ESS, HALT and HASS Accelerometer Considerations

Sensors in Extreme Environments

Environmental Stress Screening (ESS), Highly Accelerated Life Testing (HALT) and Highly Accelerated Stress Screening (HASS) each involve long duration cycling in terms of vibration, often accompanied by cycled temperatures and/or pressures. These extremes of vibration, temperature and/or pressure, which are physically taxing and are intended to prove, degrade or terminate the functioning of the product or structure under test, can be just as taxing on the monitor accelerometers providing feedback to the vibration controller.

In this extreme environment, specially designed and tested ESS versions of ICP® low impedance piezoelectric accelerometers are a great choice for a number of reasons. Foremost, special design and manufacturing considerations in the ESS versions of ICP circuits minimize the chances for failure due to thermal cycling in this critical input component of shaker control systems. For quality assurance, ESS accelerometers are thermally cycled as a proof test prior to production acceptance. The low impedance signal path is ideal in the environment that can be extremely hot, cold or humid - the latter being an extreme challenge when operating piezoelectric vibration sensors in traditional charge mode operation.

Addressing the challenge of thermal range, ESS versions of ICP accelerometers handle standard operation up to 325 degree F. For operation in extreme environments (up to 500 degree F) there are also specialized ceramic sensing elements which are operated with remote signal conditioning for impedance conversion. As far as low temperature operation, standard ESS versions of ICP accelerometers operate down to -100 degree F and special cryogenic ICP accelerometers are designed for temperatures as low as -320 degree F. Regardless of temperature extremes, the solid state style operation and no moving parts of the rugged ICP accelerometers can provide decades of reliable service in the most extreme environments. Many of the ESS accelerometers are also available with integral low pass filtering which is useful for removing out of band excitation which can sometimes be found in HALT and HASS testing.

An additional consideration is to ensure that the accelerometers are hermetically sealed by laser welding. Properly joined laser welding has proven to enhance the reliability of both the connector joint integrity and the overall seal of the sensor housing in adverse environments including humidity and thermal shock. As far as connectors and cabling, ICP accelerometers still afford the benefits of low impedance operation and cabling. While the typical is still a 10-32 microdot connector coupled through PTFE insulated signal cable, an accelerometer choice with solder terminals could be used for easy cable repair of the inevitable fatigue failures in extreme environments like repetitive shock stress screening.

This reliability and simplified operation of PCB’s accelerometers have made them the choice of many OEM vendors of vibration control systems and environmental chambers. If you have any questions about this application please ask your PCB field application engineer or contact us here directly at The Modal Shop.