Rosemount 755, Instruction Manual

Page: 60 / 94

M
ODEL
755 O
XYGEN
A
NALYZER
5-8
748183-H
Rosemount Analytical December 1997
If the analyzer is to incorporate a zero-suppressed range option, the required zero
offset is obtained by insertion of the zero suppression resistor module into receptacle
J6. This module may be inserted either during factory assembly or in subsequent field
installation of a range conversion kit.
Front-panel SPAN Control R4 provides continuously variable adjustment of closed-
loop gain for AR2, to permit establishing an upscale calibration point on the meter
scale or recorder chart. With upscale standard gas flowing through the analyzer. the
SPAN control is adjusted for the appropriate reading.
A
MPLIFIER
AR3
AND
A
SSOCIATED
R
ANGE
C
IRCUITRY
During factory assembly, or in subsequent field installation of a range conversion kit,
the analyzer is provided with the desired range option by inserting the appropriate
range resistor module into receptacle J3. In subsequent operation, the desired
operating range is selected with front-panel % RANGE switch SW1, which determines
the feedback resistance for AR3.
O
UTPUT
S
TAGE
Amplifier AR4 and Transistor Ql. The signal from range amplifier QR3 is routed
through phase lead adjust R20 to an output stage consisting of AR4 and Ql.
Potentiometer R20 provides a continuously variable adjustment of 5 to 25 seconds for
the electronic response time (90% of fullscale), and is factory-set for 20 seconds.
The output from Ql is routed to the following:
1. Output resistor network, Item 5.
2. Current output receptacle Jl. This connector accepts any of the three optional plug-
in current-output boards.
3. Alarm output receptacle J2. This connector accepts the optional dual-alarm
amplifier board.
O
UTPUT
R
ESISTOR
N
ETWORK
The output signal from Ql is routed to ground via a voltage divider. A selector plug
associated with the voltage divider provides a selectable output of 0 to 10 mV, 0 to 100
mV, 0 to 1 V, or 9 to 5 VDC to drive a voltage recorder. Potentiometer R38 permits
adjusting the meter to agree with the recorder.
5.3.3 C
ASE
B
OARD
A
SSEMBLY
The case circuit board contains power-supply and temperature-control circuitry. The
board is mounted within the analyzer case, near the top, as shown in Figure 1-2.
As shown in DWG 632363, the various circuits operate on main power transformer T1.
During instrument assembly, the two primary windings of T1 are factory-connected for
operation on either 120 VAC or 240 VAC, as noted on the name-rating plate.
The case board contains the following: