An005 Lua BACNET Client Operations

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Application NotesAN005 - Lua BACnet Client Operations

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AN005 - Lua BACnet Client OperationsApplication Notes AN005 2

Schneider Electric- Small Building Systems Tel. Americas: North Andover, MA 1-800-225 -0962 Tel. Europe: Malm, Sweden +46 40 38 68 50 Tel. Asia Pacific: Hong Kong +852 2565 0621 Product Name AN005 - Lua BACnet Client Operations - 02 www.schneider-electric.com/buildings October 2013 ct

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Introduction and ContextWhen integrating SmartStruxure Lite Managers with third-party devices, sometimes aBACnet client functionality can be useful. This application note gives an overview of the fourbasic Lua functions to access remote BACnet points.

Note that all SmartStruxure Lite Managers have full BACnet server capabilities, howeverthe BACnet client functionality is currently only available through Lua. Also, with the currentbasic client capabilities, the maximum number of devices supported on a single BACnetnetwork is 1000.

NOTE: If using BACnet client tools in version 2.6.x or later, it is necessary to modify yourscript to prevent BACnet communication from starting 90 seconds after the controllerinitialization.

This can be done by encapsulating your script logic within the fo llowing loop:

if scl.sysclock() > 90 then

Case 1: Four Lines The three basic BACnet commands that can be performed are who-is, read and wri terequests for speci points. A fourth function is available to obtain the resulting value of aread request.

The below shows a simple four-line script that does a who-is , reads a value, displays thevalue, does a write.

bacnet.whois(500, 500)

bacnet.read(500, AV1)

print(bacnet.value())

bacnet.write(500, AV1, 32)


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Step 2: Step-by-Step Process The below shows a more thorough step-by-step example on how to access a remote BACnetdevice point in Lua.


if whois ~= true then

bacnet.whois(500, 500) -- Step one: who is? (device or range)

whois = true -- Next run: skip to step two

elseif fetch ~= 0 then

fetch = bacnet.read(500, AV1) -- Step two: read! (specic point)

else

value, stamp = bacnet.value() -- Step three: check value and time

if old_stamp ~= stamp then -- If time differs: value has changed!

old_stamp = stamp -- Keep track of time stamp

print(DEV500.AV1:, value) -- Optional: display the changed value

ME.AV2_Present_Value.value = value -- Optional: keep value locally

end

fetch = false -- Next run: go back to step two (to read again)

end

end


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Case 3: More OptionsFor a simpler way to change the remote BACnet point specications, another example isprovided below. This Lua uses two top variables to specify the remote device instance andthe object name.


dev_inst = 500 -- Device instanceobj_name = AV1 -- Object type and number


bacnet.whois(dev_inst, dev_inst) -- Step one: who is? (device or range)



fetch = bacnet.read(dev_inst, obj_name) -- Step two: read! (specic point)

else


if old_stamp ~= stamp then -- If time differs: value has changed!old_stamp = stamp -- Keep track of time stamp

-- Optional: display the changed value

print(DEV .. dev_inst .. . .. obj_name .. :, value)

ME.AV2_Present_Value.value = value -- Optional: keep value locally

bacnet.write(dev_inst, obj_name, value + 1) -- Optional: increase value by +1

end

fetch = false -- Next run: go back to step two (to read again)

end

endSimply changing the dev_inst and obj_name variables will sufce in using the script in real-lifesituations.

Note that as an additional step, the above script example is also writing to the remote object. This means that every time the script is executed (e.g. every few seconds), the remotevalue will be incremented and read back again. As a result, the last optional lines should beadjusted for the specic needs of the integrator.


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Case 4: Reading Multiple Devices and CharactersWhen many BACnet remote points need to be read, the below lus function can be used.

This Lua loops through a list of device instances and object names.


obj_list = { -- Local and remote objects list

AV21 = {600, AV1},

AV22 = {700, AV2},

AV23 = {800, AV3}}


bacnet.whois(600, 800) -- Step one: who is? (devices range)



obj_link, obj_info = next(obj_list, obj_link) -- Find next objects pair

if obj_link == nil then -- Loop around on last pair

obj_link, obj_info = next(obj_list, obj_link)

end

dev_inst = obj_info[1]

obj_name = obj_info[2]

fetch = bacnet.read(dev_inst, obj_name) -- Step two: read request!

if fetch ~= 0 then -- On error: print message

print(BACnet read failure on DEV .. dev_inst .. . .. obj_name)

else

old_value, old_stamp = bacnet.value() -- Reset the timeout

end

else



ME[obj_link .. _Present_Value].value = value -- Update value

print(string.sub(os.date(), 10, 17), ME. .. obj_link,

DEV .. dev_inst .. . .. obj_name, value) -- Display value

elseif scl.sysclock() - old_stamp > 3 then -- Timeout after 3 seconds

print(BACnet read timeout on DEV .. dev_inst .. . .. obj_name)

end

fetch = false -- Next run: read next object in list

end

end

Simply adjusting the obj_list table content should sufce in using the script in real-lifesituations. This specic example fetches three remote points (DEV600.AV1, DEV600.AV2,and DEV600.AV3) from three different remote BACnet devices. It then stores the resultsinto local analog values (ME.AV21, ME.AV22, and ME.AV23).

Note the resulting update period for those variables is twice the PG script period,multiplied by the number of remote objects actively fetched. In this case, since the script

is running every second, and because three objects are read, the resulting typical objectupdate period is every 6 seconds (1 2 3).


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Case 5: Full Read and Write ScriptIn a situation where some points need to be updated more often than others, an extratime condition can be used to only perform read operations when required. On top of theread interval, the below example script adds the ability to specify which objects should bewritten when their value changes.

-- *** Variables Initialization ***


if var_init == nil then

var_init = true

-- Local and remote objects list, in the format:

-- LocalObject = {RemoteDevice, RemoteObject, ReadSecs, Write, KeptValue, KeptSecs}

obj_list = {

AV21 = {600, AV1, 10 , false, 0, 0}, -- Read DEV600.AV1 every 10s into AV21

AV22 = {700, AV2, 10 , false, 0, 0}, -- Read DEV700.AV2 every 10s into AV22

AV23 = {800, AV3, 30 , true, 0, 0}} - - Read every 10s, write if AV23 changes

-- This is just a quick function to print with a timestamp:

function display(...) print(os.date():sub(10, 17), ...) end

end

-- *** Program Execution ***


bacnet.whois(600, 800) -- Step one: who is? (devices range)


ecount = 0 -- Reset the error count

display(Sending who-is...)


repeat

obj_link, obj_info = next(obj_list, obj_link) -- Find next pair

if obj_link == nil then -- Loop around

obj_link, obj_info = next(obj_list, obj_link)

end

obj_item = ME[obj_link .. _Present_Value] -- Keep object pointer

-- Read condition, when time interval has elapsed:

obj_read = (scl.sysclock() - obj_item.time > obj_info[3])


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-- Write conditions:

obj_write = (obj_info[4] -- When writeable, and:

and ((obj_info[5] ~= obj_item.value) -- Either value changed

or (obj_info[6] ~= obj_item.time))) -- Or timestamp changed

until obj_read or obj_write -- Loop until read or write has been found...

-- Step two: read or write request!if obj_write then

display(ME. .. obj_link .. DEV .. obj_info[1]

.. . .. obj_info[2] .. write: .. obj_item.value)

bacnet.write(obj_info[1], obj_info[2], obj_item.value) -- Write value

obj_info[5] = obj_item.value -- Keep last object value

obj_info[6] = obj_item.time -- Keep last object time

else

fetch = bacnet.read(obj_info[1], obj_info[2]) -- Read at time interval

if fetch ~= 0 then -- On error: print messagedisplay(BACnet read failure on DEV .. obj_info[1] .. . .. obj_info[2])

else

old_value, old_stamp = bacnet.value() -- Reset the timeout

end

end

else



obj_item.value = value -- Update valueobj_info[5] = obj_item.value -- Keep last object value

obj_info[6] = obj_item.time -- Keep last object time

display(ME. .. obj_link .. DEV .. obj_info[1]

.. . .. obj_info[2] .. read: .. value)

ecount = 0 -- Reset the error count

elseif scl.sysclock() - old_stamp > 3 then -- Timeout after 3 seconds

display(BACnet read timeout on DEV .. obj_info[1] .. . .. obj_info[2])

-- Send another who-is? after 3 read errors:

ecount = ecount + 1if ecount >= 3 then

whois = false

end

end

fetch = false -- Next run: read next object in list

end

end


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Simply adjusting the obj_list table content should sufce in using that script in real-lifesituations. The above example fetches three remote points (DEV600.AV1, DEV600.AV2,and DEV600.AV3) from three different remote BACnet devices. It then stores the results intolocal analog values (ME.AV21, ME.AV22, and ME.AV23). It performs the read requests at thespecied ReadSecs interval for each object (10 seconds, 10 seconds, and 30

seconds).

This script a lso writes back, when specied, the object value when it changes, (in the aboveexample), only if the third line of the if obj_list table has its Write parameter set to true, whichwill write ME.AV23, if changed, into DEV600.AV3). It then performs a BACnet write operationto the remote device, effectively sending out the new value.

Note if the BACnet connectivity is completely lost, an error count gets incremented to triggeranother who-is request periodically (after every 3 failures) to effectively re-acquire the devicesonce the connectivity is restored.

An005 Lua BACNET Client Operations

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