2019/09/23 (Monday)
| Status: LN2 transfer Friday and more yesterday. Fridge passed throughput test. Electrical checkout mostly OK. | |
| 0900 | IVC = 2.2 mbar. Begin pumping out IVC with scroll pump. After a few minutes switch to turbo pump. |
| 0910 | Start Pfeiffer Leak Detector using scroll pump as the forepump. On Friday we were still having problems using the forepump in the leak detector. |
| 0910 | MC(Cernox)/Sorb = 77.29/115.8 K. G1/G2 = 592/538 mbar, slowly rising. |
| 0930 | LD signal on IVC = 40/440 pbarL/s with Turbo pump valved in/out |
| 0945 | LD signal on IVC = 27/300 pbarL/s with Turbo pump valved in/out |
| 1010 | LD signal on IVC = 16/170 pbarL/s with Turbo pump valved in/out. Leave turbo valved out in preparation to blow out LN2. |
| 1025 | LD signal on IVC = 220 pbarL/s |
| 1030 | Begin blowing out LN2. Main bath (G3) = 604 mbar above 1atm. |
| 1035 | Fill LN2 cold trap bath during blowout |
| 1035 | LD signal on IVC = 210 pbarL/s |
| 1045 | LD signal on IVC = 196 pbarL/s |
| 1105 | LD signal on IVC = 164 pbarL/s |
| 1110 | Start pumping mixture out of fridge into dump. |
| 1110 | G3 (main bath) → 270 mbar above 1atm and continues to fall. Close V1a temporarily: G3 rises. So looks like we still have helium in the cylinder and that the blowout is almost over. |
| Throughput test procedure, Cold Trap 2: |
- All mixture in dump, LN2 trap 2 cold, condenser & still valves open (3He pump on - optional)
- Open V9, V13b, V12b+speedivalve, V3. Wait for G1 to be close to G2.
- Close V12a+speedivalve and V3, open V1
- monitor G1
| 1115 | Perform mixture throughput test at MC = 77 K using above procedure with 3He pump on. Let G1 rise to 520 mbar before Step 3, then it falls to 50 mbar, then rises. Throughput = 37 mbar/min. |
|---|---|
| 1120 | G3 (main bath) fell to 150 mbar+1atm, then fell more quickly to 78 mbar+1atm, now it looks like the helium cylinder is empty. But probably blowout is finished. |
| 1120 | LD signal on IVC = 117 pbarL/s, looks like no leak. Turn off leak detector. |
| 1125 | Start pumping out main bath with scroll pump. Takes 15 minutes to fall to 1 mbar. |
| 1150 | With MB down to 0.4 mbar, close off scroll pump. Rises to about 1 mbar. Then open 1K Pot Speedivalve and Needle valve (a few turns). MB rises to 7 mbar then falls to 3.5 mbar. Pump out MB and 1K Pot with scroll pump. |
| 1200 | Pressurize MB and 1K Pot with helium to 314 mbar above 1 atm. Close both 1K Pot valves. |
| 1205 | Open both sides of fridge to Trap 2, open Trap 2 to dump. (V9, V13b, V12b, V1, V3, Condenser, Still valves open.) 3He pump on. |
| 1210 | Let 46 μbar He exchange gas into IVC. |
| 1220 | Start recording pictures of recovery meter |
| 1225 | MC(Cernox) = 77.3 K, Sorb = 118.1 K, IVC = 46 μbar, G1(fridge) = 604 mbar. G3(MB) = 113 mbar+1atm. |
| 1230 | Begin LHe transfer |
| 1230 | G3(MB) → 950 mbar+1atm |
| 1240 | MC(Cernox) = 76.6 K, Sorb = 115.8 K, IVC = 34 μbar, G1(fridge) = 601 mbar. G3(MB) = 384 mbar+1atm. Motor Coil A = 6.34 kΩ. |
| MB pressure and recovery rate have settled. Let's start pressurizing the transfer Dewar. | |
| 1255 | MC(Cernox) = 62.1 K, Sorb = 69.1 K, IVC = 74 μbar, G1(fridge) = 571 mbar. G3(MB) = 350 mbar+1atm. Motor Coil A = 6.32 kΩ. |
| why is IVC pressure increasing? I had pumped it down a little from a somewhat too high pressure. So maybe it's still settling? This is a bit concerning though. | |
| close valve on pump manifold that leads to the hoses for the scroll pump and leak detector. Maybe there's a leak there. | |
| 1300 | IVC = 100 μbar. Let's pump it down again, to 63 μbar. |
| 1310 | MC(Cernox) = 49.5 K, Sorb = 8.0 K, IVC = 86 μbar, G1(fridge) = 472 mbar. G3(MB) = 391 mbar+1atm. Motor Coil A = 6.27 kΩ. |
| 1315 | MC(Cernox) = 44.7 K, Sorb = 7.7 K, IVC = 120 μbar, G1(fridge) = 472 mbar. G3(MB) = 372 mbar+1atm. Motor Coil A = 6.24 kΩ. |
| Pump IVC down a little more, to around 100 μbar | |
| 1340 | MC(Cernox) = 22.3 K, Sorb = 6.4 K, IVC = 140 μbar, G1(fridge) = 454 mbar. G3(MB) = 313 mbar+1atm. Motor Coil A = 6.14 kΩ. |
| Pump IVC down a little more, to around 100 μbar | |
| 1345 | MB = 63.1%. Had forgotten to look at this. |
| 1346 | MC(Cernox) hits 10K. Start pumping out IVC. Motor Coil A suddenly goes superconducting, right when it's supposed to: → 32 Ω. |
| 1350 | MC(Cernox) = 4.34 K, Sorb = 5.2 K, turbo on IVC = 3.4 μbar, G1(fridge) = 440 mbar. G3(MB) = 313 mbar+1atm. Motor Coil A = 31.8 Ω. MB = 73.0%. |
| 1400 | End LHe transfer @ MB = 66.5% |
| 1415 | MC(Cernox) = 4.23 K, Sorb = 5.2 K, turbo on IVC = 250 nbar, G1(fridge) = 520 mbar. G3(MB) = 126 mbar+1atm. |
| 1515 | MC(Cernox) = 4.24 K, Sorb = 5.2 K, turbo on IVC = 250 nbar, G1(fridge) = 533 mbar. G3(MB) = 118 mbar+1atm. Pump cold LN2 trap 2 to dump. |
| 1545 | G1/P1 = 1.1/0.02 mbar. Close V12B+speedi and V6. Open V12a+speedi, V13A, and V1. Open gate valve to leave mix exposed to fridge and cold trap 1. Turn off 3He pump. |
| 1550 | Take out cold trap 2 and fill LN2 bath. |
| 1815 | Begin LHe transfer MB=64.1% |
| 1850 | End LHe transfer MB=90.3% |
Stepper Motor
| 1454 | Looking at DIB1 on breakout box. Motor Coil A/B = 33.3/31.7 Ω, Slide Pot 1-2 = 4.504 kΩ, Slide Pot 1-3 = 16.20 kΩ, Slide Pot 2-3 = 12.35 kΩ |
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| 1457 | With the standard copper coils the stepper motors each have resistances of 125 ± 0.5 Ω. It would be good to match this and to have the two coils as similar as possible so we are sending the same current down each. Added a couple 200 Ω trim pots on the Dsub50 breakout board for this purpose. Attach DIB1 to the Dsub50 breakout board and adjust the pots to get total resistances of Motor Coil A/B = 125.0/125.0 Ω. |
| 1515 | Testing stepper motor. MC Cernox = 4.23 K. Attach arduino and motor driver board to DB50 breakout board on DIB1. Power Arduino from USB. Power motor board with 7.5V from Instek Lab Power supply. Power supply says the board is currently drawing 10 mA. Slide Pot 1-2 = 4.504 kΩ. Connect to Arduino via telnet with command telnet cdms-arduino1. |
| 1522 | Send command mv +48 to step by 48 steps = 1 rotation = 1/32 inch. MC rises from 4.23 K to 4.26 K, then falls back down within ~2 min. Slide Pot 1-2 rises while motor is moving, then continues to rise as fridge heats, eventually settles at 4.569 kΩ. Looks like it worked and we guessed the polarity correctly. |
| 1528 | Slide Pot 1-2 = 4.570 kΩ, Slide Pot 1-3 = 16.19 kΩ, Slide Pot 2-3 = 12.46 kΩ (measured from Dsub50 breakout panel). Odd, it looks like Slide Pot 2-3 increased also, but maybe it's just the different breakout wiring?? |
| 1533 | Let's try to move back to 0. Send command mv -48. MC again rises to ~4.26 K, then settles back at 4.23 K. Slide Pot 1-2 initially falls to 4.51 kΩ, then rises to 4.582 kΩ. Slide Pot 1-3 = 16.19 kΩ, Slide Pot 2-3 = 12.48 kΩ. This is strange, the total resistance has remained unchanged as expected, but the two partial resistances have both increased no matter which direction we move. Could be that the contact resistance of the pot slider is unstable. |
| 1609 | Quit Arduino telnet session with the command qu. Power down Motor (Instek) power supply. Unplug Arduino USB power. Slide Pot 1-2 = 4.582 kΩ |
| Step number | SP 1-2 (kΩ) | SP 2-3 (kΩ) | SP 1-3 (kΩ) |
|---|---|---|---|
| 0 | 4.504 | 12.35 | 16.20 |
| 48 | 4.570 | 12.46 | 16.19 |
| 0 | 4.582 | 12.48 | 16.19 |
Based on bench tests, 1 rotation should move the potentiometer through 1.4% of it's total resistance. So we expect SP 1-2 and SP 2-3 to be changing by 233 Ω per rotation.
| 1720 | Let's assume there is a significant contact resistance on the slide pot. If we take the 3 measurements we have and assume a value for the stripline and other wiring resistances, we can work out the fractional position and the contact resistance. |
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We have:
| <m>R_{13} = 2 R_{SL} + R_T </m> |
| <m>R_{12} = 2 R_{SL} + R_C + f R_T </m> |
| <m>R_{23} = 2 R_{SL} + R_C + (1-f) R_T </m> |
where <m>R_{C}</m> is the contact resistance, <m>R_{SL}</m> is the stripline resistance, <m>f</m> is the fractional position, and <m>R_{T}</m> is the total pot resistance. From these we can show:
| <m>f = 1/2 (1- {R_{23}-R_{12}}/{R_{13}-2R_{SL}} )</m> |
| <m>R_C = {R_{12} + R_{23} - R_{13} - 2 R_{SL}}/2</m> |
If we use the motor coil measurements to estimate the stripline and wiring resistance, we get <m>R_{SL}~16.25 Ohm</m>. Using the expressions above, then we can calculate R_C and f. This appears consistent with the slider not moving but the contact resistance changing…
| Step number | SP 1-2 (kΩ) | SP 2-3 (kΩ) | SP 1-3 (kΩ) | R_C (Ohm) | f |
|---|---|---|---|---|---|
| 0 | 4.504 | 12.35 | 16.2 | 311 | 0.257 |
| 48 | 4.57 | 12.46 | 16.19 | 404 | 0.256 |
| 0 | 4.582 | 12.48 | 16.19 | 420 | 0.256 |