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Posts from — October 2009

New Micro PLCs Go In Different Directions

It’s interesting to compare and contrast new micro PLCs from Siemens (S7-1200) and Panasonic (FP0-R).  Both are compelling upgrades from the previous series (Siemens S7-200, Panasonic FP0), but while Siemens adds Ethernet connectivity, Panasonic adds a USB port.

The FP0-R series looks like a direct replacement for the FP0, but with more: more memory, faster instructions, faster counters, and faster pulse outputs.  The biggest upgrade is a USB port, which is very nice: no custom programming cable required!  Or save some money: I like to use PLCs with two comm ports, one for communicating with the PC, and one for debug.  With the added USB port, I can use a PLC with one serial port, saving about $30, and use the USB port for debug.

I hope Panasonic has improved the USB port speed; I’ve heard that the FPX series uses an internal serial/USB bridge, so the USB port is limited to a wimpy 115,200 bps.

The FP0-R still isn’t as capable as the FPG (FP Sigma) series, but since it’s the same price as the FP0, I’m already looking at changing over from the FP0 to the FP0-R.

The Siemens S7-1200 models appear similar to the previous S7-200 models, but with more: more memory, more analog (even the base models have analog inputs), faster instructions, faster counters, more expansion (using signal boards) and faster pulse outputs.

What’s wonderful?  Siemens added an Ethernet port with Profinet and standard TCP/IP capabilities.  Networked devices are so much more convenient and useful than PC-connected USB devices.  For example, Profinet should make it simple and inexpensive to create a peer to peer PLC network, in addition to high speed communications to HMIs.  You have to add expensive networking modules to create a Panasonic PLC network.

The S7-1200 CPUs include other goodies, such as room for extra boards on the base CPU (for extra comm ports or wimpy (2DI/2DO or 1AO) I/O boards), 1M flash memory for extra (non-program) storage, and a proprietary memory slot.

Unfortunately, Siemen’s STEP7 Basic software currently only includes Relay Ladder Logic and Function Block programming; Panasonic’s FPWinPro supports all five IEC61131 languages, including my favorite: Structured Text.

Like the previous S7-200 series, base models have limited expansion: no signal modules for the 1211, 2 for the 1212, and 7 for the 1214.

The Panasonic FP0-R PLCs are much smaller; the transistor output models use high density box header connectors , while Siemens provides screw terminals.  I much prefer the box headers, since I can easily make a cable to a custom PCB breakout board.  It’s hard to wire directly with screw terminals without additional terminal blocks (for extra power and ground, etc).

The Panasonic FPX series are more like the S7-1200, since they also use screw terminals and provide room for plug in modules.

Excluding communications (USB vs Ethernet), the S7-1200, FP0-R, and FP-X are all similar in capabilities and price (IIRC, S7-1214 DC/DC/DC, FP0R-C32CT, and FPX-C30TD are all about $280, while the FP0R-C32T is about $245).

Which will I use?  I’d love to try out the S7-1200, but for my current projects the FP0-R and FPG are a better fit, since they support Structured Text and use box header connectors.

The S7-1200 is pretty close to a no-brainer if you need Ethernet:  Panasonic’s Ethernet module (FPWeb2; ~$430) alone costs more than a S7-1214 CPU; Automation Direct’s Ethernet modules start at $175, and you still have to add the PLC CPU.

I plan to write about this in more detail: I think micro PLCs are a great alternative to PC I/O options such as PCI boards from Advantech or USB modules from Measurement Computing.  The PLC’s cost the same or less for 24V I/Os, and have the advantage of being programmable — it’s nice to have the PLC handle some I/O, while the PC handles the rest via serial, USB, or Ethernet communications to the PLC.

Final notes:

  • Panasonic has gone backwards by not listing prices and requiring registration to download PDFs.
  • If you’re interested in the S7-1200, talk to your local distributor to see if they have a package deal.  For example, in Silicon Valley, E&M periodically offers 1 day introductions with a nice deal on the S7-1211.

October 29, 2009   2 Comments

Cool Components III: Liquid Lens 2D Barcode Readers

I’ve used industrial barcode scanners a number of times, and they work well, especially the raster models.  The laser barcode scanners have a wide scan range and can handle a substantial amount of variation in label position.

My favorite  brand  is Microscan; I’ve also used other brands with good results.  The Microscan QX-870 is a typical  barcode scanner: it has 10 scan lines, can do 300 to 1400 scan/sec, has  a read range of 1″ to 30″, can read all the normal 1D barcodes (UPC, Codabar, Code 39, Code 128, etc)  as well as the PDF417 and Micro PDF417 2D barcodes.

However, most 2D barcodes (such as the popular Datamatrix) need an area sensor.  In other words, you can’t use a laser scanner, you have to use a camera.  Now finding a lens that has a 29″ depth of field (from 1″ to 30″) is challenging.  Of course, the barcode reader could use autofocus, but with a normal lens, that adds a lot of complexity, cost, and still isn’t perfect.  One Microscan 2D barcode reader had a halfway solution: the reader could cycle through a preset set of focus positions until it found a good read.  I wasn’t impressed (although to be fair, I never tried that model).

To make matters worse, Datamatrix codes are often used in direct marked applications; for example, using a laser or ball-peen to create a barcode directly on a metal aircraft part.  Creating lighting that is affordable, compact, and can work on anything from a shipping box to a reflective metal part is hard.

I’ve thought for a long time that liquid lenses (now available from optical suppliers such as Linos(apparently Linos dropped Varioptic)) could solve the depth of field problem by allowing affordable and rapid autofocus.  Well, they’re here (and both claim to be “the first”): Cognex has the Dataman 200 series, and Microscan has the QX Hawk with liquid lens and modular zoom.

I think this is a big deal; for example, the QX Hawk claims a read range of 1″ to infinity.  Unfortunately I don’t have any personal experience with either reader, but if I need to read 2D barcodes in the future, I will definitely check both out.

October 28, 2009   No Comments

My Favorite Electronics Distributor

For my Factory Software Blog projects, the winner is Mouser.

It’s easy for me to order from catalog distributors like Mouser and Digikey, and with their wide range of products, I can get almost everything I need from either one, which is convenient and saves on shipping.  Both have excellent search engines that really help pinpoint the products I need.

Mouser’s result pages are prettier than Digikey’s, but that’s not all.  Mouser shows volume pricing on the result page, allow you to sort by price, and allow you to continue to filter even with less than one page of results.  Typically Mouser is a bit cheaper than Digikey (though not always).

The real reason I’ve done all my Factory Software Blog ordering from Mouser is that that I’ve been choosing a lot of Phoenix Contact Combicon PCB connectors for various interface PCB boards, and Mouser stocks a much wider variety of Combicon components than Digikey.  Digikey won’t sell many Combicon parts in single quantities: you have to buy the whole pack (e.g. 10 parts or 50 parts).   Ugh!

Newark also has a good range of parts but is often pricier than Mouser (although I’ve heard that prices can be negotiated).  Allied Electronics has a better selection of industrial products (such as pneumatics).  But the big problem with both: their search engines are terrible.

One reader puts in a good word for Premier Farnell’s new social forum site.  It might be great, along with other such forums (e.g. TI E2E, ADI’s new one, CNCZone, Control Engineering’s LinkedIn and Facebook groups, etc), but I’m not interested in forums right now.  Been there, done that.

The jumbo distributors like Arrow and Avnet do have the widest range of electronics, but aren’t as friendly to individuals.  Neither are local automation distributors (although I’ve bought a couple items from them), but they typically do have better prices and service than the catalog distributors.  So I use them a lot at work, but they’re too much of a hassle for my Factory Software Blog projects.

October 27, 2009   1 Comment

Why I Don’t Have Any Advertising

It’s not worth it.

Based on my traffic, adding advertising would just about cover my hosting costs, which aren’t a big expense anyway.  But advertising would add a lot of annoying distractions.  The only thing I might eventually add is a referral link for my hosting company, Webfaction, since I’ve been very happy with them.

My big expense is the hardware and software I buy, play with, and then write about here. I’ve spent a lot more on CANOpen servo drives, CAN interfaces, Alibre Design, VX Innovator, connectors, breakout boards, and PCBs than I have spent on hosting.

I have not received any money or gifts for this blog, and will not accept any money.  There are some sample products that I’ve received for free (actually, work related, not blog related freebies) that I will write about, but I will make it clear when the product was a free sample, not something I bought.

One of my biggest costs is the time I spend here: each blog post does take a substantial amount of time to write, typically much more than I expect.  My drafts have an annoying way of expanding.   I don’t plan on taking quitting, but since blogging comes after family and work, at times new posts might take a while to appear.

October 22, 2009   1 Comment

Why Are Standard Servo Motors So Different?

Recently, I had to select a servo motor.  We had already chosen to use a NEMA 23 mount with a 0.25″ shaft, and had other requirements such as maximum length, torque, speed, and voltage.

I was amazed at the different shaft diameters and lengths supposedly standard NEMA 23 motors have — I recall 0.25″, 8mm, and 0.375″ diameters, and can’t remember all the lengths.  It was even worse when I had to select a NEMA 17 motor a while ago– at least one manufacturer’s supposedly NEMA 17 mount wasn’t the same as everyone else.

Then of course there are all the non-standard mount motors – but I only use those as a last resort, since I’ve already had motors go out of production twice; at least with a standard mount, there’s a possibility of finding a suitable replacement.

Maybe there are other standards: maybe the various European and Japanese 40mm, 60mm, and larger motors really do follow a standard, but I don’t have time to analyze them all.

Connectors are even worse.  I can understand why manufacturers use different kinds of connectors, and I know there are no connector standards.  A motor intended for harsh environments needs a tough but expensive connector, while a light duty motor is much better off with a cheap connector (such as Molex or Tyco/AMP crimp connectors) or flying leads.  But, just like industrial Ethernet, it’s easy to think: do we really need all those choices?  Couldn’t we have just three or four?

I personally like sub-D connectors a lot, since you can get high power (Combo-D), can use crimp pins or solder cups, and choose from a wide range of backshells (including straight, right angle, and 45 degree in metal, metalized plastic, and plastic) and manufacturers.

Of course, pin-outs are even more varied.  For example, on the controller side, Galil (DMC-21×3/AMP205x0 combo), AMC (DX30, DX60, etc), and Copley (ADP series) all use HD15 connectors for feedback, but each one uses a different pin-out.

Oh, well, at least commutation and incremental encoder signals are pretty standard: three signals, either RS-422 differential or single ended (TTL or open collector) –  except if you use some Japanese motors (e.g. Panasonic).  And I’d better leave absolute encoders for another time…I’m not even sure how many “standards” there are for them.

October 8, 2009   3 Comments