Rosemount 755A, Инструкция по эксплуатации

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E
LECTRONIC
C
IRCUIT
A
NALYSIS
6-12
April 2000 Rosemount Analytical 245364-U Model 755A Oxygen Analyzer
6.7 BUFFER AMPLIFIERS U10 AND ASSOCIATED
ANTICIPATION FUNCTION
Refer to Figure 6-9. U10 is a non-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 10VDC.
The pressure-corrected output signal from U10 is routed to two output circuits:
•
Digital Output Circuit, Section 6.8
•
Analog Output Circuits for Recorder and Alarms, Section 6.9
F
IGURE
6-9. B
UFFER
, A
NTICIPATION
,
AND
D
IGITAL
O
UTPUT
C
IRCUIT
6.8 DIGITAL OUTPUT CIRCUIT
Refer to Figure 6-10. With front panel TEST Switch in position 1, 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.
-
+
U10
R30
R29
Differentiator
Network
ADC
71C03
8052A REF
DISPLAY
DRIVER AND
CONTROL
+15V
5V
U18
5V
REGULATOR
To Analog Output Circuit
(Figure 6-9)
DIGITAL
DISPLAY