Pulse link repeater

In telecommunications, a pulse link repeater (PLR) is a device that interfaces concatenated E&M signal paths.

"Note 1:" A PLR converts a ground, received from the E lead of one signal path, to -48 Vdc, which is applied to the M lead of the concatenated signal path.

"Note 2:" In many commercial carrier systems, the channel bank cards or modules have a "PLR" option that permits the direct concatenation of E&M signaling paths, without the need for separate PLR equipment.

Source: from Federal Standard 1037C