Ludlum Measurements 299335, Руководство пользователя

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Model 78 and 78-1
Technical Manual
Section 7
Ludlum Measurements, Inc. Page 7-2 March 2021
High Voltage Supply
High voltage is developed by blocking oscillator Q241, T141, and C244 and rectified by
voltage multiplier CR041-CR043, C041-C043, and C141. High voltage increases as
current through R241 increases, with maximum output voltage and Q241 saturated.
High voltage is coupled back through R034 to op-amp pin 2 of U131. Resistor network
R027, R132 completes the HV division circuit to ground. R027 provides HV limit from
1250-2400 when the
HV
control on the Cal/Switch board is at maximum. The regulated
HV output is controlled by the
HV
1 and
HV
2 potentiometers located on the Cal/Switch
board. This control provides the reference for comparator pin 3, U131. During stable
operation, the voltage at pin 2 of U131 will equal the voltage at pin 3 of U131. Pin 1 of
U131 will cause conduction of Q141 to increase or decrease until the HV finds a level of
stability.
Detector Overload
A voltage drop is developed across R031 and sensed by comparator pins 5, 6, and 7 of
U131 as detector current increases. When the voltage at pin 5 of U012 goes below pin 6,
pin 7 goes low, signaling U111 (µP) to send the
OVERLOAD
alarm to the LCD.
OVL
control (on Cal/Switch Board) provides adjustment for the overload set point.
Microprocessor (µP)
U111 controls all of the data, control inputs, and display information. The clock
frequency is crystal-controlled by Y221 and related components at 6.144 MHz. The µP
incorporates internal memory (ROM), storing the program information. U1 resets the
µP at power-up to initiate the start of the program routine. During the program loop, the
µP looks at all the input switches for initiation or status changes and responds
accordingly. U122 is a 256 x 8 bit EEPROM used to store the setup parameters. The
information is transferred serially from the µP. The EEPROM is non-volatile, retaining
memory even after power is removed.
Audio
Click-per-event, divide-by, and alarm audio pulse frequency is generated by the µP and
coupled to Q101. Q101 then inverts the pulses and drives the bottom of T101. Bias
voltage is provided by the volume control (R002) to the top of T101.