Published on: October 31, 2019 By: Valcor Aerospace Avionics Cooling Using Motor-Operated Proportional Control Valves The role of avionics in modern air and spacecraft are becoming more complex as they control more of the functions in these vehicles. Ultra-high-speed flight computer microprocessors and related support chips perform most efficiently in a very narrow band of operating temperature. Solid State Relays (SSRs) controlling other parts of the vehicle system generate substantial heat when energized. As flight vehicle designers work to reduce the weight of the vehicle, they are moving towards Fly-By-Wire (FBW) systems to control most or all aspects of the vehicle flight controls. FBW systems require a lot of power to actuate the sub-systems in a modern aircraft. Power demand is at its highest during takeoff and landing, when rudder, stabilizer and flaps are in constant motion. In spacecraft, roll, pitch, and propulsion thrusters are controlled electronically. Maintaining the ideal avionics operating temperature requires a precision liquid cooling system capable of fast response to changes in the thermal load imposed by the avionics. Simple air-cooled systems are a thing of the past. Air cooling cannot provide the necessary temperature precision in response to load changes. Precision cooling of such sensitive avionics and related systems requires a complex system of temperature monitoring and closed-loop feedback control of the cooling media. Many different approaches are considered when designing the temperature process control scheme of an avionics cooling system. Most industrial commercial off-the-shelf (OTS) temperature controllers monitor the coolant and turn an electric heater on and off to achieve the desired temperature. While relatively inexpensive, they are unable to react to rapid changes in coolant temperature. The electric heater must warm up, and cool down, in response to changes in the coolant temperature. This could take many seconds. For air and spacecraft, these OTS solutions are certainly not sufficiently reliable or fit for use in avionics cooling systems. For flight applications where coolant temperature must be precise to protect sensitive electronics, the use of a proportional flow controller will provide faster response to changes in process temperature. Proportional flow control is achievable in many ways. Traditionally, a pulse-width modulated (PWM) solenoid valve is used to control the flow of the coolant. Pulsing the valve controls the desired temperature of the process media by increasing or decreasing the coolant flow. Also known as the bang-bang approach, the solenoid valve is pulsed by the temperature controller to alter the flow of coolant to precisely maintain the desired temperature for the electronics. Typically fast-acting, the solenoid valve provides good temperature control when new, but solenoid valves can have a finite life in high-frequency cycling, continuous duty service. As the valve wears, its performance degrades. Longer...