Gain Structure - Lab.gruppen PLM series Operation Manual

1. Three racks, each with two PLMs and a 32 A single-phase mains supply. The 32 A capacity is shared
between the two PLMs within the rack. This is beneficial as the two PLMs don't have to draw the
same current. The only limitation is that in combination they don't draw over 32 A.
2. Three racks, each with two PLMs and a 16 A three-phase mains supply. This requires central power
distribution to be configured as two 3 x 16 A circuits from 3 x 32 A. One phase is used for each PLM
within the rack. This has the benefit that each PLM has its own breaker, but they all have to operate
within the same limit of 16 A; therefore, more care must be taken to ensure that no breaker blows if
different loads are used.
The 230 V version of the PLM is equipped with a
slow-blow 30 A ceramic breaker.
10.2.2 Six PLM Series Devices with 100-120 V Mains Supply
If the mains supply is 115 V and the system requirement is 6 PLMs, then the mains capacity would need to
be able to supply two 3 x 30 A circuits. There are two methods of achieving this:
1. Two racks, each with three 230 V version PLMs and a 30 A three-phase mains supply. In the rack
the PLMs are connected between the phases, i.e. one between phase 1 and 2, one between phase
2 and 3 and the last between phase 3 and 1. Each 30 A mains breaker is shared between two PLMs
and the mains current is to some extent canceled. This has the benefit that the three PLMs don't
have to draw the same current; one can be allowed to draw a little more than the other two. The
only limitation is that in combination they don't draw over 30 A.
2. Two racks, each with three 115 V version PLMs and a 30 A three-phase mains supply. One phase is
used for each PLM within the rack. This has the benefit that each PLM has its own breaker, but they
all have to operate within the same limit of 30 A; therefore, more care must be taken to ensure that
no breaker blows if different loads are used.

10.3 Gain Structure

The PLM Series architecture provides gain adjustments at various points in the signal path and therefore,
various places for muting and level adjustment. Each mute or gain adjustment point serves a different
purpose. The signal flow diagrams in chapter 6 provide a useful reference for the signal path. The following
sections describe the various adjustment points, all of which are available via the Lake Controller software.
10.3.1 Input Headroom (Analog Inputs Only)
Input Headroom should be set to 12 dBu if the source can be limited to 12 dBu; otherwise it should be set to
26 dBu. This setting does not affect the other gain stages, or the overall noise floor; it allows control of the
appropriate headroom at the input stage only.
PLM Series Operation Manual rev 1.1.9
Application Guide
81