Money4Nothing

I have a ControlNet network with six 1788-CN2DN linking devices to scan six of my DeviceNet networks. I am in the process of commissioning, and everything works great.....except....... When I power up the network (all CNet and DNet modules together), sometimes one or two of my CN2DN devices will not initialize communication with its DeviceNet network. The Module Status LED will flash red and the DNet Network status LED will also flash red. This apparently indicates a communication timeout, even though all devices are powered up simultaneously. But the rest of the networks will come online just fine. All 6 networks are identical, with 18 nodes each, and using ADR. The DNet devices are Allen-Bradley E3 overload relays. Whenever I power up, it seems like one or two of the networks will randomly fail to initialize. RSLinx and RSNetworx can both see the CNet modules, but the DNet is not online. Only by recycling power again to the CN2DN module can I get the DNet network to come online. This is a problem because the operator might not notice the communication timeout message until its too late; also, modules are in a remote location, so its difficult to recycle power to each one individually, and its undesireable to recycle power to the entire system. Besides, I don't want to ever have to recycle power, I want the doggone networks to come online at power up correctly! I'm working with Allen Bradley on the problem right now, but if anyone has any experience with CN2DN networks or any ideas, please give your suggestions. FYI these CN2DN networks are part of a larger system with 15 Control Net nodes and a Redundant Control Logix processing platform, multiple HMIs, ethernet, etc, but everything else is working fine. Thanks $

Does whining alot work? If so, I think I'm just the man for the job $

My mistake, I got a little ahead of myself. You are right. If you want the negative of a number in two's compliment from 1 to 16 (in decimal), subtract 1 and do a Bitwise NOT. $

Gravitar gave you the right answer. If you One-Shot the pushbutton, it doesn't matter how long the button is held down, nothing will happen until its pushed again. The One-Shot won't be reset until the rung-in condition goes false, e.g. the button is let go. Your only problem then is sequencing what happens when the button is pushed each time. $

Alaric is correct. To find the binary negative of a number in two's complement form that is n bits long, you subtract it from 2^n. So if you have a 15 bit number, and you want its negative, subtract it from 1000 0000 0000 0000. The twos compliment of binary 0000 through 1111 can be found by doing a bitwise NOT, but beyond that you should use proper binary arithmetic. $

If your I/O status and Mod/Net status LEDs are not on, then you have a problem with your connection to the network. Check the voltage of the device net power at the module. Make sure the polarity and level are right. Make sure your CAN lines are not crossed. You may have a problem in your tap or drop. Check the connections very carefully. If all that checks out, you probably have a faulty module, and you'll need to replace it or get tech support form Allen Bradley. Try to swap that module with another one in your network, and see if you can connect. $

Thx, I learned something new 1 million reputation points for you. $

I've found that the case of web pages is similar to PLC programs in that Simpler is Better Eye candy will only get you so far....simple, intuitive, and functional contect is where the quality is. $

I had this exact same thing happen to me about a week ago. I removed the ADN from the scan list. Then I disconnected the DeviceNet plug, recycled module supply power, reset the node address, and reconnected the DeviceNet plug....in that order. Then I added it back to the scan list and was up and running with no problems. Also, I was using 125kb or autobaud on everything on my network. $

You cannot split an RS232 signal, its 1 to 1. If the HMI is connected to the serial port of the PLC, and it's using RS232 communication, you can't do anything unfortunately. If there is no other free port on the plc you would have to reconfigured the PLC port to use DH485 DF1, then you can have multiple nodes. You would have to use DH485 drivers for the HMI and your PC serial port. I've never used a splitter or anything similar for wiring an RS485 bus, i've always just wired the individual conductors to custom db9 connectors. Correct me if i'm wrong. $

Determine the input impedance and on-current level of your PLC input. Then take the prox switch voltage output and subtract the LED drop. V=IR will let you know if you'll have enough voltage to power your LED and still detect the signal level. $

I got away from Omron when I discovered that I liked AB's communication with distributed I/O better. On a side note, for small systems, nothing beats the Toshiba T1-enhanced. For $150 with free software you won't find more processing power anywhere in the world. Plenty of instructions, I/O and comm expansion. Easy to program. Much more functional than those "budget" PLC like EZ. $

Exactly what object did you create? Did you make a Numeric Display object, a String Display object, or a Text Display object? $

Create a local message display. In the connections tab of the local message display, create an expression that is equal to 1 when pushbutton 1 is pressed, 2 when pushbutton 2 is pressed, etc. You can either use a numeric tag from the PLC or use If, Then, Else. Create a new local message. For Trigger Value 1, enter Data1...etc.etc Assign your local message display to point to the new local message, in the General tab of the local message display properties. Use RSView Studio help files to search for "local message" for more info. $

Obviously understanding the process that is being controlled is the #1 way to understand the controller code. In Allen-Bradley's new Logix5000, tag names help with commenting. As a programmer, the best way to help future readers of your code is to make it efficient and logical. I have seen too many programs where the programmer seemed like he was trying to invent a jigsaw puzzle. And I have seen others that were so beautifully written that I didn't need the comments at all to understand exactly what was going on. Structure the code into groups by function, priority, and other criteria that is logical for the process. Don't overload your rungs, but don't spread out your instructions too much either. Group your I/O into sequencial, logical groups. Keep your communication code and mapping seperate from I/O and computation. A great exercise is to read your own code without comments, and then let a colleague do so as well. I always read my own code without comments to make sure that I can at least understand myself. Good luck. $

The way I learned to program from scratch: Took a system. Learned about it. Programmed it from scratch. Fixed mistakes and learned as I went along. It wasn't really too difficult. $

If you have a coil or winding burn out, you only have to replace one single phase transformer instead of a 3 phase transformer. Once we even used a bank of 4 single phase transformers, so if we lost one, we had immediate redundancy available for a single phase. But in general, for space-savings and ease of maintenance, its best to use a 3-phase. Its also slightly less costly. $

ACME (haha) is correct. The VA of 3 phases is the sum of the VA on each individual phase. KVA per phase = V(phase)I(phase)sqrt(3). Total KVA = 3x(KVA_per_phase). The square root of 3 factor comes from the difference between the line and phase currents or voltages. If you vectorally sum them around a whole 360 degrees with three phases as you calculate power, they cancel out. A wye or delta load connection does not matter either. Total KVA = 3 x Per Phase KVA. My comany has many times in the past used banks of single phase transformers instead of a 3-phase transformer, and they used the same calculation. And it worked, too $ Edit: I'd be happy to go more in depth with the math if you really want me to.

In one of my recent projects I did this quite a bit. I had about 8 different programs each with about 10 subroutines. I used OTE of the same coil in different subroutines, becuase they were called differently depending on what operating mode I was in. $

OK good find. I'm satisfied. $

What is the general consensus on what type of functions are appropriate for control via virtual pushbuttons on an HMI sceen or should remain hardwired to plc (or other controller type) inputs? I am in disagreement with some at my company about what is appropriate. There are certain critical control functions that we cannot risk being accidentally activated by someone bumping an HMI panel, yet also require a very fast response to human input. It made me think of what types of controls would you never put on a virtual pushbutton on an HMI or Scada device. Some believe that all critial control features that should be protected from accidental activation should be hardwired to introduce a physical, mechanical element into the process of activation. Maybe this type of protection can be implemented in logic in some applications? Obviously E-stops (which should be independent of a control system anyway) are an exception....but I'm talking about hardwired PLC inputs vs virtual. For example, I've never seen a hellfire missle launch enable switch in a jet fighter cockpit on a touch sceen button, its always a toggle switch with a mechanical safety. But I've seen a radar countermeasure activated by a touch sceen control. I'm sure that very few of us are desining control systems for such critical functions, but I'm curious about the prevailing philosophies on this matter. Thanks. $

You could very well be correct TW. I have not looked closely at this in a about 18 months. For example, when I reviewed OSHA’s General Industry Regulations (29 CFR Part 1910), Subparts R and S concerning electrical Safety Related Work Practices, it did not appear that arc flash protection is required for employees. I am not a lawyer and will not pretend to know all of the rules, but NFPA 70E specifically is (was?) not included in the list in 1910.6’s “Incorporation by reference”. The National Electric Code NFPA 70 is included by reference and in rule 110.16 which requires electrical equipment to have a flash protection warning label, the fine print note refers to NFPA 70E. This may have changed recently, I don't know. However, implementing the provisions of NFPA 70E reduces the risk and/or extent of worker injury and should always be followed in my opinion. Since I'm relatively ignorant of this issue at this point in time, I'm open to clarification. $

OK I'll go a little bit more in depth on this issue. First of all, the NFPA 70E is a standard addressing electrically safe work practices, while the NFPA70 is an electrical installation document and protects employees under normal circumstances. NFPA 70 (aka the National Electric Code) Article 517 contains regulations for grounding in health care facilities. 517.19 Critical Care Areas (F) Isolated Power System Grounding. Where an isolated ungrounded power source is used and limits the first-fault current to a low magnitude, the grounding conductor associated with the secondary circuit shall be permitted to be run outside of the enclosure of the power conductors in the same circuit. 517.20 Wet Locations (A) Receptacles and Fixed Equipment. All receptacles and fixed equipment within the area of the wet location shall have ground-fault circuit-interrupter protection for personnel if interruption of power under fault conditions can be tolerated, or be served by an isolated power system if such interruption cannot be tolerated. (B) Isolated Power Systems. Where an isolated power system is utilized, the equipment shall be listed for the purpose and installed so that it meets the provisions of and is in accordance with 517.160. 517.21 Ground-Fault Circuit-Interrupter Protection for Personnel. Ground-fault circuit-interrupter protection for personnel shall not be required for receptacles installed in those critical care areas where the toilet and basin are installed within the patient room. 517.160 Isolated Power Systems (A) Installations. (1) Isolated Power Circuits. Each isolated power circuit shall be controlled by a switch that has a disconnecting pole in each isolated circuit conductor to simultaneously disconnect all power. Such isolation shall be accomplished by means of one or more transformers haveing no electrical connection between primary and secondary windings, by means of motor generator sets, or by means of suitably isolated batteries. etc, etc...... Interstingly enough, (and humorously enough) you don't need ground fault protection if you classify your receptacle as a "shaver". 422-40 Polarity in Cord- and Plug-Connected Appliances. If the appliance is provided with a manually operated, line-connected, single-pole switch for appliance on-off operations, an Edison-base lampholder, or a 15- or 20-ampere receptacle, the attchment plug shall be of the polarized or grounding type. A 2-wire, nonpolarized attachment plug shall be permitted to be used on a listed double-insulated shaver. In my case, several of my installations use isolating transformers, and meet the isolation protection described in 517.160. The surveyor having authority over my installation is the American Bureau of Shipping. They require a method for grounding and ground fault protection that is defined in NFPA70. It doesn't matter to ABS that the scope of the article is Health Care Facilities, just as long as it is a method that's defined in the NFPA70. Now of course my first consideration is whether or not the installation is actually safe, regardless of what the regulations say. I am convinced that it is, from an electrical design standpoint. Its impossible to receive an electric shock due to a ground fault, because no potential exists between ground and hot (not even 50-250V, ). Anyway, I only use this method in a couple of places where it's convenient. The majority of my installations use GFCIs. For some of you, keep in mind that NFPA70E is not Incorporated by Reference in 29 CFR 1910.6 (Therefore, OSHA does not enforce it). However, OSHA has several comparable requirements that are enforceable, but these have to do with the use of protective equipment. But OSHA is not my regulatory agency, ABS and IMO are, so I don't have to worry about them. I hope this helps! Cheers! $

With all respect my friend, there's nothing legal about it (the voltage that is). If your neutral is ungrounded at the source, and you short the hot to ground, no matter what the voltage is (within 250V or so ), you won't cause a shock hazard because there is no conducting path from ground to the voltage source (in my case, a Delta-Wye 480/208 transformer). This is a well-established technology, its used in many hospitals and other facilities throughout the USA and the world, and is accepted by many governing bodies throughout the world. Cheers! $

Opening the circuit breaker off while working with outlets will protect from shock. It seems to me that if the 120VAC shorts to floating "ground", nothing will change, because there is no conducting path to the neutral through ground. The current must still travel on the neutral conductor to get back to the transformer. $