Reports until 12:27, Thursday 25 June 2026
H1 SUS
oli.patane@LIGO.ORG - posted 12:27, Thursday 25 June 2026 - last comment - 09:07, Friday 26 June 2026(90758)
BBSS Satamp to Coil Driver Checks

Jeff, Arnaud, Betsy, Oli

Yesterday we checked the coil response for the BBSS QOSEMs. We did this at the BBSS M1 QOSEM satamp. Everything is looking good and as we expected.

We did this by putting the BBSS in SAFE, then unplugging the db15's that go to the coil drivers. In their place Jeff plugged in a fancy breakout board that separated out each of the 4 channel pins. The resistance of each of the reading device channels is listed below:

Coil Voltage (Satamp to Coil Driver)
Resistance of reading device
(no uncertainty to 0.1 Ohm)
Used to measure
Breakout (B/O) Channel 1 24.3 Ohm CH1 (F1), CH5 (LF)
Breakout (B/O) Channel 2 20.9 Ohm CH2 (F2), CH6 (RT)
Breakout (B/O) Channel 3 23.1 Ohm CH3 (F3)
Breakout (B/O) Channel 4 23.4 Ohm CH4 (SD)

 With this channel breakout board we then went channel by channel to measure voltage. We turned the master switch ON so counts can head out from the COILOUTF filter bank. For each channel, we noted the COILOUTF filter bank gain sign, and if there was any voltage read out when no offsets were put in. Then we put an OFFSET in the COILOUTF filter bank and noted the voltage that we were reading. We did this for multiple OFFSETs for each channel. After testing each channel, with an offset still on, we would check the other channels to see if anyone else was seeing anything more than their default reading with no offsets, which they never saw anything different from that. Here is that data:

Cable SUS_BS_85 SUS_BS_87
Channel CH1 CH2 CH3 CH4 CH5 CH6
OSEM F1 F2 F3 SD LF RT
COILOUTF gain -1 -1 1 1 -1 1
  COILOUTF OFFSET Voltage (V)
(+/- 0.5 mV)
COILOUTF OFFSET Voltage (V)
(+/- 0.5 mV)
COILOUTF OFFSET Voltage (V)
(+/- 0.5 mV)
COILOUTF OFFSET Voltage (V)
(+/- 0.5 mV)
COILOUTF OFFSET Voltage (V)
(+/- 0.5 mV)
COILOUTF OFFSET Voltage (V)
(+/- 0.5 mV)
  20,000 -2.825 20,000 -2.837V 20,000 2.848 20,000 2.839 20,000 -2.826 20,000 2.836
  10,000 -1.413 10,000 -1.419 10,000 1.424 10,000 1.419 10,000 -1.413 10,000 1.418
  0 0 0 -1.00E-03 0 0 0 0 0 -1.00E-03 0 0
  -10,000 1.412 -10,000 1.416 -10,000 -1.424 -10,000 -1.42 -10,000 1.412 -10,000 -1.418
  -20,000 2.825 -20,000 2.83 -20,000 -2.849 -20,000 -2.839 -20,000 2.825 -20,000 -2.837
  With OFFSET of -20,000 (in V): With OFFSET of -20,000 (in V): With OFFSET of -20,000 (in V): With OFFSET of -20,000 (in V): With OFFSET of -20,000 (in V): With OFFSET of -20,000 (in V):
  CH1 (B/O Ch1) -- CH1 (B/O Ch1) 0 CH1 (B/O Ch1) 0 CH1 (B/O Ch1) 0 CH5 (B/O Ch1) -- CH5 (B/O Ch1) -1.00E-03
  CH2 (B/O Ch2) -1.00E-03 CH2 (B/O Ch2) -- CH2 (B/O Ch2) -1.00E-03 CH2 (B/O Ch2) -1.00E-03 CH6 (B/O Ch2) 0 CH6 (B/O Ch2) --
  CH3 (B/O Ch3) 0 CH3 (B/O Ch3) 0 CH3 (B/O Ch3) -- CH3 (B/O Ch3) 0        
  CH4 (B/O Ch4) 0 CH4 (B/O Ch4) 0 CH4 (B/O Ch4) 0 CH4 (B/O Ch4) --        

You can see that the voltage signs are all consistant with the sign of the OFFSET * COILOUTF gain, and the values are all pretty consistant as well.

After we were done reading out the voltages for SUS_BS_85, we put offsets of -20,000 in F1, F2, and F3 and checked the voltages on all three channels. All three channels read the same voltage as they had when we had tested them individually at -20,000 counts. That table is below.

OFFSET of -20,000 for F1, F2, F3 (in V)
CH1 (F1) 2.825 V
CH2 (F2) 2.831 V
CH3 (F3) -2.849 V
Comments related to this report
jeffrey.kissel@LIGO.ORG - 09:07, Friday 26 June 2026 (90772)
Some pictures of the "DAC Voltage to Coils" setup that gathered the above data.

2026-06-24_QOSEM_CoilDriveDACVoltage_BigPicture.jpg
    Zoomed out photo of SUS_BS_85 cable disconnected from the Coil Driver 1-4 channel input to the QOSEM satamp chassis in SUS-R2, and connected to the dummy OSEM system (what Oli calls the "fancy breakout board"), with a DVM reading out the voltage across the resistors. In the pictured case, we're using the DVM (placed in the rack for convenience) reading out the voltage across the Channel 1 resistor of the dummy OSEM which is connects across the + and - legs of the Channel 1 output of the cable (i.e. F1).

2026-06-24_QOSEM_CoilDriveDACVoltage_Zoom_DummyCoilResistor.jpg
    Zoomed in photo of the clip leads hooked across the resistor. Since the sign of the voltage is critical, I made sure to find a dummy OSEM that had the + and - legs clearly called out, ensuring the positive, red, signal lead for the BNC connection was connected to the + leg of the drive signal, and black to the -, return, leg. 

2026-06-24_QOSEM_CoilDriveDACVoltage_Zoom_DVM.jpg
    Zoom in photo of an example of the DVM read-out voltage during the given offset (in this case, it was the CH1, F1, 10,000 [ct] offset -- multipled by the -1 COILOUTF gain -- to read -1.413 [V]_DC). Note -- again because signs are under question in this investigation -- careful attention was paid to ensure the orientation of the BNC to banana adapter into the DVM; connecting in the standard "nub is negative" configuration i.e. the shield of the BNC cable, connected to the black clip lead on the other end, is connected to the black COM input of the DVM.

2026-06-24_QOSEM_CoilDriveDACVoltage_DisconnectedSatampCable.jpg
    Zoom in photo of where the SUS_BS_85 DAC drive cable connects into the QOSEM satamp.
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