Mendon Systems

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Posts posted by Mendon Systems

  3. Posted

    Well .... I suppose it could but there would have to be sufficient noise to generate current flow. Possibly something like a radio antenna? The most common source of ground loops is grounding a shield at both ends of the wire. If there is a difference in ground potential the shield becomes a current conductor. I ran into one case where this happened becaue two separate buildings were running from different sub-stations which were not in phase. The ground potential between them was about 20 volts.

  4. Posted

    If the bonding was done correctly there shouldn't be any difference but ..... If you have high ground currents going to those blocks it is possible that you might see some difference. The question becomes .... why do you have current flowing through the grounds? IF you do there is something wrong with the system design.

  5. Posted

    Yeah, I know what the differences are. I don't need about 90% of what the NC482 does for this application, just speed control on one axis and position control on the other one. I should be able to edit out the 3rd and 4th axis and remote I/O in the symbol tables so I could use them but I doubt that would even be worth the effort. What I was mostly looking for was some sample code to initialize the module at startup without having to re-invent the wheel. There's a small cxp file in the quickstart but it only supports their NS terminal sample code.

  6. Posted

    Does anyone have some sample code for setting up a CJ1W-NC281 with G5 servos on a CJ2M using the NCx8x FB library?? The application program itself is fairly simple (similar to a CNC thread cutting operation) but the NC281 module configuration appears to be a real nightmare. The W487 manual is only slightly shorter than War & Peace and is written in Omron's typical nearly unintelligble style. I did find a "quick start" file for the NC482 on Omron Europe but I'm not sure how much of that might actually translate to the NC281.

  8. Posted

    Bob: you might look into one of the small Weintek (Maple Systems here) touchscreens. They are relatively inexpensive and have an email capability built in that you can trigger by setting bits in the PLC. The 4.3" version is about $300 US.

  16. Posted

    The CP1L-EM series did not even exist prior to version 9.4 of CX Programmer. It is not too surprising that the older versions of CX Programmer did not support it. That is why you need to run the automatic update of CX Programmer regularly.

  19. Posted

    The problem I see with a shift register is that they are not very convenient for anything that isn't an even multiple of 8 or 16. It might be easier just to write individual ladder logic. You will also have to deal with the conditions where one unit is offline that will require ladder logic. One method you could use to equalize runtime is to change the operating time of the lead compressor. For example you might run the compressor with the least hours as lead for six hours, the middle one for as lead 5 hours and the on with the most hours as lead for four hours. Of course you would need to have the run time stored in the PLC. I have used this trick with pumps to equalize runtime and it works very well.

  20. Posted

    I would definitely add the ETN21 card to handle those HMI's as a separate network. That should allow the two PLC's to communicate without concerns about the traffic level. If the HMI's slow down, that is something the customer will have to live with. It was their idea to run this configuration. It might work the way they have it configured, but if it doesn't you will of course get the blame for it.

  22. Posted · Edited by Mendon Systems

    Unfortunately PLC replacement programs seem to be controlled by two old addages, "Out of sight, out of mind" and "If it ain't broke don't fix it". Most PLCs are extremely reliable so they tend to last much longer than the parts supply chain does. Very few customers are willing to shelf stock spare parts. All of this leads to the problems that you have described and warnings to the customer of impending doom seldom do any good. I have one system rignt now (Omron CQM1) which was obsolete when the machine was installed and is now difficult (but not impossible) to find parts for. The customer won't allow a retrofit because "that takes too long and we're behind on production". It's only a matter of time until this machine suffers a permanent failure. I have another customer replacing a 1970's control system for a waste treatment plant with all new components. They decided that the recommended spare parts list was not necessary because all the parts are currently available. Of course by the time they have a failure the parts won't be available anymore!

  23. Posted

    You need a CS1W-CN226 cable, CX Programmer software, and a real RS-232 port or an Omron USB/serial adpater. Instructions for uploading are included with the CX Programmer documentation.

  25. Posted

    The actual pulse rate will determine the best approach (particularly for low flow rates), but here's a couple of ideas: 1) Use a high speed counter to capture the number of pulses. 2) Create a scheduled task that runs periodically to handle the data collection. 3) Read the pulse count using a PRV instruction. 4) Average the pulse counts using an AVG instruction (see notes). 5) Convert the average pulses to flow in GPM or LPM and store in a DM register. Averaging notes: 1) The AVG instruction resets itself if the control line cycles so it needs to be "always on". 2) Use the scheduled task timing to control how often the data is averaged. 3) For low counts multiply the pulse count by 100 before averaging to improve the resolution. Flow_Monitor.pdf