Bergoz MX-BPM, Руководство пользователя

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Synchronous detection of the if signal requires a reference frequency. This
reference is generated by a voltage controlled oscillator (VCO). A phase detector compares
the reference with a filtered sample of the carrier frequency and controls the VCO in a
phase locked loop (PLL). The dynamic response of the PLL loop is controlled by the loop
filter.
If the pick-up signals applied to the BPM signal processor inputs are not in
phase, the switching from one input channel to the next would produce sudden phase
jumps of up to 180˚. Even a fast PLL loop would have difficulties to follow and this
would seriously limited the maximum scanning frequency.
Many of the BPM systems presently in use require indeed precise phase
matching on all signal cables coming from the pick-ups. We preferred to solves this
problem in a different way. Our loop filter has an electronic switch (not shown in Fig. 1)
which reduces the time constants during 10 µs after channel switching. This allows the
receiver to settle on a new signal level; as a result, phase errors up to 180˚ are tolerated.
Fig. 3 Frequency response of if-amplifier (BPM processor for ALS)
Bandwidth (-3 dB) = 434 kHz
Marker indicate the sidebands for a revolution frequency of 1523.4 kHz
Electromagnetic interference
The BPM signal processor will be used in machine protection interlocks,
where reliable operation is extremely important. In addition to shielding the sensitive parts
of the board, a number of special precautions have been incorporated in the design to
improve immunity to electromagnetic interference.
• The coaxial inputs pass via an uninterrupted ground plane before connecting to the
circuit board.