keita.kawabe@LIGO.ORG - posted 14:18, Tuesday 10 September 2013 - last comment - 09:07, Thursday 12 September 2013(7704)
TMSX ISC cable test: Done
We're done with in-vac cable test.
Tomorrow Corey needs to re-rout the cables on ISI back to the intended position (i.e. closer to the real feedthrough).
IR QPDs:
Connected a dirty DB25 cable with a breakout board via dummy feedthrough.
No short circuit, no ground loop.
Used the diode check mode of the DVM to see the continuity of the quadrants, and they are all conductive only from anode to cathode. DVM didn't beep but it showed 500 Ohm-ish number.
Connected a handheld QPD tester and a breakout board, used a strong flash light (Stinger), and the voltage across anode-cathode dropped by about a volt or so when there was a light for all quadrants for both QPD1 and QPD2. Note that the common cathode was biased at +5Volt by the QPD tester, so this was more like the change from 5V to 4V. The drop itself depends on the load impedance of the tester which I don't know and I'm too lazy to look it up. But the basic message is that everything is good.
Green QPDs:
Diode test mode of DVM didn't work, DVM told that nothing was connected to anything.
The cable section between the ISC table and the feedthrough was exonerated after using this section for the IR QPDs and confirming that IR QPDs looked good.
Swapped the cable back to original configuration, connected the handheld QPD tester, used a flash light, and all quadrants responded to the light correctly. Seems like everything is working.
Disconnected the tester, "measured" the resistance by using DVM though this is in DC and the number the DVM reports doesn't mean much.
In each of the anode-cathode pair in a single QPD, in one direction it was pretty much 1 MOhm and in the other it was about 2 MOhm for both of the two QPDs.
Also, for some cathode pairs in a single QPD, it was about 500kOhm. Doesn't make sense, but I don't know how the DVM sets the voltage and the internal load either.
The green QPDs (Perkin Elmer C30845EH ) are silicon diodes with 8mm diameter while IR QPDs (OSI Q3000) are InGaAs with 3mm diameter. It might be that the photocurrent against ambient light, which is higher in the green ones, was enough to throw off anything done by DVM, or something else is going on that I don't know of.
Bottom line is, the QPD tester result looks good, and probably it's not a good idea to rely on DVM without using the QPD tester. If the handheld tester was the only thing I used (which was the case in EY) I would have said that everything is perfect.
Beam diverter:
No short circuit, no ground loop. Reed SWs work. Coil measured to be about 12Ohm.
Picomotors:
Connected the picomotor driver to the air side of the feedthrough via a flipper cable.
Used the picomotor test interface to manually control each picomotor.
Everything worked.
The only thing to remember is, "motor 1" of the controller is connected to the picomotor labeled "D", 2 to C, 3 to B and 4 to A. I'll wait until Sheila comes back next week to see how things were wired in Beckhoff world at EY.
Ok, I just noticed Keita added all of these sub-entries. But I just made a picture of the oddity with labeling of the Picomotor cable & Driver assignment. Oh, and it's also useful to know where each picomotor is where on the Table. Anyways, it's attached.