Analog inputs (AI)¶
Analog inputs are continuous readbacks used for normalization, alignment, temperature monitoring, and timing diagnostics. Channel indices 0–20 are fixed on this beamline; names below match the human-readable labels used in control and acquisition software.
| Index | Name | What it represents | Typical use |
|---|---|---|---|
| 0 | EPU Polarization | Undulator polarization mode readback | Confirm circular vs linear settings |
| 1 | Coolstage Temp C | Cryogenic holder temperature | Low-T experiments |
| 2 | CCD Temperature | Detector sensor or camera-stack temperature (legacy channel name; hardware is CMOS) | Verify cooling or thermal stability before long exposures |
| 3 | Beam Current | Storage ring current | Long-term drift and ring fill state |
| 4 | TEY signal | Total electron yield from sample | Surface-sensitive NEXAFS |
| 5 | Izero | Upstream intensity (often mesh) | Normalize absorption or scattering |
| 6 | Photodiode | Main GaAs diode in direct beam | Alignment, flux, transmission |
| 7 | AI 0 | Spare analog input | User-defined front-end |
| 8 | AI 3 Izero | Gold mesh downstream of HOS, before first JJ slits | Alternate normalization path |
| 9 | AI 5 | Spare analog input | User-defined |
| 10 | AI 6 BeamStop | Small Si diode on beamstop | Flux while the area detector (CMOS) is in scattering geometry |
| 11 | AI 7 | Spare analog input | User-defined |
| 12 | Temperature Controller | Hot stage readback | Annealing or high-T chemistry |
| 13 | PZT Shutter | Piezo shutter position or status analog | Shutter diagnostics |
| 14 | Pause Trigger | Pause line level | Scan pause / interlock visibility |
| 15 | LV Memory | LabVIEW memory usage | Operator health of control host |
| 16 | Deriv Photodiode | Time derivative of photodiode signal | Detect fast beam flicker |
| 17 | Time Stamp Error | Clock sync error | Diagnose timing between subsystems |
| 18 | Time Stamp Transmit Time | Stamp message latency | Network or driver timing |
| 19 | Time Stamp Server Time | Server-side time base | Correlate events to host clock |
| 20 | Camera Temp Setpoint | Camera cooling setpoint readback (legacy name) | Confirm commanded detector temperature |
Sign conventions: some channels may read negative after cabling polarity, amplifier offset, or direction convention. Always zero or calibrate before precision absorption work.
Choosing a normalization channel: use Photodiode when the main diode is in the beam; use AI 3 Izero or Izero when the mesh path matches your energy and harmonic conditions; use AI 6 BeamStop when the CMOS area detector is exposed and the direct beam must stay off the main diode.