Aprilaire 8800 - Page 34

OT, R
Outdoor temperature COS: C3
Permissions: Read/Write
Query
Command
Syntax: SN[#] OT?<CR>
SN[#] R?<CR>
Description: Requests the outdoor temperature sensor reading.
Assignment
Command
Syntax: SN[#] OT=[value][scale]<CR>
Description: Sets the outdoor temperature to [value]. The alternate R version does not apply.
Examples: SN1 OT=55F<CR>
SN OT=-10F<CR>
Response or
COS Message
Syntax: SN[#] OT=[value][scale]<CR>
SN[#] R=[value][scale]<CR>
Description: Sets the outdoor temperature to [value]. The OT version is used for COS Messages and the alternate R
version is only used for responses.
Example: SN1 OT=-10F<CR>
Node address 1 responds with an outdoor temperature of -10°F.
Parameters Range
value: sensor value
Fahrenheit [-40 – 130]
Celsius [-40 – 55]
no sensor attached or error [--]
scale: temperature scale [F, C]
F: Fahrenheit
C: Celsius
The source of the outdoor temperature value is dependent on the available sensors.
Priority Source
1 Direct-wired outdoor temperature sensor (S1 and S2 terminals).
2 Support Module 1, Sensor 1 configured as monitor.
3 OT assignment command.
If a query command is received and the node does not have an outdoor temperature sensor (direct-wired or via support module 1, sensor 1), it
responds with SN[n] OT=--[scale]<CR>. If an assignment command is received and the node does have an outdoor temperature
sensor, the command is ignored and no response sent.
The assignment command is used to allow one node to share the outdoor temperature sensor value. This is accomplished through the Host
controller by determining which node has the outdoor temperature then periodically sending a global outdoor temperature assignment
command to all other thermostats.
The Host controller must ensure that the outdoor temperature value is current. Otherwise, the thermostats without an outdoor temperature
sensor assume that the previously received value is no longer valid. The validity period is 10 minutes and is reset each time the Host
controller receives the temperature value from the node with the outdoor temperature sensor. If the validity period expires, the Host controller
sends a query command to the node with the outdoor temperature sensor to get the latest value then send a global outdoor temperature
assignment command to all other thermostats.
If more than one node has an outdoor temperature sensor, the Host controller uses the value from the lowest address.
If the value of the outdoor temperature changes by 1° or more, a C3 COS unsolicited message is issued (if C3 is ON).
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