¶ Power Line (60 Hz)
Description:
Power line glitches usually look narrow in frequency, are centered around 60 Hz or one of its harmonics, and usually last for about 0.2–0.5 seconds in time.
In the United States, the mains power is alternating current (AC) at a frequency of 60 Hz. Because of this, quasi-periodic frequencies of 60 Hz and its harmonics (120, 180, etc.) are present in the LIGO data. Additionally, when large equipment that runs on this AC power, such as heater units or air compressors, switch on or off, glitches can occur at 60 Hz or one of its harmonics.
Power Line glitches have still been happening occasionally during O3 and O4, but at LIGO-Livingston during O4b we've also seen many similar-looking glitches around 62-64 Hz that are something else. For example,
this is a power line, while
this is something else that may make its way into a new glitch class. They may show one or two "eyes" at their ends, and loud ones may come with additional noise below 60 Hz.
Cause:
Equipment run at 60 Hz alternating current in the US.
Status:
Active.
Examples:
(3).gif)
Audio Example:
Make sure to wear good headphones!
More Information:
- For an example of finding and fixing one source of 60 Hz glitches at LIGO Hanford, see this electronic logbook entry from 17 November 2015
- For an example of fixing 60 Hz glitches at LIGO Livingston, see this electronic logbook entry from 20 March 2017