am looking at a return to steel cabinetry that can be done with little or no up front tooling. I
prefer the quality of a metal cabinet, but without extensive tooling it's hard to produce one that looks fantastic. And I would like to make the cabinet optional for applications where it simply isn't needed. How does that sound?

> I am not a huge fan of open card racks, but, if the tiny market niche you
> are trying to fill accepts it, what difference does it make?
>
> > On the subject of power. Bulk power is much less expensive that the
> > dedicated supplies that plug into a rack. Almost any collection of
> > automation hardware is going to have a 24VDC supply there anyway. Would
> > 9-30 VDC power only be acceptable? If not, why not? I have seen
> > enclosures that had 6 or 8 separate power supplies in them from wall
> > warts to very spendy din mounts, all providing 24 VDC.
>
> I'd prefer 24V input power. More flexibility that way - you can use a
> generic power supply rather then an expensive model sold only by one
> manufacturer. Isn't most of the logic level stuff going to be 5VDC
> anyway? You can make that onboard pretty cheap (if somewhat
> inefficiently) from the external 24V supply. Reverse polarity
> protection is a real good idea.

We pretty much agree there, The industrial rated PC104 processor cards I'm looking at are usable with 9-30VDC input and would provide the 5V
neccessary for the small amount of logic I need. The modules would all be 9-30V devices except for some linear stuff that wants split supplies. Any small amounts of 5V power needed on the module cards could be best handled with local regulators. The 9-30 rating and design of the
backplane and modules should also allow operation on vehicle power systems and portable applications which seems to pop up frequently
these days. Low power operation should be possible by choosing loads carefully. The technology that has become available lately makes this fairly easy to do and would be a big plus for a lot of applications. The driven IO will be the major power consumer. A processor core is
only 10-20 watts in most cases.

Regards

cww
 
S

Steve Myres, PE

I wasn't saying Siemens is my all time favorite PLC, although I do like them. My comment was in regard to the esthetics of the platform, as mentioned by the original poster.
 
T
As far as asthetics is concerned, it doesn't cost any more to mass produce an injected molded nice looking plastic rack vs a utilitarian plastic rack. I don't care one way or the other. A metal rack is another matter all together. I keep waiting for someone to build a din-rail mount unit/din rail modules with easy module removal and connections. So far every one I've seen has some shortcommings.

Anyways, its whats inside that counts. The more work it saves you in programming the better, thats one reason I like the Controllogix so much.

Translation: big engineering cost savings. Its a step in the right direction, and I don't care if the curves are there or not. Mr. Myres mentioned removable terminals. That is an absolute must. The terminal quality must also be high, with attention paid to how the wires are bundled and how they exit the rack so that the module can be sensibly serviced.

We just completed a joint education project with the engineering students at a university across town. We lent them an Allen Bradley SLC500 PLC, rack, and IO for the project, but they had to take it back and forth between class where the mock up was and our offices where the real equipment was. On the last day they were complaining about how long it took to unhook the wires from the cards, and our electrician pointed out that the terminal strips were removable. The point is it wasn't obvious to them that they were removable, I had to wonder how many technicians not familiar with the PLC replaced a module the hard way. Definitely room for improvement.

I never liked the Modicon 984s much, personal taste, but I did like the way they designed the wiring to stay in place when a module was removed. If you were designing something from scratch, I would like to see something that is rackless, din rail mounted, easy to hook up, removable under power without disrupting the rest of the system, and rugged.

As for bulk power, most PLCs use multiple voltages internally, at least 5v and 24v, maybe others as well. While many panels have 24v in them, that supply can typically have many "dirty" devices on it. It think is better to keep the PLC on a "clean" supply. There are also lots of panels, probably either barely a majority or barely a minority, that don't have 24volts but are all 120 volt controls.

I hope Hoffman keep Euro designers out of their cans. I've built more systems for European installation than I care to, in fact I'm going back across the pond next weekend for another startup. The Euro cans are flimsy, crowded, and IEC components underated. They do look nice, but check any ten year old box and you'll find lots of burn marks and starters that have been replaced. I do think Hoffman could improve the exterior looks, because exterior asthetics is another matter and can be very important in certian settings, but that is not the subject of this thread.
 
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Curt Wuollet

Hi Geoff

Sounds a lot like the direction I'm thinking in, only yours will probably look better. I want to do something that almost any sheet metal shop could provide and stay as close to zero tooling as possible. We used to see some good examples, but the trend is to flashy "resin" or "carbon" and other amusing terms for plastic. The trick is to make something that isn't butt-ugly yet purely
functional. I really want to focus on the innards but packaging is a necessary evil. I'd like for the only tooled part to be a substantial card cage.

Regards

cww
 
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Ranjan Acharya

I think we went a little off-topic with regards to calling European systems designers austere i.e., cheap.
 
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Steve Myres, PE

Probably the only thing I liked about the Siemens S5 platform and one of many things I liked about the Texas Instruments 5x0 series was the wire terminations on the backplane/chassis as opposed to on the module edge. This is a small item, and I don't dislike the way everyone is doing it now, but it did eliminate one extra step in module replacement. Another potential problem it avoided is when the electrician occasionally makes the wiring arm bundle too short to accomodate removal with the module in place.

I also don't like "rackless" designs like the AB 1769 series, where the backplane bus is made up of numerous pieces, one in each module. I think so many connectors in series on a comms and power bus is asking for trouble.
 
C

Curt Wuollet

Check!

I intend for the unit to be din rail mountable, the power supply will be whatever you want to pay for. Panel mount generics are much, much, cheaper than the rack mount variety. I can get high quality bulk power for about $0.50/watt qty 10. It's interesting. most people use traditional brand name linear supplies. But most PLC's use switchers.

cww
--
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Machine Automation Tools (LinuxPLC) Free, Truly Open & Publicly Owned Industrial Automation Software For Linux. mat.sourceforge.net.
Day Job: Heartland Engineering, Automation & ATE for Automotive Rebuilders.
Consultancy: Wide Open Technologies: Moving Business & Automation to Linux.
 
C

Curt Wuollet

T. Connolly wrote:
> As far as asthetics is concerned, it doesn't cost any more to mass
> produce an injected molded nice looking plastic rack vs a utilitarian
> plastic rack. I don't care one way or the other. A metal rack is
> another matter all together. I keep waiting for someone to build a
> din-rail mount unit/din rail modules with easy module removal and
> connections. So far every one I've seen has some shortcommings.
> Anyways, its whats inside that counts. The more work it saves you in
> programming the better, thats one reason I like the Controllogix so much.
> Translation: big engineering cost savings. Its a step in the right
> direction, and I don't care if the curves are there or not. Mr. Myres
> mentioned removable terminals. That is an absolute must. The terminal
> quality must also be high, with attention paid to how the wires are
> bundled and how they exit the rack so that the module can be sensibly
> serviced. We just completed a joint education project with the
> engineering students at a university across town. We lent them an Allen
> Bradley SLC500 PLC, rack, and IO for the project, but they had to take it
> back and forth between class where the mock up was and our offices where
> the real equipment was. On the last day they were complaining about how
> long it took to unhook the wires from the cards, and our electrician
> pointed out that the terminal strips were removable. The point is it
> wasn't obvious to them that they were removable, I had to wonder how many
> technicians not familiar with the PLC replaced a module the hard way.
> Definitely room for improvement. I never liked the Modicon 984s much,
> personal taste, but I did like the way they designed the wiring to stay
> in place when a module was removed. If you were designing something from
> scratch, I would like to see something that is rackless, din rail
> mounted, easy to hook up, removable under power without disrupting the
> rest of the system, and rugged.

What do you mean by rackless exactly? Something like Beckhoff/Wago Bus Terminal? The rest is pretty clear.

Regards

cww
--
Free Tools!
Machine Automation Tools (LinuxPLC) Free, Truly Open & Publicly Owned Industrial Automation Software For Linux. mat.sourceforge.net.
Day Job: Heartland Engineering, Automation & ATE for Automotive Rebuilders.
Consultancy: Wide Open Technologies: Moving Business & Automation to Linux.
 
E

Electro Mechanical Systems

For what it is worth...

I personally would be happy with a conformal coated PCB assembly with no metal or plastic housing. Everything I build ends up in a NEMA 12 box anyways. I would prefer to see the board or card oriented on its edge so that its footprint is minimized. I always have at least 6" of enclosure depth to work with, sometimes more, by mounting your unit on its edge, you make more effective use of the enclosure volume, rather than just the back panel area.

I like your thoughts on power 9-30VDC is good seems there is always 24V readily available. Just be sure not to skimp on decoupling capacitors
and all the other things that go into good digital design/board layout practices.

As far as connectors go I keep trying to think of any easy way to implement D connectors since they are so readily available, easy to PCB mount and rugged. It seems that all of my PLC I/O is wired through DIN rail mount terminal blocks, so it seems redundant to have terminals on the PLC which are then wired to terminals on the rail. I guess the problem boils down to an easy way to go from the D connector to the DIN rail terminal strip. I keep trying to envision some mass produced multi-conductor cable that can be cut in half and stripped back for this purpose... trouble is most of the ones I have seen have very small wire AWG conductors.

Thanks,
Mike Adkins
Electro Mechanical Systems, Inc.
 
C

Curt Wuollet

Hi Steve

I've heard from both sides on rack/rackless. You'll be glad to know racks are winning, if only because it'll take a lot of money to package
a rackless system unless I used something kludgy like plugs and sockets. I have to think about the terminals on the backplane. It would make the
backplane larger and more expensive but would make the modules much less expensive and greatly ease their mounting requirements. If they didn't
have to carry terminals they could simply plug into the back plane with no mechanical stress on them. With a longtail pin header they could almost be self supporting eliminating or greatly simplifying the card rack. I could shorten the cards making shock and vibration easier to tame. I wonder if a backplane that big would be a problem on a din rail?

I knew if I asked you guys, I'd get some really good input. Maybe all designers should do that :^)

Regards

cww
--
Free Tools!
Machine Automation Tools (LinuxPLC) Free, Truly Open & Publicly Owned Industrial Automation Software For Linux. mat.sourceforge.net.
Day Job: Heartland Engineering, Automation & ATE for Automotive Rebuilders.
Consultancy: Wide Open Technologies: Moving Business & Automation to Linux.
 
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