Seismic safety switch provides high-integrity earthquake protection

Its SA series of safety seismic switches are a good example of the company's seismic monitoring and protection systems which are trusted by the UK nuclear industry. The SA-3 seismic safety switch provides triaxial vibration detection and is suitable for protecting vulnerable structures from ground borne vibration events, incorporating a range of safe shutdown options depending on the application.

The SA-3 model features three high-integrity low-noise piezoelectric seismometers positioned at 90º to each other, along with the associated alarm circuitry housed within a robust weatherproof painted steel enclosure.

It is seismically qualified to IEEE-344 (Standard for Seismic Qualification of Equipment for Nuclear Power Generating Stations) and utilises technology operationally proven in harsh environments. The switch operates on seismic events and when the signal from any axis exceeds the pre-set alarm level, the alarm relay is activated.

The sensors comprise a system of matched piezoelectric elements arranged in a ‘reciprocal’ configuration, providing a functional test capability.  Application of a 1Hz signal to the calibration crystal element mechanically excites the measuring elements resulting in a defined signal output which can be used to perform a full loop check of the seismic switch. 

Such a facility is essential for applications where the switch is located in a hazardous area and requires full-proof testing on a regular basis.

As well as the usual seismic and EMC approvals the SA-3 switch is available for functional safety applications up to SIL-2 and can also be provided in an explosive-proof housing for intrinsically safe applications.