Detector¶
The flat-panel and pixel area detectors, the two detector towers, the beamstops, and the flux monitor. PVs verified against startup/80-areadetector2.py, 81-pilatus.py, 72-two-detector.py, 11-motors.py, 10-machine.py.
PDF's measurement is the total-scattering pattern on a large area detector. To reach the high Q a pair distribution function needs, the detector sits close to the sample; a near panel and a far panel are merged across two distances to cover the full range. This two-distance, two-detector geometry is the shape that distinguishes PDF from its twin XPD.
| Asset | Family | PV | Role |
|---|---|---|---|
AreaDetector |
Camera | XF:28ID1-ES{Det:PE1} |
PerkinElmer flat panel, primary PDF detector |
PixelDetector |
Camera | XF:28ID1-ES{Det:Pilatus} |
Pilatus photon-counting pixel detector |
DetectorStage1 |
LinearStage | XF:28ID1B-ES{Det:1} |
first detector tower (static distance) |
DetectorStage2 |
LinearStage | XF:28ID1B-ES{Det:2} |
second detector tower (moving distance) |
BeamStop |
BeamStop | XF:28ID1B-ES{BS:1} |
direct-beam stop |
FluxMonitor |
FluxMonitor | XF:28ID1B-OP{Det:1-Det:2} |
background photodiode (I0) |
Two detectors, two distances¶
The AreaDetector is a PerkinElmer flat panel (a second panel sits alongside), the primary total-scattering / powder detector; the PixelDetector is a Pilatus photon-counting detector with an energy-thresholded readout, used for high-Q or low-background frames. Both reuse Camera, the flat-panel precedent XPD already carries.
The DetectorStage1 and DetectorStage2 are the two detector towers (Det_1 and Det_2, each X / Y / Z). The Z axis sets the sample-to-detector distance and hence the accessible Q. PDF carries two towers so a near and a far panel can be merged into one wide-Q dataset: one panel stays static while the other steps in and out of the beam, the explicit two-detector acquisition the TwoDetectors plan sequences. Which tower is static versus moving, and how the panels merge, are DIST-1. Each BeamStop (BStop1, with BStop2 and a table-mounted stop alongside) blocks the direct beam ahead of its panel.
Reuse, not new vocabulary¶
This is the reinforcement point of PDF as a CORA exercise: a high-energy total-scattering beamline with flat-panel and pixel detectors, two distance towers, and beamstops that needs no new Family. The detectors reuse Camera, the FluxMonitor photodiode reuses the graduated flux Family (#353), and the beamstops reuse BeamStop. The total-scattering detector chain is the same shape its twin XPD carries; PDF adds the second physical detector tower for the simultaneous near / far merge, but the families are unchanged.