There is often the need to deploy computer systems at environmental extremes for monitoring purposes. A Windows, GNU/Linux, or FreeBSD/OpenBSD operating system is installed on the computer. Environmental measurement sensors are connected to the computer using USB, RS-232 or RS-485/RS-422 interfaces. Data is cached to an SD card or flash-based hard-drive. The computer can be networked and a VPN system used for remote access. WiFi access points (such as the one shown above) can be interfaced with the system.
The above picture shows two single board computers in an enclosure with a Power-Over-Ethernet (PoE) power injector. Also visible is a network switch. All of the hardware is powered using AC-to-DC converters with an output voltage of 12 VDC.
There is a growing trend to use fanless computers since fans have a propensity to break in cold or hot weather at a field site. In addition, systems such as Raspberry Pi or an Arduino-based board are popular due to low cost and small size.
However, most single board computers (SBCs) such as the Raspberry Pi are prone to filesystem corruption if there are power cuts. This is because the SBC root file system is often FAT32. After years of testing these systems at cold temperatures, I am convinced that most SBCs are not reliable at temperature extremes.
I've tested the fitlet2 system from CompuLab for some time. This is a fanless SBC with an Intel processor that is specified for low temperature operation. The computer will operate at temperatures as low as -50 deg C and as high as 112 deg C and at 12 VDC using power supply sources commonly available at a field site.
The computer is slightly challenging to assemble, and the user has to select appropriate SDRAM and flash memory, but the system is robust and will operate at hot and cold temperatures often associated with extreme environmental locations. Note that the Intel Atom processor line might have some issues with the Linux kernel and random crashes due to kernel or power supplies. This can be mitigated by changing the speed of the processor by using a CPU frequency scaling utility.
Another great choice for this type of application is any of the SBCs from VersaLogic. These are small and rugged SBCs that are designed for high-reliability applications. Most of the SBCs offered by this company will operate over an Industrial temperature range of -40 deg C to 85 deg C.
To adequately use a computer system for environmental measurements:
- Choose a single board computer (SBC) that is designed to function at temperature extremes.
- Ensure that the SBC and associated hardware can run on a power supply of 12 VDC for off-grid and solar-power applications.
- Do not use a SBC with a file system that is easily corrupted due to power cuts. Use reliable flash-based media, not hard-drives with moving parts.
- Ensure that the SBC can fit into an enclosure that is easily deployed at a field site. Use zip-ties, grommets, and rail-mounting systems to ensure that all of the network hardware can fit into the enclosure.
- Extensively test the system before deployment. Systems can easily fail at a field site, so it is better to initially test any system at an accessible location before deploying the system at a field site that can only be accessed during a few months of the year (i.e. during the summer).