Pete,
> What aproaches are people taking to performing on-the-fly scans? What I
> mean is, a scan in which one launches a motor move and reads a detector
> as the motor is moving, rather than the more typical step-scan.
We use the SIS 3801 multi-channel scaler for this, as Bill Lavender outlined. One can get away without the hardware synchronization Bill discussed for some applications, if you can trust timing reproducability and absolute position at the very highest accuracy is not needed.
For a particular application, scanning with our Newport diffractometer driven by the Newport MM4005 controller, we have a nice EPICS-based "trajectory scanning" application. The MM4005 can drive up to 8 axes in coordinated trajectories in 8-space, and output synchronization pulses at user-defined positions along the scan. Those pulses are used as the MCS channel advance. I've written Spec macros that use the trajectory scanning for all low-level spec scans. Thus one can execute HKL scans, angle scans, etc. on-the-fly. It speeds things up 1-2 orders or magnitude for many applications.
See
http://cars.uchicago.edu/software/epics/trajectory_scan.html
for details.
The OMS-58 motor controller documentation says it can do similar coordinated motion, but in a more limited way. It should be possible to do something like I did for the MM4005 for that controller, which is in much wider use. spec could then do on-the-fly scanning for the Huber diffractometers that are used at NSLS, APS and elsewhere.
Mark
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