Teledyne UA-6, Installation And Operation Manual

Page: 60 / 122

UA-6 Detector
Section 4 Theory of Operation
4-6
When the UA-6 is switched to operate, U403B begins to oscillate
at a rate of 13 Hz. Initially, only U407 is clocked by U403B.
During the first 10 minutes of operation U403D limits the lamp
current to 270 mA and the power LED will be red. After approxi-
mately 10 minutes, U407 pin 3 will go high producing the fol-
lowing results: U403B will begin clocking U405; U403A inhibits
any further clocking of U407; U402D and Q405 shift the oscil-
lator frequency of U403B to about 500 Hz.
Now that U405 is being clocked, the circuit will begin to adjust
the lamp current to the value selected by S401. U405 performs
two functions: The three most significant bits adjust the fre-
quency of U403B progressively slower in 8 steps to around 50 Hz.
This helps maintain the rate of lamp current change since the
amount of change per step increases as U405 advances its count.
U405 also adjusts lamp current by biasing U402B and the regu-
lating photocell in the optical unit. As the lamp current decreases
from 270 mA, U402A will change the power LED to green and
shift the frequency of U403B to around 1 Hz.
U403C monitors lamp current through R463. When the current
through R463 matches that selected by S401, U403C will stop
the oscillator U403B. This latches the entire circuit. Now the bias
provided by U405 will remain fixed and the regulating photocell
in the optical unit will maintain the lamp brightness.
Should the lamp current fall below 183 mA or exceed 260 mA
after the 10 minute warm-up cycle, U402A will change the power
LED from green to red. This notifies the user that the lamp
current is out of regulation and may require adjustment. To rein-
itialize the circuit, rotate the sensitivity switch (S05) to “SET
LAMP & OPTICS”. U402C will send a reset pulse to U403C and
U405. Lamp current will change to 270 mA and slowly adjust
down to the value selected by S401. Within 2 minutes the current
should be set and the power LED green.
4.2.9 Power Supply
The UA-6 power supply has five voltage sources: +24 VB, unregu-
lated, supplies power for optical unit lamps; +24 V, unregulated,
main +24 V source, also provides power to +15 V regulator VR01;
+15 V, regulated by VR01, supplies power to all analog and
digital circuitry. (VR01 is a linear regulator); -24 V, unregulated,
only -24 V source, also supplies power to -15 V regulator VR401;
-15 V, regulated by VR401, supplies power to all analog and
digital circuitry (VR401 is a linear regulator).
When the UA-6 is connected to an AC power source and is in the
standby mode, three heater resistors (R449, 516, and 523) warm
the unit. This prevents moisture from condensing inside the unit
should it be in a humid environment.
CAUTION
These resistors should not be touched when power is con-
nected to the UA-6.