Created by coupling an infrared sensor to a standard NASA initiator earned its developer NASA’s Patent Award. Dr. Alex Stein, founder of Harmon Sensors, received the award at a ceremony NASA hosted at the Johnson Space Center in Houston.
The innovative sensor measures bridge wire temperature in NASA initiators. At the heart of the system is a piece of industrial thermal processing temperature-measuring equipment familiar to many: the micro IRt/c sensor, manufactured by Exergen, Watertown, Mass.
The device is designed to measure the temperature of the bridge wire in the initiator as a function of the electrical current going through that wire. The wire is mounted inside a metal shell close to an explosive charge and is connected to electrical feedthroughs. When voltage is applied to the feedthroughs, it sends a current through the wire and heats it, raising the wire temperature to a value at which an explosive charge is triggered to actuate functions such as shearing a bolt.
Because initiators are used extensively in the aerospace industry, it is important to understand how the electric current running through the bridge wire may impact its temperature. The thin bridge (2 mils diameter) precludes the use of standard single-color pyrometers as a measurement tool.
Dr. Stein paired Exergen’s micro IRt/c to the initiator housing, allowing him to obtain a measurable signal from the sensor at the wire temperature of 572°F (300°C).