C
IRCUIT
A
NALYSIS
748213-P Rosemount Analytical June 1997
6-11
Model 755R Oxygen Analyzer
TP16
R37
2M
R38
100K
-
+
U10
C36
.47uF
R30
20K
R31
2K
TP11
C31
1.0uF
R36
1M
R61
1M
C38
.22uF
TP16
R49
20K
R39
11K
C40
1.0uF
ADC
71C03
8052A
REF
DISPLAY
DRIVER AND
CONTROL
+15V
5V
U18
5V
REGULATOR
To Analog Output Circuit
(Figure 6-8)
DIGITAL
DISPLAY
6.7 BUFFER AMPLIFIERS U8 AND U10 WITH ASSOCIATED
ANTICIPATION FUNCTION
Refer to Figure 6-8. U8 is a unity gain amplifier that provides zeroing capability and a
buffered output for the anticipation circuit feeding U10.
U10 is an inverting buffer amplifier that incorporates an anticipation arrangement in its
input network, thus providing slightly faster response on the readout device(s).
Potentiometer R30 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.
Since the anticipation network attenuates the signal, a gain of 10 is provided by the
feedback network associated with U10 to restore the signal to the desired fullscale
range of 0 to 10 VDC.
The output signal from U10 is routed to two output circuits:
Digital output circuit (See Section 6.8).
Analog output circuits for recorder, V/I and alarms (See Section 6.9).
6.8 DIGITAL OUTPUT CIRCUIT
Refer to Figure 6-7. The output signal from buffer amplifier U10 is routed through an
attenuator and filter network to an integrating analog-to-digital converter. It converts
the signal into an equivalent digital value in the range of 0.00% to 99.99%. Any value
above 99.99% will be preceded by an over-range bit, for example, 1.1123.
The output of the ADC consists of binary-coded decimal characters that are input to
the liquid crystal controller and display chip characters sequentially in time. The BCD
characters are converted into seven-line codes to drive the bar segments of the liquid
crystal display.
A separate regulator circuit, which operates from the +15 VDC supply, provides a
regulated 5 VDC for the digital functions associated with the display.
F
IGURE
6-7. B
UFFER
, A
NTICIPATION
,
AND
D
IGITAL
O
UTPUT
C
IRCUITS
