Racal Instruments 2461 User Manual page 33

2461Type C User Manual
counted in the start counting chain. When the capacitor is
discharged then the count in the start counting chain
represents the error between the opening of the gate and the
next counting edge of the reference (See Figure 3-2).
This process is repeated at the closure of the gate by a
separate TEC and counting circuit (the stop counting chain).
After the measurement results have been read out of all
counters, calibrated pulses derived from the reference are fed
to the TEC circuits. This is done for two pulse widths for both
start and stop circuits. The resultant counts are then used to
calibrate the TEC circuits. Once these are calibrated the value
of the frequency of the input can be calculated to a much
greater resolution.
Racal Instruments  1998
Theory Of Operation 3-6
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