Transceivers must be installed in a NEMA–4 rated secondary enclosure or instrument box to protect them from moisture and extreme temperatures. Use of a secondary enclosure is often required to comply with the transceiver manufacturer's warranty.
Transceivers are packaged in weather–resistant, steel enclosures during manufacture, but these enclosures must also be protected during outdoor use.
For reliable operation of the transceiver, temperatures within the instrument box must be maintained between –20 and 70°C.
Cold weather is not usually a cause for concern because electronics generate enough heat during operation to remain above minimum operating temperature. However, heat may accumulate to raise temperatures beyond the specified maximum when:
|•||The sun shines directly on an enclosure|
|•||Ambient temperature is high|
|•||Heat generated by electronic components is not dissipated|
Excess heat can shorten the life of the transceiver or cause it and other electronic components to stop functioning.
Many transceivers have an alarm that can be set for when temperature reaches a predetermined point (e.g., 65°C); however, these alarms do not shut off the transceiver.
To protect instream monitoring electronics from overheating, researchers have used the following methods:
|•||Installing the instrument box in a location that is sheltered from direct sunlight|
|•||Surrounding the box with reflective materials|
|•||Installing small fans and/or air vents fans in the enclosure|
|•||Burying the secondary instrument box|
Burial works well, as earth is a natural thermal insulator from both cold and heat. Burial also provides full or partial camouflage of the instrument box, which reduces the risk of vandalism.
Disadvantages to burial arise in accessing the equipment during heavy rain or when snow has covered the box. Burial may also increase the risk of flooding the box during high stream flows.
Ancillary equipment such as computers and batteries housed in a secondary instrument box are also effected by temperature fluctuations. Most lap tops will cease to operate at temperatures below about –6°C or above 38°C, and low temperatures can affect their screens.
Battery storage capacity also decreases with lower temperatures; thus cold weather can shorten the time a system can operate before batteries must be recharged or replaced. Temperature effects on batteries can be moderated using the same methods used to protect the transceiver.
Additional considerations in selecting a secondary instrument box include:
|•||Stability in windy conditions|
|•||Ability to vent battery fumes and heat|
|•||Portability, meaning the weight, size, and shape of the box, as well as any handles or attachment points|
|•||Color in terms of heat from light absorption vs. reflection|
|•||Durability in terms of resistance to vandalism|