Kurt

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  1. @AzeoTech Can you share the code for the autotune procedure and/or comment on my last bullet above? Thanks!
  2. Kurt

    Simple reset?

    Thanks! I'll try the script. Saves sanity compared to having to hunt for typos etc. I'm surprised I'm the only person in this situation, but I'm new to SCADA and it may be I'm designing my alarms to be overly simplistic.
  3. Kurt

    Simple reset?

    Hi AzeoTech and forum users, My alarm needs are pretty simple and I want my alarms to reset as soon as the fire condition is no longer met. I know I can do: Alarm.MyAlarm.strCondition = "a long and complex fire condition" Alarm.MyAlarm.strResetCondition = "!(a long and complex fire condition)" But it would be simpler and easier to maintain if I could do something like the following, rather than having to copy the fire condition into the reset box: Alarm.MyAlarm.strResetCondition = "!FireCondition" Is there a way to reference the fire condition in the reset condition statement? I tried Alarm.MyAlarm.strResetCondition = "!evaluate(Alarm.MyAlarm.strCondition)" but it is inconvenient when duplicating alarms, plus it doesn't seem to work. Another option would be to set up my alarms outside DAQFactory and import, but I noticed that the Help field is not included in exported alarms.
  4. Hi again. Since your last message I've tested some more using smaller relay heights. I should note that our PID loop runs at 10 Hz, so it may be that a shorter oscillation time than the 20-30s is appropriate for us, as you mentioned in your last message. I observed the following: > Starting from a low relay height of ca. 1% of steady-state output and increasing gradually, I started to get decent results with a relay height of around 5-10% of SS output. > Control is still not great, with the autotuned parameters frequently making the integral contribution too large (numerically small), causing (sometimes undamped) oscillations in post-tuning control. Control is also quite slow, taking 30 s or more to reach setpoint. > Most concerning - no matter what I select for the relay height and how long I wait during tuning (usually 120 s), the "settling in" you hint at above never seems to happen. It's hard to be sure, but it seems more like the autotune is recalculating the parameters afresh after each oscillation, rather than adding to an average or fine-tuning, etc. Can you share the code for the autotune procedure? Thanks again for your help.
  5. In our case, we need to autotune every cell, every run, because the heated system changes slightly. But spending 2-3 minutes is no problem if we get better results. What you said about the noise also makes sense; with each successive oscillation the tune seems to get no closer to a fit - the P parameter, for example, keeps bouncing around over a 5-fold range. Will test your advice and report back. Thanks! As a side note, it would be helpful for your advice of targeting an oscillation every 20-30 s and a minimum of 3-4 oscillations to be included in the user guide.
  6. Thanks for your reply. We generally let the autotune run for 30 s and this is enough time for 15-20 or so oscillations. As I recall, the autotuned PID parameters have fully stabilized by the time the tuning is shut off, but the values are just bad. I'll try running it longer and see if I get better results, then report back.
  7. Hi AzeoTech and forum users, We have a number of heating elements supplied with controllable DC power supplies whose current output is set by a DAQFactory PID loop. This system has worked well for us, including autotuning. However, we recently increased the size of the system being heated, resulting in a larger current needed to achieve similar temperatures. For these larger systems, autotuning no longer works well. When we try to autotune using the larger systems, the autotuning appears to work, but post-tuning control (including at the same setpoint used for tuning) is poor. We see large oscillations (sometimes undamped). We tried increasing the relay height to ca. 80% of steady-state output (i.e., if the steady-state output at the setpoint is 100, the relay tuning sweeps from an output of 20 to an output of 180), but the resulting autotuned parameters still result in oscillation. As a result, we've had to manually tune by trial and error. We suspect the autotuning problem is because of increased process lag with our larger system. As one example, once power is cut, the larger system takes 30-45 s for its temperature to decrease by half. Is there another autotuning method, or a way to adjust the methods used by the relay tuning method, that we could try to improve our results? We were wondering if there might be a way to fit our data to a "first order plus deadtime" model (whether in real space or Laplace space). Or if there might be other known tuning correlations we could use. Thanks for your help!