SERIES
9900
9000
SERIES
GAUSSMETERS
SECTION VIII continued
Series-9900 Theory o f Operation
voltage, probe input impedance matching and calibration sources. Several
other lines control the flow of serial data from a monolithic 16-bit A/D
converter.
All clock lines used by the module are synchronized with the master clock
lines in the digital section of the gaussmeter. This reduces switching noise
and prevents harmonics and beat frequencies that could deteriorate the
overall performance of the gaussmeter.
Each module contains a 512-byte non-volatile EEPROM device programmed
with the module's operating characteristics; frequency response, offset
information, temperature coefficients, etc.
When measuring alternating (ac) fields, the module is configured to provide a
constant dc current to the Hall device in the probe. The magnitude of the
current depends on the type of probe being used (bulk or thin film) and the
present range of the gaussmeter.
The voltage output of the Hall device is instantaneously proportional to the
magnetic flux density being measured. This signal is ac-coupled into the first
amplifier stages, converted to a proportional dc level by a true rms converter,
and finally converted to a digital value.
When measuring steady-state (dc) fields, the module generates a 5 kHz
constant ac (sinusoidal) current to the Hall device. Again the magnitude of the
current depends on the type of Hall device and the present range. The
voltage output from the
Hall
device is an amplitude-modulated sinewave
proportional to the flux density being measured. This signal is ac-coupled into
the first amplifier stages, converted to a proportional dc level by a
synchronous demodulator and finally converted to a digital value.
The module provides a calibrated analog output to its rear-panel BNC
connector. In the ac mode, the signal is the actual field density waveform
calibrated to 3 Vrms full scale. In the dc mode, the signal is proportional in
amplitude and polarity to the field level, calibrated to -±3 Vdc. The signal
represents the raw (uncorrected) waveform produced by the Hall device.
VIII-F 4TH GENERATION HALL GENERATOR PROBE
The F.W. Bell 4th generation probe assembly consists of a Halt Generator
probe element terminated by a 9-pin circular, non magnetic twist-lock
connector. The connector houses a 512-byte non-volatile EEPROM device
programmed with the probes operating characteristics; frequency response,
field amplitude linearity, temperature response, and so on, as well as the
serial number, date code and device type information for the assembly.
Space is also provided to install a linearizing resistor when required.
Four of the connector pins interface to the Hall device itself. Another four
control the transfer of information to the EEPROM. The remaining pin is used
by the processor to sense if the probe is physically connected to the
interface module.
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