Rosemount 7D, Инструкция по эксплуатации

Страница: 38 / 54

T
HEORY
26
December 2000 Rosemount Analytical 748221-L Model 7D Thermal Conductivity Analyzer
5.2 ELECTRONIC CIRCUITRY
Electronic circuitry of the Model 7D is shown in the schematic diagram of drawing
654616. Internal circuitry of plug-in boards and other electronic assemblies is shown
in separate schematic diagrams, found at the end of this manual, and is described in
the following sections.
5.2.1 M
ASTER
B
OARD
The Master Board (PN 654620), Figure 2-6, provides two stages of amplification
utilizing integrated-circuit amplifiers AR1 and AR2.
F
UNCTIONS
A
SSOCIATED WITH
AR1
AR1
Gain Adjust Potentiometer R4. This screwdriver-adjustable, factory-set trimming
potentiometer determines feedback resistance for AR1 and thus permits adjustment of
AR1 gain from X1 to X100. This adjustment sets the sensitivity for Range 1, i.e., the
highest-sensitivity range.
R
ANGE
P
ROVISIONS
In the basic single-range Model 7D, a jumper is connected from TB3-1 to TB3-4, thus
routing the unattenuated output from AR1 directly to the non-inverting input of AR2.
During factory assembly of a dual-range or triple-range instrument, the jumper is
omitted and a front panel RANGE Switch is connected as shown below. The output
from AR1 is then routed to AR2 through a network that provides adjustable
attenuation for ranges 2 and 3.
RANGE
AR1 OUTPUT
ATTENUATION
RANGE SWITCH
POSITION
TB3 POSITION
1 X1, fixed 1 1
2 adjustable by R7 2 2
3 adjustable by R9 3 3
wiper 4
T
ABLE
5-1. R
ANGE
S
WITCH
C
ONNECTIONS
C
OARSE ZERO AND ZERO
-
SUPPRESSION
Pots R26, R6 or R8, depending upon range number, provide the zero correction at the
non-inverting input of AR1.