Announcement

Collapse
No announcement yet.

governor

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts


  • governor

    I install troubleshoot and sometimes write governor software. I am wondering if I could use a productivity 3000 or other Automation direct PLC? Some requirements.

    1. Steady fixed program scan of 10MS. If there are delays due to communications or others the controls will be rough. I am working on getting the program size.
    2. Critical analog of 10 ms seconds. So I need 4/20 ma inputs that scan 10 ms or less.
    3. TC scan rate of 100ms. I can use tc modules and then feed through a 4-20ma if need be.
    4. Analog output with a scan less then 10 ms.

    I think the productivity 3000 meets 2 to 4 above, what about #1? Other PLCs I could use for this application?

    thanks all



  • #2
    The Pac 3000 and the BRX plc's both are fast enough to run fairly advanced programs under 10ms.
    Communications may take longer than that depending upon what type of comm is being used, how many secondary devices are being polled, and what data is being transferred.
    The analog times should not be a problem.

    Comment



    • #3
      I did aome research on the BRX PLCs a few years ago. Seems they have erratic scan times because of communications. Is this true with the productivity 3000?

      Comment



      • #4
        Originally posted by fitz View Post
        I did aome research on the BRX PLCs a few years ago. Seems they have erratic scan times because of communications. Is this true with the productivity 3000?
        About a 1ms bump due to Ethernet comms.

        Comment



        • #5
          Sounds good Bob O. Is this for the productivity or the BRX or both? Sounds a lot better. Can I set a constant scan time and not just let it scan as fast as possible?

          Comment



          • #6
            Originally posted by fitz View Post
            Sounds good Bob O. Is this for the productivity or the BRX or both? Sounds a lot better. Can I set a constant scan time and not just let it scan as fast as possible?
            This is for Do-more/BRX.

            The primary scan just runs as fast as possible, no fixed scan option. BRX also supports microsecond timer triggered interrupts that have extremely low latency (~10us) that could be used to perform time critical operations. Analog channels are not updated during interrupts, but onboard discretes are. There is also a microsecond time stamp math function (TICKUS()) that is updated intra-scan, so you can use that for other precision timing.

            The onboard analog outputs on the BRX are quite fast, around 200us for 2. Onboard analog inputs update at about 1.2ms for up to 4. BRX analog expansion modules are considerably slower though.

            Comment



            • #7
              So a timer could be used to do blocks of code on a fixed scan rate? Only the governor really needs on be on fixed scan, must pumps, fans etc dont need fixed scan rates.

              Comment



              • #8
                Originally posted by fitz View Post
                So a timer could be used to do blocks of code on a fixed scan rate? Only the governor really needs on be on fixed scan, must pumps, fans etc dont need fixed scan rates.
                They are interrupt service routines, so I wouldn't do a lot of work in them, but yes. That may not help you though, since analog I/O is still updated during the normal scan.

                Do-more does provide good methods for breaking up processing between different scans, so you should be able to keep the scan time quite low. With a low enough scan time, you shouldn't have any problem keeping the 10ms calc very predictable.

                Comment



                • #9
                  Thanks bob o. do you have the same info for the productivity plc?

                  Comment



                  • #10
                    Originally posted by fitz View Post
                    Thanks bob o. do you have the same info for the productivity plc?
                    I'm one of the lead developers for Do-more/BRX. Not involved with PxK.

                    Comment



                    • #11
                      On the productivity you can set up a leader to run at a specific intervals but I myself have not used it. I do know on my applications that are heavy on Ethenet coms are running at 1ms scan times

                      Comment



                      • #12
                        Thanks guys, great information.

                        Comment



                        • #13
                          I believe the P2000 would be more suited for your application. P2000 has the same power as the P3000 just not as many I/O points. The P2000 has a smaller footprint than the P3000 and cost less. As for the analog output, the P2-04DA would meet your speed requirements by updating all 4 channels in 0.6 ms. The P2-04AD analog input module has a Sample Duration Time of 2 ms per channel (4 channels in all). As for your TC connections, using a TC to 4-20 ma converter would defiantly will improve the TC Sample Duration Time. The Sample Duration Time for the TC module is slow like 270ms per channel. I do think the TC module is more suited for furnace control. As for the cpu scan time, yes you can set a maximum scan time through the hardware config.

                          I hope this info helps you in your decision.

                          Comment



                          • #14
                            Helped a lot Grey, one step closer. I am going to open the productivity software now and see where to set can times.

                            Governors dont have huge Io counts, so I will look into the P2000.

                            Comment



                            • #15
                              You can set a maximum scan time in productivity, but I dont believe you can set a fixed scan time.

                              Comment

                              Working...
                              X