Hi Andy,

Attached is the most up to date discussion of the chopping secondary
available to the SI teams.  I'd thought I'd forward it to you
to see if you had any comments etc.

It's in pdf format, but I can obtain the Powerpoint file as well,
if you'd prefer.

Initially, I'd thought we'd just use a TTL waveform for chopping for
CASIMIR and later implement an analog drive signal.  Also, we'd probably
only be interested in two point chopping.

The most interesting slides for us are:

Slides: 3-7 On synchronization modes, waveforms and settling times.

And:

Slides: 11-13 phase delays and phase stability.


The simplest mode I think to start with would be:

1) Use their reference waveform, it has a lower phase jitter than the
   external reference we could provide.  We would program, frequency,
   throw and direction.

2) Monitoring the analog drive signals, we would vary the phase delay
   on the Chop Phase Ref TTL output, as shown in Slide 3.  We could run
   the signals through coax cables already in the Cable Drape.

      We would vary the phase by issuing commands through the MCCS.
      However, I don't know how long it would take, to issue a command and
      observe the phase shift.  We'd have to determine if that was a
      reasonable time, to know if this idea is practical. 

4) We'd vary the phase until phase delay was longer than the settling
   time for the chopper.

5) By a straight forward combination of the reference signal, and the
   phase shifted signal, perhaps as simple as a exclusive or gate, we
   could generate a suitable integrate signal for WASP. 

This would be an extremely basic scheme for generating integrate and
synchronization signals for CASIMIR.

I'd certainly like to hear your opinions and preferences for the
signals for WASP.

Mick




p.s. I'll be out all next week, but I'll be here constantly 
after that.