DwalterE

In the early days, industrial instrumentation used pneumatic signals. 3 - 15 psi was the standard, although 6 - 30 psi was also not uncommon. When electronics were introduced, a lot of the pneumatic techniques were kept. ie force balance transmitters and the elevated zero. The use of current instead of Voltage eliminates wire resistance as a factor in signal accuracy. It also permits the use of 2-wire transmitters, where the same pair of wires carries the signal, but also provides the operating power to the field device. This is also one reason for the elevated zero - 4 mA. Early on, 4 - 20 mA was not the only signal in use. Some manufacturers, Foxboro for one, used 10 - 50 mA. As far as the choice of 4 and 20 mA values, a non-engineering friend of mine suggests that these numbers were chosen by a couple of engineers in the bar late one evening. Until someone comes up with a better explanation, I think I'll stick with that one.

The HART signal rides on top of the 4-20 mA, and doesn't interfere with it. It's very handy for configuring field instruments while they're in service. Usually you use a hand-held calibrator which you simply clip onto the 4-20 mA circuit the way you would with a Voltmeter. Your 4-20 mA devices won't even see the HART signal. You can read up on it at www.hartcomm.org

Congratulations Ken! I went thru the same experience 23 years ago. I was up to almost 3 full packs a day. I think I must have been physically addicted, because for about 3 weeks, I couldn't walk down a hallway without bouncing off both walls. I lucked into a course run by a couple of psychologists from one of the local hospitals (Foothills Hospital in Calgary). On their recommendation, we used the cold turkey method also. Only downside, I was diagnosed with diabetes less than 6 months after I quit. Have since discovered that the medical community has for years been trying to avoid the truth that quitting smoking significantly increases you risk of developing diabetes. There's now a study, quoted on the Johns Hopkins Hospital's website that outs the truth. (http://www.hopkinsmedicine.org/Press_releases/2010/01_04_10.html Hope you have better luck than I did. In any event, congratulations. Keep up the good work. It's well worth it!

Unless I've blown it somewhere, I think the H2 term cancels out: -(H - 6.605)**2 + H**2 = - (H**2 - 2 * 6.605 + 6.605**2) + H**2 = -H**2 + 2 * 6.605 - 6.605 **2 + H**2 If r and b are both constants, it should be possible to reduce this whole mess to the form A * H * (1 + B * H) One needs to know the values of r and b to calculate A and B of course.

If I read your expression correctly, it should be possible to reduce it to: 1.570795 * H * ( 3 * b * b + r * r - 13.21 * H + 43.626) where 1.570795 is (Pi / 6 ) * 3 or Pi / 2 13.21 is 2 * 6.605 43.626 is 6.605 ** 2 which would involve only 6 multipies and 3 adds, no great challenge for a PLC-5 Of course, if any of H, b or r is a constant value, you could also calculate them by hand as well.

Hi Daniel: There's another reason to have a programming standard in writing. It seems the latest fad among the MBA's is to require that equipment be purchased with the PLC program supplied by the equipment vendor as part of a lump sum price. I've seen customers of mine who have received PLC programs (not from me) that were totally unmaintainable, very poorly documented, and often not even safe! The problem is that if they try to require the vendor to clean it up, his reply is "That's what our price included. If you want any more, it's going to cost extra". Of course, the MBA's didn't allow any money in the budget to cover program cleanup. If there was a written program standard which could be included in the purchase documents, the owner's people would have some way to enforce at least minimum programming and documentation requirements. A forum like this would be a great vehicle to produce a document that people writing the programs could agree to, and wouldn't be hesitant to agree to adhere to.

Saw this in a plant that does work for the railways. The plant manager told me that the railways required the certification. He also mentioned that they'd found someone using a tape that was two feet short! Saw this in a plant that does work for the railways. The plant manager told me that the railways required the certification. He also mentioned that they'd found someone using a tape that was two feet short!

Thank you for sharing your experience. We'll look forward to your future posts. You don't mention operating system. Would it be safe to assume you've gone from XP to Vista?

You could also use two-dimension array for your recipe storage ie Recipe_Storage[10,10] To save a recipe to this array, set Product_Select to the desired recipe, then COP Current_Product[0] Recipe_Storage[Product_Select, 0] LEN 10 To retrieve a recipe: COP Recipe_Storage[Product_Select,0] Current_Product[0] LEN 10 I don't have a PLC here to test it on, but did enter this code into Logix5000, and it accepted it without complaint. There's also a synchronous copy instruction CPS, which ensures that none of the data changes during the copy process.

Here's a quick and dirty solution in RSView. Define an input tag "Intag" as a double integer, and two output tags, "Outag1 and Outag2" as integers. Set Intag's limits to 0 - 999999 and Outag1 and 2 to 0-999 The two output tags can be mapped to their locations in the PLC, Intag can be just a memory variable. Then, in the derived tag editor, define Outag1 = Intag / 1000 and Outag2 = Intag - Outag1 * 1000 It's important to define the tags in the database as integers, and do so before you use them in expressions. RSView, left to its own devices, likes to store data as a floating point, which doesn't work worth a darn when using integer expressions like these ones.