PCB Piezotronics, Inc. – Low Outgassing Sensors and Cables for Space Vehicle Vacuum Testing

Low Outgassing Accelerometers and Cables for Thermal Vacuum Vibration Testing

Aerospace & Defense Test Measurement? Sure We Do!

Exposure to the high vacuum level of a space environment induces material outgassing in ordinary accelerometers and cables. Any substance subjected to a vacuum has the potential to release trapped gasses. Contaminants from outgassing can condense onto nearby surfaces such as photo-optic devices and obscure them, rendering them useless during their intended application.

During random vibration or shock testing prior to flight, space craft payloads are often fitted with accelerometers in hard to reach mounting locations. As the space structure is built up around them, it can become impossible to remove the accelerometers. Sensors installed for ground vibration testing (GVT) must therefore remain on the structure even if they are no longer needed for testing purposes.

Accelerometers

Cables

Calibration

Many hermetic accelerometer designs naturally have low outgassing qualities. Cables with rubberized boots or shrink tubing typically do not have low outgassing qualities. For all non-metallic materials outside of a hermetic package required for an application in a vacuum environment, PCB® verifies that the material has less than or equal to 1% TML (total mass loss) and a CVCM (collected volatile condensable mass) less than or equal to 0.1%. This is verified either using NASA documentation or test results from an outside laboratory.

Leak testing on hermetic sensors can be performed. PCB® incorporates two levels of testing dependent on the required level of hermeticity documentation.

Stage 1 – A gross bubble test is provided on all hermetic accelerometers. The test verifies <1x10-3 cc/sec flow. This is a quick bubble test with a heated fluid. The heated fluid causes any internal gasses to bubble out and be visible during the test. Refer to Figure 1 for a schematic of the heated bubble test.

Stage 2 – A fine helium test uses a helium tank to pressurize the sensors. Refer to Figure 2 for a schematic of the Helium tank test set up. The fine leak test is a vacuum test, where the Helium tank is pressurized to 300 psi for a minimum of 30 minutes. A mass spectrometer vacuum leak detector then verifies a leak flow rate of <2x10-8 cc/sec.

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