What is meant by dB attenuation in an SPD?
Generally this applies to surge protective devices (SPDs), which incorporate filters. The dB of attenuation stated is usually the point at which the filter has reduced the incident transient by 3dB (or the voltage by a factor of 20). A more effective surge filter will have a higher dB at a lower frequency. For example, an SPD with 60dB attenuation at 30kHz is more effective than a filter with 60dB at 100kHz. The attenuation can also apply to in-line, series connected, type SPDs used in data communications. In such a case the SPD should have a low attenuation (dB number) at the operating frequency of the data system. For SPDs protecting ac power circuits, it is common for SPD manufacturers to quote the dB result at 100kHz, rather than the frequency at which 3dB attenuation occurs. Rather than quote a single performance figure, a graph of frequency response from 10kHz to 1MHz is more useful. Performance above 1MHz is of little value as at these higher frequencies large variations will oc
