AutoSQUID 0.2.0

Automated DAQ + flux-lock control for STAR Cryoelectronics PFL-102 SQUID systems

AutoSQUID — SQUID measurement-cycle

This package is developed specifically for performing/automating superconducting quantum interference device (SQUID) measurements. It's developed using STAR Cryoelectronics PFL-102, PCI-1000, and DAC-2568 and a National Instruments (NI) data-acquisition (DAQ) card PCIe-6320. All settings live in the notebook as one Config object; all logic lives in the modules here. The package imports nidaqmx + pyserial (it assumes a STAR Cryo + NI rig); the MXC thermometer is not imported — the site's reader is injected into cfg.temp_reader in the notebook.

Full reference: docs/AutoSQUID_protocol.pdf — the configuration table, the PCIe-6320 DAQ and PFL-102/SCC details, the reset protocol, the run loop, the operating procedure, and the auto-S-tune procedure. This README is the orientation + quick-start; the protocol is the bench reference.

What it does

For one fixed temperature, and for each scan interval, collect a target number of clean, gap-free time-series runs at the chosen sample rate. It can watch for a flux-lock jump while acquiring, resets the feedback locked loop (FLL) and re-acquires on a failure, optionally logs the MXC temperature throughout, and saves each trace in the standard PCS102 text format with an append-only run ledger. A companion notebook centers the locked output near 0 mV before the run (auto-S-tune).

Wiring

Analog: SQUID/PFL-102 (Bluefors) → PCI-1000 ch.1 → PCI-1000 OUTPUT → DAC-2568 ANALOG IN → ANALOG OUT (68-pin) → PCIe-6320 ai0 (read over the PCIe bus via nidaqmx). Control: PC → PCI-1000 RS232 → PFL (SCC serial, write-only). Sync: PCI-1000 SYNC OUT → DAC-2568 (1-pin LEMO).

Project layout

AutoSQUID/
├─ pyproject.toml          # pip install AutoSQUID   (src layout)
├─ README.md  CHANGELOG.md  LICENSE (GPLv3)
├─ src/AutoSQUID/          # the importable package (modules below)
├─ examples/               # example_*.ipynb showcases (local working copies are gitignored)
└─ docs/                   # AutoSQUID_protocol.pdf, squid_wiring_diagram.png

Modules

module	role	deps
util.py	generic helpers (clamp)	—
config.py	Config dataclass — every knob + derived paths / filename stem / PFL register	—
scc.py	SCC framing:assemble_command, pfl_register, dac_data (OpenSQUID-derived)	—
analysis.py	detection + truncation + I/O:is_surge_spec, chunk_jump, usable_points_from_spec, truncate_to_clean, fmt_npts, format_temp_label, PCS102 read/write, ledger, scan_indices/accepted_trace_names	numpy, pandas
serial_io.py	SCC writes:reset, fire_reset, s_lock/s_tune, set_squid_flux, set_squid_bias, set_array_bias, set_array_flux	pyserial
daq.py	NI reads:daq_read, daq_mean, live_mean, classify, detect_ai_channel, acquire_finite_chunked	nidaqmx
temperature.py	MXC read_temp (via injected cfg.temp_reader) + optional background TempLogger and logging helpers	— (injected)
measurement.py	state machine:run_cycle (one interval), reset_and_verify, resolve_temp_label; the interval loop lives in the notebook	—
tuning.py	auto_s_tune — live-center the locked output near 0 by stepping S-flux (secant search)	—
plotting.py	plot_run / plot_usable / plot_overlay / plot_psd — raw trace + temperature, usable-prefix, V/T overlay, and one-sided Welch PSD, all read back from disk	matplotlib, pandas

util/config/scc use only stdlib; analysis/plotting add numpy/pandas/matplotlib; serial_io/daq import their instrument backends (pyserial/nidaqmx) at module top — the package assumes the STAR Cryo + NI rig — while temperature imports no thermometer backend and reads through the injected cfg.temp_reader. So import AutoSQUID needs nidaqmx, pyserial, numpy, pandas, and matplotlib (but no lab thermometer library). Dependency order: util → scc/config → analysis → serial_io/daq/temperature → measurement/tuning/plotting.

Notebooks (examples/)

• example_measurement_cycle.ipynb — the minimal showcase: build Config (set data_root/user/date and your cfg.temp_reader) → detect_ai_channel → resolve_temp_label → the interval loop (sq.run_cycle(cfg, tau)). Copy it and fill in your lab's values.
• example_auto_s_tune.ipynb — build Config → sq.s_lock(cfg) then sq.auto_s_tune(cfg).

Each example just import AutoSQUID; you set cfg.temp_reader to your thermometer reader (fn(channel) -> T in K) in the first cell.

Quick start (bench PC)

import AutoSQUID as sq
cfg = sq.Config(scan_interval_s=[100e-6], n_trials=2, port="COM3",
                data_root=r"", user="", date="")     # set your data_root / user / date
# plug in your lab's thermometer reader: fn(channel) -> T in K
cfg.temp_reader = lambda ch: ...                     # define for your thermometer (returns T in K)
dev, cfg.daq_ai = sq.detect_ai_channel(cfg)          # §1 pick the live ai0
print(sq.read_temp(cfg))                             # confirm the MXC backend
for tau in cfg.scan_intervals:                       # §2 acquire (lock the FLL first!)
    if sq.run_cycle(cfg, tau) == "reset_fail":
        break
sq.plot_run(cfg)                                     # §3 plot from disk

First run on the hardware: do the one-time bring-up in the protocol (§ Operating procedure) as a supervised dry run — do not "Run All" blind.

Required fields (validated at the use site)

run_cycle() raises before any reset or write unless data_root, user, and daq_ai are set; with temp_label="auto" it also requires temp_reader. auto_s_tune() requires daq_ai, port, data_root, and user so its S-flux result always has an action_log.txt destination. Config() itself is passive — it doesn't validate.

Temperature logging is gated by cfg.temp_logger (default True): run_cycle() then runs a background TempLogger that reads cfg.temp_reader every temp_every_s into each trace's TEMP_*.csv, so set cfg.temp_reader for any logged run (without it the CSV is all nan). Set cfg.temp_logger=False to skip temperature entirely — no thread, no TEMP_*.csv, and no temp_reader required (for a literal temp_label). A literal temp_label (e.g. "14mK") only sets the filename label; it does not by itself disable logging — use temp_logger=False for that.

Behavior (per scan interval)

Collect n_trials accepted traces within max_attempts real acquisitions. Each acquisition is order-indexed i and evaluated for a usable clean prefix; a full clean trace is kept unchanged. When a live jump/rail flag fires, its exact boundary is final — the chunk that tripped is dropped, the strict prefix before it is kept (buf[:chunk_start]), and the locator is not called. When an acquisition completes without a live flag, the post-hoc locator runs regardless of whether live_jump_check was on (so a slip that the live check missed, or any run drained with live checking off, is still caught). The saved file's point-count tag is the trace's usable length, not the target — e.g. a 10 M-point run that slipped at 8.43 M is written DAQ_{MonDD}_{tau}us_{label}_8p4Mpts_{i}.txt. Files carry only a bare name, _SURGE, or _BADBASE suffix — there is no _JUMP/_RAIL file; that provenance lives in the ledger's event column. i continues past existing files, so re-running resumes / tops up and never overwrites.

After the initial reset, additional resets fire only after a slipped acquisition (truncated or non-clean), never after a full clean trace; if the final accepted trace itself left the lock slipped, an exit reset clears it before the interval returns. A non-clearing reset — or a bad baseline at the start (the reset didn't hold) — is systemic and stops the whole sweep (run_cycle returns "reset_fail"). Every acquisition is appended to experiment_log.txt; resets, temperature reads, and MEASURE/BAD_BASELINE events go to action_log.txt (a reset failure also gets a ledger row). Each RESET action records the number of reset/verify tries needed to clear the baseline; RESET_FAIL records not cleared.

The ledger separates three things per row: event — the trigger/provenance (JUMP/RAIL/FROZEN/DEAD/BAD_BASELINE/NONE); outcome — the integrity of the saved prefix (CLEAN/SURGE/DEAD/BAD_BASELINE, where a post-hoc is_surge_spec check sets SURGE); and accepted (0/1) — whether the trace counts toward n_trials. It also records usable_points / usable_seconds, the clean-prefix length. A trace is accepted only when outcome=CLEAN and usable_points ≥ min_usable_frac × n_points — min_usable_frac (default 0.90) is the fraction of the target a clean prefix must reach to count, so a 90%-complete clean trace still counts; set 1.0 to require full-length only. A DEAD trace (zero usable points — flat/dead throughout) is ledgered but never written to disk. Resume counting comes from the ledger: progress toward n_trials is the number of accepted=1 rows whose file still exists, and the next index is taken from the filesystem — immune to filename rounding. (Still re-run the standalone integrity gate before downstream analysis.)

vrange = ±1 V (matches previous measurements): finer ADC resolution, but the ADC clips ~1 V, so jump_v (default 0.5 V) catches an in-range slip and rail_v (9.5 V) is dormant until the card returns to ±10 V.

terminal_config (default "DIFF") sets the NI analog-input reference: DIFF reads ai0 against its paired negative input (ai0/ai8) and rejects common-mode / ground-loop pickup — the right choice for this floating SQUID output; "RSE" (single-ended vs board ground) and "NRSE" (vs AI SENSE) are the alternatives. live_jump_check (default True) runs the mid-run jump/rail abort during acquisition; set it False to drain each run without it. Either way, any acquisition that finishes without a live flag is then passed through the post-hoc prefix locator and the is_surge_spec gate, so a missed slip is still caught.

Data layout

Everything is written under cfg.outdir = data_root / user / date:

<data_root>/                                       # cfg.data_root  (set per install)
└─ <user>/                                         # cfg.user
   └─ <date>/                                      # cfg.date   ("" → the bare <user>/ folder)
      ├─ DAQ_{MonDD}_{tau}us_{label}_{usable_npts}_{i}.txt   # trace; npts tag = USABLE length, e.g. ..._10Mpts_1.txt (full) or ..._8p4Mpts_2.txt (truncated)
      ├─ DAQ_..._{i}_{SURGE|BADBASE}.txt                     # non-clean trace (DEAD = ledgered only, no file; no _JUMP/_RAIL files)
      ├─ TEMP_{MonDD}_{tau}us_{label}_{usable_npts}_{i}.csv  # MXC log when temp_logger=True (time_s, T_K)
      ├─ experiment_log.txt                                  # per-acquisition ledger (event, outcome, usable_points/seconds, accepted, …)
      └─ action_log.txt                                      # results-free event log (resets, temp, attempts)

{i} is the order index and continues across days; matching ignores the {MonDD} date and the {usable_npts} tag, so traces from any day (and any usable length) in <date>/ belong to the same {tau}us_{label} core. Only files the ledger marks accepted=1 count toward n_trials — a bare-suffix file can still be a sub-min_usable_frac prefix that does not count.

Analysis (PSD)

sq.plot_psd(path, filename, conversion, P=…, clean_only=True) reads a trace back from disk and plots its PSD. Traces are stored in raw volts with no calibration baked in; plot_psd multiplies by the per-cooldown conversion factor (f₀/V) to give a flux PSD (f₀²/Hz), so you must pass the correct cooldown calibration yourself — it isn't recorded with the trace. clean_only=True runs the is_surge_spec integrity gate on each trace and skips any that fail.

Auto-S-tune

auto_s_tune automates the manual "nudge S-flux until the trace is centered at 0 mV": with the SQUID locked, it steps the SQUID-flux DAC and reads a short finite live-mean each step, using a secant update (dx = (target − mean)/slope) so the sign and gain are measured, not assumed — no reset between steps. Its first response probe is 10% below start_sflux; if that side is flat, it retries once 10% above the same starting point before returning no_response. Stops when the live mean is within tol_V (default 20 mV) of target, or at one DAC LSB. Returns dict(status ∈ {converged, dac_limited, no_response, max_iter}, flux_sflux, mean_V, std_V, n_iter) (dac_limited = as centered as one DAC LSB allows, still outside tol_V). no_response means the live mean doesn't move with the S-flux steps — typically not locked, wrong daq_ai, or S-flux not reaching the SQUID. See the protocol's auto-S-tune section for the full procedure.

Contact

For questions, bug reports, or setup issues, please feel free to contact:

• Zhengyue Chen — [e-mail]
• Sheng Ran — [e-mail]