Instruction Manual

748213-S April 2002

5-7 BUFFER AMPLIFIERS U8 AND U10 WITH ASSOCIATED ANTICIPATION FUNCTION

Refer to Figure 5-8, page 5-12. 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 5-8, page 5-10).

Model 755R

Analog output circuits for recorder, V/I and alarms (See Section 5-9, page 5-11).

5-8 DIGITAL OUTPUT CIRCUIT

Refer to Figure 5-7 below. 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.

 

 

R37

 

R38

 

 

 

 

 

2M

 

100K

 

 

 

TP11

 

C38

R39

 

 

 

 

 

.22uF

TP16

REF 8052A

 

 

C31

 

 

11K

 

 

 

 

1.0uF

R61

 

 

 

 

DIGITAL

 

 

 

 

 

 

 

R30

-

 

 

 

DISPLAY

 

 

 

 

 

 

20K

1M

 

 

ADC

DISPLAY

 

 

 

 

 

71C03

DRIVER AND

 

 

 

U10

 

 

 

R36

 

 

 

 

CONTROL

 

C36

+

 

 

 

 

 

 

 

R49

C40

 

 

1M

.47uF

 

 

 

 

 

 

1.0uF

 

 

R31

 

 

 

20K

 

 

 

 

 

 

 

U18

 

2K

 

 

 

 

 

 

 

 

 

 

TP16

5V

+15V

 

 

 

 

 

 

 

 

 

 

 

5V REGULATOR

 

 

 

 

 

 

 

 

 

 

 

To Analog Output Circuit

 

 

 

 

 

 

 

(Figure 6-8)

 

 

 

Figure 5-7. Buffer, Anticipation, and Digital Output Circuits

5-10 Circuit Analysis

Rosemount Analytical Inc. A Division of Emerson Process Management