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Aprilaire RS-232 control

asadlerasadler Posts: 19
in NetLinx Studio
Hi all,

I've got a problem with some Aprilaire thermostats. I'm using the AMX module for all my control and state tracking. The problem is that the thermostats seem to, after a very short time, sort of lock up and become unresponsive to commands from the controller.

I've done a bunch of reading on the forums here to see if anyone else has had the same problem, and it sounds as though I might be polling them too often. Currently, I'm polling them for mode, set points, and temperature every 30 seconds, but from what I've read, it sounds like this is maybe causing my problem and that I don't actually need to poll them at all. Can anyone verify that this is the case, or help me work out what I'm doing wrong?

Thanks in advance.

Comments

  • TurnipTruckTurnipTruck Posts: 1,485
    Which Aprilaire stats? The 8870?
  • asadlerasadler Posts: 19
    Yes, I believe those are the ones.
  • viningvining Posts: 4,368
    are you polling in addition to what the comm module does and if so are using send_commands to the comm module for this polling or are you sending directly to the stats? If you're sending to the comm module It should put strings in a queue and control the timing of the strings sent to the stats so that shouldn't really be an issue. If your sending it directly via the passthru function then you have to controll the timing between strings which depending on command will vary from something like 250ms to 450ms. I think the last thing I did with the stats I actually stored strings in my own queue and sent the queued strings to the comm module one at a time via a 500ms timeline just because I had no idea how the comm module really does handle this.

    On the hardware side you there's alot of steps that should be taken as far as wiring and addressing to minimize comm problems. Address everyone sequentially starting at 1, put the total number of stats in each tsat in their individual set up. Use a seperate power supply to power your stat at the dist panel, if you have more that one dist panel you'll likely need a second power supply in which case you might consider using the REF termial to tie the ground reference through to all device.

    These stats can be very finicky so you have to ensure that every set up step is adhered to.
  • asadlerasadler Posts: 19
    Everything I send to the stats is through the comm module, so I guess it should all be getting queued properly. I hadn't realized that the comm module did any polling, so I guess that makes what I'm doing redundant.

    As for power supplies, that's really beyond what I even know how to do, but I'll talk with the installers and see how it's all set up.

    For now, I'm going to remove my manual polling code and see if that helps.
  • DHawthorneDHawthorne Posts: 4,584
    8870's aren't supposed to need to be polled at all; they report whenever a change occurs. I only query them when a page opens so the data will be fresh, but even that wouldn't be necessary if I had separate pages for each stat ... but I share the page and want to make sure it isn't still showing data for the last stat displayed.

    It is possible you have a problem on your comm buss as well. I just recently had a system where the data appeared to be locked ... all the stats on the site showed no communications. I found one stat buried in a mechanical room that was in an endless re-boot cycle (good for me it wasn't controlling a furnace, it was just there to monitor the temperature and humidity). It turns out someone had connected the wrong wires to it's external sensor terminals, and that was causing the reboot. The annoying part was that one stat having an issue took down the entire system. This kind of thing is pretty much par for the course with the 8870, sadly.

    Excessive polling is definitely another issue, and produces the same effect. the 422 buss is simply not managed very well. Any excessive traffic (be it legit notifications, or reeboot activity) shuts the whole thing down. It's reliable enough when all is well, but I am sorry to say, I would not entrust these thermostats to any kind of critical system. Heck, if my home gets a bit too cold, I will notice it and can temporarily shut down comms until it is fixed; but the wine cellar with those vintage bottles ... or the computer room ... no, I would absolutely not trust an 8870 that far.
  • asadlerasadler Posts: 19
    Hi guys,

    Just want to follow up on how this turned out. Once I took out my polling routines, everything started working famously. Well, I have one stat that's sending back garbage strings when I try to talk to it, so I have either a bad stat or a bad wire there, but everything else works great now.

    Thanks for all the input and advice.
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