CSIII (MODEL 4310B) User’s Guide
DS50003057A-page 34
2021 Microchip Technology Inc.
The gain servo is composed of two elements: the digitally controlled hardware gain
(DAC GAIN) and the software-implemented Numerical Gain.
FIGURE 5-7:
CBT Signal and RF Tuning.
The function of the DAC gain is to amplify the DC Level, measured at the clock Ramsey
interrogation points, to approximately 3 volts, to make optimal use of the resolution of
the 16 analog-to-digital converter which reads the CBT signal. The DAC gain varies
from 1.4 to 256 over the life of the instrument as 256/N, where N is an integer that
varies from 180 to 0. This relatively coarse adjustment is performed only when the DC
level falls below 2.0 V or rises above 4.0 V. A minor alarm (0x18) is declared when the
DAC gain reaches 256, which indicates that the CBT is nearing the end of its useful life.
The function of the numerical gain is to present a consistent discriminator slope to the
control servos, independent of the signal or background levels or DAC gain adjustment.
The numerical gain is a floating- point number, typically of order 1, which varies
continuously throughout instrument life so as to guarantee that the clock level is 2200
mV. If the clock level falls below 1320 mV or rises above 3080 mV a major alarm (0x01)
is declared.
In normal operation, the CsIII periodically measures the background, mid-way between
the clock transition and the Zeeman transition. The numerical gain is adjusted
continuously and the DAC gain is discretely adjusted if necessary.
5.6
MICROWAVE POWER SERVO
The short-term stability, accuracy, and environmental sensitivity of the CsIII are all
optimized when the microwave power in the RF resonator is optimized to provide
maximum signal level at the clock Ramsey interrogation points.
shows the microwave power dependence of the 7610 CBT signal,
measured at the clock Ramsey interrogation point as the output.
Summary of Contents for 4310B
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