How-to: Measure Temperature Rise of AP in an Enclosure

Not applicable

This procedure is a very simple method to evaluate the temperature rise of an AP and other equipment in a proposed NEMA enclosure or other protective enclosure. For background information on when this procedure may be useful, see the article on the use of indoor rated access points in outdoor enclosures. The objective of temperature rise measurement is to provide a rough estimate for adjusting the AP operating termperature specficiation in a given installation environment. In simple terms if the AP is rated for some given temperature range without the enclosure or other equipment in proximity, what we want to know is the new allowable temperature range for the combined AP+Other Equipment+Enclosure.


Here is the basic procedure, note this is not a formal qualification which would require high/low temp testing and cold start testing to ensure the enclosure can heat enough to start the equipment in the event of a power outage/reset. This procedure is just a basic check of high temp performance again with the intent to characterize the temperature rise and derate the allowed environment ambient temperature.


 1.      Put everything into the enclosure in the proposed configuration.  It is important that the installation of the equipment is as close as possible to the actual proposed installation so that proximity of components to each other, thermal drafts, etc are all approximated as best as possible.


2.     Set a throughput and radio utilization objective: The goal is to run traffic through the system at a load level that is worst case, but typical of the proposed installation. For example even though the AP can support 300 Mbps concurrent TCP traffic by using two radios (2.4G and 5G) simultaneously, in some example use case perhaps only the 802.11a radio is active for mesh and exceeding 100 Mbps would be unusual.  The use case and expected peak or typical worst case throughput for each radio should be defined.


3.      The test setup is as follows


a.      Iperf server –wired connection-- Enclosure with switch, poe injectors, AP -----wireless---- Iperf Client


b.      Note: using a wireless client for the iperf client is important in that the radio needs to be active, alternatively a second enclosure with mesh AP and wired iperf client could be used.


4.      You need an indoor/outdoor thermometer like this one from radio shack (or an actual calibrated temperature probe for both inside and outside the enclosure)


4.      The dual temperature probe is needed to measure the “rise” in the enclosure, which is the amount of temperature increase over the outside ambient. For this reason make sure the inside probe is in the air and not directly (conductively) influenced by contact with anything and the ambient probe is a good distance away from the test setup to measure ambient air temperature and not be influenced by the test setup.


5.      Measure the temperature rise with the test setup idle and enclosure fans disabled. Most likely this will be about 3-5 °C.


6.      Next, start traffic running on the iperf setup. I recommend using UDP for testing since this allows a specific offered load. Otherwise iperf will just run at full speed (~150 Mbps TCP)

The recommended iperf commands are

Server: On a laptop connected to the enclosure port

iperf -s -u -w 512k

Client(Load) : associate a client to each desired radio and run

iperf -c <ipaddress of server> -w 512k -u -b 100M -t 20000 -i 5

This will send a 100 Mbps UDP stream for 20,000 seconds and give a report every 5 seconds

                 (any other iperf commands or ways to generate traffic such as Ixia, file transfers are fine also, we just want the radios active at the objective load)


8.      After a while the temperature will stabilize, likely at 10 °C to 25 °C rise internally over the ambient depending on the enclosure. It is recommend to run the test at least one hour, but more than 2 hours is likely not needed.  Anytime the temperature stops rising it is OK to end the test and record the temperature rise (=inside temp - outside temp).

It is recommend to run the test with any enclosure fans disabled (vented enclosure only) and then with fans enabled (and filters installed if applicable) to see how well the fans limit the temperature rise.

Once the temperature rise data is in hand, see the article indoor rated access points in outdoor enclosures which had information on how this information can be used to derate the operating temperature specfications for a given installation location.

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