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Intelligently heating your computer

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article image Basic Proportional Control Feedback Loop
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Extreme cold can be a bigger problem than heat for computers. Frigid temperatures can, for instance cause display distortions such as spotting and motion blur, corrupt the output of onboard components in unpredictable ways, or even trigger system failure. 

Outdoor industrial sites located in icy environments and seeking to add digital control and automation will need to consider these problems.

Any petroleum industry line technician who has had to manage a panel HMI on an arctic oil rig will confirm that protecting computers from freezing cold is at least as much of a problem as managing heat. Cold isn’t less of a problem; it’s a bigger one. Adding external heaters is inefficient and, often ineffective. 

The solution lies in building systems with built-in heating controls. Unfortunately, many systems equipped with heating controls don’t go much beyond the average mirror defogger. 

Industrial applications need more than corner-store tech

A computing system that will be used in open, icy cold environments will need something more than just the basic mirror defoggers. These simple on-off heaters are referred to as ‘bang-bang control loops’, which in sensitive applications are too prone to premature system failures, hardware deterioration, and performance degradation to be of much use. A built-in heating system cannot simply set a target temperature and let the heater run. Advanced industrial computing hardware demands more sensitive controls, where the system temperature is adjusted relative to a target state that is constantly measured: an intelligent heating system.

Proportional controls for intelligent heating

Proportional heating controls deliver a spectrum of wattage rather than just full on/ full off. As shown in the diagram below, electricity supply is calibrated according to a sensor that must monitor heat output, managed by software systems that constantly compare the relationship.  

In this figure we see the basic components of a proportional feedback design. The temperature sensor feeds its output to a comparator, which then instructs the wattage controller (PWM) to either shut down the system (because things are too hot), or increase or decrease electrical output, and in turn the heat. Changes in heat output are registered by a thermistor, which then feeds that information back to the comparator. The control loop is a continuous cycle, and can only be said to end when it breaks out of the loop and turns itself off. For all of these reasons, even crudely precise proportional controls can deliver considerably greater system efficiency and safety in comparison to a bang-bang approach.

Engineering proportional controls

The tricky part in the design is the conservation of system resources, both in terms of software and hardware. This is a challenge when calibrating electrical output to target temperatures. Guaranteeing that the electrical supply delivers predictable heat output for each temperature in the target range is not as easy as it sounds. For one, each hardware platform carries a unique heat profile, and will exhibit unique behaviour at different temperatures. For another, hardware components can sometimes behave erratically relative to the overall system and may even cause a system crash.

Consequently, considerable experimentation and measurement of each platform is required to calculate heat curves across the full range of electrical supply. In this way, the underlying software may be tailored to each platform to consistently deliver the target conditions.

An overview of a working design

With proportional controls, when an automated heating system receives a power-on signal, its comparator first checks the temperature, and finds that its thermistor is registering, say -40°C. The heating elements are thus activated at full power. The software subsystem then continuously monitors wattage relative to heat output; as changes in temperature are logged by the thermistor, the values are passed to the comparator, which decides whether or not to continue powering the system, and then next, through the controller that decides how much power to cut (or add).

Eventually, the system will heat to a temperature somewhere just beyond 0°C, whereupon the controller will either establish a state of equilibrium, or if the heat generated by internal platform components is great enough to maintain the system above the target temperature, the comparator will turn it off. This is the sort of refinement and efficiency offered by proportional control; it is what puts the intelligence into an intelligent system.

Wrapping it all up

By taking the time and care to select the right components, build effective system fail-safes, and perform extensive testing and full platform profiling, a safe, reliable heating system will intelligently support computer operations over an extremely wide range of cold temperatures that would render other platforms useless.

The latest line of panel computers from Moxa , the EXPC-1319 now comes with Moxa IHS Intelligent Heating System. Moxa has developed a number of patented technologies for IHA that provide a safe, reliable, and energy-efficient heating solution, ensuring these computers will rise up out of the freezing cold to securely and dependably deliver the performance required for mission-critical industrial applications.

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