2019/09/24 (Tuesday)
| Status: Initial LHe transfer yesterday. Fridge passed 77K throughput test. Electrical checkout mostly OK. Motor status under investigation. | |
| 0929 | Fill LN2 cold trap |
| 0930 | MC(Cernox) = 4.23 K, Sorb = 5.4 K, turbo on IVC = 250 nbar, G1(fridge) = 528 mbar. G3(MB) = 99 mbar+1atm. |
| 0940 | Slide Pot 1-2/2-3/1-3 = 4.591/12.50/16.20 kΩ which corresponds to R_C = 429 Ω and f = 0.255 (see definitions here) Motor Coils A/B = 125.1/126.8 Ω measured at the Dsub50 breakout, including the trim pots. Adjust trim pots again to achieve Motor Coils A/B = 125.1/125.1 Ω. |
| 0952 | Let's try again to move the stepper motor. Yesterday we tried 1 rotation at 7.5 V, now lets try 10V and a few rotations. Power on Arduino via USB and connect to it via telnet. Turn on motor power supply to 10V. |
| 0956 | Send command mv +48 MC rises from 4.22 K to 4.26 K then recovers (same as yesterday). Slide Pot 1-2 falls initially, then rises and settles. Slide Pot 1-2/2-3/1-3 = 4.570/12.47/16.21 kΩ which corresponds to R_C = 399 Ω and f = 0.256. Seems like it didn't move. |
| 1000 | Send command mv +96 MC rises from 4.22 K to 4.275 K then recovers. Slide Pot 1-2 falls initially, then rises and settles. Seems to have settled by the time MC temp peaks. Slide Pot 1-2/2-3/1-3 = 4.566/12.46/16.20 kΩ which corresponds to R_C = 397 Ω and f = 0.256. No movement. |
| 1005 | Adjust motor power supply current limit to half its full value. Send command mv -96 MC rises from 4.22 K to 4.275 K then recovers. Power supply current reading goes to 70 mA when motor is energized. Slide Pot 1-2/2-3/1-3 = 4.518/12.36/16.20 kΩ which corresponds to R_C = 323 Ω and f = 0.257. No movement. |
| 1010 | Adjust dwell between motor steps from 15 ms to 30 ms by sending command wr dwell 30. Send command mv -96 MC rises from 4.22 K to 4.30 K then recovers. Slide Pot 1-2/2-3/1-3 = 4.585/12.50/16.19 kΩ which corresponds to R_C = 431 Ω and f = 0.255. No movement. |
| 1018 | Adjust motor power supply to 12.5V. Send command mv +96 MC rises from 4.22 K to 4.33 K then recovers. Slide Pot 1-2/2-3/1-3 = 4.55/12.43/16.20 kΩ which corresponds to R_C = 374 Ω and f = 0.256. No movement. |
| 1024 | Power down Arduino and motor power supply. Test setup with spare room-temp stepper motor. This motor works as expected. |
| 1105 | Maybe the turns ratio for the coils are not 1:1. Assuming linear room-temp resistivity of NbTi, the turns ratio goes like the room-temp resistance ratio. Then, to get the same B field in each coil given a constant driving voltage, we need to adjust the trim pots to be the same ratio. Set Motor Coils A/B = 125/131.9 Ω. Power up Arduino, set power supply to 10.0V. MC heats a little when turning this on. Might have turned on the motor power supply before the controller board was fully initialized. |
| 1110 | Connect to Arduino via telnet and sent command mv +96 MC rises from 4.22 K to 4.275 K then recovers. Slide Pot 1-2/2-3/1-3 = 4.552/12.43/16.20 kΩ which corresponds to R_C = 375 Ω and f = 0.256. No movement. |
| 1117 | Adjust motor power supply to 20.2V. Send command mv +96 MC rises from 4.22 K to 4.37 K then recovers. Slide Pot 1-2/2-3/1-3 = 4.568/12.45/16.20 kΩ which corresponds to R_C = 393 Ω and f = 0.256. No movement. |
| 1216 | Connect oscilloscope to measure the voltages across the coils (not including the trim pot). With the motor voltage at 5V, can see a square wave on Coil A with an amplitude of ±3V Actually, this may be coil A going normal. Since we're looking across the ~30 Ω coil+wiring resistance, we should only see about 1/4 of the total voltage drop. I think here the total voltage is limited by the power supply, and the driver sends ~0.7x that to each coil, so we expect 5V*0.7*30 ohm/125 Ohm = 0.84 V |
| 1228 | With the motor voltage at 10V, both coils show clean square wave drive signals with ±8.5 V |
| 1409 | Try room-temp motor with EasyDriver current-limiting pot turned all the way down to 152 mA (Test-point 1 = 0.912 V). It still turns just fine with power supply > 4.5 V. With Power supply = 5.0V, monitor room-temp motor coil voltages with oscilloscope. Observe ±3.5V square waves (=5V*0.7 as expected) with ±5.5V transient spikes.  |
| 1423 | I'm thinking now that we may have been driving the motor coils normal with a combination of too high a drive current and too fast of stepping combined with low cooling power. Once the fridge gets settled, we can try again without pushing these quantities so hard. |
| 1622 | Play with the room-temp motor some more. With 5V power, the can go down to a dwell of 3 ms without skipping steps. At 2 ms, it skips 3/4 of the steps and at 1 ms it doesn't move. |
| 1235 | MC(Cernox) = 4.22 K, Sorb/1K Pot = 5.4/4.38 K, G1 (fridge) = 529 mbar. Mixture is open to cold LN2 Trap 1 and to dump, 3He pump is off. |
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| 1235 | Pump out lines leading to 1K Pot with scroll pump |
| 1240 | Switch over to 4He pump. Change pump exhaust to recovery and open valve to recovery lines. |
| 1245 | Check pressure in 1K Pot by closing V4A and opening 1K Pot speedivalve: the mechanical gauge goes up about 0.5 bar. 1K Pot temperature falls to 3.5 K then starts to rise again. |
| 1250 | Pump out 1K Pot in steps, alternating between V4a and the 1K Pot speedivalve. After 5 iterations get pot down to < 0.1 bar. Then leave 4He pump pumping on pot continuously. |
| 1255 | 1K Pot = 4.37 K / 0.4 mbar. MC (Cernox) = 4.22 K. G1 = 529 mbar. |
| 1255 | Open 1K Pot needle valve → 10°. 1K Pot → 2.9 K / 8.0 mbar. |
| 1300 | MC = 4.19 K and falling, G1 = 505 mbar and falling. |
| 1300 | Open 1K Pot needle valve → 20°. 1K Pot → 2.5 K / 13 mbar. Open 1K Pot needle valve → 30°. 1K Pot → 2.2 K / 30 mbar. |
| 1305 | MC = 4.09 K and falling, G1 = 469 mbar and falling. |
| 1305 | Open 1K Pot needle valve → 40°. 1K Pot → 1.9 K / 50 mbar. |
| 1305 | MC = 4.09 K and falling, G1 = 469 mbar and falling. MC temperature falls dramatically faster to about 3.4 K, then slows again |
| 1310 | MC(Cernox) = 3.41 K and falling, G1 = 434 mbar and falling. |
| 1310 | Switch to Tower thermometer. Tower = 3.68 K. |
| 1330 | Tower = 3.63 K and falling in a strangely jagged way, rising and falling between about 3.6 and 3.7 K. G1 = 376 mbar and falling. 1K Pot = 1.86 K / 50 mbar, stable. |
| 1330 | Tower/MC(Cernox)/MC(H35) = 3.60/3.29/3.25 K. MC(Cernox) looks like it's cooling at a regular rate. Normally at this stage I guess we monitor MC, so I'll stick to that. Use the H35 thermometer. |
| 1345 | MC(Cernox) = 3.25 K. Cooling seems sluggish compared to last couple runs. Also 1K Pot pressure is very flat, rather than oscillating. Apart from that 1K Pot seems like it's working OK, at 1.86 K / 50 mbar. |
| 1350 | Check IVC pressure. With turbo: IVC pumping pressure = 250 nbar. Without turbo: IVC = 14 μbar. This is much higher than usual. |
| 1400 | MC(Cernox) = 3.23 K, G1 = 340 mbar, both kind of flat. That's not very good. 1K Pot = 1.85 K / 45 mbar. Let's try boosting the 1K Pot power… |
| 1405 | Open 1K Pot needle valve → 50°. 1K Pot → 1.89 K / 200 mbar. Looks like MC temperature and Fridge pressure are falling again. |
| 1415 | MC(Cernox) = 3.16 K, G1 = 304 mbar, both falling. That's better. 1K Pot = 1.89 K / 220 mbar, pressure oscillating. That's an unusually high pressure but the fact that it's oscillating suggests (from experience) that it's actually working. |
| 1425 | MC(Cernox) spikes up corresponding with a 1K Pot spike. MC maxes aroudn 3.5 and only partially recovers, settling around 3.45 K. Pot pressure falls back to 80 mbar and flattens. Fridge pressure stops falling. |
| 1450 | MC temp, Fridge pressure, 1K Pot were pretty flat, then Pot pressure spiked again, oscillating around 800 mbar. MC and Fridge pressure not responding much. |
| 1500 | MC(Cernox) = 3.40 K, G1 = 264 mbar, both pretty flat (MC maybe falling slowly, oscillating a bit). 1K Pot = 1.90 K / 900±100 mbar, pressure oscillating. This doesn't look very good. (n.b. the pot pressure is measure with Pirani gauge P2, so “1000 mbar” just means it's off scale. Mechanical gauge suggests pressure is less than 40 mbar. Still this is very high compared to normal operation.) |
| question: is the problem with the 1K Pot, or is it a thermal short of fridge to bath? The apparently high IVC pressure may point to the latter. But I've been wrong before… Nick recalls that last time the Pot didn't work, it was insensitive to the needle valve. That's not the case here. |
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| 1540 | MC(Cernox) = 3.39 K, G1 = 264 mbar, both flat. 1K Pot = 1.90 K / 850±100 mbar, pressure oscillating. No change since 15:00. |
| 1540 | Reduce 1K Pot needle valve → 40° (give the pump a break). 1K Pot → 1.86 K / 60 mbar. |
| 1555 | Turn on leak detector and connect to IVC, valve out turbo. Signal very high: 3.3e-2 mbarL/s (or 330,000,000 pbarL/s in our usual units). |
| Let's try pumping mixture out of the fridge to the dump, to see if leak signal falls. (This may not work - mixture is partly condensed.) | |
| 1600 | Begin pumping mixture out of fridge to dump. Pumping on both sides, through V1, V3, V6=12.8%. This causes a short spike in 1K Pot pressure and a sudden rise in MC temperature, to >4K. Why did MC temperature rise? |
| 1605 | MC falls to 3.9 K, still much higher than before we started pumping mixture out of the fridge. |
| 1605 | G1 (fridge) fell to 25 mbar but then rose back to around 40 mbar |
| 1610 | Increase V6 → 13.5%. G1→23 mbar. Increase V6 → 14.2%. G1→12.5 mbar. P1 falls into range. Increase V6 → 15.0%. G1/P1→7.5/7.0 mbar. G2 (dump+Trap1)→634 mbar. Looks like we're getting most of the mixture out of the fridge. |
| 1615 | Leak detector on IVC = 5.2e-2 mbarL/s. It has gone up. So no sign that the leak into the IVC is from the fridge. |
| 1620 | G1/P1(fridge) = 2.7/2.0 mbar. G2 (dump+Trap1) = 682 mbar. IVC = 5.6e-2 mbarL/s. So it doesn't look like the fridge is leaking into the IVC. That's good. |
| 1620 | Close V6, we'll let the mixture back into the fridge. |
| 1625 | Open V12a+speedi to let mixture back into fridge, turn off 3He pump. |
| 1634 | MC = 3.26 K, 1K Pot is settling back at 1.86 K / 50 mbar. |
| 1636 | Power Arduino and set motor power supply to 5.0V. EasyDriver current limit is set to minimum (152 mA). Connect to Arduino via telnet and set the dwell to 5 ms. Slide Pot 1-2/2-3/1-3 = 4.754/13.01/16.92 kΩ which corresponds to R_C = 406 Ω and f = 0.256. |
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| 1640 | Send command mv +12. No fridge response. Coil voltage signals are ±1 V with ±6 V spikes. Slide Pot 1-2/2-3/1-3 = 4.792/13.07/16.93 kΩ which corresponds to R_C = 450 Ω and f = 0.255. |
| 1645 | Send command mv +24. No fridge response. Coil voltage signals start at ±1 V but rise to ±2 V, always with ±6 V spikes. Slide Pot 1-2/2-3/1-3 = 4.689/12.88/16.94 kΩ which corresponds to R_C = 298 Ω and f = 0.258. |
| 1650 | Send command mv +24 again. No fridge response. Coil voltage signals start at ±1 V but rise to ±2 V, always with ±6 V spikes. Slide Pot 1-2/2-3/1-3 = 4.700/12.91/16.94 kΩ which corresponds to R_C = 319 Ω and f = 0.257. |
| 1656 | Reduce dwell to 3 ms. Send command mv +24 again. No fridge response. Coil voltage signals start at ±1 V and rise to ±1.5 V, with ±6 V spikes. Slide Pot 1-2/2-3/1-3 = 4.706/12.91/16.95 kΩ which corresponds to R_C = 317 Ω and f = 0.258. |
| 1700 | Increase motor power supply to 5.5 V. Dwell still 3 ms. Send command mv +24 again. No fridge response. Coil voltage signals start at ±1.5 V and rise to ±2 V, with ±7 V spikes. Slide Pot 1-2/2-3/1-3 = 4.682/12.87/16.95 kΩ which corresponds to R_C = 285 Ω and f = 0.258. |
| 1703 | Increase motor power supply to 7.0 V. Dwell still 3 ms. Send command mv +24 again. No fridge response. Coil A voltage signals start at ±3.75 V and rise to ±4.25 V, with ±6 V spikes but coil B is only ±3 V with ±10 V spikes. Slide Pot 1-2/2-3/1-3 = 4.737/12.96/16.95 kΩ which corresponds to R_C = 357 Ω and f = 0.257. |
| 1708 | Set motor power supply to 6.0 V and dwell to 4 ms. Send command mv +24 again. No fridge response. Coil A voltage signals start at ±2 V and rise to ±3 V, with ±6 V spikes but coil B is only ±1 V with ±8 V spikes. Slide Pot 1-2/2-3/1-3 = 4.737/12.96/16.95 kΩ which corresponds to R_C = 246 Ω and f = 0.259 |
| 1713 | Send command mv +24 again. No fridge response. Coil A voltage signals start at ±2 V and rise to ±3 V, with ±6 V spikes but coil B is only ±1 V with ±8 V spikes. Slide Pot 1-2/2-3/1-3 = 4.658/12.81/16.96 kΩ which corresponds to R_C = 238 Ω and f = 0.259 |
| 1715 | Power down Arduino and power supply. |
| 1716 | MC = 3.20 K and falling slowly, 1K Pot = 1.85 K / 50 mbar, G1 (fridge) = 325 mbar, turbo pumping pressure = 250 ubar. Fill LN2 cold trap. |