Thermal Vacuum Vibration Testing
PCB's Low Outgassing Accelerometers and Cables are standard products whose specifications are designed for use in high-vacuum applications such as satellite ground testing and in space.
Highlights:
- Vibration measurements in Thermal Vacuum or Space environment
- Welded hermetic accelerometer designs have low outgassing qualities
- Hermeticity testing is performed on all hermetic products at PCB®
- Cables with strain relief use polymers are verified for Total Mass Loss and Collected Volatile Condensable Material
- Materials selected using NASA guidelines
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 obscuring them, rendering them useless during their intended application.
Many hermetic accelerometer designs have inherent 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 material) less than or equal to 0.1%. This is verified either using NASA documentation or test results from an outside laboratory.
In any application involving a vacuum environment, the important things to consider when selecting low outgassing accelerometers and cables are: welded hermetic housings, polymers and epoxies that have low TML and CVCM values, and leak testing services for low outgas verification of accelerometers.
Low Outgassing ICP® (IEPE) Accelerometer Types & Their Applications
Mini-triaxial Accelerometers
Spacecraft structures are often made of thin, light-weight materials and require low mass accelerometers. Full-scale spacecraft random vibration responses are three-dimensional, so the combination of a triaxial, low-mass ICP® (IEPE) accelerometer with low outgassing properties is recommended. PCB® Model 356M208 meets this requirement with a low mass of one gram and low outgassing characteristics.
Shock Accelerometers
Separation of booster stages cause shock events that may be transmitted to the spacecraft payload. Low outgassing ICP® (IEPE) accelerometers such as PCB® Model 350M72 may be launched with the payload or used in a vacuum chamber to simulate launch conditions.
High Temperature Accelerometers
Environmental stress screening is often performed in thermal vacuum chambers to verify operating characteristics. PCB® Model 357A07, (p. 10) offers a hermetic, low-mass package with a wide operating temperature range from -100 to +500 °F (-73 to +260 °C).
Frequently Asked Questions
- Accelerometers are designed with hermetic housings and connectors to ensure there is no outgassing.
- PCB’s hermetic connectors are designed using compression metal to glass bonds to provide both electrical insulation and a hermetic seal. The melt occurs during a 90 to 120 minute process at approximately 1000°C. Each connector is leak rate tested for hermeticity.
- We have two levels of hermeticity - gross bubble test and fine helium leak test.
- The gross bubble test verifies a leak rate with less than 1x10¯³ cc/sec flow. (Variation of MIL-STD-883E, Seal Test Method 1014.10, Section 3.3.1).
- For fine helium leak test, accelerometer and connectors are pressurized in helium. A mass spectrometer vacuum leak detector than verifies a leak flow rate of less than 2x10¯8 cc/sec.
- The cables fulfill the requirements to ensure that the materials have less than or equal to 1% TML (total mass loss) and a CVCM (collected volatile condensable mass) less than or equal 0.1%.
- A Standard test Method for TML and CVCM was developed by ASTM (American Society for Testing and Materials). Standard: ASTM E595 “Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment”.
- The Products are tested in accordance with the report NASA RP-1124, “Outgassing Data for Selecting Spacecraft Materials”. PCB uses these materials that NASA has previously tested to be low outgassing.
- PCB uses low outgassing cable materials such as FKM and FEP, which are known to have low TML and CVCM values. The cable assemblies are vacuum baked out before delivery.
- PCB does not provide TML and CVCM values.
PCB also provides space qualified sensors for use in orbit upon special request. They are qualified to customer specific acceptance test criteria such as radiation hard, thermal cycling, EMI/RFI, and shock and vibration.