Installation guide

14
1020 DUAL LEM
MODEL 1020 DUAL LEM (D-LEM)
The Model 1020 Dual Line Encoder Module (D-LEM) is used to multiplex two devices (e.g., a
door contact, a PIR, etc.) onto the LEM line. The LEM operates in an analogue mode allowing
the APLEX control panel to measure the signal amplitude from a zone, compare it with a preset
value, and therefore determine whether the particular zone is open (Alarm), closed (Restored),
disconnected (LEM-cover tamper switch open or Break in loop wiring) or shorted (Cross in loop
wiring). Transorbs and "spark-gap" staggered traces on each LEM printed circuit board protect
against lightning and induced voltage transients on the LEM line.
The three LEM-line conductors used by the D-LEM are designated LEM NEGATIVE (use
L black, if available), LEM CLOCK (use yellow), and LEM DATA (use green). It is good
practice to parallel the black wire with the red wire to provide a heavier negative return.
ON VERY LARGE SYSTEMS WITH LONG WIRE RUNS, THIS DOUBLING OF THE NEGATIVE
RETURN IS ABSOLUTELY NECESSARY!!
By convention only, these colours are connected in to
terminals 1, 3, and 4 respectively on the left side of the D-LEM and out to terminals 9, 11, and
12 on the right side of the D-LEM. The D-LEM tracking provides continuity through the printed
circuit board. This cable may be branched at any point by connecting it in parallel with the main
cable.