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101 lines
4.0 KiB
Python
101 lines
4.0 KiB
Python
#!/usr/bin/env python3
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# Copyright 2026 514 LLC d/b/a OpenGlow
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# Written by Scott Wiederhold
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# https://community.openglow.org
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# SPDX-License-Identifier: MIT
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"""Characterize a SHORT periodic flow re-check for use DURING a job.
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Why a separate design from the job-start check: with the laser firing
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and coolant flowing, tube heat raises BOTH sensors, inflating a plain
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downstream-rise metric toward a false fault. With the pump stopped that
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heat never reaches the sensors at all (stagnant loop), so the no-flow
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signature stays at its idle value. The two signatures therefore
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converge during a cut. The differential rise
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(downstream_end - downstream_start) - (upstream_end - upstream_start)
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cancels that common-mode heating and is the metric this measures.
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TWO DEAD ENDS, recorded so they are not re-invented:
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1. Absolute over-temperature does NOT detect a failed pump. The
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sensors read the water at their own location; with no circulation
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the tube's heat stays in the tube and never reaches them. The loop
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can read perfectly comfortable while the tube cooks. Over-temp
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monitoring detects a hot CIRCULATING loop - a different failure.
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2. "The coolant should warm up while cutting" is NOT a usable
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indicator either. A low-duty engrave (say 5% duty at 30% power) can
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put so little heat in that the cooling system absorbs it with no
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measurable rise, so a flat trend is equally consistent with a light
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load working correctly and with a dead pump. Ambiguous evidence is
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worse than none - it invites false confidence.
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Hence: periodic ACTIVE interrogation with the heater, which creates a
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known stimulus instead of waiting for one, is the only valid method on
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this hardware (there is no pump tach or pump current sense anywhere in
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the machine).
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Usage: flow_recheck_char.py [heater_pct] [window_s] (default 50 30)
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Runs both flow and no-flow cases from a comparable loop state and
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prints the differential separation. Aborts if downstream passes 45 C.
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Drives the heater and pump directly: run with forgectrl and the
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controller stopped (the bench page's takeover does that). Runs on the
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board or from a host (gfbench: GF_HOST).
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"""
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import sys
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import time
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from gfbench import board, degc
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DOWN_ABORT_C = 45.0
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def sample():
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o = board('cat /sys/glowforge/pic/water_temp_1 /sys/glowforge/pic/water_temp_2').split()
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return degc(int(o[0])), degc(int(o[1]))
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def settle(seconds=100):
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board('echo 1 > /sys/glowforge/thermal/water_pump_on; echo 0 > /sys/glowforge/thermal/heater_pwm')
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time.sleep(seconds)
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def check(tag, pump_on, pct, window):
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board('echo %d > /sys/glowforge/thermal/water_pump_on' % (1 if pump_on else 0))
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time.sleep(2)
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d0, u0 = sample()
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board('echo %d > /sys/glowforge/thermal/heater_pwm' % int(65535 * pct / 100))
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t0 = time.time()
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d, u = d0, u0
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while time.time() - t0 < window:
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time.sleep(5)
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d, u = sample()
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print(' %-8s t=%2.0fs down=%5.2f (%+5.2f) up=%5.2f (%+5.2f) diff=%+5.2f'
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% (tag, time.time() - t0, d, d - d0, u, u - u0, (d - d0) - (u - u0)), flush=True)
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if d >= DOWN_ABORT_C:
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print(' abort: downstream at safety limit', flush=True)
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break
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board('echo 0 > /sys/glowforge/thermal/heater_pwm; echo 1 > /sys/glowforge/thermal/water_pump_on')
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return (d - d0) - (u - u0), d - d0
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pct = int(sys.argv[1]) if len(sys.argv) > 1 else 50
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window = int(sys.argv[2]) if len(sys.argv) > 2 else 30
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print('=== periodic re-check characterization: %d%% heater, %d s window' % (pct, window))
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settle()
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print(' flow case:')
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flow_diff, flow_rise = check('flow', True, pct, window)
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settle()
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print(' no-flow case:')
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noflow_diff, noflow_rise = check('noflow', False, pct, window)
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settle(60)
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print()
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print('differential rise: flow %+.2f no-flow %+.2f separation %.2f C'
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% (flow_diff, noflow_diff, noflow_diff - flow_diff))
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print('plain down rise: flow %+.2f no-flow %+.2f separation %.2f C'
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% (flow_rise, noflow_rise, noflow_rise - flow_rise))
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print('suggested differential threshold: %.2f C' % ((flow_diff + noflow_diff) / 2))
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