Gain Structure - Lab.gruppen PLM series Operation Manual

12. Application Guide
▸ 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.
▸ 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.
All of the examples given will work, although the first examples for both 230 V and 115 V operation have a
slight advantage due to their "power sharing" ability.
As the PLM is equipped with PAL, the power supply will limit its mains current draw (both momentary
current draw and current draw over time) to be less than 28 A for the 230 V version and less than 53 A for
the 115 V version over time.
The 230 V version of the PLM is equipped with a slow-blow 30 A ceramic fuse.
The 115 V version is equipped with a metal cylinder instead of a fuse due to suitable fuses at the required
current rating being unavailable.
Safety approved equipment is not required to have a fuse, as long as this does not pose any fire hazard
under fault conditions, as is the case with the PLM.

12.3 Gain Structure

The architecture of the PLM Series provides gain adjustments at a number of points in the signal flow path.
Thus, there are many places in which one can adjust the levels in the PLM. Each point serves a different
purpose. The following can be used as guidelines for adjustment of the gain settings, from input to output.
The block signal flow diagram (figure 8.1 on page 32-33) is useful as a reference to help in understanding the
signal path through the PLM's architecture.
Locations for setting gain in the following para-
graphs refer to the Lake Controller software.
Input headroom (Analog Inputs). As a rule, this should be set to 12 dBu if the source is (or can be) limited
to 12 dBu; otherwise it should be at 26 dBu. This setting has no direct influence on the rest of the gain
stages in the PLM, or on the overall noise floor. The PLM's variable input gain is strictly meant to provide the
appropriate headroom at the input stage. (Adjustments made in I/O Config window, Input Configuration, left
side.)
Input mixer. This setting should be left at "0" or most setups. If only one input channel is used, the other
can be set to "- inf". (Adjustments made in I/O Config, module pane.)
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PLM Series Operation Manual rev 1.1.3