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  1. #1
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    Hmm Bacnet IP write property

    Hello, I am new to BACnet IP protocol. I'm trying to write a new value for set temperature but it seems like that is possible only when I set "out of service" to active. Since I have two devices that broadcast bms, once I change "out of service" to active, one of device cannot monitor nor set temp. Is it possible to make both device available to monitor and control the same system in the same time? And is that any free scada bacnet available for download?

  2. #2
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    Would help if you specified the devices at hand specifically.

    Google search for BACnet discovery should turn a wad of free tools that can monitor, change, discover BACnet points. There is also a sticky post at the top of this forum on BACnet specifically that offers different tools.
    Propagating the formula. http://www.noagendashow.com/

  3. #3
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    Are the points physical inputs or values?

    I think YABE is one of the better full featured BACnet freeware on the uberwebz.

    kontrol out
    "Good" - Jocko
    "Open is as open does." - Forrest Gump
    "Can't we all just get a Lon?" - Garry Jack
    "BACnet: integration or interrogation?" - The Janitor
    "Interoperability? You can't handle interoperability!" - Nathan R. Jessup
    “What’s that? Aaa… open protocols? Don’t talk about…. open protocols? Are you kidding me? Open protocols? I just hope we can hardwire an interface!” - Jim Mora Watch it here!

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  5. #4
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    Quote Originally Posted by orion242 View Post
    Would help if you specified the devices at hand specifically.

    Google search for BACnet discovery should turn a wad of free tools that can monitor, change, discover BACnet points. There is also a sticky post at the top of this forum on BACnet specifically that offers different tools.
    It's MT3 with Bacnet card. I'm trying to set temperature from Bacnet explorer, but it said access denied. However, present value of set temp could be change when I set "out of service" to "true". But that make another device unable to monitor and control system.

  6. #5
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    Priority levels?
    Keep it simple to keep it cool!

  7. #6
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    Quote Originally Posted by myname View Post
    It's MT3 with Bacnet card. I'm trying to set temperature from Bacnet explorer, but it said access denied. However, present value of set temp could be change when I set "out of service" to "true". But that make another device unable to monitor and control system.
    What type of object is it. Even the present value of a input object will be writable when Out-Of-Service.
    If it is a output object, the present value is always writable even there is a prior value taking effect.
    Carrier CCN Modbus/BACnet gateway
    BACnet router for BIP, MS/TP, Ethernet
    http://www.hvacrcontrol.com/?lang=en

  8. #7
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    Quote Originally Posted by lin View Post
    What type of object is it. Even the present value of a input object will be writable when Out-Of-Service.
    If it is a output object, the present value is always writable even there is a prior value taking effect.
    It is analog value.

  9. #8
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    Quote Originally Posted by myname View Post
    It is analog value.
    Present value of analog value is not required to be writable. But Out-Of-Service make it writable.
    Carrier CCN Modbus/BACnet gateway
    BACnet router for BIP, MS/TP, Ethernet
    http://www.hvacrcontrol.com/?lang=en

  10. #9
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    As others have pointed out, the AV you are trying to write to is most likely read-only, which is why you cannot write to it. As you've noticed, you can write to it when the Out-Of-Service property is TRUE, but this is only intended to be used for test purposes since this action decouples the BACnet object's value from the actual process value. Out-Of-Service can be useful for testing logic in other controllers such as control, alarms, warnings, etc. to see how the equipment reacts to different input values.

    Take a look at the MT3's BACnet object list documentation. There should be a column for Read/Write Access. The AV you are currently accessing will likely show an R, indicating read-only. You want to find an object that has a C in that column, indicating that it is commandable (read/write) and supports a priority array.

    The priority array is important if you need to have two systems control the same BACnet object. Every commandable BACnet object can be written with a priority, 1 - 16, with 1 being the highest priority and 16 being the lowest. If no priority is specified, priority 16 is used. The BACnet object's present value will take on the highest priority value in its priority array. A client can relinquish a value that was previously written so that the object's value takes on the next highest priority, or the relinquish default value of the object if no other values are in the priority array. This is how BACnet arbitrates control over an object from multiple sources.

  11. #10
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    Quote Originally Posted by jschulze View Post
    As others have pointed out, the AV you are trying to write to is most likely read-only, which is why you cannot write to it. As you've noticed, you can write to it when the Out-Of-Service property is TRUE, but this is only intended to be used for test purposes since this action decouples the BACnet object's value from the actual process value. Out-Of-Service can be useful for testing logic in other controllers such as control, alarms, warnings, etc. to see how the equipment reacts to different input values.

    Take a look at the MT3's BACnet object list documentation. There should be a column for Read/Write Access. The AV you are currently accessing will likely show an R, indicating read-only. You want to find an object that has a C in that column, indicating that it is commandable (read/write) and supports a priority array.

    The priority array is important if you need to have two systems control the same BACnet object. Every commandable BACnet object can be written with a priority, 1 - 16, with 1 being the highest priority and 16 being the lowest. If no priority is specified, priority 16 is used. The BACnet object's present value will take on the highest priority value in its priority array. A client can relinquish a value that was previously written so that the object's value takes on the next highest priority, or the relinquish default value of the object if no other values are in the priority array. This is how BACnet arbitrates control over an object from multiple sources.
    It say R/W. is it possible to set it to always out of service because I want to integrate the system with BMS?

  12. #11
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    Quote Originally Posted by lin View Post
    Present value of analog value is not required to be writable. But Out-Of-Service make it writable.
    any method to set it out of service permanently? I want it to be controlled via node-red. Thank you in advance

  13. #12
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    You don't want to set the object to Out-Of-Service because the setpoint temperature will not change when you write to the object. Out-Of-Service decouples the BACnet value from the actual setpoint. When the object is in Out-Of-Service, neither of your BACnet clients will be able to read the actual setpoint value or change the actual setpoint on the device. The object's preset value will simply be scratchpad memory and will stay at any value that was written to it, regardless of the value of the actual setpoint.

    Can you provide a link to the BACnet object list documentation you're using? What AV instance are you trying to write to?

    Have you tried writing to the AV using YABE when the object is not in Out-Of-Service?

  14. #13
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    "because the setpoint temperature will not change"
    hehe,
    This is of course the one thing that Bacnet should make entirely available from a functionality stand point.
    the ability to change a set point,
    after all its actually the only thing thats really needed at all,
    once upon a time it was ez, last in, wins..
    then they made it better...??
    Bacnet priority arrays can be ,, useful at times, i guess,
    have used em, although they are alternatives,
    thing is not all the Bacnet devices made, implemented arrays,
    and not always, correctly, add the r/w possibility in and it gets even less clear..
    but if your app supports it you should be able to code it to write at what ever priority you want,
    priority 8 would be outofservice, as far as other controllers are concerned,
    code in another controller setting the value over a network would normally write at priority 10,
    so two or more different controllers on the network could write to the AV at priority 10,
    actually u get 3 with Bacnet, present value, current value, and default value,
    its all very confusing, but its better..
    now how the individual controller responds to the AV property array value is a choice of the manuf.
    which might not impact your situation, is just a part of my rant ,
    i have to believe its the one thing most have spent time resolving in doing system integrations
    that seems to just consume to much effort.
    its a lot better than it was, but it may depend on the age of device your trying to integrate
    ,

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