HP 437B Service Manual

HP 437B
Service Sheet BD1
8-20
SERVICE
The
analog-to-digital
converter
consists
of
three
parts:
a
ramp
generator,
a
@
comparator,
and
a
counter
(the
analog
timer
circuit).
The
ramp
generator
produces a voltage that ramps from -.78V to +10.0V. Upon receiving the
STRAMP signal from the Digital Section, the ramp voltage begins ramping
up. The comparator compares the low pass filter output from the A-to-D
input multiplexer to the ramp voltage. When the ramp voltage matches the
voltage from the low pass filters, the comparator issues the RAMPEND
signal. The analog timer measures the time between the STRAMP and
RAMPEND signals. The measured time is used by the Digital Section to
determine the power level at the input power sensor.
The recorder output circuitry scales the signal from the output of the low
pass filters to a voltage between OV and +1.0v that is proportional to the
power input at the power sensor. This voltage is sent to the RECORDER
OUTPUT connector on the back panel of the Power Meter. The
RECORDER OUTPUT voltage range is from OV to +1V for each power
range. This voltage is not corrected for the calibration factor. The
RECORDER OUTPUT voltage is set to 1.00V during calibration.
The 220 Hz multivibrator provides the 220 Hz square wave drive signals to
the power sensor and the synchronous phase detector. These signals are 180°
out of phase with each other. This ensures that the output of the
synchronous phase detector is a full-wave rectified voltage.
The 50 MHz Reference Oscillator provides a 50.0 +0.5 MHz output at 1.0
mW +0.7%, This output is used during operation to calibrate the individual @
power sensors used with the Power Meter. The output is provided at the
POWER REF connector on the front panel or the rear panel (Option 003
only).
Power Supply
The Power Supply provides three regulated voltages plus a fourth regulated
standby voltage. The three regulated voltages are +15V, -I5V, and +5V.
These voltages are used throughout the instrument. When the LINE switch is
set to STBY, these voltages are switched off.
The standby voltage is a regulated +5V. This voltage is connected to the
RAM components in the digital section. The standby voltage remains on
constantly, even when the LINE switch is set to STBY. This prevents data
loss when the Power Meter is in STBY mode. The standby voltage will
switch off when the line (mains) voltage is disconnected from the Power
Meter. A backup battery is installed in the Digital Section to prevent data
loss when the line (mains) voltage is disconnected.

HP 437B Specifications

General

Brand	HP
Model	437B
Category	Measuring Instruments
Language	English