Rosemount 755, Инструкция по эксплуатации

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I
NSTRUMENT
T
HEORY
748183-H
5-7
Rosemount Analytical
December 1997
E
LECTRONIC
R
ESPONSE
T
IME
If readout is noisy despite observance of the precautions mentioned, obtain slower
electronic response by counter-clockwise adjustment of R20, Figure 3-1.
5.3 ELECTRONIC CIRCUITRY
Electronic circuitry is shown in the circuit-door schematic diagram, DWG 632363, and
is described briefly in the following sections. For detailed circuit analysis refer to
Section Six. Schematic diagrams and other engineering drawings are placed at the
back of this manual.
5.3.1 D
ETECTOR
/M
AGNET
A
SSEMBLY
A cross-sectional view of the optical bench and detector assemblies is shown in Figure
5-3B. Source lamp DS1 powered by a supply section within the case circuit board
assembly, see Section 5.3.3, directs a light beam onto the mirror attached to the test
body. The mirror reflects the beam onto dual photocell BTI, BT2. The difference
between the signals developed by the two halves of the photocell constitutes the error
signal supplied to the input of amplifier AR1 on the control board assembly. Amplifier
AR1 drives AR2, which in turn supplies the restoring current to the titanium wire loop
on the test body, refer to Section 5.1.
E
LEMENTS OF
D
ETECTOR
T
EMPERATURE
C
ONTROL
C
IRCUIT
Detector temperature is sensed by thermistor RT1, an integral part of the detector
assembly, see Figure 5-3B. The thermistor provides the input signal to the detector
temperature control section of the case circuit board assembly. The output from this
section is applied to two heaters within the detector/magnet assembly: HR1. mounted
on the top of the magnet, and HR2, mounted permanently on the rear of the detector
assembly.
5.3.2 C
ONTROL
B
OARD AND
A
SSOCIATED
C
IRCUITRY
The control board contains signal-conditioning and control circuitry. The board is
mounted on the inside of the analyzer door, as shown in Figure 1-2.
The control board contains the following:
I
NPUT
A
MPLIFIER
AR1
This amplifier receives the error signal from the dual photocell of the detector
assembly and, in turn, drives amplifier AR2.
A
MPLIFIER
AR2
AND
A
SSOCIATED
Z
ERO AND
S
PAN
C
IRCUITRY
Amplifier AR2 supplies the restoring current to the titanium wire loop of the test body
within the detector assembly. Front-panel ZERO Control R10 applies an adjustable
zero-biasing signal to the input of AR2, to permit establishing a downscale calibration
point on the meter scale or recorder chart. With downscale standard gas flowing
through the analyzer, the ZERO control is adjusted for the appropriate reading.