Detecting a blown bulb - key input MIA

Discussion in 'C-Bus Wireless Hardware' started by KevinH, Mar 27, 2011.

  1. KevinH

    KevinH

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    When a bulb blows on a wireless relay switch then the whole switch is out of action, which causes user frustration So I wondered if there was some C-Bus function I could leverage to advise me of this as soon as it happened, and present the info on a touch screen ?

    Is there for example an easy / logic engine way to get a group to turn on when a C-Bus hardware device vanishes from the network ? If it could be on at a level that reflected the devices C-Bus hardware address even better :) I realise it could still be either of the two channels that failed on the relay switch.

    If not then is there a recommended approach using the C-Bus protocol...? The group will remain 'present' because it is maintained in the MMI by an output unit. Will I have to poll periodically or is there something evented that I can monitor ?

    Failing that can I install a 1uF X2 capacitor across such incandescent bulbs to keep the switch functional at all times. This might be better as at least then in the dark other lights could still be switched on from that switch.

    K
     
    KevinH, Mar 27, 2011
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  2. KevinH

    Newman

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    Most people don't have the opportunity to make a phone call prior to having a car crash. It's the same here, i.e. when the unit dies, it dies and there is no event that the unit sends to say that it's just had it's bulb fail.

    If you're running C-Gate on the site it will be checking in on all the units every few minutes. You will see the messages in the C-Gate log if a unit disappears at all.
     
    Newman, Mar 30, 2011
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  3. KevinH

    KevinH

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    I hadn't expected the unit to announce it's impending demise itself but perhaps some supervisory C-Bus message might be available - or maybe a C-Bus wireless gateway would notice the RF node abscence and could advise.

    I don't usually have C-Gate running so I guess I'll have to poll myself then.... it doesn't have to be frequently, which is I assume how C-Gate is doing it..

    Is the X2 capacitor alternative viable ?

    K
     
    KevinH, Mar 31, 2011
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  4. KevinH

    Newman

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    C-Gate goes out and queries all units in a C-bus installation on a semi-regular basis. It will notice the missing unit.

    The X2 cap is definitely a viable option, and that's how I've made the relay units work with puny CFL's and the like in the past.
     
    Newman, Mar 31, 2011
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  5. KevinH

    KevinH

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    I'll likely go the X2 route I think - they're physically big capacitors though.

    One thing I was just thinking about... as the switches effectively have an output unit within them .. do these behave the same as wired output units and contribute their group state to an MMI on that network ?

    If so can I examine the MMI's and notice that the group has become absent ?

    K
     
    KevinH, Mar 31, 2011
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  6. KevinH

    Newman

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    Wireless units do report their status in MMI's but, being Wireless, the whole MMI mechanism is completely different. It might take quite a while for a group to show up as missing in the MMI using this method so I wouldn't rely upon it to give you timely notification.
     
    Newman, Mar 31, 2011
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  7. KevinH

    ashleigh Moderator

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    Well, actually, wireless units have an MMI-like mechanism that goes on. Its not exactly the same. In fact, its quite different in many reepects.

    But the end result is that units continually chat amongst themselves (at ever decreasing intervals) to confirm the state of a group.

    There is however nothing that mashes all that up and says "ooh this unit is not there any more".

    The gateway watches all the chatter and uses this to internally build a network model of what is happening in wireless-land. It then takes MMI requests that come in from the wired side (in the form of "hey you do an MMI for me and tell me the results"). It sees that request come in, and then fakes up a bunch of replies from its internal wireless network model.

    So as far as the wired side is concerned, it looks like there is an MMI being done. In fact, its a little bit of smoke and mirrors.

    And again, this model does not age-out a unit so it it can't see a unit stop chattering and then remove it from the MMI reports. As far as the gateway is concerned, once seen, a unit continues to exist. UNLESS you explicitly talk directly to that unit and that unit alone and this fails, in which cases in some circumstances that unit address can become removed from the model. This is not foolproof though and cannot be relied upon.
     
    ashleigh, Mar 31, 2011
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  8. KevinH

    KevinH

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    What's a good message type to use for this presence verification that doesn't change states and is usable from a PCI interface, similar to a ping .. and that I can rapidly detect the delivery failure of ?

    K
     
    KevinH, Apr 2, 2011
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  9. KevinH

    ashleigh Moderator

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    Let c-gate do it.

    Wireless is not designed for polling, which is what you are trying to do. You are far more likely to have false alarms than in a wired system.
     
    ashleigh, Apr 3, 2011
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  10. KevinH

    KevinH

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    I don't have that option for this installation. Is there not a way using the public C-Bus protocol ?

    K
     
    KevinH, Apr 3, 2011
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  11. KevinH

    ashleigh Moderator

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    Refer to the Serial Interface Users Guide that you can download.

    See pages 38 - 41.

    Issue an IDENTIFY $01 to the unit (so, a CAL command 2101). The full command would look something like:

    \06xxyyzz2101

    Where xx = your gateway unit address, yy= the network route (probably 00 as things wont go more than through a single gateway), and zz = the address of the unit on the other side.

    You should get an answer back, which is a REPLY containing the unit type.

    BEWARE:

    1. The reply may take a while to come back - you should set a timeout on the expected reply of about 5 to 10 seconds. More is better.

    2. Wireless networks have a higher level of packet loss than wired, you should expected failures.

    3. You should not flag a unit as dead or missing until you see about 5 failures in a row.

    4. NEVER POLL A UNIT MORE FREQUENTLY THAN ONCE PER 30 MINUTES IN WIRELESS. (This means that if a unit fails you will have a detection time of about 2.5 hours because of the need to detect 5 failures, and you can only do a check every 30 minutes.).

    Bear in mind the scaling - if you check a single unit every 30 minutes and have 30 wireless units, thats a check of a unit every 1 minute which is NOT MAKING FRIENDS. You really should be limiting the TOTAL interrogation rate to no more than 1 per 10 minutes.

    Also bear in mind that wireless communication to a non-present unit causes a large number of retries (about a dozen); during this period the on-air bandwidth utilisation goes VERY high, and other wireless communication WILL be compromised. Normally this kind of thing only happens during commissioning, and its no big deal. If you are going to have it running all the time you must limit the number and rate of interrogations or you will have some unpleasant consequences.

    If all this does not work very well... you were warned!
     
    ashleigh, Apr 3, 2011
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