Ludlum Measurements 177, Руководство пользователя

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Model 177
Technical Manual
Section 8
Ludlum Measurements, Inc. Page 8-2 October 2018
discharged by R124. The average voltage on C122 is coupled through
HV
,
BAT
, and
ALARM TEST
switch to voltage-follower Pin 5 of U311. Pin 7 of
U311 drives the meter and recorder output.
Time Constant
The meter time constant is determined by R124 and C122. For a slower time
constant, C122 is paralleled by C101. When C101 is not used, it is connected
to Pin 7 of U311 (voltage follower), maintaining the same voltage level as
C122. This allows C101 to be switched in or out of the circuit without
transients.
Alarm
An alarm is provided by U021, Pins 1, 2, and 3. The alarm set control biases
the op-amp U021 for a low output. When the meter signal at Pin 3 exceeds
the bias of Pin 2, the output at Pin 1 goes high. Q102 and Q103 saturate,
allowing supply voltage to be coupled to:
Lamp voltage through R004.
Audio oscillator U16 through CR112.
R116 couples back to base of Q102, locking up the Alarm On.
Through CR113 to audio transformer T211, allowing full voltage for full
volume.
Through R111 to saturating current sink Q101 for external use.
Reset
Reset is provided by coupling a voltage to the base of transistors U012 pins
1, 2, 3, and 4, 5, 6. Both transistors saturate. One discharges C122, causing
the meter to zero. Pin 3 U012 turns Q102 off, allowing the alarm to reset.
Audio
A high on Pin 4 U111 turns the oscillator on, saturating Q111 with each
positive swing of the oscillator. T211 couples the pulses to the unimorph.
Audio volume is controlled by voltage, applied to Pin 2 of T211. This is
either 4.3 volts from the alarm circuit or 0 to 4.3 volts from external volume
control through emitter follower Q104.