Thomas K Ales [MSE]
137 lines
5.5 KiB
Python
Executable File
137 lines
5.5 KiB
Python
Executable File
"""Oscilloscope configuration for pre-scan angle inspection.
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Inspection is read-on-the-instrument: nothing in this module transfers or
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plots waveform data. The app puts the scope into a free-running, edge-
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triggered state and drives the stage to the point being inspected; the
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operator judges the SAW response and the bias levels on the scope screen.
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That split is deliberate. A scan's acquisition trigger is the logic AND of
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the laser pulse and the stage's max-velocity gate, and its transfers are
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FastFrame blocks — neither is useful for looking at one point by eye. Here
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the trigger is a plain edge on the laser pulse, FastFrame is off, and the
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acquisition free-runs, so the display updates continuously while the stage
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sits still.
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CH1 keeps the acquisition front-end so what is on screen is what a scan would
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record. CH3 and CH4 are rescaled as DC bias monitors (see BIAS_* below).
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``read_bias_mv`` is the one exception to "nothing is transferred": it reads
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the two bias levels back as scalars, not waveforms, because the auto-align
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procedure (core.auto_align) has to close a loop on them. The operator still
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watches the same screen this configures.
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"""
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from __future__ import annotations
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import logging
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from dataclasses import replace
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from core.scope_sras import SAMPLE_RATE_HZ, SRAS_CHANNELS, configure_channels
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logger = logging.getLogger(__name__)
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# CH2 carries the laser pulse. The scan triggers it at 0.5 V as one term of a
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# logic AND; inspection triggers well above that so a slow edge or a noisy
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# baseline cannot free-run the display.
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INSPECT_TRIG_LEVEL_V = 2.0
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# CH3/CH4 are the DC bias monitors during inspection. The signal never goes
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# negative and spans roughly 0–700 mV, so both channels get the *same* scale
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# and position — the point of inspecting them is comparing the two by eye, and
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# that only works if a division means the same thing on each.
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#
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# Ground sits BIAS_POSITION_DIV divisions below centre, which puts the whole
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# 0–700 mV range above the centre line with a little room underneath for
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# undershoot. With 100 mV/div and ground 3.5 divisions low, the visible window
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# runs from about -50 mV to +750 mV on an 8-division display and wider on a
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# 10-division one, so 0–700 mV sits comfortably inside either.
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BIAS_CHANNELS = (3, 4)
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BIAS_WINDOW_V = 0.700
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BIAS_SCALE_V_DIV = 0.100
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BIAS_POSITION_DIV = -3.5
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BIAS_LABELS = {3: "Bias - A", 4: "Bias - B"}
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# One MEAN measurement carries the shot-to-shot noise of a single record, and
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# the alignment loop has to resolve 5 mV. The median of a handful of reads
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# rejects the odd outlier without the averaging acquisition mode, which would
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# hide exactly the intermittent response the operator is watching CH1 for.
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BIAS_READS = 5
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def inspect_channel_profiles() -> dict:
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"""Channel front-end config for inspection.
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CH1 and CH2 are the acquisition profiles verbatim. CH3 and CH4 differ
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only in label, scale and position — termination, coupling and bandwidth
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stay as the scan sets them, so the bias reading is the same measurement
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the scan records, just displayed usefully.
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"""
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profiles = dict(SRAS_CHANNELS)
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for ch in BIAS_CHANNELS:
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profiles[ch] = replace(
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SRAS_CHANNELS[ch],
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label=BIAS_LABELS[ch],
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scale_v_div=BIAS_SCALE_V_DIV,
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position_div=BIAS_POSITION_DIV,
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)
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return profiles
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def configure_inspection(scope) -> None:
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"""Put the scope into free-running inspection mode.
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Leaves the acquisition running, so the display stays live while the
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operator moves between angles and points.
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"""
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configure_channels(scope, inspect_channel_profiles())
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# Plain edge trigger on the laser pulse — no logic pattern, so the stage
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# gate plays no part and a stationary stage still triggers.
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scope.write("TRIGger:A:TYPe EDGE")
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scope.set_trigger_source(2)
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scope.set_trigger_slope("RISE")
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scope.set_trigger_level(2, INSPECT_TRIG_LEVEL_V)
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scope.set_trigger_mode("NORMAL")
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# No averaging: a weak or intermittent SAW response is exactly what the
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# operator is looking for, and averaging would hide it.
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scope.set_acquire_mode("SAMPLE")
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scope.set_fastframe_state(False)
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scope.set_sample_rate(SAMPLE_RATE_HZ)
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scope.write("HORizontal:POSition 30")
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# Free-run rather than single-sequence, so the trace keeps updating.
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scope.write("ACQuire:STOPAfter RUNSTop")
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scope.write("ACQuire:STATE RUN")
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def stop_inspection(scope) -> None:
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"""Halt the free-running acquisition.
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The next scan reconfigures the scope from scratch, so this only needs to
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stop the sweep — it does not try to restore the acquisition profile.
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"""
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scope.write("ACQuire:STATE STOP")
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def read_bias_mv(scope, reads: int = BIAS_READS) -> tuple[float, float]:
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"""Read the two DC bias levels in millivolts.
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Returns ``(ch3_mv, ch4_mv)`` — DC 1 and DC 2 in the auto-align channel
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map. Each channel is read ``reads`` times and reduced by the median.
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The two channels are read in separate batches rather than interleaved:
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switching the immediate-measurement source costs a round trip, and these
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are DC levels, so the few milliseconds between the batches are not a
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source of error the way they would be for a transient.
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"""
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if reads < 1:
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raise ValueError("read_bias_mv needs at least one read per channel")
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levels = []
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for ch in BIAS_CHANNELS:
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samples = sorted(scope.measure_immediate(ch, "MEAN") for _ in range(reads))
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levels.append(samples[len(samples) // 2] * 1000.0)
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return levels[0], levels[1]
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