Rosemount 755, Инструкция по эксплуатации

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M
ODEL
755 O
XYGEN
A
NALYZER
6-6
748183-H Rosemount Analytical
December 1997
25 VAC
C31
.01uF
-
+
AR6
R56
149K
Q2
CR12
120 V
RMS
Q3
R60
100
R61
2.0
R62
1K
R58
5M
R88
5M
R55
700K
R59
700K
RT1
+15V
-15V
2
3
6
HR1 +2
F1
CR6
WO4
resistance of the bridge (R55, R56, R59, and RT1) equals 149 K.
If the temperature goes down, RT1 increases in resistance and causes the junction of
RT1 and R59 to go positive in voltage value. Since R55 and R56 are of equal
resistance, their junction is at zero volts. Therefore terminal 3 of AR6 is more positive
than terminal 2 and the base of Q2 is positive. Q2 conducts, allowing alternating
current to flow through heaters 1 and 2. The voltage drop across the heaters. when
completely cold, would be around 20 VAC and, when controlling, would be AC of very
low amplitude.
As the temperature increases the resistance of RT1 decreases and the junction point
between RT1 and R59 becomes less positive. Terminal 3 of AR6 becomes less
positive with respect to Terminal 2. The output of AR causes Q2 and Q3 to conduct
less. When terminal 3 equals Terminal 2, or is less than terminal 2, the output of AR6
is zero or less. Q2 and Q3 do not conduct and the heater would not be supplying heat
energy to the detector.
F
IGURE
6-4. D
ETECTOR
H
EATER
C
ONTROL
C
IRCUIT
6.4 DETECTOR LIGHT SOURCE CONTROL CIRCUIT
The detector light source control circuit maintains the light output from the bulb (DS1)
as uniform as possible, regardless of voltage fluctuations or aging of the bulb, see
Figure 6-5
The power source for the light bulb is a center-tapped secondary of transformer T1.
This AC voltage is rectified by CR7 and CR8, and filtered (C32), presenting an
appro8.5 V bus to the current-limiting Darlington configuration of Q4.Q4
controls the basic amount of current through DS1.
Amplifier U7 has a fixed value, approxi2.2 VDC on Terminal 3. The output of
U7 is positive, causing Q4 to conduct. As Q4 conducts, electrons flow from the center-