2020/10/27 (Tuesday)

Previous Day

• Lab in-person: Michael
• Virtual partner: Ruiren, Matt

Todo: move the source a little more, see if we hit the endstop.

• The endstops are copper bars seen in the lower right and upper left of the photo on the Run 71 summary page. When the source carriage hits an endstop it grounds it, and we can check the resistance between endstop and ground to see whether the carriage is in contact.
• The carriage should be close to (or touching) the far endstop now
• The far endstop is connected to Pin1 on the side panel attached to the Breakout Box below the HVbox. This panel is labeled SP (for Slide Potentiometer, a previous failed attempt to measure the source position). Pin2 is connected to the Near Endstop, and Pin3 is connected to an unused wire.
• A convenient point of connection to the DAQ ground is the HV ground. The HV enters the HV box with a BNC connection on the right side of the box. There's an adapter from BNC to banana jacks; the red one is covered in tape, and the black one is exposed. That's DAQ ground.
• To check for contact, measure the resistance between DAQ ground and Pin1. You could try Pin2 and Pin3 too, in case I somehow got the IDs wrong. These will generally read open if there is no contact. With the fancier multimeter you can press the Range button multiple times to get to nS. nS is inverse GΩ, so <1 nS indicates >1 GΩ, essentially open. To get back to normal scale, it's easiest to just turn the meter off and back on. If there is contact I expect the resistance to be less than a few 100 Ω (this will read offscale if the meter is set to nS).
• After verifying that there is no contact, you should try moving the source, one 4-step move. To do that, go to the Arduino Editor tab in the browser, type “mv -4” in the box next to the Send button, then press the Send button. Our standard procedure is to wait 4 minutes after each move before doing another move.
• To keep track of the source position, there is a spreadsheet open on the Fridge computer, Run73SourceMover.xlsx. You can copy and paste a new column after each move. The top cell in the column is the number of moves (1 in this case). The bottom cell is Distance from Endstop.
• As of the last move the Distance from Endstop is -0.24 mm, meaning we should already be touching it. But resistance measurements say we aren't. The point at which it should touch the endstop is based on Run71 calculations. One difference with Run73 is that the source holder is upside down now relative to that run, so the carriage may be tilted a little to the side, which may change the point at which it touches.
• In addition to just doing a move, checking the resistance, waiting 4 minutes, then doing another move, you can look at a few other things:
  • The temperature pattern after a move. In the OmniLogger vi you can still see the temperatures from yesterday's moves - generally it goes up to around 1.1 K, then over 4 minutes fall to about 0.8 K. If this pattern changes significantly it could mean that the source carriage is jammed and can't move further
  • The endstop resistance in nS. If it's reading low on this scale, that means there is no contact. But if you watch it during a move, it might change a little during the move. (This number is not totally stable to begin with, but you may see a variation.) If it does vary during the move, that's a hint that we found the right wire. If it doesn't vary, that doesn't say much one way or the other.
• Repeat the process every 4 minutes - move the source, update the spreadsheet, check the endstop resistance (try all 3 pins, but it should be Pin1). If you can verify contact, you should stop. Otherwise I think we should stop when “Distance to Endstop” reaches -1.0 mm. Probably you won't want to stay long enough to get that far (it would take 48 minutes). Hopefully you'll verify contact before that. If the temperature pattern changes a lot, you should stop even if the endstop resistance doesn't change.

Next Day